Substituting dietary linoleic acid with alpha-linolenic acid improves insulin sensitivity in sucrose fed rats

Current Insights into the Effects of Dietary α-Linolenic Acid Focusing on Alterations of Polyunsaturated Fatty Acid Profiles in Metabolic Syndrome

The plant-derived α-linolenic acid (ALA) is an essential n-3 acid highly susceptible to oxidation, present in oils of flaxseeds, walnuts, canola, perilla, soy, and chia. After ingestion, it can be incorporated in to body lipid pools (particularly triglycerides and phospholipid membranes), and then endogenously metabolized through desaturation, elongation, and peroxisome oxidation to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), with a very limited efficiency (particularly for DHA), beta-oxidized as an energy source, or directly metabolized to C18-oxilipins. At this moment, data in the literature about the effects of ALA supplementation on metabolic syndrome (MetS) in humans are inconsistent, indicating no effects or some positive effects on all MetS components (abdominal obesity, dyslipidemia, impaired insulin sensitivity and glucoregulation, blood pressure, and liver steatosis). The major effects of ALA on MetS seem to be through its conversion to more potent EPA and DHA, the impact on the n-3/n-6 ratio, and the consecutive effects on the formation of oxylipins and endocannabinoids, inflammation, insulin sensitivity, and insulin secretion, as well as adipocyte and hepatocytes function. It is important to distinguish the direct effects of ALA from the effects of EPA and DHA metabolites. This review summarizes the most recent findings on this topic and discusses the possible mechanisms.

Dietary fat intake with risk of gestational diabetes mellitus and preeclampsia: a systematic review and meta-analysis of prospective cohort studies

CONTEXT

Gestational diabetes mellitus (GDM) and preeclampsia (PE) are commonly observed medical complications in pregnancy. Dietary total fat and fatty acids associated with GDM and PE risk have been examined in several epidemiological studies. In some instances, systematic reviews and meta-analyses might provide more accurate dietary recommendations.

OBJECTIVES

This systematic review and dose-response meta-analysis was conducted to investigate the association between dietary total fat and fatty acids and the risk of GDM and PE.

DATA SOURCES

Research on dietary fat intake and the risk of GDM and PE was conducted through systematic searches of the PubMed, Scopus, and Web of Science databases for articles published up to August 19, 2023. An investigation of associations between dietary intake of total fat and fatty acids and the risk of GDM and PE was performed using prospective cohort study designs.

RESULTS

Twenty-one prospective cohort studies were considered eligible. Findings indicated that higher intakes of total fat (relative risk [RR], 1.08; 95% confidence interval [CI], 1.02-1.14), animal fat (RR, 1.56; 95%CI, 1.34-1.89), vegetable fat (RR, 1.23; 95%CI, 1.05-1.45), dietary cholesterol (RR, 1.48; 95%CI, 1.10-2.00), and omega-3 fatty acid (RR, 1.11; 95%CI, 1.02-1.20) are associated with a greater risk of GDM. However, no significant association was found between dietary total fat and fatty acids and the risk of PE. Dose-response meta-analyses suggested every 10% increment in total energy intake from total fat, 5% from animal fat, 5% from vegetable fat, and 100 mg from cholesterol was related to 15%, 12%, 7%, 14%, and 20% higher GDM risk, respectively.

CONCLUSIONS

Overall, total fat, animal fat, vegetable fat, dietary cholesterol, and omega-3 fatty acid consumption are associated with a small but statistically significant increase in GDM risk.

PROTOCOL REGISTRATION

PROSPERO (CRD42023466844).

Beneficial effects of monounsaturated fatty acid-rich blended oils with an appropriate polyunsaturated/saturated fatty acid ratio and a low n-6/n-3 fatty acid ratio on the health of rats

BACKGROUND

The effects of dietary fat on health are influenced by its fatty acid profile. We aimed to determine the effects of monounsaturated fatty acid (MUFA)-rich blended oils (BO) containing a balance of polyunsaturated fatty acids (PUFAs) and saturated fatty acids (SFAs) and with a low n-6/n-3 PUFA ratio on the health of rats fed normal or high-fat diets. The BO was obtained by mixing red palm oil, rice bran oil (RO), tea seed oil and flaxseed oil in appropriate proportions.

RESULTS

BO consumption reduced the serum low-density lipoprotein cholesterol (LDL-C), non-esterified fatty acid (NEFA), insulin (INS), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1 (IL-1), high-sensitivity C-reactive protein (hs-CRP), malondialdehyde (MDA), lipid peroxide (LPO) and oxidized LDL (ox-LDL) concentrations and the homeostasis model assessment of insulin resistance (HOMA-IR); it increased the high-density lipoprotein cholesterol (HDL-C), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) concentrations, and the bone mineral density (BMD) versus control oil-containing normal and high-fat diets. BO also reduced the triglyceride (TG), hs-CRP, MDA, ox-LDL and reactive oxygen species (ROS) concentrations; and increased the serum HDL-C and SOD, and BMD versus RO-containing high-fat diets. Finally, BO reduced the glucose (GLU) and INS, and HOMA-IR; it increased HDL-C, SOD, femoral weight and BMD versus RO-containing normal diets.

CONCLUSION

BOs with an appropriate fatty acid profile have beneficial effects on the glucolipid metabolism, inflammation, oxidative stress and bone quality of rats when included in both normal and high-fat diets. © 2022 Society of Chemical Industry.

Associations of Plasma Fatty Acid Patterns During Pregnancy With Gestational Diabetes Mellitus

Background

Limited studies have explored the difference of fatty acid profile between women with and without gestational diabetes mellitus (GDM), and the results were inconsistent. Individual fatty acids tend to be interrelated because of the shared food sources and metabolic pathways. Thus, whether fatty acid patters during pregnancy were related to GDM odds needs further exploration.

Objective

To identify plasma fatty acid patters during pregnancy and their associations with odds of GDM.

Methods

A hospital-based case-control study including 217 GDM cases and 217 matched controls was carried out in urban Wuhan, China from August 2012 to April 2015. All the participants were enrolled at the time of GDM screening and provided fasting blood samples with informed consent. We measured plasma concentrations of fatty acids by gas chromatography-mass spectrometry, and derived potential fatty acid patterns (FAPs) through principal components analysis. Conditional logistic regression and restricted cubic spline model were used to evaluate the associations between individual fatty acids or FAPs and odds of GDM.

Results

Twenty individual fatty acids with relative concentrations ≥0.05% were included in the analyses. Compared with control group, GDM group had significantly higher concentrations of total fatty acids, 24:1n-9, and relatively lower levels of 14:0, 15:0, 17:0, 18:0, 24:0, 16:1n-7, 20:1n-9,18:3n-6, 20:2n-6, 18:3n-3, 20:3n-3, 22:5n-3. Two novel patterns of fatty acids were identified to be associated with lower odds of GDM: (1) relatively higher odd-chain fatty acids, 14:0, 18:0, 18:3n-3, 20:2n-6, 20:3n-6 and lower 24:1n-9 and 18:2n-6 [adjusted odds ratio (OR) (95% confidence interval) (CI) for quartiles 4 vs. 1: 0.42 (0.23-0.76), P-trend = 0.002], (2) relatively higher n-3 polyunsaturated fatty acids, 24:0, 18:3n-6 and lower 16:0 and 20:4n-6 [adjusted OR (95% CI) for quartiles 4 vs. 1: 0.48 (0.26-0.90), P-trend = 0.018].

Conclusion

Our findings suggested that two novel FAPs were inversely associated with GDM odds. The combination of circulating fatty acids could be a more significant marker of GDM development than individual fatty acids or their subgroups.

Neurodevelopment, nutrition and genetics. A contemporary retrospective on neurocognitive health on the occasion of the 100th anniversary of the National Institute of Nutrition, Hyderabad, India

In celebration of the centenary of the National Institute of Nutrition (NIN), Hyderabad, India (1918-2018), a symposium highlighted the progress in nutrition knowledge made over the century, as well as major gaps in implementation of that knowledge. Brain famine caused by a shortage of nutrients required for perinatal brain development has unfortunately become a global reality, even as protein-calorie famine was largely averted by the development of high yield crops. While malnutrition remains widespread, the neglect of global food policies that support brain development and maintenance are most alarming. Brain disorders now top the list of the global burden of disease, even with obesity rising throughout the world. Neurocognitive health, remarkably, is seldom listed among the non-communicable diseases (NCDs) and is therefore seldom considered as a component of food policy. Most notably, the health of mothers before conception and through pregnancy as mediated by proper nutrition has been neglected by the current focus on early death in non-neurocognitive NCDs, thereby compromising intellectual development of the ensuing generations. Foods with balanced essential fatty acids and ample absorbable micronutrients are plentiful for populations with access to shore-based foods, but deficient only a few kilometres away from the sea. Sustained access to brain supportive foods is a priority for India and throughout the world to enable each child to develop to their intellectual potential, and support a prosperous, just, and peaceful world. Nutrition education and food policy should place the nutritional requirements for the brain on top of the list of priorities.

A plasma fatty acid profile associated to type 2 diabetes development: from the CORDIOPREV study

PURPOSE

The prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide. For this reason, it is essential to identify biomarkers for the early detection of T2DM risk and/or for a better prognosis of T2DM. We aimed to identify a plasma fatty acid (FA) profile associated with T2DM development.

METHODS

We included 462 coronary heart disease patients from the CORDIOPREV study without T2DM at baseline. Of these, 107 patients developed T2DM according to the American Diabetes Association (ADA) diagnosis criteria after a median follow-up of 60 months. We performed a random classification of patients in a training set, used to build a FA Score, and a Validation set, in which we tested the FA Score.

RESULTS

FA selection with the highest prediction power was performed by random survival forest in the Training set, which yielded 4 out of the 24 FA: myristic, petroselinic, α-linolenic and arachidonic acids. We built a FA Score with the selected FA and observed that patients with a higher score presented a greater risk of T2DM development, with an HR of 3.15 (95% CI 2.04-3.37) in the Training set, and an HR of 2.14 (95% CI 1.50-2.84) in the Validation set, per standard deviation (SD) increase. Moreover, patients with a higher FA Score presented lower insulin sensitivity and higher hepatic insulin resistance (p < 0.05).

CONCLUSION

Our results suggest that a detrimental FA plasma profile precedes the development of T2DM in patients with coronary heart disease, and that this FA profile can, therefore, be used as a predictive biomarker. CLINICAL TRIALS.GOV.

IDENTIFIER

NCT00924937.

Partial Replacement of Dietary Fat with Krill Oil or Coconut Oil Alleviates Dyslipidemia by Partly Modulating Lipid Metabolism in Lipopolysaccharide-Injected Rats on a High-Fat Diet

This study investigated the effects of partial replacement of dietary fat with krill oil (KO) or coconut oil (CO) on dyslipidemia and lipid metabolism in rats fed with a high-fat diet (HFD). Sprague Dawley rats were divided into three groups as follows: HFD, HFD + KO, and HFD + CO. The rats were fed each diet for 10 weeks and then intraperitoneally injected with phosphate-buffered saline (PBS) or lipopolysaccharide (LPS) (1 mg/kg). The KO- and CO-fed rats exhibited lower levels of serum lipids and aspartate aminotransferases than those of the HFD-fed rats. Rats fed with HFD + KO displayed significantly lower hepatic histological scores and hepatic triglyceride (TG) content than rats fed with HFD. The KO supplementation also downregulated the adipogenic gene expression in the liver. When treated with LPS, the HFD + KO and HFD + CO groups reduced the adipocyte size in the epididymal white adipose tissues (EAT) relative to the HFD group. These results suggest that KO and CO could improve lipid metabolism dysfunction.

Partial Replacement of Dietary Fat with Polyunsaturated Fatty Acids Attenuates the Lipopolysaccharide-Induced Hepatic Inflammation in Sprague-Dawley Rats Fed a High-Fat Diet

In this study, we investigated whether the partial replacement of dietary fat with polyunsaturated fatty acids (PUFAs) ameliorated the lipopolysaccharide (LPS)-induced hepatic inflammation in rats fed a high-fat diet. Male Sprague-Dawley rats were divided into three groups and provided each of the following diets: (1) high-fat diet (HFD), (2) HFD with perilla oil (PO), and (3) HFD with corn oil (CO). After 12 weeks of dietary intervention, the rats were intraperitoneally injected with LPS (5 mg/kg) from Escherichia coli O55:B5 or phosphate-buffered saline (PBS). Following LPS stimulation, serum insulin levels were increased, while PO and CO lowered the serum levels of glucose and insulin. In the liver, LPS increased the triglyceride levels, while PO and CO alleviated the LPS-induced hepatic triglyceride accumulation. In the LPS injected rats, the mRNA expression of genes related to inflammation and endoplasmic reticulum (ER) stress was attenuated by PO and CO in the liver. Furthermore, hepatic levels of proteins involved in the nuclear factor kappa-light-chain-enhancer of activated B cells/mitogen-activated protein kinase pathways, antioxidant response, and ER stress were lowered by PO- and CO-replacement. Therefore, the partial replacement of dietary fat with PUFAs alleviates LPS-induced hepatic inflammation during HFD consumption, which may decrease metabolic abnormalities.

Effects of Lifestyle Intervention in Tissue-Specific Lipidomic Profile of Formerly Obese Mice

Lipids are highly diverse in their composition, properties and distribution in different biological entities. We aim to establish the lipidomes of several insulin-sensitive tissues and to test their plasticity when divergent feeding regimens and lifestyles are imposed. Here, we report a proton nuclear magnetic resonance (1H-NMR) study of lipid abundance across 4 tissues of C57Bl6J male mice that includes the changes in the lipid profile after every lifestyle intervention. Every tissue analysed presented a specific lipid profile irrespective of interventions. Glycerolipids and fatty acids were most abundant in epididymal white adipose tissue (eWAT) followed by liver, whereas sterol lipids and phosphoglycerolipids were highly enriched in hypothalamus, and gastrocnemius had the lowest content in all lipid species compared to the other tissues. Both when subjected to a high-fat diet (HFD) and after a subsequent lifestyle intervention (INT), the lipidome of hypothalamus showed no changes. Gastrocnemius and liver revealed a pattern of increase in content in many lipid species after HFD followed by a regression to basal levels after INT, while eWAT lipidome was affected mainly by the fat composition of the administered diets and not their caloric density. Thus, the present study demonstrates a unique lipidome for each tissue modulated by caloric intake and dietary composition.

Diets with low n-6:n-3 PUFA ratio protects rats from fructose-induced dyslipidemia and associated hepatic changes: Comparison between 18:3 n-3 and long-chain n-3 PUFA

In the present study, we investigated the impact of substituting alpha-linolenic acid (ALA) or long-chain n-3 PUFA (eicosapentaenoic acid and docosahexaenoic acid) for linoleic acid and hence decreasing n-6:n-3 PUFA ratio on high-fructose diet-induced hypertriglyceridemia and associated hepatic changes. Weanling male Wistar rats were divided into four groups and fed with starch-diet (n-6:n-3 PUFA ratio 215:1) and high-fructose diets with different n-6:n-3 PUFA ratio (215:1, 2:1 with ALA and 5:1 with long-chain n-3 PUFA) for twenty-four weeks. Substitution of linoleic acid with ALA (n-6:n-3 PUFA ratio of 2) or long-chain n-3 PUFA (n-6:n-3 PUFA ratio of 5) protected the rats from fructose-induced dyslipidemia, hepatic oxidative stress and corrected lipogenic and proinflammatory gene expression. Both ALA and long-chain n-3 PUFA supplementation also reversed the fructose-induced upregulation of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) gene, which is involved in the generation of active glucocorticoids in tissues. Although both ALA and LC n-3 PUFA prevented fructose-induced dyslipidemia to a similar extent, compared to ALA, LC n-3 PUFA is more effective in preventing hepatic oxidative stress and inflammation.

Substitution of linoleic acid with α-linolenic acid or long chain n-3 polyunsaturated fatty acid prevents Western diet induced nonalcoholic steatohepatitis

Imbalance in the n-6 polyunsaturated fatty acids (PUFA) and n-3 PUFA in the Western diet may increase the risk of nonalcoholic fatty liver disease (NAFLD). This study investigates the impact of substitution of linoleic acid with α-linolenic acid (ALA) or long chain (LC) n-3 PUFA and hence decreasing n-6:n-3 fatty acid ratio on high fat, high fructose (HFHF) diet induced nonalcoholic steatohepatitis (NASH). Male Sprague-Dawley rats were divided into four groups and fed control diet, HFHF diet (n-6:n-3 ratio of 200), HFHF diet with ALA (n-6:n-3 ratio of 2) or HFHF diet with LC n-3 PUFA (n-6:n-3 ratio of 5) for 24 weeks. Rats fed HFHF diet with n-6:n-3 ratio of 200 resulted in hepatic steatosis, induced glucose intolerance, insulin resistance and oxidative stress accompanied by increase in markers of inflammation, plasma lipids and aminotransferase levels. Histopathological examination of liver further confirmed the establishment of NASH. ALA and LC n-3 PUFA supplementation prevented hepatic steatosis and dyslipidemia by inhibiting lipogenesis and increasing insulin sensitivity. Furthermore, n-3 PUFA supplementation attenuated hepatic oxidative stress by restoring antioxidant status, decreased inflammation and preserved hepatic architecture. These finding suggest that decreasing n-6:n-3 ratio prevented HFHF induced NASH by attenuating oxidative stress and inflammation.

The effect of alpha-linolenic acid on glycemic control in individuals with type 2 diabetes: A systematic review and meta-analysis of randomized controlled clinical trials

BACKGROUND

Polyunsaturated fats (PUFAs) have been shown to reduce type 2 diabetes (T2DM) risk and improve insulin responsiveness in T2DM subjects, but whether the plant sources of omega-3 PUFA (alpha-linolenic acid [ALA]) have an effect on glycemic control requires further investigation.

METHODS

The parameters of interest were glycated hemoglobin (HbA1c), fasting blood glucose (FBG), fasting blood insulin (FBI), homeostatic model assessment for insulin resistance (HOMA-IR), fructosamine, and glycated albumin. A comprehensive search was conducted with MEDLINE, Embase, CINAHL, and Cochrane. Eligible studies included randomized controlled trials (RCTs) ≥1 month in duration that compared diets enriched in ALA with usual diets on glycemic parameters. For each study, the risk of bias as well as the study quality was assessed. Using the statistical software RevMan (v5.3), data were pooled using the generic inverse method with random effects model, and final results were expressed as mean differences (MD) with 95% confidence intervals (CI). Heterogeneity was assessed by the Cochran Q statistic and quantified by the I statistic.

RESULTS

A total of 8 trials (N = 212) were included in the meta-analysis. Compared to a control diet, a median dose of 4.4 g/day of ALA intake for a median duration of 3 months did not affect HbA1c (%) (MD = -.01; [95%: -.32, .31], P = .96). A median ALA dose of 5.4 g/day did not lower FBG (MD = .07; [95% CI: -.61, .76], P = .84) or FBI (MD = 7.03, [95% CI: -5.84, 19.89], P = .28). Summary effect estimates were generally compromised by considerable and unexplained heterogeneity (I ≥75%). In the subgroup analysis of continuous predictors, a reduction in HbA1c (%) and FBG (mmol/L) was significantly associated with an increased intake of ALA. Further adjustment for Publication Bias using Duval and Tweedie's trim-and-fill analysis provided an adjusted, significant MD of -.25 (95% CI: -.38, -.12; P <.001) for HbA1c (%).

CONCLUSIONS

ALA-enriched diets did not affect HbA1c, FBG, or FBI. The scarce number of existing RCTs and the presence of heterogeneity in our meta-analysis limit the ability to make firm conclusions about ALA in T2DM management. The potential for ALA to have dose-dependent effects warrants further research in this area.

Could post-weaning dietary chia seed mitigate the development of dyslipidemia, liver steatosis and altered glucose homeostasis in offspring exposed to a sucrose-rich diet from utero to adulthood?

The present work analyzes the effects of dietary chia seeds during postnatal life in offspring exposed to a sucrose-rich diet (SRD) from utero to adulthood. At weaning, chia seed (rich in α-linolenic acid) replaced corn oil (rich in linoleic acid) in the SRD. At 150 days of offspring life, anthropometrical parameters, blood pressure, plasma metabolites, hepatic lipid metabolism and glucose homeostasis were analyzed. Results showed that chia was able to prevent the development of hypertension, liver steatosis, hypertriglyceridemia and hypercholesterolemia. Normal triacylglycerol secretion and triacylglycerol clearance were accompanied by an improvement of de novo hepatic lipogenic and carnitine-palmitoyl transferase-1 enzymatic activities, associated with an accretion of n-3 polyunsaturated fatty acids in the total composition of liver homogenate. Glucose homeostasis and plasma free fatty acid levels were improved while visceral adiposity was slightly decreased. These results confirm that the incorporation of chia seed in the diet in postnatal life may provide a viable therapeutic option for preventing/mitigating adverse outcomes induced by an SRD from utero to adulthood.

Transient Decrease in Circulatory Testosterone and Homocysteine Precedes the Development of Metabolic Syndrome Features in Fructose-Fed Sprague Dawley Rats

Background. Increased fructose consumption is linked to the development of metabolic syndrome (MS). Here we investigated the time course of development of MS features in high-fructose-fed Sprague Dawley rats along with circulatory testosterone and homocysteine levels. Methods. Rats were divided into control and experimental groups and fed with diets containing 54.5% starch and fructose, respectively, for 4, 12, and 24 weeks. Plasma testosterone and homocysteine levels were measured along with insulin, glucose, and lipids. Body composition, insulin resistance, and hepatic lipids were measured. Results. Increase in hepatic triglyceride content was first observed in metabolic disturbance followed by hypertriglyceridemia and systemic insulin resistance in fructose-fed rats. Hepatic lipids were increased in time-dependent manner by fructose-feeding starting from 4 weeks, but circulatory triglyceride levels were increased after 12 weeks. Fasting insulin and Homeostatis Model Assessment of Insulin Resistance (HOMA-IR) were increased after 12 weeks of fructose-feeding. Decreased visceral adiposity, circulatory testosterone, and homocysteine levels were observed after 4 weeks of fructose-feeding, which were normalized at 12 and 24 weeks. Conclusions. We conclude that transient decrease in circulatory testosterone and homocysteine levels and increased hepatic triglyceride content are the earliest metabolic disturbances that preceded hypertriglyceridemia and insulin resistance in fructose-fed SD rats.

Effect of an avocado oil-enhanced diet ( Persea americana ) on sucrose-induced insulin resistance in Wistar rats

A number of studies have been conducted to evaluate the effects of vegetable oils with varying percentages of monounsaturated and polyunsaturated fatty acids on insulin resistance. However, there is no report on the effect of avocado oil on this pathologic condition. The aim of this work was to evaluate the effect of avocado oil on sucrose-induced insulin resistance in Wistar rats. An experimental study was carried out on Wistar rats that were randomly assigned into six groups. Each group received a different diet over an 8-week period (n = 11 in each group): the control group was given a standard diet, and the other five groups were given the standard feed plus sucrose with the addition of avocado oil at 0%, 5%, 10%, 20%, and 30%, respectively. Variables were compared using Student t test and analysis of variance. Statistically significant difference was considered when p < 0.05. Rats that were given diets with 10% and 20% avocado oil showed lower insulin resistance (p = 0.022 and p = 0.024, respectively). Similar insulin resistance responses were observed in the control and 30% avocado oil addition groups (p = 0.85). Addition of 5–30% avocado oil lowered high sucrose diet-induced body weight gain in Wistar rats. It was thus concluded that glucose tolerance and insulin resistance induced by high sucrose diet in Wistar rats can be reduced by the dietary addition of 5–20% avocado oil.

Effect of Increasing Doses of Linoleic and α-Linolenic Acids on High-Fructose and High-Fat Diet Induced Metabolic Syndrome in Rats

Doses and ratio of linoleic acid (LA) and α-linolenic acid (ALA) preventing metabolic syndrome (MS) were investigated. SD rats were fed (i) basal diet, (ii) high-fructose and high-fat diet (HFFD), (iii) HFFD with increasing-dose LA (0.75 energy-% ALA + 3, 6, 9, 12, 15, and 30 energy-% LA), and (iv) HFFD with increasing-dose ALA (6 energy-% LA + 0.3, 0.5, 0.75, 1.5, 2.25, and 3.75 energy-% ALA) for 18 weeks. Results showed 6, 12, 15, and 30 energy-% LA significantly ameliorated central obesity, hyperlipidemia, glucose homeostasis, and leptin status; 0.5 and 0.75 energy-% ALA significantly improved insulin sensitivity, adiponectin, and anti-inflammatory status. Moreover, high intakes of ALA (1.5, 2.25, and 3.75 energy-%) presented a pro-oxidant activity. In conclusion, dose instead of ratio determines the prevention of MS. The optimal doses are 6 energy-% LA and 0.75 energy-% ALA; high intakes of ALA may have side effects.

Indices of dietary fat quality during midpregnancy is associated with gestational diabetes

OBJECTIVE

To investigate the relationship between gestational diabetes mellitus (GDM) and the usual intake of fatty acids and indices of dietary fat quality [the atherogenicity (AI) and thrombogenicity indices (TI), and the ratios of hypo-and hypercholesterolemic (hH), ∑n-3/∑n-6, and polyunsaturated/saturated fatty acids (P:S)], during mid-pregnancy.

METHODS

799 adult pregnant women living in Ribeirão Preto, SP, Brazil were screened and accepted for this cross-sectional GDM study. The Multiple Source Method was used to estimate participants' usual diet, using two 24-hour dietary recalls during mid-pregnancy. Diagnosis of GDM was defined by the American Diabetes Association criteria of 2015. Logistic regression analysis were used to assess the association between GDM and dietary fat, adjusted for age, education, parity, gestational age at the time of the interview, pre-pregnancy and current BMI, prior GDM, family history of diabetes, smoking, physical activity, energy, fiber, and fatty acids.

RESULTS

The mean (standard deviation) age of the women was 28 (5) years, and 19% had GDM. After multiple adjustments, inverse associations between the highest tertile of ∑n-3 fatty acids intake [0.21 (0.08-0.56)], α-linolenic intake [0.15 (0.05-0.42)], and GDM were found. A positive association between GDM and the highest tertile of TI [2.66 (1.34-5.29)], and a negative association with the highest tertile of hH ratio [0.41 (0.22-0.77)], were observed. No association between GDM and other indices of dietary fat quality were found.

CONCLUSION

The quality of dietary fat during pregnancy is strongly associated with GDM. Randomized clinical trial are needed to confirm these findings.

The evaluation of the healing proprieties of pumpkin and linseed oils on deep second-degree burns in rats

CONTEXT

Medicinal plants have been recognized as useful remedies for primary health care. Accordingly, Cucurbita pepo L. (Cucurbitaceae) (pumpkin) and Linum usitatissimum (L.) Griesb. (Linaceae) (linseed) which have extracted oil with prominent pharmacological properties are investigated as possible burn healing treatments.

OBJECTIVE

The present study assesses the healing potential of pumpkin and linseed extracted oils on rats.

MATERIALS AND METHODS

Uniform deep second-degree burns were induced on the dorsum of 24 rats, randomly divided into four groups. The burns were measured, photographed, and topically treated with saline solution, "Cytol Centella®", pumpkin, and linseed-extracted oils (0.52 µl/mm(2) of oil) each 2 d (up until day 33). Post-burning of the 33rd day, biopsies were histologically assessed.

RESULTS

At the end of the experiment, the rat groups treated with linseed, pumpkin oils, and "Cytol Centella®" had higher percentage of wound contraction (98.68, 96.71, and 92.54%, respectively) than the control group (58.38%). Wound biopsies from rats treated with extracted oils showed the best tissue regeneration proprieties as compared with the other groups. The histomorphometric analysis of biopsies revealed that linseed oil could significantly stimulate angiogenesis (55.6% ± 7.25). The pumpkin oil, and Cytol Centella® could significantly increase the collagen production 64.9% ± 5.94, and 61.2% ± 7.36, respectively.

DISCUSSION AND CONCLUSION

Overall, our study has given for the first time scientific evidence of the healing efficiency of pumpkin and linseed oils on burn-wounds.

Effects of Grifola frondosa non-polar bioactive components on high-fat diet fed and streptozotocin-induced hyperglycemic mice

CONTEXT

Consumption of medicinal mushrooms for disease prevention and maintaining health has a very long history in Asia. Grifola frondosa (Fr) S.F. Gray (GF) (Meripilaceae) is a medicinal fungus popularly used for enhancing immune systems, lowering blood glucose, and improving spleen, stomach, and nerve functions.

OBJECTIVE

This study examines the hypoglycemic effects of GF in vitro and in vivo, and analyzes the chemical profiles of its bioactive components.

MATERIALS AND METHODS

In vitro hypoglycemic effects of GF was evaluated enzymatically using α-amylase and α-glucosidase inhibition assays, whereas in vivo study was conducted on high-fat diet fed and streptozotocin (HFD + STZ)-induced hyperglycemic mice. GC-MS was used to determine the chemical profiles of bioactive components.

RESULTS

The non-polar fraction of GF exhibited a stronger anti-α-glucosidase activity (IC50: 0.0332 mg/ml) than acarbose, but its anti-α-amylase activity (IC50: 0.671 mg/ml) was weaker. Oral administration of GF at 600 mg/kg (GF600) significantly lowered the blood glucose, HbA1c, average blood glucose, and serum total cholesterol levels in hyperglycemic mice. Although GF was found to contain mainly oleic acid and linoleic acid, their levels in the fungus were low, suggesting that the effects of GF on HFD + STZ-induced hyperglycemic mice could be due to factors other than these fatty acids.

CONCLUSION

These results conclude that GF possesses anti-α-glucosidase activity, and hypoglycemic effect in HFD + STZ-induced hyperglycemic mice.

Mechanisms of enhanced insulin secretion and sensitivity with n-3 unsaturated fatty acids

The widespread acceptance that increased dietary n-3 polyunsaturated fatty acids (PUFAs), especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), improve health is based on extensive studies in animals, isolated cells and humans. Visceral adiposity is part of the metabolic syndrome, together with insulin resistance, dyslipidemia, hypertension and inflammation. Alleviation of metabolic syndrome requires normalization of insulin release and responses. This review assesses our current knowledge of the mechanisms that allow n-3 PUFAs to improve insulin secretion and sensitivity. EPA has been more extensively studied than either ALA or DHA. The complex actions of EPA include increased G-protein-receptor-mediated release of glucagon-like peptide 1 (GLP-1) from enteroendocrine L-cells in the intestine, up-regulation of the apelin pathway and down-regulation of other control pathways to promote insulin secretion by the pancreatic β-cells, together with suppression of inflammatory responses to adipokines, inhibition of peroxisome proliferator-activated receptor α actions and prevention of decreased insulin-like growth factor-1 secretion to improve peripheral insulin responses. The receptors involved and the mechanisms of action probably differ for ALA and DHA, with antiobesity effects predominating for ALA and anti-inflammatory effects for DHA. Modifying both GLP-1 release and the actions of adipokines by n-3 PUFAs could lead to additive improvements in both insulin secretion and sensitivity.

High-fat diet from perilla oil induces insulin resistance despite lower serum lipids and increases hepatic fatty acid oxidation in rats

Background

The purpose of this study is to investigate the effects of a high-fat diet from perilla oil on serum lipids, hepatic lipid metabolism and insulin sensitivity.

Methods

Male Sprague–Dawley (SD) rats were fed either a control (CT) diet or a diet high in perilla oil (HP). After 16 weeks of feeding, the serum lipids were measured, and the gene expressions involved in hepatic fatty acid oxidation and synthesis were determined. In addition, hepatic fat deposition was detected, and insulin sensitivity was evaluated by means of euglycemic-hyperinsulinemic clamp.

Results

Compared with the rats in the CT group, the HP-feeding significantly decreased the levels of triglyceride (TG), total cholesterol (TCH) and HDL-cholesterol (HDL-c). HP-feeding did not change the levels of LDL-cholesterol (LDL-c), free fatty acid (FFA), intrahepatic lipids or body weight. Moreover, the HP-feeding dramatically increased the mRNA expressions of fatty acid oxidation markers (PPAR-alpha, CPT1A) and fatty acid synthesis markers (SREBP-1, FASN and ACC) in the liver. The HP-feeding induced increased protein levels of CPT1A, while reducing the protein levels of FASN and ACC in the liver. However, the glucose infusion rate significantly increased in the HP group compared with the CT group.

Conclusions

Our data show that, in rats, excessive perilla oil intake may significantly lower serum lipids, strengthen hepatic fatty acid oxidation, and inhibit hepatic fatty acid synthesis, but at the same time may also lead to insulin resistance.

Dietary Salba (Salvia hispanica L) seed rich in α-linolenic acid improves adipose tissue dysfunction and the altered skeletal muscle glucose and lipid metabolism in dyslipidemic insulin-resistant rats

This work reports the effect of dietary Salba (chia) seed rich in n-3 α-linolenic acid on the morphological and metabolic aspects involved in adipose tissue dysfunction and the mechanisms underlying the impaired glucose and lipid metabolism in the skeletal muscle of rats fed a sucrose-rich diet (SRD). Rats were fed a SRD for 3 months. Thereafter, half the rats continued with SRD while in the other half, corn oil (CO) was replaced by chia seed for 3 months (SRD+chia). In control group, corn starch replaced sucrose. The replacement of CO by chia seed in the SRD reduced adipocyte hypertrophy, cell volume and size distribution, improved lipogenic enzyme activities, lipolysis and the anti-lipolytic action of insulin. In the skeletal muscle lipid storage, glucose phosphorylation and oxidation were normalized. Chia seed reversed the impaired insulin stimulated glycogen synthase activity, glycogen, glucose-6-phosphate and GLUT-4 protein levels as well as insulin resistance and dyslipidemia.

Inhibitory potential of fatty acids on key enzymes related to type 2 diabetes

This study aimed to examine the inhibitory mechanisms of fatty acids on key enzymes related to type 2 diabetes, and their effects on starch digestion rate. Among the 10 fatty acids analyzed, oleic acid showed the strongest anti-α-glucosidase activity, followed by linoleic acid, and their activities were more potent than acarbose, but they possessed a weaker anti-α-amylase activity. Kinetic assays demonstrated that oleic acid and linoleic acid were competitive inhibitors, and their interactions with α-glucosidase exhibited a character of static quenching, which indicates that they would bind to α-glucosidase to form a complex. However, they had little effects on the secondary structures of α-glucosidase. In vitro study showed that oleic acid and linoleic acid were more potent than acarbose in inhibiting starch digestion. Taken together, these results conclude that oleic acid and linoleic acid possess potent inhibitory effects on α-glucosidase activity.

Early cardiac changes in a rat model of prediabetes: brain natriuretic peptide overexpression seems to be the best marker

Background

Diabetic cardiomyopathy (DCM) is defined as structural and functional changes in the myocardium due to metabolic and cellular abnormalities induced by diabetes mellitus (DM). The impact of prediabetic conditions on the cardiac tissue remains to be elucidated. The goal of this study was to elucidate whether cardiac dysfunction is already present in a state of prediabetes, in the presence of insulin resistance, and to unravel the underlying mechanisms, in a rat model without obesity and hypertension as confounding factors.

Methods

Two groups of 16-week-old Wistar rats were tested during a 9 week protocol: high sucrose (HSu) diet group (n = 7) – rats receiving 35% of sucrose in drinking water vs the vehicle control group (n = 7). The animal model was characterized in terms of body weight (BW) and the glycemic, insulinemic and lipidic profiles. The following parameters were assessed to evaluate possible early cardiac alterations and underlying mechanisms: blood pressure, heart rate, heart and left ventricle (LV) trophism indexes, as well as the serum and tissue protein and/or the mRNA expression of markers for fibrosis, hypertrophy, proliferation, apoptosis, angiogenesis, endothelial function, inflammation and oxidative stress.

Results

The HSu-treated rats presented normal fasting plasma glucose (FPG) but impaired glucose tolerance (IGT), accompanied by hyperinsulinemia and insulin resistance (P < 0.01), confirming this rat model as prediabetic. Furthermore, although hypertriglyceridemia (P < 0.05) was observed, obesity and hypertension were absent. Regarding the impact of the HSu diet on the cardiac tissue, our results indicated that 9 weeks of treatment might be associated with initial cardiac changes, as suggested by the increased LV weight/BW ratio (P < 0.01) and a remarkable brain natriuretic peptide (BNP) mRNA overexpression (P < 0.01), together with a marked trend for an upregulation of other important mediators of fibrosis, hypertrophy, angiogenesis and endothelial lesions, as well as oxidative stress. The inflammatory and apoptotic markers measured were unchanged.

Conclusions

This animal model of prediabetes/insulin resistance could be an important tool to evaluate the early cardiac impact of dysmetabolism (hyperinsulinemia and impaired glucose tolerance with fasting normoglycemia), without confounding factors such as obesity and hypertension. Left ventricle hypertrophy is already present and brain natriuretic peptide seems to be the best early marker for this condition.

Serum Omega-6/Omega-3 Ratio and Risk Markers for Cardiovascular Disease in an Industrial Population of Delhi

High omega-6/omega-3 ratio intake promotes development of many chronic diseases. Secondary prevention studies though have demonstrated a decline in progression of many such diseases after reducing the intake, specific biochemical indices of cardiovascular disease risk markers have not been evaluated. We have evaluated the circulating levels of omega-6/omega-3 ratio and its effect on cardiovascular risk markers in India. Present study was conducted in industrial setting where employees were randomly selected. Data on their demographic characteristics were collected using pre-tested questionnaire. Fasting blood samples were collected from all the participants. Serum was separated and stored at −80°C till the time of analysis. Lipids were estimated using standard kits. Fatty acids in serum were estimated by Gas chromatography. The identified Omega-3 fatty acid included were 18:3 (Alpha-linolenic acid), 20:5 (Eicosapentenoic acid) & 22:6 (Docosahexenoic acid). Among omega-6 included were 18:2 (linoleic acid), 18:3 (gamma-linolenic acid) & 20:4 (Arachidonic acid). Complete data was available for 176 participants (89% males and 11% females) with mean age of 47.23 ± 6.00 years. The bmi of the participants was 24.88 ± 3.43 Kg/m² and waist circumference was 91.50 ± 9.56 cm. The median of omega-6/omega-3 ratio in the study population was 36.69 (range: 6.21 - 183.69). The levels of total cholesterol, triglycerides, ldl-cholesterol and cholesterol/hdl ratio and apo B correlated significantly with omega-6/3 ratio. There was no correlation observed with hsCRP and LDL-particle size. A direct relationship of omega-6/omega-3 ratio with dyslipidemia was observed in our study.

Dietary chia seed induced changes in hepatic transcription factors and their target lipogenic and oxidative enzyme activities in dyslipidaemic insulin-resistant rats

The present study analyses the effect of dietary chia seed rich in n-3 α-linolenic acid on the mechanisms underlying dyslipidaemia and liver steatosis developed in rats fed a sucrose-rich diet (SRD) for either 3 weeks or 5 months. The key hepatic enzyme activities such as fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), glucose-6-phosphate dehydrogenase (G-6-PDH), carnitine palmitoyltransferase-1 (CPT-1) and fatty acid oxidase (FAO) involved in lipid metabolism and the protein mass levels of sterol regulatory element-binding protein-1 (SREBP-1) and PPARα were studied. (1) For 3 weeks, Wistar rats were fed either a SRD with 11 % of maize oil (MO) as dietary fat or a SRD in which chia seed replaced MO (SRD+Chia). (2) A second group of rats were fed a SRD for 3 months. Afterwards, half the rats continued with the SRD while for the other half, MO was replaced by chia for 2 months (SRD+Chia). In a control group, maize starch replaced sucrose. Liver TAG and the aforementioned parameters were analysed in all groups. The replacement of MO by chia in the SRD prevented (3 weeks) or improved/normalised (5 months) increases in dyslipidaemia, liver TAG, FAS, ACC and G-6-PDH activities, and increased FAO and CPT-1 activities. Protein levels of PPARα increased, and the increased mature form of SREBP-1 protein levels in the SRD was normalised by chia in both protocols (1 and 2). The present study provides new data regarding some key mechanisms related to the fate of hepatic fatty acid metabolism that seem to be involved in the effect of dietary chia seed in preventing and normalising/improving dyslipidaemia and liver steatosis in an insulin-resistant rat model.

Omega-3 fatty acids and incident type 2 diabetes: a systematic review and meta-analysis

The relationship between omega-3 polyunsaturated fatty acids (n-3 PUFA) from seafood sources (eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA) or plant sources (alpha-linolenic acid, ALA) and risk of type 2 diabetes mellitus (DM) remains unclear. We systematically searched multiple literature databases through June 2011 to identify prospective studies examining relations of dietary n-3 PUFA, dietary fish and/or seafood, and circulating n-3 PUFA biomarkers with incidence of DM. Data were independently extracted in duplicate by 2 investigators, including multivariate-adjusted relative risk (RR) estimates and corresponding 95 % CI. Generalized least-squares trend estimation was used to assess dose-response relationships, with pooled summary estimates calculated by both fixed-effect and random-effect models. From 288 identified abstracts, 16 studies met inclusion criteria, including 18 separate cohorts comprising 540,184 individuals and 25,670 cases of incident DM. Consumption of fish and/or seafood was not significantly associated with DM (n = 13 studies; RR per 100 g/d = 1·12, 95 % CI = 0·94, 1·34); nor were consumption of EPA+DHA (n = 16 cohorts; RR per 250 mg/d = 1·04, 95 % CI = 0·97, 1·10) nor circulating levels of EPA+DHA biomarkers (n = 5 cohorts; RR per 3 % of total fatty acids = 0·94, 95 % CI = 0·75, 1·17). Both dietary ALA (n = 7 studies; RR per 0·5 g/d = 0·93, 95 % CI = 0·83, 1·04) and circulating ALA biomarker levels (n = 6 studies; RR per 0·1 % of total fatty acid = 0·90, 95 % CI = 0·80, 1·00, P = 0·06) were associated with non-significant trend towards lower risk of DM. Substantial heterogeneity (I²~80 %) was observed among studies of fish/seafood or EPA+DHA and DM; moderate heterogeneity ( < 55 %) was seen for dietary and biomarker ALA and DM. In unadjusted meta-regressions, study location (Asia vs. North America/Europe), mean BMI, and duration of follow-up each modified the association between fish/seafood and EPA+DHA consumption and DM risk (P-interaction ≤ 0·02 each). We had limited statistical power to determine the independent effect of these sources of heterogeneity due to their high collinearity. The overall pooled findings do not support either major harms or benefits of fish/seafood or EPA+DHA on development of DM, and suggest that ALA may be associated with modestly lower risk. Reasons for potential heterogeneity of effects, which could include true biologic heterogeneity, publication bias, or chance, deserve further investigation.

A bioactivity guided study on the antidiabetic activity of Juniperus oxycedrus subsp. oxycedrus L. leaves

ETHNOPHARMACOLOGICAL RELEVANCE

Juniperus (Cupressaceae) species are widely used as folk medicine in spreading countries. Decoction of Juniperus oxycedrus subsp. oxycedrus L. leaves is used internally to lower blood glucose levels in Turkey.

AIM OF THE STUDY

To determine hypoglycaemic and antidiabetic activities of Juniperus oxycedrus subsp. oxycedrus leaves and to identify active compounds through bioactivity guided isolation technique.

MATERIALS AND METHODS

Ethanol and water extracts of Juniperus oxycedrus subsp. oxycedrus (Joso), leaves on oral administration were studied using in vivo models in normal, glucose-hyperglycemic and streptozotocin-induced diabetic rats. Through in vivo bioactivity-guided fractionation processes, a nonpolar fraction was separated from the n-hexane subextract by silica gel column chromatography as the main active fraction. Subfractions of this fraction was found to possess antidiabetic activity and their chemical composition was investigated by GC-FID and GC-MS, simultaneously.

RESULTS

This is the first report on the antidiabetic constituents of Joso leaves. Fatty acids, such as palmitic, linoleic and linolenic acid were found as the major compounds in subfractions.

CONCLUSION

Results indicated that Joso leaf extract and its active constituents might be beneficial for diabetes mellitus.

Supplementation of n3 long-chain polyunsaturated fatty acid synergistically decreases insulin resistance with weight loss of obese prepubertal and pubertal children

BACKGROUND AND AIMS

Supplementation with n3 long-chain polyunsaturated fatty acids (n3-LCPUFA) appears to affect body weight, adipokines, and insulin resistance (IR) in obese individuals. However, it is unclear whether the effect on IR is independent of weight loss and if the same effect is observed in children. We undertook this study to analyze the effect of supplementation with n3-LCPUFA on adipokine concentration and IR of prepubertal and pubertal children, independent of weight loss.

METHODS

Included were 76 children, 9- to 18-years of age. Subjects were overweight and insulin resistant, but otherwise healthy. They were randomly assigned to receive 900 mg n3-LCPUFA daily (Omega III, Salmon Oil, GNLD) or placebo for 1 month. No dietary intervention was conducted. Dietary information, anthropometry, and blood samples to measure adipokines and IR were obtained at baseline. Anthropometry and measurement of biochemical parameters were repeated at the end of follow-up. For analysis, children were stratified by treatment (placebo and n3-FA) and according to changes in body weight (increase, decrease, unchanged).

RESULTS

Twenty seven children received placebo and 49 received the n3-LCPUFA. Despite no differences at baseline, only the n3-FA group decreased fasting insulin and HOMA-IR (p <0.010). Significant differences between groups were observed for changes in TNF-α, leptin and adiponectin after supplementation (p <0.050). At the end of the 1-month period, 16 children lost weight and 27 children gained weight. Multiple analysis demonstrated that supplementation with n3-LCPUFA decreased HOMA-IR by 15% after adjusting for puberty, treatment adherence, changes in adipokines, and weight loss. Interaction between supplementation and weight loss was significant (p = 0.007).

CONCLUSIONS

Supplementation with n3-LCPUFA is a potential beneficial tool for obese at-risk children.

Attenuation of colonic inflammation by partial replacement of dietary linoleic acid with α-linolenic acid in a rat model of inflammatory bowel disease

Increasing prevalence of inflammatory bowel disease may be due to imbalance in the intake of n-6 and n-3 PUFA in the diet. This study investigates the impact of varying ratios of dietary linoleic acid (LA, 18 : 2n-6) to α-linolenic acid (ALA, 18 : 3n-3) on the inflammatory response in dextran sulphate sodium (DSS)-induced colitis. Weanling male Sprague-Dawley rats were divided into five groups: a non-colitic group with a LA:ALA ratio of 215 (CON-215), and colitic groups with LA:ALA ratios of 215 (DSS-215), 50 (DSS-50), 10 (DSS-10) and 2 (DSS-2). Blends of groundnut, palmolein and linseed oils were used to provide varying LA:ALA ratios. All the rats were fed the respective experimental isoenergetic diets containing 10 % fat for 90 d and DSS was administered during the last 11 d. Colonic inflammation was evaluated by clinical, biochemical and histological parameters. The results showed attenuation of colitis in the DSS-2 group as evidenced by significant reductions in disease activity index, mucosal myeloperoxidase activity (P < 0·05), alkaline phosphatase activity (P < 0·01) and increase in colon length (P < 0·01) compared to the groups fed with higher ratios (DSS-215). This was accompanied by significant reductions in mucosal proinflammatory cytokines TNF-α (P < 0·01) and IL-1β (P < 0·01) and improvement in the histological score. Further, ALA supplementation increased long-chain (LC) n-3 PUFA and decreased LC n-6 PUFA in colon structural lipids. These data suggest that substitution of one-third of LA with ALA (LA:ALA ratio 2) mitigates experimental colitis by down-regulating proinflammatory mediators.

A decreased n-6/n-3 ratio in the fat-1 mouse is associated with improved glucose tolerance

A reduction in skeletal muscle fatty acid oxidation (FAO), manifested as a reduction in mitochondrial content and (or) FAO within mitochondria, may contribute to the development of insulin resistance. n-3 polyunsaturated fatty acids (PUFA) have been observed to increase the capacity for FAO and improve insulin sensitivity. We used the fat-1 mouse model, a transgenic animal capable of synthesizing n-3 PUFA from n-6 PUFA, to examine this relationship. Fat-1 mice exhibited a approximately 20-fold decrease in the n-6/n-3 ratio in skeletal muscle, and plasma glucose and the area under the glucose curve were significantly (p < 0.05) lower in fat-1 mice during a glucose challenge test. The improvement in whole-body glucose tolerance in the fat-1 mouse was associated with a approximately 21% (p < 0.05) decrease in whole-muscle citrate synthase (CS) activity (in red muscle only), without alterations in CS activity of isolated mitochondria (either red or white muscle; p > 0.05). These data suggest that the fat-1 mouse has decreased skeletal muscle mitochondrial content. However, the intrinsic ability of mitochondria to oxidize fatty acids was not altered in the fat-1 mouse, as rates of palmitate oxidation in isolated mitochondria from both red and white muscle were unchanged. Overall, this study demonstrates that a decrease in the n-6/n-3 ratio can enhance glucose tolerance in healthy animals, independent of changes in mitochondrial content.

The ω-3 and ω-6 fats in meals: a proposal for a simple new label

OBJECTIVE

The ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are separate essential dietary fatty acids that play a key role in many physiologic processes in higher animals. The content of these PUFAs is relatively well described for many individual food components. Our goal in this study was to analyze the PUFA content of whole meals and produce a simple measurement to estimate the intake of these fatty acids.

METHODS

The fatty acid profile and macronutrient composition were determined for a range of fast food, cuisine (restaurant-prepared), and home-prepared whole meals commonly consumed by Australians.

RESULTS

Across the different meals there was significant variation in protein (4-fold), fat (13-fold), and carbohydrate (23-fold) contents. With regard to the fatty acid profile, saturated and monounsaturated fatty acids made up approximately 80% of total fatty acids for most meals. The ω-6 PUFAs were substantially more abundant than ω-3 PUFAs for most meals. The balance of dietary ω-3 and ω-6 PUFAs is an important determinant of their metabolic effects within the body, and accordingly we calculated the percentage of the total PUFA comprised of ω-3 PUFAs and referred to this as the PUFA Balance. This parameter showed the greatest variation among the different meals (>45-fold).

CONCLUSION

The relative proportions of ω-3 and ω-6 PUFAs vary greatly across meals. PUFA Balance is a useful tool that will allow individuals to more easily monitor and balance their intake of ω-3 and ω-6 fats.

Flax oil-mediated activation of PPAR-γ correlates with reduction of hepatic lipid accumulation in obese spontaneously hypertensive/NDmcr-cp rats, a model of the metabolic syndrome

Flax oil feeding has been proposed to have beneficial effects on the outcome of the metabolic syndrome due to the high n-3 fatty acid content of flax oil; however, the mechanisms of its action remain largely unknown. We investigated the effects of flax oil feeding on hyperlipidaemia, hyperglycaemia, hepatic steatosis and oxidative stress in the spontaneously hypertensive (SHR)/NDmcr-cp rats, a genetic model of the metabolic syndrome. Hepatic gene expression of PPAR-α, PPAR-γ and sterol-regulatory element-binding protein-1c was also assessed in order to investigate the possible underlying mechanisms. Obese and lean SHR/NDmcr-cp rats were fed high-fat diets enriched with either lard or flax oil for a period of 4 weeks. Obese rats exhibited higher body weight, liver weight and mesenteric fat-, epididymal fat- and renal fat-pad weights, and also TAG and cholesterol concentrations in serum and VLDL, LDL and HDL fractions, when compared with the lean rats (P < 0·001), irrespective of the diets. Concentrations of fasting serum insulin and urinary thiobarbituric acid reactive substances were lower in flax oil-fed obese (FO) rats compared with the lard-fed obese (LO) rats (P < 0·01). Flax oil feeding also revealed a significant reduction in hepatic TAG and cholesterol concentrations in obese rats compared with the LO rats (P < 0·05). In addition, FO rats exhibited significantly higher hepatic mRNA expression of PPAR-γ, which negatively correlated (r - 0·98, P < 0·05) with their hepatic lipid levels. These findings suggest that flax oil feeding may activate PPAR-γ-dependent pathways to alter the hepatic lipid metabolism and to increase insulin sensitivity in the obese SHR/NDmcr-cp rats.

Skeletal muscle structural lipids improve during weight-maintenance after a very low calorie dietary intervention

Background

The objective was to investigate in a group of obese subjects the course in skeletal muscle phospholipid (SMPL) fatty acids (FA) during a 24-weeks weight maintenance program, which was preceded by a successful very low calorie dietary intervention (VLCD). Special focus was addressed to SMPL omega-3 FA, which is a lipid entity that influences insulin action.

Methods

Nine obese subjects (BMI = 35.7 ± 1.0 kg/m²), who had completed an 8 weeks VLCD (weight-loss = -9.7 ± 1.6 kg, P < 0.001), had obtained skeletal muscle biopsies (vastus lateralis) before and after a dietician-guided 24-weeks weight-maintenance program (-1.2 ± 1.5 kg, P = ns). SMPL FA composition was determined by gas liquid chromatography. During the preceding VLCD, insulin sensitivity (HOMA-IR) and glycemic control (HbA1c) improved but no change in SMPL omega-3 FA was observed. During the weight-maintenance program five subjects received the pancreas lipase inhibitor Orlistat 120 mg t.i.d. versus placebo.

Results

HOMA-IR and HbA1c stabilized and SMPL total omega-3 FA, docosahexaenoic acid and ratio of n-3/n-6 polyunsaturated FA increased by 24% (P < 0.01), 35% (P < 0.02) and 26% (P < 0.01), respectively, whereas saturated and monounsaturated FA did not change. Plasma total-cholesterol and LDL-cholesterol, which decreased during the VLCD, reverted to pre-VLCD levels (P < 0.01). Orlistat therapy was associated with weight-loss (P < 0.05), trends for better glycemic control (P = 0.15) and greater increase in SMPL docosahexaenoic acid (P = 0.12) but similar reversal of plasma cholesterols compared to placebo.

Conclusion

The data are consistent with the notion that greater SMPL omega-3 FA obtained during a weight-maintenance program may play a role for preserving insulin sensitivity and glycemic control being generated during a preceding VLCD.

Are all n-3 polyunsaturated fatty acids created equal?

N-3 Polyunsaturated fatty acids have been shown to have potential beneficial effects for chronic diseases including cancer, insulin resistance and cardiovascular disease. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in particular have been studied extensively, whereas substantive evidence for a biological role for the precursor, alpha-linolenic acid (ALA), is lacking. It is not enough to assume that ALA exerts effects through conversion to EPA and DHA, as the process is highly inefficient in humans. Thus, clarification of ALA's involvement in health and disease is essential, as it is the principle n-3 polyunsaturated fatty acid consumed in the North American diet and intakes of EPA and DHA are typically very low. There is evidence suggesting that ALA, EPA and DHA have specific and potentially independent effects on chronic disease. Therefore, this review will assess our current understanding of the differential effects of ALA, EPA and DHA on cancer, insulin resistance, and cardiovascular disease. Potential mechanisms of action will also be reviewed. Overall, a better understanding of the individual role for ALA, EPA and DHA is needed in order to make appropriate dietary recommendations regarding n-3 polyunsaturated fatty acid consumption.

Lipogenic enzyme activities and glucose uptake in fat tissue of dyslipemic, insulin-resistant rats: effects of fish oil

OBJECTIVE

The purposes of the present work were twofold: (1) investigate same mechanisms involved in the development of fat cell hypertrophy in the experimental model of dyslipidemia and whole-body insulin resistance induced in rats chronically fed a sucrose-rich diet (SRD); and (2) analyze the possible beneficial effect of fish oil on these mechanisms.

METHODS

For 6 mo, male Wistar rats received a sucrose-rich diet (62.5% w/w sucrose, 8% corn oil) or a control diet in which sucrose was replaced by starch. After this period, the sucrose-fed animals were divided randomly into two groups: the first one continued with the same diet up to 8 mo and the second one received the same diet, but with corn oil replaced by 7% fish oil+1 % corn oil. Rats were fed with this diet for the next 2 mo.

RESULTS

Although an enlarged fat cell lipolysis and an impaired insulin-stimulated glucose uptake were present in the fat cells of SRD-fed rats, an increase of several key enzymes of the novo lipogenesis could be one of the possible mechanisms involved in visceral adiposity. The addition of dietary fish oil restored or improved the above abnormalities.

CONCLUSION

This study shows possible mechanisms conditioning the influence of nutrients on the development and management of dyslipidemia, insulin sensitivity, and fat cell accretion, all abnormalities present in the metabolic syndrome.

High vitamin intake by Wistar rats during pregnancy alters tissue fatty acid concentration in the offspring fed an obesogenic diet

Diet during pregnancy affects the long-term health of the offspring. Vitamins are known to modulate lipid metabolism, which may be reflected in tissue fatty acid (FA) concentrations. The objective of this study was to investigate the effect of high vitamin intake during pregnancy on tissue FA concentration of the offspring. Wistar rats were fed an AIN-93G diet with either the recommended vitamin or 10-fold higher amounts (HV) during pregnancy. Afterward, offspring were weaned onto an obesogenic diet. Liver, quadriceps, adipose, and brain were collected over 48 weeks. Fatty acid concentration of tissue total lipids was analyzed by gas chromatography. At birth, the liver from HV offspring was higher in monounsaturated, stearic, and arachidonic acids. At weaning, the liver from HV offspring was higher in stearic and oleic acids; and in adipose tissue, n-6 and n-3 FAs were lower only in the male HV offspring (P < .05). At 12 weeks, HV offspring had higher concentrations of total fat, saturates, monounsaturates, and n-6 FA in muscle (P < .05), but not in other tissues. At 48 weeks, gestational diet did not affect tissue total lipid FA concentrations; but differences remained in specific tissue phospholipids species. Liver phospholipids from HV offspring were lower in monounsaturates and n-6 FA. Brain phosphatidylethanolamine was higher in oleic, n-6 FA, and docosahexaenoic acid in the HV offspring. Phosphatidylinositol was lower in saturates, monounsaturates, arachidonic, and docosahexaenoic acids only in HV female offspring. These observations demonstrate that high vitamin intake during pregnancy has short- and long-term effects on tissue FA concentration in the offspring.

Impact of maternal dietary fatty acid composition on glucose and lipid metabolism in male rat offspring aged 105 d

In recent years the intake ofn-6 PUFA andtrans-fatty acids (TFA) has increased, whereasn-3 PUFA intake has decreased. The present study investigated the effects of maternal diet high inn-6 PUFA,n-3 PUFA or TFA on glucose metabolism, insulin sensitivity and fatty acid profile in male offspring. Female weanling Wistar/NIN rats were randomly assigned to receive either a diet high in linoleic acid (LA), or α-linolenic acid (ALA), or long-chainn-3 PUFA (fish oil; FO), or TFA, for 90 d, and mated. Upon weaning, pups were randomly divided into seven groups (mother's diet-pup's diet): LA-LA, LA-ALA, LA-FO, ALA-ALA, FO-FO, TFA-TFA and TFA-LA. At the age of 105 d, an oral glucose tolerance test, adipocyte glucose transport and muscle phospholipid fatty acid composition were measured in the pups. All animals displayed normal insulin sensitivity as evidenced by similar plasma insulin and area under the curve of insulin after an oral glucose load. Maternal intake ofn-3 PUFA (ALA or FO) resulted in highern-3 PUFA in the offspring. Plasma cholesterol and NEFA were significantly higher in the TFA-TFA group compared with the other groups. Adipocyte insulin-stimulated glucose transport and adiponectin mRNA expression were lower in TFA-TFA and TFA-LA offspring compared with the other groups. While most mother-pup fatty acid combinations did not influence the measured variables in the pups, these results indicate that maternal intake of TFA led to an unfavourable profile in the pups through to the age of 105 d, whether the pups consumed TFA, or not.

Long-chain (n-3) polyunsaturated fatty acids prevent metabolic and vascular disorders in fructose-fed rats

The crossover relationship between cardiometabolic risk, in terms of insulin resistance and vascular dysfunction, and the fatty acid (FA) profile of insulin-sensitive tissues as well as the dietary FA impact has almost never been explored in the same experiment. In this study, the intake of alpha-linolenic acid (ALA) alone and/or with its higher metabolites, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) were evaluated in a nonobese, hypertriglyceridemic and insulin-resistant rat model, that exhibits the 2 main characteristics of metabolic syndrome. Wistar rats were fed either a cornstarch and (n-6) PUFA-based diet (C-N6) or a 66% fructose diet over a 10-wk period. Fructose-fed rats received a diet containing ALA alone (F-ALA group) or ALA plus EPA and DHA (F-LC3 group) or no (n-3) PUFA (F-N6 group). The 10-wk high-fructose diet (F-N6) induced an insulin-resistant state, as assessed by glucose and insulin tolerance tests. Insulin resistance was linked to a specific FA pattern in insulin-sensitive tissues, which probably involved modifications of Delta9, Delta6, and Delta5-desaturases. This pathological status was related to high cardiovascular risk as assessed by increases in systolic and diastolic blood pressures and particularly by the increase of pulse pressure, an index of vascular stiffness obtained from telemetry investigations. The (n-3) experimental diets prevented changes in the FA patterns in insulin-sensitive tissues, insulin resistance, and vascular dysfunction. This beneficial effect was large with an intake of long chain (n-3) PUFA (ALA+EPA+DHA) and to a lesser extent with dietary ALA alone.

Diet during early pregnancy and development of gestational diabetes

Diet composition may be a modifiable predictor of risk for abnormal glucose tolerance during pregnancy. Prior studies suggest that diets high in total fat, saturated fat, red and processed meats, and with high glycaemic load increase the risk of developing gestational diabetes mellitus (GDM), while polyunsaturated fats, carbohydrates and fibre are protective. The aim of this study was to investigate associations of these and other nutrients and foods, including n-3 fatty acids, trans fats, whole grains and dietary patterns, with risk of GDM. We studied 1733 women with singleton pregnancies enrolled in Project Viva, a prospective pregnancy and birth cohort study in eastern MA. Using multinomial logistic regression, we examined associations of first trimester diet, assessed by validated food frequency questionnaire, with results of glucose tolerance testing at 26-28 weeks of gestation. A total of 91 women developed GDM and 206 women had impaired glucose tolerance (IGT). Pre-pregnancy body mass index (BMI) was a strong predictor for GDM risk (OR 3.44 [95% CI 1.88, 6.31] for pre-pregnancy BMI > or =30 vs. <25 kg/m(2)). After adjustment for confounders, the OR [95% CI] for risk of GDM for total dietary fat was 1.00 [0.96, 1.05], for saturated fat 0.98 [0.88, 1.08], for polyunsaturated fat 1.09 [0.94, 1.26], for trans fat 0.87 [0.51, 1.49], and for carbohydrates 1.00 [0.96, 1.03] per each 1% of total energy. The adjusted OR [95% CI] for risk of GDM for a one standard deviation increase in energy-adjusted glycaemic load (32 units, about two soft drinks) was 0.96 [0.76, 1.22] and for each daily serving of whole grains was 0.90 [0.73, 1.13]. Dietary patterns and intake of red and processed meats were not predictive of glucose tolerance outcome. Estimates for IGT were similar to those for GDM. Intake of n-3 fatty acids was associated with increased GDM risk (OR 1.11 [95% CI 1.02, 1.22] per each 300 mg/day), but not with IGT risk. Except for this finding, perhaps due to chance, these data do not show that nutrient or food intake in early pregnancy is linked to risk of GDM. Nutritional status entering pregnancy, as reflected by pre-pregnancy BMI, is probably more important than pregnancy diet in development of GDM.

α-Linolenic acid attenuates high glucose-induced apoptosis in cultured human umbilical vein endothelial cells via PI3K/Akt/eNOS pathway

OBJECTIVE

High glucose-induced apoptosis in vascular endothelial cells contributes to the acceleration of atherosclerosis associated with diabetes. We hypothesized that alpha-linolenic acid (ALA) might attenuate high glucose-induced apoptosis in cultured human umbilical vein endothelial cells (HUVECs).

METHODS

HUVECs were cultured at 5.5 and 33 mmol/L for 72 h. ALA with different concentrations was added with defatted bovine serum albumin as a carrier for 18 h before incubation with high glucose.

RESULTS

Exposure of HUVECs to high glucose media for 72 h significantly increased the number of apoptotic cells compared with normal glucose control, as evaluated by flow cytometry and terminal deoxyuridine triphosphate nick end labeling assay. Pretreatment with low concentrations of ALA (10, 50, and 100 micromol/L) significantly attenuated high glucose-induced apoptosis of HUVECs, but increasing ALA to 200 micromol/L exerted the opposite effect. Furthermore, high glucose reduced phosphorylation of Akt and endothelial nitric oxide synthase (eNOS) with subsequent nitric oxide production, whereas ALA treatment attenuated the reduction caused by high glucose. Pretreatment with phosphatidylinositol 3' -kinase kinase inhibitor LY294002 and eNOS inhibitor N(G)-nitro-arginine methyl ester eliminated ALA' antiapoptotic effect.

CONCLUSION

ALA exerts an antiapoptotic effect by the phosphatidylinositol 3'-kinase/Akt/eNOS pathway in HUVECs exposed to high glucose and thus may represent a candidate therapeutic agent for diabetic cardiovascular complications.

Dietary palatinose and oleic acid ameliorate disorders of glucose and lipid metabolism in Zucker fatty rats

Excessive dietary intake of carbohydrates and fats has been linked to the development of obesity. However, the mechanism by which these dietary factors interact to bring about metabolic changes has not been elucidated. We examined the combined effects of different types of dietary carbohydrates and fats on the etiology of obesity and its complications in the Zucker fatty (fa/fa) rat, a model of obesity. Specifically, these rats were fed an isocaloric diet containing various combinations of carbohydrates [palatinose (P), an insulin-sparing sucrose analogue, and sucrose (S)] and fatty acids [oleic acid (O) and linoleic acid (L)]. After 8 wk, palatinose feeding (PO and PL) led to significant reductions in visceral fat mass, adipocyte cell size, hyperglycemia, and hyperlipidemia compared with sucrose feeding (SO and SL); pancreatic islet hypertrophy was also prevented by palatinose feeding. Linoleic-acid-fed rats (PL and SL) exhibited reduced insulin-immunoreactive staining of the pancreatic islets, enhanced macrophage infiltration in adipose tissue, and an elevated plasma tumor necrosis factor-alpha concentration when compared with oleic-acid-fed rats (PO and SO). Furthermore, sucrose and linoleic acid synergistically increased the expression of genes involved in hepatic gluconeogenesis and lipogenesis [sterol regulatory-element binding protein (SREBP)-1c and SREBP-2]. In conclusion, a diet containing palatinose and oleic acid may prevent diet-induced metabolic abnormalities. The combination of palatinose and oleic acid holds promise for a new approach to preventing and treating obesity and its complications.

Comparative review of diets for the metabolic syndrome: implications for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a significant health problem and affects 70 million adults in the United States (30% of the adult population), and an estimated 20% of these individuals have the most severe form of NAFLD-nonalcoholic steatohepatitis (NASH). The mechanisms underlying disease development and progression are awaiting clarification. Insulin resistance and obesity-related inflammation, among other possible genetic, dietary, and lifestyle factors, are thought to play a key role. A program targeting gradual weight reduction and physical exercise continues to be the gold standard of treatment for all forms of NAFLD. Even though weight loss and dietary and lifestyle changes are recommended as primary treatment for fatty liver, little to no scientific evidence is available on diet and NAFLD. This article reviews the implications of current dietary approaches, including national guidelines and popular weight-loss diets, with a focus on determining the optimal diet to prescribe for NAFLD and NASH patients. The effects of macronutrient content (carbohydrate, fat, and protein ratios) and specific food components, such as soluble fiber, n-3 fatty acids, and fructose, are discussed. The premises, effects, barriers, and issues related to current dietary guidelines and specific diets are discussed, and the question, "Will it work for the pathogenesis of NAFLD and NASH? ", is addressed.

Interactions between protein and vegetable oils in the maternal diet determine the programming of the insulin axis in the rat

The available evidence suggests that metabolic control mechanisms are programmed early in life. Previous studies of pregnant rats fed low-protein diets have suggested that the vegetable oils used in the experimental diets influence the outcome. The present study investigated the offspring of female rats fed semi-synthetic diets containing either 180 or 90 g casein/kg with 70 g/kg (w/w) of either corn oil or soya oil during gestation. During lactation, the dams received stock diet, and the offspring were subsequently weaned onto the stock diet. The offspring of dams fed the low-protein diets were smaller at birth. At 25 weeks of age, the offspring were subjected to an oral glucose tolerance test. In the offspring of dams fed the diet containing soya oil, the area under the insulin curve was affected by the protein content of the maternal diet. There was no effect of protein on the area under the insulin curve in the offspring of dams fed the diet prepared with corn oil. There were no differences in plasma glucose concentrations. The levels of mRNA for acetyl-CoA carboxylase-1 in the livers of female offspring were affected by the protein and oil content of the maternal diet. The level of carnitine palmitoyl transferase mRNA was affected by the protein content of the maternal diet. The present study suggests that PUFA in the maternal diet can interact with protein metabolism to influence the development of the offspring. This may involve the higher content of α-linolenic acid in soya oil compared with corn oil.

Gender-related response of lipid metabolism to dietary fatty acids in the hamster

Gender and dietary fatty acids are involved in the regulation of lipid metabolism, disturbances of which can lead to pathologies such as metabolic syndrome or CVD. Possible interactions between these factors were investigated in male and female hamsters fed diets rich in either saturated fatty acids (‘butter’ diet) or in α-linolenic acid (‘linseed oil’ diet). Gender effect predominated over the diet effect on cholesterol (CH) metabolism; compared to males, females exhibited lower concentrations of plasma total CH (−20%,P<0·001), LDL-CH (−40%,P<0·001) and HDL-CH (−16%,P<0·001), together with higher LDL receptor (+40%) and lower HDL receptor (−60%) hepatic content. Triacylglycerol (TG) metabolism was affected by diet above all: compared to animals fed the ‘butter’ diet, those fed the ‘linseed oil’ diet exhibited lower plasma (−23%,P=0·046) and liver TG (−20%,P=0·026) concentration which may result from both an increased β-oxidation (P<0·001), without any change in PPARα mRNA, and a decreased hepatic lipogenesis (P=0·023), without increased sterol response element binding protein 1c (SREBP1c) mRNA. The response to diet was much more pronounced in males than in females, without gender effect on the transcription level of PPARα and SREBP1c. Finally, the ‘linseed oil’ diet decreased the insulin resistance index (−80%,P<0·001) with a more marked effect in males, in relation to their higher hepatic PPARγ expression (+90%,P=0·012). In conclusion, in our model, the response of either TG or CH to dietary fatty acids is modulated differently by gender. The possible relevance of these interactions to dietary practice should be taken into account in man.

Desaturation of skeletal muscle structural and depot lipids in obese individuals during a very-low-calorie diet intervention

OBJECTIVE

This study investigated whether a very-lowcalorie dietary intervention (VLCD) may influence composition of skeletal muscle cell membrane phospholipid and composition and concentration of intramyocellular triglyceride (IMTG) in obese subjects. The working hypothesis proposed that a VLCD would decrease saturated fatty acids (FAs) and increase long-chain polyunsaturated FAs (LCPUFAs) in muscular structural lipids, as such changes have been associated with improved insulin sensitivity.

RESEARCH METHODS AND PROCEDURES

Skeletal muscle biopsies (vastus lateralis) were obtained from 13 obese subjects (nine women) before and after 8 weeks on VLCD (approximately 600 to 800 kcal/d). FA composition in muscle cell membrane phospholipid and concentration and FA composition of IMTG were determined by gas-liquid chromatography.

RESULTS

Baseline BMI was 36.0 +/- 3.4 kg/m2. Weight loss was 9.3 +/- 1.1 kg (8.8 +/- 1.1%; p < 0.0001); loss of adipose tissue was 5.9 +/- 0.9 kg (p < 0.0001). Insulin resistance (by homeostasis model assessment) decreased (-44 +/- 7%; p < 0.001). Muscle cell membrane phospholipid saturated FAs decreased (-3.2 +/- 1.3%; p < 0.05), whereas monounsaturated FAs (4.3 +/- 1.7%; p < 0.05), LCPUFAs (11 +/- 6%; p < 0.05), and the ratio of LCPUFAs to saturated FAs (12 +/- 5%; p < 0.05) increased. IMTG decreased, but not significantly (-5%). IMTG-saturated FAs decreased (-3.3 +/- 1.5%; p < 0.05), whereas LCPUFAn-3 (29 +/- 9%; p < 0.01), LCPUFAn-6 (33 +/- 9%; p < 0.01), and the ratio of LCPUFAs to saturated FAs (34 +/- 8%; p < 0.001) increased. Plasma total cholesterol (-15 +/- 6%; p < 0.05), low-density lipoprotein-cholesterol (-16 +/- 5%; p < 0.01), high-density lipoprotein-cholesterol (-8 +/- 2%; p < 0.01), and plasma triglyceride (-19 +/- 12%; p = 0.10) all decreased during the VLCD.

DISCUSSION

Desaturation of both muscle cell membrane phospholipid and IMTG was significant but modest during a VLCD in obese subjects. Further research must delineate whether such changes in skeletal muscle structural and depot lipid composition themselves are enough to promote the observed improvements in insulin action.

Dietary intervention increases n-3 long-chain polyunsaturated fatty acids in skeletal muscle membrane phospholipids of obese subjects. Implications for insulin sensitivity

OBJECTIVE

Cross-sectional studies suggest that the fatty acid (FA) composition of phospholipids in skeletal muscle cell membrane may modulate insulin sensitivity in humans. We examined the impact of a hypocaloric low-fat dietary intervention on membrane FA composition and insulin sensitivity. DESIGN Muscle membrane FA profiles were determined in muscle (vastus lateralis) biopsies from 21 obese subjects before and after 6 months of dietary restriction. Diet instructions emphasized low intake of FA of marine origin by recommending lean fish and prohibiting fatty fish and fish oil supplements. Insulin resistance was estimated by the homeostasis model assessment (HOMA-IR). RESULTS The mean weight loss was 5.1 kg (range -15.3 to +1.3 kg). BMI decreased from 36.5 to 34.9 kg/m(2) (P=0.003). Saturated FA (SFA) decreased 11% (P=0.0001). Polyunsaturated FA (PUFA)n-6 increased 4% (P =0.003). Long-chain PUFAn-3 increased 51% (P= 0.0001), mainly due to a 75% increase (P<0.0001) in docosahexaenoic acid. Changes in HOMA-IR correlated significantly with changes in long-chain PUFAn-3 (R=-0.57, P< 0.01), SFA (R=0.58, P<0.01) and waist circumference (R=0.46, P<0.05). A multivariate linear regression analysis that included changes in weight, fat mass, waist circumference, plasma lipids, PUFA, SFA and long-chain PUFAn-3 indicated that SFA and long-chain PUFAn-3 were independent predictors of HOMA-IR (R(2)=0.33, P<0.01).

CONCLUSIONS

A hypocaloric low-fat dietary intervention programme increased incorporation of long-chain PUFAn-3 and reduced SFA in skeletal muscle membrane phospholipids of obese subjects, a setting that may impact on insulin action.