Relationship of dietary fat to glucose metabolism

Modulatory Effect of Rice Bran and Phytic Acid on Glucose Metabolism in High Fat-Fed C57BL/6N Mice

The effect of dietary feeding of rice bran and phytic acid on the glucose metabolism in high fat-fed C57BL/6N mice fed was investigated. The mice were given with either a high fat diet only (HF group) or a high fat diet supplemented with rice bran (HF-RB group) or phytic acid (HF-PA group) for 7 weeks. The control mice (NC group) received a normal diet. At the end of the experimental period, the HF group exhibited substantially higher blood glucose level than the NC group. However, the HF-RB and HF-PA groups showed a marked decrease in the blood glucose level relative to HF mice. Furthermore, significantly higher glucokinase (GK) activity and lower phosphoenolpyruvate carboxykinase (PEPCK) activity were observed in HF-RB and HF-PA mice compared with that of the NC and HF ones. It was also found that the glucose-6-phosphatase (G6pase) activity and hepatic glycogen concentration were considerably higher in HF-RB and HF-PA groups, respectively, than that of the HF mice. These findings demonstrate that both rice bran and phytic acid could reduce the risk of high fat diet-induced hyperglycemia via regulation of hepatic glucose-regulating enzyme activities.

Postprandial effects of a lipid-rich meal in the rat are modulated by the degree of unsaturation of 18C fatty acids

The fatty acid composition of high-fat diets is known to influence the magnitude of postprandial events that increase the risk of metabolic syndrome. These variations in magnitude may be directly ascribed to differences in the channeling of lipids toward oxidation or storage. A study was designed to compare the effects of 4 dietary fats on postprandial energy expenditure and on some risk factors of the metabolic syndrome. To avoid usual confounding factors due to simultaneous variations in chain length and double-bounds number of fatty acids, dietary fats were chosen to provide mainly 18-carbon fatty acids with 0 (stearic acid [SA]), 1 (oleic acid [OA]), 2 (linoleic acid [LA]), or 3 (alpha-linolenic acid [ALA]) double bounds. They were given as single high-fat test meals to 4 different groups of male rats. The resting metabolic rate and the lipid and carbohydrate oxidation were measured from oxygen consumption and carbon dioxide production using indirect calorimetry 2 hours before and 6.5 hours after the test meal. Plasma glucose, triglyceride, and chylomicron concentrations were determined at 0, 1.5, and 4 hours after the test meal. Postprandial concentration of glucose and triglyceride did not vary with the nature of the test meals, whereas that of chylomicrons was the highest after the LA test meal and the lowest after the SA test meal. Postprandial increase in resting metabolic rate was the highest after the LA and OA test meals, and the lowest after the SA and ALA test meals. Compared with the 3 other diets, the ALA test meal enhanced lipid oxidation and decreased glucose oxidation during the early postprandial period (0.25-3.25 hours). This suggests that stearic acid may not induce all the adverse effects classically described for other saturated fatty acids and that alpha-linolenic acid may beneficially influence energy partitioning, especially during the early postprandial state.

Oligofructose and inulin modulate glucose and amino acid metabolism through propionate production in normal-weight and obese cats

The effect of dietary oligofructose and inulin supplementation on glucose metabolism in obese and non-obese cats was assessed. Two diets were tested in a crossover design; a control diet high in protein (46 % on DM basis), moderate in fat (15 %), low in carbohydrates (27 %), but no soluble fibres added; and a prebiotic diet, with 2·5 % of a mixture of oligofructose and inulin added to the control diet. Eight non-obese and eight obese cats were allotted to each of two diets in random order at intervals of 4 weeks. At the end of each testing period, intravenous glucose tolerance tests were performed. Area under the glucose curve (AUCgluc) was increased (P = 0·022) and the second insulin peak was delayed (P = 0·009) in obese compared to non-obese cats. Diets did not affect fasting plasma glucose concentrations, blood glucose response at each glucose time-point after glucose administration, AUCgluc, fasting serum insulin concentrations, area under the insulin curve, and height and appearance time of insulin response. Yet, analysis of acylcarnitines revealed higher propionylcarnitine concentrations (P = 0·03) when fed the prebiotic diet, suggesting colonic fermentation and propionate absorption. Prebiotic supplementation reduced methylmalonylcarnitine (P = 0·072) and aspartate aminotransferase concentrations (P = 0·025), both indicating reduced gluconeogenesis from amino acids. This trial evidenced impaired glucose tolerance and altered insulin response to glucose administration in obese compared to non-obese cats, regardless of dietary intervention; yet modulation of glucose metabolism by enhancing gluconeogenesis from propionate and inhibition of amino acid catabolism can be suggested.

Dietary patterns and metabolic syndrome factors in a non-diabetic Italian population

Objective

To examine the relationship between dietary patterns and metabolic syndrome.

Design

Population-based cross-sectional study. The K-means clustering method was used to identify dietary patterns and logistic regression models were used to compare the adjusted prevalence rates of metabolic syndrome factors, stratifying by obesity status.

Setting

The 1992–3 Italian Bollate Eye Study, a population-based survey carried out in the town of Bollate (Milan), Italy.

Subjects

A total of 1052 non-diabetic Italian subjects, 527 men and 525 women, aged 42–74 years.

Results

Five dietary clusters were identified: common, animal products, starch, vegetal/fat and vitamin/fibre. After adjusting for potential confounders, the starch group showed the highest prevalence of metabolic syndrome (36 %) followed by the animal products group (30 %); the vitamin/fibre (20 %) and vegetal/fat groups (19 %) showed the lowest prevalence. The starch group had more dyslipidaemia (higher TAG and lower HDL cholesterol levels) and the animal products group had a higher prevalence of impaired fasting glucose. The vitamin/fibre group had the lowest prevalence of abdominal obesity. The beneficial effect of the vegetal/fat and vitamin/fibre dietary patterns seemed stronger among the obese.

Conclusions

Our results confirm the deleterious effect of a very-low-fat, high-carbohydrate diet and also of high intakes of animal products. The consumption of a diet high in vegetal fats or rich in fruits and vegetables is associated with a healthier metabolic profile. Reducing obesity is essential to prevent metabolic syndrome, but even among the obese dietary habits are important for preserving healthy lipid and glycaemic profiles.

Protection from high-fat-diet-induced impaired glucose tolerance in female Sprague-Dawley rats

In this study, we examined the long-term influence of a high-fat (HF) diet compared with a standard chow (SC) diet on glucose metabolism in genetically normal Sprague-Dawley rats. As the diet was given for a period of 14 months it represents almost a life-long exposure of the rats to the diet. Results showed that (1) after exposure to 14 months of SC or HF feeding, the fasting glucose levels were below 5.1 mmol/l in both genders; (2) the 2 h plasma glucose concentration (2 h PG) of male rats after an intraperitoneal glucose tolerance test for the SC groups and for the HF groups was significantly higher than for females; (3) the liver triglycerides content was significantly enhanced by HF feeding as compared with SC-feeding, and histological staining showed that both genders of the HF group developed severe liver steatosis; (4) the fasting insulin concentration in blood of HF-fed males was significantly higher than that of females and homeostasis model assessment of insulin resistance was also significantly higher; (5) the insulin secretion capabilities in response to glucose stimulation were significantly higher in HF-fed female rats than that of males. Taken together, these data indicate that glucose intolerance produced by a HF diet in rats shows a gender difference, and females are protected against development of impaired glucose tolerance under HF condition.

Dietary fat intake and cognitive decline in women with type 2 diabetes

OBJECTIVE

Individuals with type 2 diabetes have high risk of late-life cognitive impairment, yet little is known about strategies to modify risk. Targeting insulin resistance and vascular complications-both associated with cognitive decline-may be a productive approach. We investigated whether dietary fat, which modulates glucose and lipid metabolism, might influence cognitive decline in older adults with diabetes.

RESEARCH DESIGN AND METHODS

Beginning in 1995-1999, we evaluated cognitive function in 1,486 Nurses' Health Study participants, aged >or=70 years, with type 2 diabetes; second evaluations were conducted 2 years later. Dietary fat intake was assessed regularly beginning in 1980; we considered average intake from 1980 (at midlife) through initial cognitive interview and also after diabetes diagnosis. We used multivariate-adjusted linear regression models to obtain mean differences in cognitive decline across tertiles of fat intake.

RESULTS

Higher intakes of saturated and trans fat since midlife, and lower polyunsaturated to saturated fat ratio, were each highly associated with worse cognitive decline in these women. On a global score averaging all six cognitive tests, mean decline among women in the highest trans fat tertile was 0.15 standard units worse than that among women in the lowest tertile (95% CI -0.24 to -0.06, P = 0.002); this mean difference was comparable with the difference we find in women 7 years apart in age. Results were similar when we analyzed diet after diabetes diagnosis.

CONCLUSIONS

These findings suggest that lower intakes of saturated and trans fat and higher intake of polyunsaturated fat relative to saturated fat may reduce cognitive decline in individuals with type 2 diabetes.

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.

Dietary fats and prevention of type 2 diabetes

Although type 2 diabetes is determined primarily by lifestyle and genes, dietary composition may affect both its development and complications. Dietary fat is of particular interest because fatty acids influence glucose metabolism by altering cell membrane function, enzyme activity, insulin signaling, and gene expression. This paper focuses on the prevention of type 2 diabetes and summarizes the epidemiologic literature on associations between types of dietary fat and diabetes risk. It also summarizes controlled feeding studies on the effects of dietary fats on metabolic mediators, such as insulin resistance. Taken together, the evidence suggests that replacing saturated fats and trans fatty acids with unsaturated (polyunsaturated and/or monounsaturated) fats has beneficial effects on insulin sensitivity and is likely to reduce risk of type 2 diabetes. Among polyunsaturated fats, linoleic acid from the n-6 series improves insulin sensitivity. On the other hand, long-chain n-3 fatty acids do not appear to improve insulin sensitivity or glucose metabolism. In dietary practice, foods rich in vegetable oils, including non-hydrogenated margarines, nuts, and seeds, should replace foods rich in saturated fats from meats and fat-rich dairy products. Consumption of partially hydrogenated fats should be minimized. Additional controlled, long-term studies are needed to improve our knowledge on the optimal proportion of different types of fats to prevent diabetes.

Dietary fat and risk of renal cell carcinoma in the USA: a case-control study

An increased risk of renal cell carcinoma (RCC) has been linked with obesity. However, there is limited information about the contribution of dietary fat and fat-related food groups to RCC risk. A population-based case-control study of 406 cases and 2434 controls aged 40-85 years was conducted in Iowa (1986-89). For 323 cases and 1820 controls from the present study, information on dietary intake from foods high in fat nutrients and other lifestyle factors was obtained using a mailed questionnaire. Cancer risks were estimated by OR and 95 % CI, adjusting for age, sex, smoking, obesity, hypertension, physical activity, alcohol and vegetable intake and tea and coffee consumption. In all nutrient analyses, energy density estimates were used. Dietary nutrient intake of animal fat, saturated fat, oleic acid and cholesterol was associated with an elevated risk of RCC (OR = 1.9, 95 % CI 1.3, 2.9, P trend < 0.001; OR = 2.6, 95 % CI 1.6, 4.0, P trend < 0.001; OR = 1.9, 95 % CI 1.2, 2.9, P trend = 0.01; OR = 1.9, 95 % CI 1.3, 2.8, P trend = 0.006, respectively, for the top quartile compared with the bottom quartile of intake). Increased risks were also associated with high-fat spreads, red and cured meats and dairy products (OR = 2.0, 95 % CI 1.4, 3.0, P trend = 0.001; OR = 1.7, 95 % CI 1.0, 2.2, P trend = 0.01; OR = 1.8, 95 % CI 1.2, 2.7, P trend = 0.02; OR = 1.6, 95 % CI 1.1, 2.3, P trend = 0.02, respectively). In both the food groups and nutrients, there was a significant dose-response with increased intake. Our data also indicated that the association of RCC with high-fat spreads may be stronger among individuals with hypertension. These findings deserve further investigation in prospective studies.

Serum phospholipid and cholesteryl ester fatty acids and estimated desaturase activities are related to overweight and cardiovascular risk factors in adolescents

AIM/HYPOTHESIS

The objective of this study was to describe the relation of serum fatty acids and desaturase activity (DA) to overweight, insulin sensitivity and cardiovascular disease (CVD) risk factors in adolescents.

METHODS

The relations of % serum phospholipid (PL) and cholesteryl ester (CE) fatty acids and estimated DA with CVD risk factors were examined in 264 adolescents (average age 15 years). Fatty acids were determined by gas liquid chromotography. Surrogate measures of DA were expressed as ratios of serum fatty acids: Delta9 DA=16:0/16:1; Delta6 DA=20:3,n6/18:2,n6 (PL) or 18:3,n6/18:2,n6 (CE); and Delta5 DA=20:4,n6/20:3,n6. Spearman partial correlations of fatty acids (%) and DA ratios with CVD risk factors were reported, adjusting for age, sex, race, Tanner stage, energy intake and physical activity.

RESULTS

Overweight adolescents compared to normal weight had more adverse levels of CVD risk factors, composition of PL and CE fatty acids in serum, and Delta6 DA and Delta5 DA ratios. Linoleic acid was inversely related to body mass index (BMI), waist circumference and triglycerides (P

CONCLUSION

These findings support those observed in adults, that factors, such as type of dietary fat, physical activity, and obesity, may influence fatty acid metabolism and are important in the development of adverse CVD risk factors as early as adolescence.

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Key Words Collapse

MESH Headings

• Adolescent
• Body Mass Index
• Cardiovascular Diseases/etiology
• Cholesterol Esters/blood
• Fatty Acid Desaturases/blood
• Fatty Acids/blood
• Female
• Humans
• Insulin Resistance
• Male
• Overweight/blood
• Overweight/physiopathology
• Phospholipids/blood
• Risk Factors
• Waist Circumference

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Grants

• M01 RR000400 NCRR NIH HHS
• R01 HL052851-13 NHLBI NIH HHS
• MO1RR00400 NCRR NIH HHS
• HL52851 NHLBI NIH HHS
• R01 HL052851 NHLBI NIH HHS

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Affiliation(s)

L M Steffen Division of Epidemiology and Community Health, University of Minnesota School of Public Health, Minneapolis, MN 55454, USA.
B Vessby
D R Jacobs
J Steinberger
A Moran
C-P Hong
A R Sinaiko

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Ghrelin secretion is not reduced by increased fat mass during diet-induced obesity

Ghrelin is a stomach hormone that stimulates growth hormone (GH) secretion, adiposity, and food intake. Gastric ghrelin production and secretion are regulated by caloric intake; ghrelin secretion increases during fasting, decreases with refeeding, and is reduced by diet-induced obesity. The aim of the present study was to test the hypotheses that 1) an increase in body adiposity will play an inhibitory role in the reduction of gastric ghrelin synthesis and secretion during chronic ingestion of a high-fat (HF) diet and 2) chronic ingestion of an HF diet will suppress the rise in circulating ghrelin levels in response to acute fasting. Adult male Sprague-Dawley rats were fed a standard AIN-76A (approximately 5-12% of calories from fat) or an HF (approximately 45% of calories from fat) diet. The effect of increased adiposity on gastric ghrelin homeostasis was assessed by comparison of stomach ghrelin production and plasma ghrelin levels in obese and nonobese rats fed the HF diet. HF diet-fed, nonobese rats were generated by administration of triiodothyronine to lower body fat accumulation. Our findings indicate that an increased fat mass per se does not exert an inhibitory effect on ghrelin homeostasis during ingestion of the HF diet. Additionally, the magnitude of change in plasma ghrelin in response to fasting was not blunted, indicating that a presumed, endogenous signal for activation of ingestive behavior remains intact, despite excess stored calories in HF-fed rats.

Fatty acids and insulin sensitivity

PURPOSE OF REVIEW

Given the pathophysiological importance of insulin resistance, the potential impact of dietary fatty acids is highly relevant. The effects of different types of dietary fatty acids on insulin sensitivity in humans are discussed, with focus on recent controlled studies.

RECENT FINDINGS

Observational studies assessing fatty acid composition in serum or tissues suggest that insulin resistance is associated with relatively high intakes of saturated fat (e.g. palmitic acid) and low intakes of polyunsaturated fat (e.g. linoleic acid), findings that are supported by recent clinical data. Most controlled studies have hitherto examined the effect of monounsaturated fat on insulin sensitivity, several indicating that it has beneficial effects when substituted for saturated fat. More clinical data comparing n-6 polyunsaturated, monounsaturated and saturated fat are needed to identify the optimal dietary fat composition, especially in patients with insulin resistance/obesity and diabetes. The total fat content of the background diet should also be considered in future studies. Finally, we and others hypothesize that dietary fatty acids may partly mediate their effects on insulin action by regulating the activity of lipogenic enzymes and desaturases.

SUMMARY

Substituting saturated fat with unsaturated fat seems to have beneficial effects on insulin sensitivity, although the clinical significance of modifying fat quality alone is still unclear.

Low-carbohydrate-diet score and risk of type 2 diabetes in women

BACKGROUND

Low-carbohydrate weight-loss diets remain popular; however, the long-term effects of these diets are not known.

OBJECTIVE

The objective was to examine the association between low-carbohydrate-diet score and risk of type 2 diabetes

DESIGN

We prospectively examined the association between low-carbohydrate-diet score (based on percentage of energy as carbohydrate, fat, and protein) and risk of diabetes among 85 059 women in the Nurses' Health Study.

RESULTS

During 20 y of follow-up, we documented 4670 cases of type 2 diabetes. The multivariate relative risk (RR) of diabetes, after adjustment for body mass index and other covariates, in a comparison of the highest decile of low-carbohydrate-diet score with the lowest was 0.90 (95% CI: 0.78, 1.04; P for trend = 0.26). The multivariate RR for the comparison of extreme deciles of low-carbohydrate-diet score based on total carbohydrate, animal protein, and animal fat was 0.99 (95% CI: 0.85, 1.16; P for trend = 1.0), whereas the RR for a low-carbohydrate-diet score based on total carbohydrate, vegetable protein, and vegetable fat was 0.82 (95% CI: 0.71, 0.94; P for trend = 0.001). A higher dietary glycemic load was strongly associated with an increased risk of diabetes in a comparison of extreme deciles (RR: 2.47; 95% CI: 1.75, 3.47; P for trend < 0.0001)). A higher carbohydrate consumption was also associated with an increased risk of diabetes in a comparison of extreme deciles (RR: 1.26; 95% CI: 1.07, 1.49; P for trend = 0.003).

CONCLUSION

These data suggest that diets lower in carbohydrate and higher in fat and protein do not increase the risk of type 2 diabetes in women. In fact, diets rich in vegetable sources of fat and protein may modestly reduce the risk of diabetes.

The influence of olive oil on human health: not a question of fat alone

Olive oil is the most representative food in the traditional Mediterranean diet and its most important source of MUFA. The healthy benefits of MUFA-rich diets on plasma cholesterol levels, were the first to generate interest in this dietary model. In addition to the benefits conferred by its lipids, olive oil has other biological effects, some of them also related to MUFA. However, most recent studies have shown that there are a number of properties that depend on, or are potentiated by, the consumption of olive oil, such as virgin olive oil, that is rich in microcomponents. This foodstuff, thanks to its double set of benefits, thus tends to produce a better lipid profile and a less prothrombotic environment, promoting antioxidant and anti-inflammatory effects, with a greater endothelial protective capacity. In view of these effects, it would appear that when olive oil is the basic source of dietary alimentary fat it has a major antiatherogenic capacity, which is not shared to the same extent by other oils that are rich in oleic acid but lack its characteristic micronutrients.

Glucose transport in human peripheral blood lymphocytes influenced by type 2 diabetes mellitus

INTRODUCTION

The objective of this study was to evaluate glucose transport into lymphocytes in healthy subjects and patients with type 2 diabetes mellitus (DM) treated either with diet only or with insulin and to propose peripheral blood lymphocytes as a convenient model for cellular glucose transport studies.

MATERIALS AND METHODS

Sixty subjects with type 2 DM, 30 treated with diet only and 30 with insulin, were investigated. Thirty healthy subjects matched for age, weight, and sex served as a control group. Deoxy-D-glucose, 2-[(3)H(G)] transport was studied in isolated peripheral blood lymphocytes. Expression of glucose transporters was ascertained by immunocytochemical identification and by Western blotting.

RESULTS

In lymphocytes from the control group, deoxy-D-glucose uptake increased gradually with the duration of the experiment. In diabetics treated with insulin, the maximal increase in deoxy-D-glucose uptake was observed after 30 min of the investigation, followed by a plateau phase. In diabetics treated with diet, deoxy-D-glucose uptake increased slowly during the first 30 min. The presence of GLUT1 and GLUT3 in lymphocytes was confirmed in this study.

CONCLUSIONS

Glucose transport into lymphocytes is altered in type 2 DM. In lymphocytes from diabetics, the dynamics of deoxy-D-glucose uptake significantly differed from that in healthy subjects. There was also a significant difference between the diabetic groups, representing different modes of therapy and stages of the disease. Glucose transport into lymphocytes is apparently influenced by DM as well as by the mode of therapy. We suggest that peripheral blood lymphocytes may become a promising model for studies on glucose transport in diabetes.

Diet, nutrition and the prevention of type 2 diabetes

Objectives:

The overall objective of this study was to evaluate and provide evidence and recommendations on current published literature about diet and lifestyle in the prevention of type 2 diabetes.

Design:

Epidemiological and experimental studies, focusing on nutritional intervention in the prevention of type 2 diabetes are used to make disease-specific recommendations. Long-term cohort studies are given the most weight as to strength of evidence available.

Setting and subjects:

Numerous clinical trials and cohort studies in low, middle and high income countries are evaluated regarding recommendations for dietary prevention of type 2 diabetes. These include, among others, the Finnish Diabetes Prevention Study, US Diabetes Prevention Program, Da Qing Study; Pima Indian Study; Iowa Women's Health Study; and the study of the US Male Physicians.

Results:

There is convincing evidence for a decreased risk of diabetes in adults who are physically active and maintain a normal body mass index (BMI) throughout adulthood, and in overweight adults with impaired glucose tolerance who lose weight voluntarily. An increased risk for developing type 2 diabetes is associated with overweight and obesity; abdominal obesity; physical inactivity; and maternal diabetes. It is probable that a high intake of saturated fats and intrauterine growth retardation also contribute to an increased risk, while non-starch polysaccharides are likely to be associated with a decreased risk. From existing evidence it is also possible that omega-3 fatty acids, low glycaemic index foods and exclusive breastfeeding may play a protective role, and that total fat intake andtransfatty acids may contribute to the risk. However, insufficient evidence is currently available to provide convincing proof.

Conclusions:

Based on the strength of available evidence regarding diet and lifestyle in the prevention of type 2 diabetes, it is recommended that a normal weight status in the lower BMI range (BMI 21–23) and regular physical activity be maintained throughout adulthood; abdominal obesity be prevented; and saturated fat intake be less than 7% of the total energy intake.

Trans fatty acids, insulin resistance, and type 2 diabetes

Type 2 diabetes, a growing global health problem, has a complex etiology involving many interactions between genetic and environmental factors. Essential to the development of the disease is insulin resistance of the peripheral tissues. Insulin resistance may be partly modified by the specific types of dietary fatty acids. Trans fatty acids (TFAs), created through the transformation of polyunsaturated fatty acids from their natural cis form to the trans form, are abundant in the Western diet. TFAs take on similar properties as saturated fats, and appear to be more atherogenic. High intakes of saturated fats may promote insulin resistance. It is therefore reasonable to hypothesize that high intakes of TFAs would have similar, or stronger, effects. In this review, all current evidence on the topic of TFAs, insulin resistance, and type 2 diabetes is summarized and interpreted. Although there is some support from observational and experimental studies for the hypothesis that high intakes of TFAs may increase the risk for type 2 diabetes, inconsistencies across studies and methodological problems make it premature to draw definitive conclusions at this time. More experimental research in humans is needed to further address this question.

Effect of sucrose and saturated-fat diets on mRNA levels of genes limiting muscle fatty acid and glucose supply in rats

In this study, we examined whether the increased availability of lipids in blood resulting from two types of diet manipulation regulated metabolic gene expression in the skeletal muscle of rats. Feeding for 4 wk on an isocaloric-sucrose or a hypercaloric-fat diet increased plasma TAG in the fed condition by increments of 70 and 40%, respectively, and increased fasting insulinemia (approximately 3-fold) compared with a starch diet. The fat diet impaired glucose tolerance and caused obesity, whereas sucrose-fed rats maintained their normal weight. We analyzed the expression of genes that regulate the exogenous FA supply (LPL, FAT/CD36, FATP1), synthesis (ACC1), glucose (GLUT4, GLUT1, HK2, GFAT1, glycogen phosphorylase) or glycerol (glycerol kinase) provision, or substrate choice for oxidation (PDK4) in gastrocnemius and soleus muscles at the end of the glucose tolerance test. LPL, FAT/CD36, FATP1, PDK4, and GLUT4 mRNA as well as glycogen phosphorylase and glycerol kinase activity levels in both muscles were unchanged by the diets. Increased mRNA levels of GLUT1 (1.6- and 2.6-fold, respectively) and GFAT1 (about 1.7-fold) in gastrocnemius, and of ACC1 (about 1.5-fold) in soleus, were found in both the sucrose and fat groups. In the fat group, HK2 mRNA was also higher (1.8-fold) in the gastrocnemius. Both sucrose and saturated-fat diets prompted hyperinsulinemia and hyperlipemia in rats. These metabolic disturbances did not alter the expression of LPL, FAT/CD36, FATP1, PDK4, and GLUT4 genes or glycogen phosphorylase and glycerol kinase activity levels in either analyzed muscle. Instead, they were linked to the coordinated upregulation in gastrocnemius of genes that govern glucose uptake and the hexosamine pathway, namely, GLUT1 and GFAT1, which might contribute to insulin resistance.

Effects of dietary cis and trans unsaturated and saturated fatty acids on the glucose metabolites and enzymes of rats

The aim of the present study was to examine whether the level of dietary cis fatty acid (cFA), or the isomers (trans or cis) and/or the saturation of the fatty acids at high dietary fat levels altered the intracellular glucose metabolites and certain regulatory enzyme activities in the skeletal muscle and liver of rats. The animals were fed for 30 d on either a recommended control diet (7 % cFA, w/w) or a high-fat diet (20 % fatty acids, w/w). The high-fat diet was enriched with either cFA, trans fatty acid (tFA), a moderate proportion of saturated fatty acid (MSFA), or a high proportion of saturated fatty acid (HSFA). The most striking findings were observed in the gastrocnemius muscle with a HSFA diet. There was a significant increase in glucose-6-phosphate (306 %), glucose-1-phosphate (245 %), fructose-6-phosphate (400 %), fructose-1,6-bisphosphate (86 %), glyceraldehyde-3-phosphate (38 %), pyruvate (341 %), lactate (325 %), citrate (79 %) and the bisphosphorylated sugars as compared with the cFA diet. These changes were paralleled by an increase in muscle triacylglycerol content (49 %) and a decrease in glucose (39 %). In addition, the amount of cFA and the other types of fatty acid (i.e. tFA and MSFA) led to no great differences in glucose metabolism as compared with the respective control group. These data support the hypothesis that glucose changes induced by a HSFA diet are a multifaceted abnormality. Glucose and lactate transport and intracellular glucose metabolism could be the key biochemical defects involved in this detrimental effect on glucose metabolism.

Dietary (n-3) long chain polyunsaturated fatty acids prevent sucrose-induced insulin resistance in rats

This study was designed to determine the effect of substituting (n-3) long-chain PUFAs (LCPUFAs) for linoleic acid and hence decreasing the (n-6):(n-3) fatty acid ratio on sucrose-induced insulin resistance in rats. Weanling male Wistar rats were fed casein-based diets containing 100 g/kg fat for 12 wk. Insulin resistance was induced by replacing starch (ST) with sucrose (SU). The dietary fats were formulated with groundnut oil, palmolein, and fish oil to provide the following ratios of (n-6):(n-3) fatty acids: 210 (ST-210, SU-210), 50 (SU-50), 10 (SU-10), and 5 (SU-5). Compared with starch (ST-210), sucrose feeding (SU-210) significantly increased the plasma insulin and triglyceride concentrations and the plasma insulin area under the curve (AUC) in response to an oral glucose load. Adipocytes isolated from rats fed SU-210 had greater lipolytic rate, lower insulin stimulated glucose transport, and lower insulin-mediated antilipolysis than those from rats fed ST-210. Decreasing the dietary (n-6):(n-3) ratio in sucrose-fed rats (SU-10 and SU-5) normalized the plasma insulin concentration and the AUC of insulin after a glucose load. The sucrose-induced increase in plasma triglyceride concentration was normalized in rats fed SU-50, SU-10 and SU-5. Further, sucrose-induced alterations in adipocyte lipolysis and antilipolysis were partially reversed and glucose transport improved in rats fed diets SU-5 and SU-10. In diaphragm phospholipids, decreasing the (n-6):(n-3) ratio in the diet increased the concentration of (n-3) LCPUFAs with concomitant decreases in the concentration of (n-6) LCPUFAs. These results suggest that (n-3) LCPUFAs at a level of 2.6 g/kg diet [0.56% energy (n-3) LCPUFAs, (n-6):(n-3) ratio = 10] may prevent sucrose-induced insulin resistance by improving peripheral insulin sensitivity.

Effects of dietary fats versus carbohydrates on coronary heart disease: A review of the evidence

Recommendations arising from the traditional diet-coronary heart disease (CHD) paradigm, which focuses on effects of total and saturated fat on serum total and low-density lipoprotein cholesterol, may have failed to reduce CHD risk and inadvertently exacerbated dyslipidemia, insulin resistance, and weight gain, particularly among individuals who are older, female, sedentary, or obese. A suitable dietary paradigm must consider types and qualities of fats and carbohydrates consumed, their effects on a range of intermediary risk factors, and characteristics that may modify individual susceptibility. Based on current evidence, replacement of total, unsaturated, and even possibly saturated fats with refined, high-glycemic index carbohydrates is unlikely to reduce CHD risk and may increase risk in persons predisposed to insulin resistance. In contrast, a diet that is 1) rich in whole grains and other minimally processed carbohydrates; 2) includes moderate amounts of fats (approximately 30%-40% of total energy), particularly unsaturated fats and omega-3 polyunsaturated fats from seafood and plant sources; 3) is lower in refined grains and carbohydrates; and 4) eliminates packaged foods, baked goods, and fast foods containing trans fatty acids, will likely reduce the risk of CHD.

The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity

PURPOSE

This study investigated the effect of a low-fat, plant-based diet on body weight, metabolism, and insulin sensitivity, while controlling for exercise in free-living individuals.

SUBJECTS AND METHODS

In an outpatient setting, 64 overweight, postmenopausal women were randomly assigned to a low-fat, vegan diet or a control diet based on National Cholesterol Education Program guidelines, without energy intake limits, and were asked to maintain exercise unchanged. Dietary intake, body weight and composition, resting metabolic rate, thermic effect of food, and insulin sensitivity were measured at baseline and 14 weeks.

RESULTS

Mean +/- standard deviation intervention-group body weight decreased 5.8 +/- 3.2 kg, compared with 3.8 +/- 2.8 kg in the control group (P = .012). In a regression model of predictors of weight change, including diet group and changes in energy intake, thermic effect of food, resting metabolic rate, and reported energy expenditure, significant effects were found for diet group (P < .05), thermic effect of food (P < .05), and resting metabolic rate (P < .001). An index of insulin sensitivity increased from 4.6 +/- 2.9 to 5.7 +/- 3.9 (P = .017) in the intervention group, but the difference between groups was not significant (P = .17).

CONCLUSION

Adoption of a low-fat, vegan diet was associated with significant weight loss in overweight postmenopausal women, despite the absence of prescribed limits on portion size or energy intake.

Peroxisome proliferator-activated receptor-gamma co-activator 1alpha-mediated metabolic remodeling of skeletal myocytes mimics exercise training and reverses lipid-induced mitochondrial inefficiency

Peroxisome proliferator-activated receptor-gamma co-activator 1alpha (PGC1alpha) is a promiscuous co-activator that plays a key role in regulating mitochondrial biogenesis and fuel homeostasis. Emergent evidence links decreased skeletal muscle PGC1alpha activity and coincident impairments in mitochondrial performance to the development of insulin resistance in humans. Here we used rodent models to demonstrate that muscle mitochondrial efficiency is compromised by diet-induced obesity and is subsequently rescued by exercise training. Chronic high fat feeding caused accelerated rates of incomplete fatty acid oxidation and accumulation of beta-oxidative intermediates. The capacity of muscle mitochondria to fully oxidize a heavy influx of fatty acid depended on factors such as fiber type and exercise training and was positively correlated with expression levels of PGC1alpha. Likewise, an efficient lipid-induced substrate switch in cultured myocytes depended on adenovirus-mediated increases in PGC1alpha expression. Our results supported a novel paradigm in which a high lipid supply, occurring under conditions of low PGC1alpha, provokes a disconnect between mitochondrial beta-oxidation and tricarboxylic acid cycle activity. Conversely, the metabolic remodeling that occurred in response to PGC1alpha overexpression favored a shift from incomplete to complete beta-oxidation. We proposed that PGC1alpha enables muscle mitochondria to better cope with a high lipid load, possibly reflecting a fundamental metabolic benefit of exercise training.

Differential effects of dietary saturated and trans-fatty acids on expression of genes associated with insulin sensitivity in rat adipose tissue

OBJECTIVE

Trans-fatty acids (TFAs) are formed during partial hydrogenation of vegetable oils and are shown to be more atherogenic than saturated fatty acids (SFAs). Our previous study showed that dietary TFAs decrease adipose tissue insulin sensitivity to a greater extent than SFAs in rats. We hypothesized that the effects of these fatty acids on insulin sensitivity could be mediated through an alteration in gene expression. In the current study we have investigated the effects of dietary TFAs or SFAs on expression of genes associated with insulin sensitivity in rat adipose tissue.

DESIGN AND METHODS

Male weanling Wistar/NIN rats were divided into four groups and fed one of the following diets containing 10% fat (g/100 g diet) differing only in the fatty acid composition for 3 months: control diet (3.7% linoleic acid (LA)), SFA diet (5% SFA), TFA diet 1 (1.5% TFA + 1% LA) and TFA diet 2 (1.5% TFA + 2% LA). The mRNA expression of peroxisome proliferator-activated receptor gamma (PPARgamma), lipoprotein lipase (LPL), glucose transporter-4 (GLUT4), resistin and adiponectin was analyzed in epididymal fat using RT-PCR. The effects of TFA were studied at two levels of LA to understand the beneficial effects of LA over the effects of TFA.

RESULTS

Both dietary SFA and TFA upregulated the mRNA levels of resistin. Dietary SFA downregulated adiponectin and GLUT4 and upregulated LPL, while TFA downregulated PPARgamma and LPL. The effects of dietary TFA on PPARgamma and resistin were not counteracted by increased LA (TFA diet 2).

CONCLUSION

The effects of SFAs on the aforementioned genes except PPARgamma could be extrapolated towards decreased insulin sensitivity, while only the alteration in the mRNA levels of PPARgamma and resistin could be associated with insulin resistance in TFA-fed rats. These findings suggest that dietary SFAs and TFAs alter the expression of different genes associated with insulin sensitivity in adipose tissue.

Primary prevention of diabetes: what can be done and how much can be prevented?

Although it is widely believed that type 2 diabetes mellitus is the result of a complex interplay between genetic and environmental factors, compelling evidence from epidemiologic studies indicates that the current worldwide diabetes epidemic is largely due to changes in diet and lifestyle. Prospective cohort studies and randomized clinical trials have demonstrated that type 2 diabetes can be prevented largely through moderate diet and lifestyle modifications. Excess adiposity is the most important risk factor for diabetes, and thus, maintaining a healthy body weight and avoiding weight gain during adulthood is the cornerstone of diabetes prevention. Increasing physical activity and reducing sedentary behaviors such as prolonged TV watching are important both for maintaining body weight and improving insulin sensitivity. There is increasing evidence that the quality of fat and carbohydrate plays a more important role than does the quantity, and thus, public health strategies should emphasize replacing saturated and trans fats with unsaturated fats and replacing refined grain products with whole grains. Recent studies have also suggested a potential role for coffee, dairy, nuts, magnesium, and calcium in preventing diabetes. Overall, a healthy diet, together with regular physical activity, maintenance of a healthy weight, moderate alcohol consumption, and avoidance of sedentary behaviors and smoking, could nearly eliminate type 2 diabetes. However, there is still a wide gap between what we know and what we practice in the field of public health; how to narrow that gap remains a major public health challenge.

Substrate dependence of the postischemic cardiomyocyte recovery: Dissociation between functional, metabolic and injury markers

Defining the substrate that influences the most favourably the myocardial post-ischemic recovery is subject of debates, due to dissociation between functional and biochemical benefits. Hence, we studied the effects of either glucose or different fatty acids on the functional and metabolic recovery of post-ischemic cardiomyocytes in a substrate-free hypoxia model of simulated ischemia-reperfusion. Rat cardiomyocytes were submitted to a 2.5 h simulated ischemia followed by a 2 h reoxygenation without substrate (control), or with either glucose, octanoic acid, oleic acid, or elaidic acid. During simulated ischemia, electromechanical function gradually disappeared while the cellular viability and mitochondrial function declined. During control simulated reperfusion, cardiomyocytes recovered near normal function but a significant reduction in the action potential amplitude and rate persisted. The addition of glucose or oleic acid during simulated reperfusion promoted a faster, better and sustain functional recovery. Amongst the fatty acids, the functional recovery was slower with elaidic and octanoic acids as compared with oleic acid. The mitochondrial function was better improved during simulated reperfusion with glucose than with the tested fatty acids, among which elaidic acid was the less unfavourable. Paradoxically, the addition of whichever substrate during simulated reperfusion tended to worsen the cellular viability. Thus, cardiomyocytes recovery strongly relies on the characteristics of the substrate supplied at the onset of simulated reperfusion: glucidic or lipidic nature, chain-length, insaturation degree. Moreover, these data suggest that defining the appropriateness of a given substrate for the post-ischemic cardiomyocyte recovery is closely related to the functional and the biological endpoints in consideration.

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

This study describes the effect of substituting dietary linoleic acid (18:2 n-6) with alpha-linolenic acid (18:3 n-3) on sucrose-induced insulin resistance (IR). Wistar NIN male weanling rats were fed casein based diet containing 22 energy percent (en%) fat with approximately 6, 9 and 7 en% saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) respectively for 3 months. IR was induced by replacing starch (ST) with sucrose (SU). Blends of groundnut, palmolein, and linseed oil in different proportions furnished the following levels of 18:3 n-3 (g/100 g diet) and 18:2 n-6/18:3 n-3 ratios respectively: ST-220 (0.014, 220), SU-220 (0.014, 220), SU-50 (0.06, 50), SU-10 (0.27, 10) and SU-2 (1.1, 2). The results showed IR in the sucrose fed group (SU-220) as evidenced by increase in fasting plasma insulin and area under the curve (AUC) of insulin in response to oral glucose load. In SU-220, the increase in adipocyte plasma membrane cholesterol/phospholipid ratio was associated with a decrease in fluidity, insulin stimulated glucose transport, antilipolytic effect of insulin and increase in basal and norepinephrine stimulated lipolysis in adipocytes. In SU-50, sucrose induced alterations in adipocyte lipolysis and antilipolysis were normalized. However, in SU-2, partial corrections in plasma insulin, AUC of insulin and adipocyte insulin stimulated glucose transport were observed. Further, plasma triglycerides and cholesterol decreased in SU-2. In diaphragm phospholipids, the observed dose dependent increase in long chain (LC) n-3 PUFA was associated with a decrease in LC-n-6 PUFA but insulin stimulated glucose transport increased only in SU-2. Thus, this study shows that the substitution of one-third of dietary 18:2 n-6 with 18:3 n-3 (SU-2) results in lowered blood lipid levels and increases peripheral insulin sensitivity, possibly due to the resulting high LCn-3 PUFA levels in target tissues of insulin action. These findings suggest a role for 18:3 n-3 in the prevention of insulin resistant states. The current recommendation to increase 18:3 n-3 intake for reducing cardiovascular risk may also be beneficial for preventing IR in humans.

Long-chain ω6 polyunsaturated fatty acids in erythrocyte phospholipids are associated with insulin resistance in non-obese type 2 diabetics

BACKGROUND

Associations have been described between insulin action and long-chain omega6 polyunsaturated fatty acids in skeletal muscle and erythrocytes of healthy individuals. We evaluated whether there was an association between insulin resistance and long-chain omega6 polyunsaturated fatty acids in erythrocyte phospholipids of type 2 diabetics.

METHODS

Erythrocyte phospholipid fatty acid composition was determined in 43 adult non-obese type 2 diabetics. Insulin resistance was estimated by the HOMA mathematical approximations. Individual omega6 fatty acids and the sum of long-chain omega6 polyunsaturated fatty acids were correlated with insulin resistance. The same association was assessed for fatty acid product/precursor ratios taken as measures of Delta5 desaturase, Delta6 desaturase and their combined action.

RESULTS

Except for 18:2omega6, 20:2omega6 and 20:3omega6, the individual omega6 fatty acids tested and the sum of long-chain omega6 polyunsaturated fatty acids correlated negatively with insulin resistance at p<0.005. Likewise, a negative correlation was found for the combined action of Delta5 and Delta6 desaturases (p<0.005).

CONCLUSIONS

Our results indicate that formation of long-chain omega6 fatty acids from 18:2omega6 by desaturation-elongation is impaired under insulin resistant conditions and reduced desaturase activities may be involved. In view of our results, we hypothesize that in insulin resistant conditions, insulin-mediated activation of Delta5 and Delta6 desaturases may not occur.

Carbohydrate intake is correlated with biomarkers for coronary heart disease in a population of overweight premenopausal women

The associations between macronutrient intake and plasma parameters associated with increased risk for coronary heart disease (CHD) were evaluated in 80 overweight premenopausal women. We hypothesized that higher carbohydrate intake would be associated with a more detrimental plasma lipid profile. Dietary data were collected using a validated food frequency questionnaire (FFQ). Plasma total cholesterol (TC), triglycerides (TGs), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) were determined from two fasting blood samples. In addition, selected apolipoproteins (apo) and LDL peak size were measured. Values for TC, TG and HDL were not in the range of risk classification; however, the mean values of LDL-C, 2.7 +/- 0.7 mmol/L, were higher than the current recommendations. Carbohydrate intake was positively associated with TG and apo C-III (P < .01) concentrations, and negatively associated with LDL diameter (P < .01). Participants were divided into low (<53% of energy) or high (> or = 53% energy) carbohydrate intake groups. Individuals in the <53% carbohydrate group consumed more cholesterol and total fat, but also had higher intake of polyunsaturated and monounsaturated fatty acids (SFAs). In contrast, subjects in the > or =53% group consumed higher concentrations of glucose and fructose than those in the low-carbohydrate (LC) group. In addition, subjects consuming <53% carbohydrate had lower concentrations of LDL-C and apo B (P < .01) and a larger LDL diameter (P < .05) than the > or =53% group. These results suggest that the lower LDL-C in the LC group may be related to both the amount of carbohydrate and the type of fatty acids consumed by these subjects.

Differential effect of saturated and polyunsaturated fatty acids on hepatic glucose metabolism in humans

Prolonged infusions of lipid and heparin that achieve high physiological free fatty acid (FFA) concentrations inhibit hepatic (and peripheral) insulin sensitivity in humans. These infusions are composed largely of polyunsaturated fatty acids (PUFA; linoleic and linolenic). It is not known whether fatty acid composition per se affects hepatic glucose metabolism in humans. To address this issue, we examined the impact of enteral infusions of either palm oil (48% palmitic, 35% oleic, and 8% linoleic acids) or safflower oil (6% palmitic, 12% oleic, 74% linoleic acids) in 14 obese nondiabetic subjects. (2)H(2)O was administered to determine the contribution of gluconeogenesis to endogenous glucose production (EGP), and a primed continuous infusion of [6,6-(2)H]glucose was administered to assess glucose appearance. As a result of the lipid infusions, plasma FFA concentrations increased significantly in both the palm oil (507.5 +/- 47.4 to 939.3 +/- 61.3 micromol/l, P < 0.01) and safflower oil (588.2.0 +/- 43.0 to 857.8 +/- 68.7 micromol/l, P < 0.01) groups after 4 h. EGP was similar at baseline (12.4 +/- 1.8 vs. 11.2 +/- 1.0 micromol x kg FFM(-1) x min(-1)). During a somatostatin-insulin clamp, the glucose infusion rate was significantly lower (AUC glucose infusion rate 195.8 +/- 50.7 vs. 377.8 +/- 38.0 micromol/kg FFM, P < 0.01), and rates of EGP were significantly higher (10.7 +/- 1.4 vs. 6.5 +/- 1.5 micromol x kg FFM(-1) x min(-1), P < 0.01) after palm oil compared with safflower oil, respectively. Baseline rates of gluconeogenesis and glycogenolysis were also similar. However, after lipid infusion, rates of glycogenolysis were suppressed by safflower oil but not by palm oil. Thus these studies demonstrate, for the first time in humans, a differential effect of saturated fatty acids and PUFA on hepatic glucose metabolism.

Determinants of insulin sensitivity in chronic heart failure

OBJECTIVE

To describe the determinants of insulin sensitivity (IS) in chronic heart failure (CHF), we created a model in which the influence of lifestyle factors and etiology of heart failure on IS were incorporated concomitantly with age, left ventricular ejection fraction (LVEF) and parameters of body composition.

DESIGN

Observational cohort study.

SETTING

Outpatient clinic for chronic heart failure.

PATIENTS

Fifty-seven male CHF patients [NYHA class II-III, age 61+/-9 years, body mass index (BMI) 26.9+/-3.3 kg/m2 (mean+/-S.D.)].

INTERVENTIONS

Euglycemic hyperinsulinemic clamp, cycle ergometry, anthropometric measurements, LVEF and a physical activity questionnaire.

MAIN OUTCOME MEASURES

A model explaining the variance of IS in CHF.

RESULTS

IS was 18.2+/-8.6 microg.kg(-1).min(-1).mU(-1).l(-1), fasting insulin level was 15.9+/-11.0 mU/l and fasting glucose level was 5.5+/-0.6 mmol/l. Peak VO2 was 19.1+/-4.9 ml.kg(-1).min(-1) and LVEF 26.2+/-7.1%. IS was inversely associated with fasting insulin concentration (r=-0.50, P<0.001) and BMI (r=-0.54, P<0.001). After controlling for BMI, IS also revealed a correlation with age (r=-0.36, P<0.01). The model explained 60% of variance in IS: BMI contributed 20%, smoking 17%, age 17% and physical activity in daily life (DPA) 16% (all P<0.05) to the variance of IS, whereas LVEF (9%) and etiology of heart failure (8%) contributed moderately.

CONCLUSIONS

In CHF patients, IS is for a major part predicted by BMI, smoking, age, daily physical activity, LVEF and etiology of heart failure.

Dietary fat and cholesterol and the risk of cardiovascular disease among women with type 2 diabetes

BACKGROUND

Nutritional therapy is a cornerstone of diabetes management, but no epidemiologic studies have investigated the relation between specific dietary fatty acids and cholesterol and cardiovascular disease (CVD) risk among diabetic patients.

OBJECTIVE

This study assessed the relation between specific dietary fatty acids and cholesterol and CVD risk among women with type 2 diabetes.

DESIGN

Among 5672 women with type 2 diabetes from the Nurses' Health Study, diet was assessed prospectively and updated periodically. Relative risks of CVD were estimated from Cox proportional hazards analysis after adjustment for potential confounders.

RESULTS

Between 1980 and 1998, we identified 619 new cases of CVD (nonfatal myocardial infarction, fatal coronary heart disease, and stroke). The relative risk (RR) of CVD for an increase of 200 mg cholesterol/1000 kcal was 1.37 (95% CI: 1.12, 1.68; P = 0.003). Each 5% of energy intake from saturated fat, as compared with equivalent energy from carbohydrates, was associated with a 29% greater risk of CVD (RR: 1.29; 95% CI: 1.02, 1.63; P = 0.04). The ratio of polyunsaturated to saturated fat (P:S) was inversely associated with the risk of fatal CVD. We estimated that replacement of 5% of energy from saturated fat with equivalent energy from carbohydrates or monounsaturated fat was associated with a 22% or 37% lower risk of CVD, respectively.

CONCLUSIONS

A higher intake of cholesterol and saturated fat and a low P:S were related to increased CVD risk among women with type 2 diabetes. Among diabetic persons, replacement of saturated fat with monounsaturated fat may be more effective in lowering CVD risk than is replacement with carbohydrates.

Effects of moderate-fat (from monounsaturated fat) and low-fat weight-loss diets on the serum lipid profile in overweight and obese men and women

BACKGROUND

Little evidence of the effects of moderate-fat (from monounsaturated fat) weight-loss diets on risk factors for cardiovascular disease exists because low-fat diets are typically recommended. Previous studies in weight-stable persons showed that a moderate-fat diet results in a more favorable lipid and lipoprotein profile (ie, lower serum triacylglycerol and higher HDL cholesterol) than does a low-fat diet.

OBJECTIVE

We evaluated the effects of energy-controlled, low-fat and moderate-fat diets on changes in lipids and lipoproteins during weight loss and subsequent weight maintenance.

DESIGN

We conducted a parallel-arm study design in overweight and obese [body mass index (in kg/m(2)): 29.8 +/- 2.4] healthy men and women (n = 53) assigned to consume a low-fat (18% of energy) or moderate-fat (33% of energy) diet for 6 wk to achieve weight loss, which was followed by 4 wk of weight maintenance. All foods were provided and body weight was monitored to ensure equal weight loss between groups.

RESULTS

The moderate-fat diet elicited favorable changes in the lipoprotein profile. Compared with baseline, HDL cholesterol was unchanged, whereas triacylglycerol and the ratios of total and non-HDL cholesterol to HDL cholesterol were lower at the end of the weight-maintenance period in the moderate-fat diet group. Despite similar weight loss, triacylglycerol rebounded, HDL cholesterol decreased, and the ratios of total and non-HDL cholesterol to HDL cholesterol did not change during the 10-wk interval in the low-fat diet group.

CONCLUSIONS

A moderate-fat weight-loss and weight-maintenance diet improves the cardiovascular disease risk profile on the basis of favorable changes in lipids and lipoproteins. There is merit in recommending a moderate-fat weight-loss diet.

Insulin sensitivity in Chinese ovo-lactovegetarians compared with omnivores

AIM

To compare the insulin sensitivity indices between Chinese vegetarians and omnivores.

METHODS

The study included 36 healthy volunteers (vegetarian, n=19; omnivore, n=17) who had normal fasting plasma glucose levels. Each participant completed an insulin suppression test. We compared steady-state plasma glucose (SSPG), fasting insulin, the homeostasis model assessment for insulin sensitivity (HOMA-IR and HOMA %S) and beta-cell function (HOMA %beta) between the groups. We also tested the correlation of SSPG with years on a vegetarian diet.

RESULTS

The omnivore subjects were younger than the vegetarians (55.7+/-3.7 vs 58.6+/-3.6 year of age, P=0.022). There was no difference between the two groups in sex, blood pressure, renal function tests and lipid profiles. The omnivores had higher serum uric acid levels than vegetarians (5.25+/-0.84 vs 4.54+/-0.75 mg/dl, P=0.011). The results of the indices were different between omnivores and vegetarians (SSPG (mean+/-s.d.) 105.4+/-10.2 vs 80.3+/-11.3 mg/dl, P<0.001; fasting insulin, 4.06+/-0.77 vs 3.02+/-1.19 microU/ml, P=0.004; HOMA-IR, 6.75+/-1.31 vs 4.78+/-2.07, P=0.002; HOMA %S, 159.2+/-31.7 vs 264.3+/-171.7%, P=0.018) except insulin secretion index, HOMA %beta (65.6+/-18.0 vs 58.6+/-14.8%, P=0.208). We found a clear linear relation between years on a vegetarian diet and SSPG (r=-0.541, P=0.017).

CONCLUSIONS

The vegetarians were more insulin sensitive than the omnivore counterparts. The degree of insulin sensitivity appeared to be correlated with years on a vegetarian diet.

Lifestyle factors associated with glycaemic control and body mass index in older adults with diabetes

OBJECTIVE

To investigate the relations between lifestyle factors (diet and exercise), glycated haemoglobin (HbA(1c)) and body mass index (BMI) in older adults with diabetes.

DESIGN AND SETTING

A community hospital-based cross-sectional study of 150 noninstitutionalized, ambulatory adults (>/=65 y) with diabetes, residing within New Zealand's Kapiti region.

SUBJECTS

Patients were recruited from all general practices; two diabetes clinics; local diabetes society and through advertisements in community newspapers. A total of 211 eligible people were identified, but 60 refused to participate and one withdrew. In all, 150 people completed the study (71% participation rate).

METHODS

Nutrient intakes were calculated by a food-frequency questionnaire. Physical activity was assessed by interview using a validated questionnaire. Medical history and demographic data were obtained by interview or self-completed questionnaires; height, weight and HbA(1c) were measured. Multivariate models using bootstrapping and stepwise linear regression were used to select factors associated with HbA(1c) and BMI.

RESULTS

Each five-unit increase in energy from dietary saturated fat and five-unit increase in BMI were associated with 6% (95% confidence interval=2-10%; P=0.004) and 4% (0.3-7%; P=0.031) increases in HbA(1c), respectively. For females with moderate, compared with low overall activity, there was a 14% (7-20%; P=0.000) reduction in BMI while for males the reduction was only 5% (-1-11%; P=0.116). BMI decreased 5% (2-9%; P=0.004) with each 10-y increase in age, while a five-unit increment in energy from dietary sucrose was associated with a 6% (1-11%; P=0.025) increase in BMI.

CONCLUSIONS

Reducing dietary saturated fat and excess body weight may be useful means of improving glycaemic control in older adults with diabetes. Increasing physical activity and reducing energy from dietary sucrose may assist weight control, the former particularly in women.

Saturated-fat diet induces moderate diabetes and severe glomerulosclerosis in hamsters

AIMS/HYPOTHESIS

Diets high in saturated fat are thought to be a risk factor for Type 2 diabetes and associated complications. We investigated effects of a medium and high saturated fat diet on the development of diabetes-associated pathologies in Golden Syrian hamsters, an animal that reacts to dietary lipids in a fashion similar to humans.

METHODS

Three diets containing 46.5 kcal %, 267.3 kcal %, and 488.2 kcal % as saturated fat respectively, were studied. Metabolic parameters were measured up to 20 weeks. Electron microscopy was used to examine the structure of the pancreas, aorta and kidney.

RESULTS

Increased saturated fat consumption was associated with: (i) gradual imbalance of homeostasis, and severe structural alterations of acinar, beta cells and capillaries in the pancreas, and of the kidney glomeruli; (ii) severe hypertriglyceridaemia and augmented creatinine concentrations related to disturbances of the renal function, progressing to nodular glomerulosclerosis and nephropathy; (iii) reduced early insulin secretion in response to glucose; (iv) switch of the aortic endothelium to a secretory phenotype.

CONCLUSION/INTERPRETATION

The results show that high-caloric saturated fat intake induced diabetes in hamsters, probably linked to delayed insulin secretion. The model was also associated with the development of a range of pathologies characteristic to human diabetes, including nephropathy and defects in vasculature. Thus, high-fat fed hamsters provide a new model that is likely to be useful in understanding the cellular and molecular mechanisms involved in the pathogenesis of diabetes.

Plasma fatty acid composition and incidence of diabetes in middle-aged adults: the Atherosclerosis Risk in Communities (ARIC) Study

BACKGROUND

The results of some epidemiologic studies conducted by using questionnaires suggest that dietary fat composition influences diabetes risk. Confirmation of this finding with use of a biomarker is warranted.

OBJECTIVE

We prospectively investigated the relation of plasma cholesterol ester (CE) and phospholipid (PL) fatty acid composition with the incidence of diabetes mellitus.

DESIGN

In 2909 adults aged 45-64 y, plasma fatty acid composition was quantified by using gas-liquid chromatography and was expressed as a percentage of total fatty acids. Incident diabetes (n = 252) was identified during 9 y of follow-up.

RESULTS

After adjustment for age, sex, baseline body mass index, waist-to-hip ratio, alcohol intake, cigarette smoking, physical activity, education, and parental history of diabetes, diabetes incidence was significantly and positively associated with the proportions of total saturated fatty acids in plasma CE and PL. The rate ratios of incident diabetes across quintiles of saturated fatty acids were 1.00, 1.36, 1.16, 1.60, and 2.08 (P = 0.0013) in CE and 1.00, 1.75, 1.87, 2.40, and 3.37 (P < 0.0001) in PL. In CE, the incidence of diabetes was also positively associated with the proportions of palmitic (16:0), palmitoleic (16:1n-7), and dihomo-gamma-linolenic (20:3n-6) acids and inversely associated with the proportion of linoleic acid (18:2n-6). In PL, incident diabetes was positively associated with the proportions of 16:0 and stearic acid (18:0).

CONCLUSIONS

The proportional saturated fatty acid composition of plasma is positively associated with the development of diabetes. Our findings with the use of this biomarker suggest indirectly that the dietary fat profile, particularly that of saturated fat, may contribute to the etiology of diabetes.

Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials

BACKGROUND

The effects of dietary fats on the risk of coronary artery disease (CAD) have traditionally been estimated from their effects on LDL cholesterol. Fats, however, also affect HDL cholesterol, and the ratio of total to HDL cholesterol is a more specific marker of CAD than is LDL cholesterol.

OBJECTIVE

The objective was to evaluate the effects of individual fatty acids on the ratis of total to HDL cholesterol and on serum lipoproteins.

DESIGN

We performed a meta-analysis of 60 selected trials and calculated the effects of the amount and type of fat on total:HDL cholesterol and on other lipids.

RESULTS

The ratio did not change if carbohydrates replaced saturated fatty acids, but it decreased if cis unsaturated fatty acids replaced saturated fatty acids. The effect on total:HDL cholesterol of replacing trans fatty acids with a mix of carbohydrates and cis unsaturated fatty acids was almost twice as large as that of replacing saturated fatty acids. Lauric acid greatly increased total cholesterol, but much of its effect was on HDL cholesterol. Consequently, oils rich in lauric acid decreased the ratio of total to HDL cholesterol. Myristic and palmitic acids had little effect on the ratio, and stearic acid reduced the ratio slightly. Replacing fats with carbohydrates increased fasting triacylglycerol concentrations.

CONCLUSIONS

The effects of dietary fats on total:HDL cholesterol may differ markedly from their effects on LDL. The effects of fats on these risk markers should not in themselves be considered to reflect changes in risk but should be confirmed by prospective observational studies or clinical trials. By that standard, risk is reduced most effectively when trans fatty acids and saturated fatty acids are replaced with cis unsaturated fatty acids. The effects of carbohydrates and of lauric acid-rich fats on CAD risk remain uncertain.

Glucose intolerance and resistin expression in rat offspring exposed to ethanol in utero: modulation by postnatal high-fat diet

High-fat diet and intrauterine growth retardation may predispose to obesity, insulin resistance, and type 2 diabetes. Because prenatal ethanol (ETOH) exposure causes intrauterine growth retardation, we investigated its interactions with postnatal high-fat diet on glucose tolerance and adipocyte-derived hormones in the rat offspring. High-fat-fed offspring had increased adiposity, serum leptin, and muscle uncoupling protein-3, but decreased adiponectin mRNA, compared with corresponding chow-fed groups. ETOH-exposed offspring had normal adiponectin, but increased resistin mRNA and protein, compared with controls, regardless of postnatal diet. Skeletal muscle glucose transporter-4 content was decreased after both ETOH exposure and high-fat feeding. Glycemic and insulin responses to an ip glucose challenge were equally increased in non-ETOH-exposed high-fat-fed offspring and in ETOH-exposed chow-fed offspring, with additive effects of ETOH and high-fat diet. Pancreatic insulin content was elevated only in non-ETOH-exposed high-fat-fed offspring. The data suggest that high-fat diet worsens glucose intolerance in offspring of rats exposed to ETOH. Prenatal ETOH exposure and postnatal high-fat diet might cause insulin resistance through separate mechanisms, involving resistin and adiponectin, respectively.

Alternative treatment of gallbladder disease

Major risk factors for gallbladder disease include a sedentary lifestyle and a diet rich in refined sugars. In genetically prone individuals, these two factors lead to an abnormal bile composition, altered gut microflora, and hyperinsulinemia, with resulting gallstone formation. As a large percentage of gallbladder patients have continued digestive complaints following cholecystectomy, the author examines complementary and alternative medicine (CAM) treatments to counteract gallstone formation. Herbal medicine such as turmeric, oregon grape, bupleurum, and coin grass may reduce gallbladder inflammation and relieve liver congestion. Elimination of offending foods, not necessarily 'fatty' foods, is often successful and recommended by many holistic physicians. Regular aerobic exercise has a beneficial effect on hyperinsulinemia, which is often associated with gallbladder disease. Dietary changes that lower plasma insulin levels, such as a change in dietary fats and substitution of unrefined carbohydrates for refined carbohydrates, may also be helpful.

Fat intake affects adiposity, comorbidity factors, and energy metabolism of sprague-dawley rats

OBJECTIVE

Childhood obesity is an emerging health problem. This study assesses the effects of three levels of dietary fat (10%, 32%, and 45% measured by kilocalories) on weight gain, body composition, energy metabolism, and comorbidity factors in rats from weaning through maturation.

RESEARCH METHODS AND PROCEDURES

The role of dietary fat on the susceptibility to obesity was assessed by feeding diets containing three levels of dietary fat to rats from weaning through 7 months of age. Body composition was analyzed by DXA after 6 and 12 weeks of dietary treatment. Energy metabolism was measured by indirect calorimetry.

RESULTS

Energy intake, weight gain, fat mass, and plasma glucose, cholesterol, triglyceride, free fatty acid, leptin, and insulin levels increased dose-dependently with increased dietary fat. No difference in absolute lean mass among the three groups was observed. Therefore, the differences in weight gain are accounted for primarily by increased fat accretion. Compared with rats that were relatively resistant to obesity when on a 45% fat diet, diet-induced obesity-prone rats were in positive energy balance and had an elevated respiratory quotient, indicating a switch in energy substrate use from fat to carbohydrate, which promotes body-fat accretion.

DISCUSSION

Our data support the hypothesis that administration of increasing amount of dietary fat to very young rats enhances susceptibility to diet-induced obesity and its comorbidities.

Protective effect of dietary monounsaturated fat on arteriosclerosis: beyond cholesterol

The consumption of diets enriched in monounsaturated fat has been related to a lower rate of coronary heart disease. It is well known that this dietary model decreases LDL-cholesterol plasma levels when replacing a saturated fat enriched diet. For this reason, a high monounsaturated fat diet is now being advocated to prevent cardiovascular disease, especially in Mediterranean countries. However, some expert panels-the Joint Task Force of European and other Societies on Coronary Prevention and the International Task Force for Prevention of Coronary Heart Disease-recommend replacing dietary saturated fat by complex carbohydrates, limiting the intake of total fat to <30% of the energy and monounsaturated fat to no more than 10-15% of total calories, reaching a similar effect on LDL-cholesterol plasma levels to a high monounsaturated fat diet. The most appropriate nutritional model to prevent arteriosclerosis should be supported by research into other biological effects of both diets. Therefore, it is interesting to review the non-lipid effect of monounsaturated fat, starting with its influence on other cardiovascular risk factors, such as carbohydrate metabolism and blood pressure. Moreover, substantial evidence of the effect of dietary monounsaturated fat on a wide range of healthy benefits beyond cholesterol, which have been investigated in recent years, such as lipoprotein oxidation, coagulation, fibrinolysis and endothelium, will be discussed. Furthermore, many observational epidemiological studies suggest that a high intake of monounsaturated fat is associated with reduced coronary risk and this will be analyzed in accordance with the clinical evidence to discuss the best dietary model to prevent coronary artery disease.

Serum fatty acid composition predicts development of impaired fasting glycaemia and diabetes in middle-aged men

AIMS

Dietary fatty acid intake is reflected in serum fatty acid composition. Studies prospectively investigating serum fatty acids and development of impaired fasting glycaemia (IFG) or diabetes mellitus (DM) are largely lacking. We assessed the association of serum fatty acid composition with development of IFG or DM.

METHODS

Middle-aged normoglycaemic men (n = 895) participating in a prospective cohort study were followed up after 4 years.

RESULTS

At baseline proportions of serum esterified and non-esterified saturated fatty acids were increased and polyunsaturated fatty acids decreased in men who after 4 years had developed IFG (n = 56) or DM (n = 34). No differences in dietary fatty acid composition as recorded in 4-day dietary records were noted. In logistic regression analyses adjusting for age; obesity; and fasting lipid, glucose and insulin concentrations, men with proportions of non-esterified and esterified linoleate in the upper third had nearly half the risk for IFG or DM compared with the lower third. In covariate analyses, baseline non-esterified linoleate proportions were associated with changes in fasting insulin and glucose concentrations over the 4-year follow-up. Baseline esterified fatty acid composition was also associated with changes in insulin.

CONCLUSIONS

High serum linoleate proportions decreased the risk of developing IFG or DM in middle-aged men over a 4-year follow-up, possibly mediated in part by insulin resistance. These findings support recommendations to substitute vegetable fat for animal and dairy fat in the prevention of disturbances of glucose and lipid metabolism.