Effects of trans fatty acids on glucose homeostasis: a meta-analysis of randomized, placebo-controlled clinical trials

Fat and fatty acids - a scoping review for Nordic Nutrition Recommendations 2023

Two de novo NNR2022 systematic reviews (SRs) as well as 21 qualified SRs (qSRs) were available. A literature search yielded an additional ~70 SRs, meta-analyses and biomarker papers. Diets lower in total fat are associated with reductions in body weight and blood pressure compared with diets higher in total fat in adults. Partial replacement of saturated fatty acid (SFA) with n-6 polyunsaturated fatty acid (PUFA) improves blood lipid profile, decreases the risk of cardiovascular disease (CVD), improves glucose-insulin homeostasis and may decrease the risk of total mortality. Long-chain n-3 PUFAs (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) decrease triglycerides and are associated with lower risk of CVD. Dietary PUFAs, both n-3 and n-6, may be associated with reduced risk of type 2 diabetes (T2D). There is inconclusive evidence to suggest that the type of dietary fat is associated with blood pressure, risk of hypertension or musculoskeletal health. Higher intake of total PUFA is associated with lower mortality from any cancer. Long-chain n-3 PUFA is associated with reduced risk of breast cancer, whereas biomarker levels of n-6 PUFA are associated with lower risk of any cancer. Intake of long-chain n-3 PUFA during pregnancy increases length of gestation and child birth weight and reduces the risk of preterm delivery, but there is inconclusive evidence to suggest that it may influence child neurodevelopment, growth or development of allergic disease. In studies with higher versus lower dietary cholesterol intake levels, total blood cholesterol increased or were unaffected by the dietary cholesterol, resulting in inconclusive results. Trans fatty acid (TFA), regardless of source, impairs blood lipid profile compared to unsaturated fat. In observational studies, TFA is positively associated with CVD and total mortality but whether associations differ by source is inconclusive. Ruminant TFA, as well as biomarker levels of odd-chain fatty acids, might be associated with lower risk of T2D.

Nutritional Strategies for the Management of Type 2 Diabetes Mellitus: A Narrative Review

BACKGROUND

Thinking about greater adherence to dietary planning, it is extremely important to be aware of all nutritional strategies and dietary prescriptions available in the literature, and of which of them is the most efficient for the management of T2DM.

METHODS

A search was carried out in 2023 for randomized clinical trials, systematic reviews, meta-analyses, and guidelines in the following databases: Pubmed, Scielo, Web of Science, CrossRef and Google Scholar. In total, 202 articles were collected and analyzed. The period of publications was 1983-2023.

RESULTS

There is still no consensus on what the best nutritional strategy or ideal dietary prescription is, and individuality is necessary. In any case, these references suggest that Mediterranean Diet may of greater interest for the management of T2DM, with the following recommended dietary prescription: 40-50% carbohydrates; 15-25% proteins; 25-35% fats (<7% saturated, 10% polyunsaturated, and 10% monounsaturated); at least 14 g of fiber for every 1000 kcal consumed; and <2300 mg sodium.

CONCLUSIONS

Individuality is the gold standard for dietary prescriptions, however, the Mediterranean diet with low levels of carbohydrates and fats seems to be the most promising strategy for the management of T2DM.

Comprehensive Approach to Medical Nutrition Therapy in Patients with Type 2 Diabetes Mellitus: From Diet to Bioactive Compounds

In the pathogenesis of type 2 diabetes mellitus (T2DM), diet plays a key role. Individualized medical nutritional therapy, as part of lifestyle optimization, is one of the cornerstones for the management of T2DM and has been shown to improve metabolic outcomes. This paper discusses major aspects of the nutritional intervention (including macro- and micronutrients, nutraceuticals, and supplements), with key practical advice. Various eating patterns, such as the Mediterranean-style, low-carbohydrate, vegetarian or plant-based diets, as well as healthy eating plans with caloric deficits have been proven to have beneficial effects for patients with T2DM. So far, the evidence does not support a specific macronutrient distribution and meal plans should be individualized. Reducing the overall carbohydrate intake and replacing high glycemic index (GI) foods with low GI foods have been shown as valid options for patients with T2DM to improve glycemic control. Additionally, evidence supports the current recommendation to reduce the intake of free sugars to less than 10% of total energy intake, since their excessive intake promotes weight gain. The quality of fats seems to be rather important and the substitution of saturated and trans fatty acids with foods rich in monounsaturated and polyunsaturated fats lowers cardiovascular risk and improves glucose metabolism. There is no benefit of supplementation with antioxidants, such as carotene, vitamins E and C, or other micronutrients, due to the lack of consistent evidence showing efficacy and long-term safety. Some studies suggest possible beneficial metabolic effects of nutraceuticals in patients with T2DM, but more evidence about their efficacy and safety is still needed.

Trans Fatty Acid Biomarkers and Incident Type 2 Diabetes: Pooled Analysis of 12 Prospective Cohort Studies in the Fatty Acids and Outcomes Research Consortium (FORCE)

OBJECTIVE

Trans fatty acids (TFAs) have harmful biologic effects that could increase the risk of type 2 diabetes (T2D), but evidence remains uncertain. We aimed to investigate the prospective associations of TFA biomarkers and T2D by conducting an individual participant-level pooled analysis.

RESEARCH DESIGN AND METHODS

We included data from an international consortium of 12 prospective cohorts and nested case-control studies from six nations. TFA biomarkers were measured in blood collected between 1990 and 2008 from 25,126 participants aged ≥18 years without prevalent diabetes. Each cohort conducted de novo harmonized analyses using a prespecified protocol, and findings were pooled using inverse-variance weighted meta-analysis. Heterogeneity was explored by prespecified between-study and within-study characteristics.

RESULTS

During a mean follow-up of 13.5 years, 2,843 cases of incident T2D were identified. In multivariable-adjusted pooled analyses, no significant associations with T2D were identified for trans/trans-18:2, relative risk (RR) 1.09 (95% CI 0.94-1.25); cis/trans-18:2, 0.89 (0.73-1.07); and trans/cis-18:2, 0.87 (0.73-1.03). Trans-16:1n-9, total trans-18:1, and total trans-18:2 were inversely associated with T2D (RR 0.81 [95% CI 0.67-0.99], 0.86 [0.75-0.99], and 0.84 [0.74-0.96], respectively). Findings were not significantly different according to prespecified sources of potential heterogeneity (each P ≥ 0.1).

CONCLUSIONS

Circulating individual trans-18:2 TFA biomarkers were not associated with risk of T2D, while trans-16:1n-9, total trans-18:1, and total trans-18:2 were inversely associated. Findings may reflect the influence of mixed TFA sources (industrial vs. natural ruminant), a general decline in TFA exposure due to policy changes during this period, or the relatively limited range of TFA levels.

Trans fatty acids in food: A review on dietary intake, health impact, regulations and alternatives

Trans fats are desired by the edible oil industry as they impart firmness, plasticity, and oxidative stability to oil. However, clinical trials have demonstrated the adverse effects of trans fats in food on human health and nutrition. Regulatory actions have been taken up by government and non-government bodies worldwide to eliminate the presence of trans fats in the food supply. The World Health Organization (WHO) has launched a "REPLACE" action plan to eliminate trans-fat from the global food industry by 2023. A few enabling technologies are developed to mitigate trans fats namely, trait-enhanced oils, modification in the hydrogenation process, interesterification, fractionation, blending, and oleogelation. Some of them have the drawback of replacing trans-fat with saturated fats. Interesterification and oleogelation are in-trend techniques with excellent potential in replacing trans fats without compromising the desired functionality and nutritional quality attributes. This review presents an overview of trans fatty acid for example, its dietary intake in food products, possible adverse health impact, regulations, and approaches to reduce the usage of trans fats for food application. PRACTICAL APPLICATION: The requirement for the replacement of trans fatty acids (TFAs) in food supply globally has challenged the food industry to find a novel substitute for trans fats without compromising the desired functionality and nutritional property. This review presents detailed background on trans fats, their health impacts and current trends of reformulation of oils and fats to mitigate their presence in food supply chains. Information compiled in this paper will help food scientists and technologists, chemists, food processors, and retailers as there is an urgent need to find novel technologies and substitutes to replace trans fats in processed foods.

Ruminant fat intake improves gut microbiota, serum inflammatory parameter and fatty acid profile in tissues of Wistar rats

This study tested the hypothesis that naturally and industrially produced trans-fatty acids can exert distinct effects on metabolic parameters and on gut microbiota of rats. Wistar rats were randomized into three groups according to the diet: CONT-control, with 5% soybean oil and normal amount of fat; HVF-20% of hydrogenated vegetable fat (industrial); and RUM-20% of ruminant fat (natural). After 53 days of treatment, serum biochemical markers, fatty acid composition of liver, heart and adipose tissue, histology and hepatic oxidative parameters, as well as gut microbiota composition were evaluated. HVF diet intake reduced triglycerides (≈ 39.39%) and VLDL levels (≈ 39.49%). Trans-fatty acids levels in all tissue were higher in HVF group. However, RUM diet intake elevated amounts of anti-inflammatory cytokine IL-10 (≈ 14.7%) compared to CONT, but not to HVF. Furthermore, RUM intake led to higher concentrations of stearic acid and conjugated linoleic acid in all tissue; this particular diet was associated with a hepatoprotective effect. The microbial gut communities were significantly different among the groups. Our results show that ruminant fat reversed the hepatic steatosis normally caused by high fat diets, which may be related to the remodelling of the gut microbiota and its anti-inflammatory potential.

How should we judge edible oils and fats? An umbrella review of the health effects of nutrient and bioactive components found in edible oils and fats

Dietary guidelines for many Western countries base their edible oil and fat recommendations solely on saturated fatty acid content. This study aims to demonstrate which nutritional and bioactive components make up commonly consumed edible oils and fats; and explore the health effects and strength of evidence for key nutritional and bioactive components of edible oils. An umbrella review was conducted in several stages. Food composition databases of Australia and the United States of America, and studies were examined to profile nutrient and bioactive content of edible oils and fats. PUBMED and Cochrane databases were searched for umbrella reviews, systematic literature reviews of randomized controlled trials or cohort studies, individual randomized controlled trials, and individual cohort studies to examine the effect of the nutrient or bioactive on high-burden chronic diseases (cardiovascular disease, type 2 diabetes mellitus, obesity, cancer, mental illness, cognitive impairment). Substantial systematic literature review evidence was identified for fatty acid categories, tocopherols, biophenols, and phytosterols. Insufficient evidence was identified for squalene. The evidence supports high mono- and polyunsaturated fatty acid compositions, total biophenol content, phytosterols, and possibly high α-tocopherol content as having beneficial effects on high-burden health comes. Future dietary guidelines should use a more sophisticated approach to judge edible oils beyond saturated fatty acid content.

Intake of dietary fats and fatty acids and the incidence of type 2 diabetes: A systematic review and dose-response meta-analysis of prospective observational studies

BACKGROUND

The role of fat quantity and quality in type 2 diabetes (T2D) prevention is controversial. Thus, this systematic review and meta-analysis aimed to investigate the associations between intake of dietary fat and fatty acids and T2D, and to evaluate the certainty of evidence.

METHODS AND FINDINGS

We systematically searched PubMed and Web of Science through 28 October 2019 for prospective observational studies in adults on the associations between intake of dietary fat and fatty acids and T2D incidence. The systematic literature search and data extraction were conducted independently by 2 researchers. We conducted linear and nonlinear random effects dose-response meta-analyses, calculated summary relative risks (SRRs) with their corresponding 95% confidence intervals (95% CIs), and assessed the certainty of evidence. In total, 15,070 publications were identified in the literature search after the removal of duplicates. Out of the 180 articles screened in full text, 23 studies (19 cohorts) met our inclusion criteria, with 11 studies (6 cohorts) conducted in the US, 7 studies (7 cohorts) in Europe, 4 studies (5 cohorts) in Asia, and 1 study (1 cohort) in Australia. We mainly observed no or weak linear associations between dietary fats and fatty acids and T2D incidence. In nonlinear dose-response meta-analyses, the protective association for vegetable fat and T2D was steeper at lower levels up to 13 g/d (SRR [95% CI]: 0.81 [0.76; 0.88], pnonlinearity = 0.012, n = 5 studies) than at higher levels. Saturated fatty acids showed an apparent protective association above intakes around 17 g/d with T2D (SRR [95% CI]: 0.95 [0.90; 1.00], pnonlinearity = 0.028, n = 11). There was a nonsignificant association of a decrease in T2D incidence for polyunsaturated fatty acid intakes up to 5 g/d (SRR [95% CI]: 0.96 [0.91; 1.01], pnonlinearity = 0.023, n = 8), and for alpha-linolenic acid consumption up to 560 mg/d (SRR [95% CI]: 0.95 [0.90; 1.00], pnonlinearity = 0.014, n = 11), after which the curve rose slightly, remaining close to no association. The association for long-chain omega-3 fatty acids and T2D was approximately linear for intakes up to 270 mg/d (SRR [95% CI]: 1.10 [1.06; 1.15], pnonlinearity < 0.001, n = 16), with a flattening curve thereafter. Certainty of evidence was very low to moderate. Limitations of the study are the high unexplained inconsistency between studies, the measurement of intake of dietary fats and fatty acids via self-report on a food group level, which is likely to lead to measurement errors, and the possible influence of unmeasured confounders on the findings.

CONCLUSIONS

There was no association between total fat intake and the incidence of T2D. However, for specific fats and fatty acids, dose-response curves provided insights for significant associations with T2D. In particular, a high intake of vegetable fat was inversely associated with T2D incidence. Thus, a diet including vegetable fat rather than animal fat might be beneficial regarding T2D prevention.

Effects of palm oil consumption on biomarkers of glucose metabolism: A systematic review

Introduction

Vegetable oil is an important source of fatty acids, and as palm oil being the highest consumed vegetable oil in many countries, its high saturated fatty acid content has led many concerns on cardiometabolic health. Dietary fatty acids has also been linked to affect glucose metabolism and insulin sensitivity. This systematic review is aimed at critically evaluating the available evidence on the association of palm oil with the biomarkers of glucose metabolism as compared to other vegetable oils.

Methods

We systemically searched PubMed, CENTRAL and Scopus up to June 2018. We searched for published interventional studies on biomarkers of glucose metabolism (defined as fasting glucose, fasting insulin, HOMA, 2-hour post prandial glucose and HbA1C) that compared palm oil- or palm olein-rich diets with other edible vegetable oils (such as olive oil, canola oil and soybean oil). Two reviewers independently extracted data and assessed study risks of bias. Mean differences of outcomes were pooled for the meta-analysis.

Results

We identified 1921 potentially eligible articles with only eight included studies. Seven randomised cross-over trials and one parallel trial were included. Study population were among young to middle-aged, healthy, non-diabetic, and normal weight participants. Intervention duration ranged from three to seven weeks, and fat substitution ranged from 15% to 20% energy. There were insignificant differences in fasting glucose when compared to partially hydrogenated soybean oil [-0.15mmol/L (-0.46,0.16) P = 0.33, I² = 48%], soybean oil [0.05mmol/L (-0.09,0.18) P = 0.49, I² = 0%] and olive oil [0.04mmol/L (-0.09,0.17) P = 0.76, I² = 0%]. Insignificant effects were also seen on fasting insulin when compared to partially hydrogenated soybean oil [1.72pmol/L (-11.39,14.84) P = 0.80, I² = 12%] and olive oil diet [-0.14pmol/L (-4.87,4.59) P = 0.95, I² = 0%].

Conclusion

Current evidence on the effects of palm oil consumption on biomarkers of glucose metabolism is poor and limited to only healthy participants. We conclude that little or no additional benefit will be obtained by replacing palm oil with other oils rich in mono or polyunsaturated fatty acids for changes in glucose metabolism.

Dietary total fat, fatty acids intake, and risk of cardiovascular disease: a dose-response meta-analysis of cohort studies

BACKGROUND

Several epidemiological studies have investigated the association between dietary fat intake and cardiovascular disease. However, dietary recommendations based on systematic review and meta-analysis might be more credible.

METHODS AND RESULTS

Pubmed, Embase and Cochrane library were searched up to July 1st 2018 for cohort studies reporting associations of dietary fat intake and risk of CVDs. By comparing the highest vs. the lowest categories of fat or fatty acids intake, we found that higher dietary trans fatty acids (TFA) intake was associated with increased risk of CVDs [RR:1.14(1.08-1.21)]. However, no association was observed between total fat, monounsaturated fatty acids (MUFA), saturated fatty acids (SFA), and polyunsaturated fatty acids (PUFA), and risk of CVDs. Subgroup analysis found a cardio-protective effect of PUFA in the studies that has been followed up more than 10 years [0.95(0.91-0.99), I2 = 62.4%]. Dose-response analysis suggested that the risk of CVDs increased 16% [1.16 (1.07-1.25), Plinearity = 0.033] for an increment of 2% energy/day of TFA intake.

CONCLUSIONS

This current meta-analysis of cohort studies suggested that total fat, SFA, MUFA, and PUFA intake were not associated with the risk of cardiovascular disease. However, we found that higher TFA intake is associated with greater risk of CVDs in a dose-response fashion. Furthermore, the subgroup analysis found a cardio-protective effect of PUFA in studies followed up for more than 10 years.

Dietary Fatty Acids and the Metabolic Syndrome: A Personalized Nutrition Approach

Dietary fatty acids are present in a wide variety of foods and appear in different forms and lengths. The different fatty acids are known to have various effects on metabolic health. The metabolic syndrome (MetS) is a constellation of risk factors of chronic diseases. The etiology of the MetS is represented by a complex interplay of genetic and environmental factors. Dietary fatty acids can be important contributors of the evolution or in prevention of the MetS; however, great interindividual variability exists in the response to fatty acids. The identification of genetic variants interacting with fatty acids might explain this heterogeneity in metabolic responses. This chapter reviews the mechanisms underlying the interactions between the different components of the MetS, dietary fatty acids and genes. Challenges surrounding the implementation of personalized nutrition are also covered.

Association Between Plasma Trans-Fatty Acid Concentrations and Measures of Glucose Homeostasis and Cardiovascular Risk Factors in Adults in NHANES 1999-2000

There is limited evidence on the association between plasma trans-fatty acids (TFAs) and cardiometabolic risk factors. Therefore, we examined the association between plasma TFA concentrations and glucose homeostasis and cardiovascular (CV) risk factors in adult Americans from the 1999 to 2000 National Health and Nutrition Examination Survey participants. Derivatized TFAs were separated by capillary gas chromatography. Of the 1678 participants, 46.5% were men. The mean age was 50.5 years overall, with no significant difference between men and women ( P = .101). In age-, sex- and race-adjusted analyses, mean waist circumference, fat-free mass, fat mass, C-peptide, insulin, hemoglobin A_1c (HbA_1c), homeostatic model assessment of insulin resistance (HOMA-IR), serum triglycerides (TGs), and total cholesterol (TC) increased across increasing quarters of TFAs (for all P < .001), while mean serum high-density lipoprotein cholesterol decreased across increasing quarters of plasma TFAs ( P < .001). In multivariable adjusted linear regressions, there remained significant positive associations between all plasma TFAs and body mass index, waist circumference, fat-free mass, fat mass, C-peptide, insulin, fasting blood glucose, HOMA-IR, HbA_1c, TGs, low-density lipoprotein cholesterol, and TC ( P < .001). In conclusion, our findings support a possible association between plasma TFAs concentrations and measures of glucose homeostasis and several CV risk factors.

The relationship of plasma Trans fatty acids with dietary inflammatory index among US adults

Background

It has been suggested that trans fatty acids (TFAs) play an important role in cardiovascular diseases. We investigated the association between plasma TFAs and the dietary inflammatory index (DII) ™ in US adults.

Methods

National Health and Nutrition Examination Survey (NHANES) participants with data on plasma TFAs measured from 1999 to 2010 were included. Energy-adjusted-DII ™ (E-DII ™) expressed per 1000 kcal was calculated from 24-h dietary recalls. All statistical analyses accounted for the survey design and sample weights.

Results

Of the 5446 eligible participants, 46.8% (n = 2550) were men. The mean age of the population was 47.1 years overall, 47.8 years for men and 46.5 years for women (p = 0.09). After adjustment for C-reactive protein, body-mass-index, smoking, race, age, education, and marital status in linear regressions, trans 9-hexadecenoic acid [β coefficient 0.068 (95% CI: 0.032 to 0.188)], trans 11-octadecenoic acid [β coefficient 0.143 (95% CI: 0.155 to 0.310)], trans 9-octadecenoic acid [β coefficient 0.122 (95% CI: 0.120 to 0.277)], trans 9, and trans 12-octadienoic acid [β coefficient 0.103 (95% CI: 0.090 to 0.247)] were positively associated with the DII (all p < 0.001).

Conclusion

The association of plasma TFAs with a marker of dietary inflammation suggests an underlying mechanism in the initiation and progression of cardiovascular diseases.

Plasma trans-fatty acid concentrations continue to be associated with metabolic syndrome among US adults after reductions in trans-fatty acid intake

No study examined and compared the association between intake of trans-fatty acids (TFAs) and risk of metabolic syndrome before and after significant reduction of TFA intakes in the US population. We hypothesized that the relationship might remain significant after substantial reduction of TFA intakes in the population. We used data on 1442 and 2233 adults aged ≥20 years from the National Health and Nutrition Examination Survey 1999-2000 and 2009-2010, respectively. Multivariable logistic regression analysis was used to assess the association between plasma TFA concentrations and metabolic syndrome, including each of its 5 components. The median plasma TFA concentrations were reduced from 79.8 μmol/L in 1999-2000 to 36.9 μmol/L in 2009-2010. The fully adjusted prevalence ratios comparing the highest vs the lowest quintile of plasma TFA concentrations in 1999-2000 were 3.43 (95% confidence interval, 2.39-4.92) for metabolic syndrome, 1.72 (1.38-2.14) for large waistline, 8.25 (6.34-10.74) for high triglycerides, 1.96 (1.46-2.62) for low high-density lipoprotein cholesterol, 1.14 (0.85-1.55) for high blood pressure, and 1.48 (1.19-1.85) for high fasting glucose, respectively. The corresponding prevalence ratios in 2009-2010 were 2.93 (2.41-3.54), 1.62 (1.39-1.89), 14.93 (9.28-24.02), 3.09 (2.18-4.37), 1.27 (1.11-1.46), and 1.24 (1.06-1.46), respectively. The pattern of association between TFAs and metabolic syndrome and its components did not differ by cycles. The observed associations were consistent across the subgroups examined. Despite a 54% decline in plasma TFA concentrations from 1999-2000 to 2009-2010, it was positively associated with risk of metabolic syndrome and its individual components except for blood pressure in 1999-2000. Our findings support Food and Drug Administration initiatives to remove TFAs from the industrially-produced foods.

Plasma trans-Fatty Acid Concentrations Continue to Be Associated with Serum Lipid and Lipoprotein Concentrations among US Adults after Reductions in trans-Fatty Acid Intake

Background: High intakes of trans-fatty acids (TFAs), especially industrially produced TFAs, can lead to unfavorable lipid and lipoprotein concentrations and an increased risk of cardiovascular disease. It is unknown how this relation might change in a population after significant reductions in TFA intake.Objective: This study, which used a new analytical method for measuring plasma TFA concentrations, clarified the association between plasma TFA and serum lipid and lipoprotein concentrations before and after the US FDA enacted TFA food-labeling regulations in 2006.Methods: Data were selected from the NHANES of 1999-2000 and 2009-2010. Findings on 1383 and 2155 adults, respectively, aged ≥20 y, were evaluated. Multivariable linear regressions were used to examine the associations between plasma TFA concentration and lipid and lipoprotein concentrations. The outcome measures were serum concentrations of total cholesterol (TC), LDL cholesterol, HDL cholesterol, and triglycerides and the ratio of TC to HDL cholesterol.Results: The median plasma TFA concentration decreased from 80.6 μmol/L in 1999-2000 to 37.0 μmol/L in 2009-2010. Plasma TFA concentration continued to be associated with serum lipid and lipoprotein concentrations after significant reductions in TFA intake in the population. For example, by comparing the lowest with the highest quintiles of TFA concentration in 1999-2000, adjusted mean (95% CI) LDL-cholesterol concentrations increased from 118 mg/dL (112, 123 mg/dL) to 135 mg/dL (130, 141 mg/dL) (P-trend < 0.001). The corresponding values for 2009-2010 were 102 mg/dL (97.4, 107 mg/dL) and 129 mg/dL (125, 133 mg/dL) for LDL cholesterol (P-trend < 0.001). Differences between the highest and lowest quintiles were consistent across age groups, sexes, races/ethnicities, and other covariates.Conclusions: Despite a 54% reduction in plasma TFA concentrations in US adults from 1999-2000 to 2009-2010, concentrations remained significantly associated with serum lipid and lipoprotein concentrations. There does not appear to be a threshold under which the association between plasma TFA concentration and lipid profiles might become undetectable.

Little Effect of Supplementation with 0.6% Energy Trans Fatty Acids on Serum Cholesterol Levels in Adult Japanese Women

The excessive intake of trans fatty acids (TFAs) increases serum LDL-cholesterol and reduces HDL-cholesterol. Limited data exist regarding the low-level intake of TFAs, and the tolerable upper-limit level remains to be fully elucidated. A randomized, double-blind, parallel trial was conducted to assess the effects of a low level of TFA supplementation on serum cholesterol levels in healthy adult Japanese women. The volunteers who participated in this examination took in approximately 0.4% of energy (%E) TFAs from daily meals. Fifty-one volunteers consumed one cookie containing 0.6%E (TFA) or 0.04%E (control) of TFAs every day for 4 wk, and blood was harvested after overnight fasting. The mean TFA intakes of the control and TFA groups during the experimental period were 0.4%E and 1.1%E, respectively. There were no significant differences in serum total, LDL- or HDL-cholesterol levels between the control and TFA groups. The serum glucose and insulin levels were not influenced by TFA supplementation. These results confirm that dietary supplementation with 0.6%E TFAs (a total TFA intake of approximately 1%E) would have little effect on serum cholesterol levels in healthy adult Japanese women.

Trans fatty acids: are its cardiovascular risks fully appreciated?

OBJECTIVE

The goal of this article was to review the causal link between trans fatty acids (TFA) produced from partially hydrogenated vegetable oil (PHVO) and cardiovascular disease (CVD) risk and its likely mechanisms. The potential risk of TFA from ruminant dairy and meats, which are currently the major sources of dietary TFA, is also discussed.

METHODS

Evidence was derived from observational studies of large cohorts followed up prospectively; from randomized controlled trials of clinical interventions; and from specific case-control studies that investigated biomarkers in tissues. Searches included PubMed and Medline from 1990 to 2013.

RESULTS

Despite TFA from PHVO being associated more strongly with CVD risk than even saturated fats, it may prove difficult to totally eliminate PHVO from all foods. This raises the issue of the lower limit of TFA consumption below which CVD risk is not increased. Limits of <1% of total energy have been suggested. The major mechanism underlying the increased CVD risk from TFA is an increase in LDL-C and Lp(a) lipoproteins and a decrease in HDL-C; increased inflammation and adverse effects on vascular function have also been shown. Both PHVO and ruminant TFA comprise a range of isomers, some specific to each source but including a substantial commonality that supports findings of similar adverse effects at equivalent intakes of TFA. However, the amount of TFA in ruminant fat is relatively small; this limits the CVD risk from eating ruminant products, an inference supported by analysis of prospective cohort studies.

CONCLUSIONS

Two key challenges to the health industry arise from this evidence. They must first determine whether a small intake of TFA from PHVO is safe and what constitutes a safe amount. They must also determine whether TFA from ruminant fat in currently consumed amounts represent limited cardiovascular risk that is balanced by the nutritional benefits of dairy products.

Effect of a trans fatty acid-enriched diet on biochemical and inflammatory parameters in Wistar rats

PURPOSE

Recent data regarding trans fatty acids (TFAs) have implicated these lipids as particularly deleterious to human health, causing systemic inflammation, endothelial dysfunction and possibly inflammation in the central nervous system (CNS). We aimed to clarify the impact of partially hydrogenated soybean oil (PHSO) with different TFA concentrations on cerebrospinal fluid (CSF), serum and hepatic parameters in adult Wistar rats.

METHODS

Wistar rats (n = 15/group) were fed either a normolipidic diet or a hyperlipidic diet for 90 days. The normolipidic and hyperlipidic diets had the same ingredients except for fat compositions, concentrations and calories. We used lard in the cis fatty acid group and PHSO in the trans fatty acid group. The intervention groups were as follows: (1) low lard (LL), (2) high lard (HL), (3) low partially hydrogenated soybean oil (LPHSO) and (4) high partially hydrogenated soybean oil (HPHSO). Body weight, lipid profiles and the inflammatory responses in the CSF, serum and liver tissue were analyzed.

RESULTS

Surprisingly, with the PHSO diet we observed a worse metabolic response that was associated with oxidative stress in hepatic tissue as well as impaired serum and CSF fluid parameters at both PHSO concentrations. In many analyses, there were no significant differences between the LPHSO and HPHSO diets.

CONCLUSIONS

Dietary supplementation with PHSO impaired inflammatory parameters in CSF and blood, induced insulin resistance, altered lipid profiles and caused hepatic damage. Overall, these findings suggest that fat composition is more important than the quantity of fat consumed in terms of cis and trans fatty acid diets.

Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies

OBJECTIVE

To systematically review associations between intake of saturated fat and trans unsaturated fat and all cause mortality, cardiovascular disease (CVD) and associated mortality, coronary heart disease (CHD) and associated mortality, ischemic stroke, and type 2 diabetes.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Medline, Embase, Cochrane Central Registry of Controlled Trials, Evidence-Based Medicine Reviews, and CINAHL from inception to 1 May 2015, supplemented by bibliographies of retrieved articles and previous reviews.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Observational studies reporting associations of saturated fat and/or trans unsaturated fat (total, industrially manufactured, or from ruminant animals) with all cause mortality, CHD/CVD mortality, total CHD, ischemic stroke, or type 2 diabetes.

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently extracted data and assessed study risks of bias. Multivariable relative risks were pooled. Heterogeneity was assessed and quantified. Potential publication bias was assessed and subgroup analyses were undertaken. The GRADE approach was used to evaluate quality of evidence and certainty of conclusions.

RESULTS

For saturated fat, three to 12 prospective cohort studies for each association were pooled (five to 17 comparisons with 90,501-339,090 participants). Saturated fat intake was not associated with all cause mortality (relative risk 0.99, 95% confidence interval 0.91 to 1.09), CVD mortality (0.97, 0.84 to 1.12), total CHD (1.06, 0.95 to 1.17), ischemic stroke (1.02, 0.90 to 1.15), or type 2 diabetes (0.95, 0.88 to 1.03). There was no convincing lack of association between saturated fat and CHD mortality (1.15, 0.97 to 1.36; P=0.10). For trans fats, one to six prospective cohort studies for each association were pooled (two to seven comparisons with 12,942-230,135 participants). Total trans fat intake was associated with all cause mortality (1.34, 1.16 to 1.56), CHD mortality (1.28, 1.09 to 1.50), and total CHD (1.21, 1.10 to 1.33) but not ischemic stroke (1.07, 0.88 to 1.28) or type 2 diabetes (1.10, 0.95 to 1.27). Industrial, but not ruminant, trans fats were associated with CHD mortality (1.18 (1.04 to 1.33) v 1.01 (0.71 to 1.43)) and CHD (1.42 (1.05 to 1.92) v 0.93 (0.73 to 1.18)). Ruminant trans-palmitoleic acid was inversely associated with type 2 diabetes (0.58, 0.46 to 0.74). The certainty of associations between saturated fat and all outcomes was "very low." The certainty of associations of trans fat with CHD outcomes was "moderate" and "very low" to "low" for other associations.

CONCLUSIONS

Saturated fats are not associated with all cause mortality, CVD, CHD, ischemic stroke, or type 2 diabetes, but the evidence is heterogeneous with methodological limitations. Trans fats are associated with all cause mortality, total CHD, and CHD mortality, probably because of higher levels of intake of industrial trans fats than ruminant trans fats. Dietary guidelines must carefully consider the health effects of recommendations for alternative macronutrients to replace trans fats and saturated fats.

Dietary fatty acids, dietary patterns, and lipoprotein metabolism

PURPOSE OF REVIEW

Few studies have reviewed the impact of dietary fat and dietary patterns on lipoprotein metabolism. This review intends to provide perspective on this topic, while focusing primarily on the studies that assessed intravascular lipoprotein kinetics in humans using isotope methodologies.

RECENT FINDINGS

Data suggest that dietary saturated fatty acids slow the clearance of LDL apolipoprotein (apo)B-100 and of apoA-I from the circulation, whereas possibly increasing also apoA-I production. Dietary trans fats reduce the clearance of LDL apoB-100, whereas increasing the clearance of apoA-I. n-3 polyunsaturated fatty acids (PUFAs) intake reduces the production of apoB-48-containing lipoproteins as well as of VLDL apoB-100 and increases their conversion into smaller lipoproteins. Medium-chain triglycerides appear to have no significant effect on lipoprotein kinetics. Finally, Mediterranean diet in the absence of weight loss reduces LDL cholesterol, primarily by enhancing its clearance from the circulation.

SUMMARY

Kinetic studies with tracers allow a better appreciation of the impact of specific dietary factors on plasma lipid risk factors. However, additional studies are required to better document the effect of monounsaturated fatty acids, n-6 PUFAs, and of whole diets on lipoprotein metabolism.

Nutrients other than carbohydrates: their effects on glucose homeostasis in humans

Besides carbohydrates, other nutrients, such as dietary protein and amino acids; the supply of fat, vitamin D, and vitamin K; and sodium intake seem to affect glucose homeostasis. Although their effect is less pronounced than that of the amount and composition of carbohydrates, it seems reasonable to consider how nutrient intake habits may be modified to support an improved glucose homeostasis. For instance, taking into account the effect of some nutrients to lower blood glucose concentration on a day-by-day basis might support improvement of glucose homeostasis in the long run. On the other hand, lowering sodium intake too much, as recommended to avoid the development of hypertension, particularly in sodium-sensitive people, might lead to insulin resistance and thereby might risk increasing fasting as well as postprandial blood glucose concentrations. This review summarizes the state of our knowledge of how several nutrients other than carbohydrates, such as protein, fatty acids, vitamin D, vitamin K, magnesium, zinc, chromium, and sodium, affect blood glucose concentrations. Sufficient evidence exists to show that, in prospective studies based on randomized controlled trials, these selected nutrients affect blood glucose regulation. The review describes potential mechanisms leading to the observed effect. As much as is possible from the available data, the extent of the effect, is considered.

Nutrition and healthy ageing: the key ingredients

Healthy longevity is a tangible possibility for many individuals and populations, with nutritional and other lifestyle factors playing a key role in modulating the likelihood of healthy ageing. Nevertheless, studies of effects of nutrients or single foods on ageing often show inconsistent results and ignore the overall framework of dietary habits. Therefore, the use of dietary patterns (e.g. a Mediterranean dietary pattern) and the specific dietary recommendations (e.g. dietary approaches to stop hypertension, Polymeal and the American Healthy Eating Index) are becoming more widespread in promoting lifelong health. A posteriori defined dietary patterns are described frequently in relation to age-related diseases but their generalisability is often a challenge since these are developed specifically for the population under study. Conversely, the dietary guidelines are often developed based on prevention of disease or nutrient deficiency, but often less attention is paid to how well these dietary guidelines promote health outcomes. In the present paper, we provide an overview of the state of the art of dietary patterns and dietary recommendations in relation to life expectancy and the risk of age-related disorders (with emphasis on cardiometabolic diseases and cognitive outcomes). According to both a posteriori and a priori dietary patterns, some key 'ingredients' can be identified that are associated consistently with longevity and better cardiometabolic and cognitive health. These include high intake of fruit, vegetables, fish, (whole) grains and legumes/pulses and potatoes, whereas dietary patterns rich in red meat and sugar-rich foods have been associated with an increased risk of mortality and cardiometabolic outcomes.

Supplementation with 1% energy trans fatty acids had little effect on serum cholesterol levels in healthy young Japanese women

The World Health Organization (WHO) has recommended that trans fatty acid (TFA) intake should be less than 1% of total energy intake, but few data are available as to the influence of energy TFA intake of as low as 1% on blood cholesterol levels. A randomized, double-blind, parallel trial was conducted to assess the effects of 1% TFA dietary supplementation on serum cholesterol levels in healthy young women. Sixty-five volunteers consumed cookies containing 1% (TFA) or 0.04% (control) energy of TFA for 4 weeks and blood was harvested after overnight fasting. There were no significant differences in serum LDL- or HDL-cholesterol levels between the two groups. The hemoglobin A1c level was not influenced by dietary TFA. These results suggest that energy of TFAs at less than 1% has little effect on serum cholesterol or hemoglobin A1c levels in healthy young women. This confirms the correctness of the WHO recommendation.