Adverse effects on insulin secretion of replacing saturated fat with refined carbohydrate but not with monounsaturated fat: A randomized controlled trial in centrally obese subjects

Diverse impacts of red palm olein, extra virgin coconut oil and extra virgin olive oil on cardiometabolic risk markers in individuals with central obesity: a randomised trial

PURPOSE

Dietary fats with an abundance of phytonutrients have garnered public attention beyond fatty acids per se. This study was set to investigate the impact of consuming diets with red palm olein (RPOO), extra virgin coconut oil (EVCO) and extra virgin olive oil (EVOO, as a control) on cardiometabolic risk biomarkers and lipid profile.

METHODS

We recruited a total of 156 individuals with central obesity, aged 25-45 years, with waist circumference ≥ 90 cm for men and ≥ 80 cm for women in a parallel single-blind 3-arm randomised controlled trial. The participants consumed isocaloric diets (~ 2400 kcal) enriched with respective test fats (RPOO, EVCO or EVOO) for a 12-week duration.

RESULTS

The mean of the primary outcome plasma high sensitivity C-reactive protein was statistically similar between the three diets after a 12-week intervention. EVOO resulted in significantly lower mean LDL cholesterol compared with RPOO and EVCO, despite similar effects on LDL and HDL cholesterol subfractions. The RPOO diet group showed elevated mean α and β -carotenes levels compared with EVCO and EVOO diet groups (P < 0.05), corresponding with the rich carotenoid content in RPOO.

CONCLUSION

The three oils, each of which has unique phytonutrient and fatty acid compositions, manifested statistically similar cardiometabolic effects in individuals with central obesity at risk of developing cardiovascular diseases with distinct circulating antioxidant properties.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov (NCT05791370).

Impact of saturated compared with unsaturated dietary fat on insulin sensitivity, pancreatic β-cell function and glucose tolerance: a systematic review and meta-analysis of randomized, controlled trials

BACKGROUND

The impact of the dietary fat type on type 2 diabetes (T2D) remains unclear.

OBJECTIVES

We aimed to evaluate the effects of replacing dietary saturated fatty acids (SFA) with mono- or poly-unsaturated fatty acids (MUFA and PUFA, respectively) on insulin sensitivity, pancreatic β-cell function, and glucose tolerance, as surrogate endpoints for T2D.

METHODS

We conducted a systematic review and meta-analysis of randomized controlled trials that replaced ≥5% of total energy intake provided by SFA with MUFA or PUFA and reported indexes of insulin sensitivity, β-cell function, and/or glucose tolerance. We searched MEDLINE, Scopus, and the Cochrane Library (CENTRAL) up to 9 January, 2023. Eligible interventions had to be isocaloric, with no significant difference in other macronutrients. Data were synthesized using random-effects model meta-analysis.

RESULTS

Of 6355 records identified, 10 parallel and 20 crossover trials with 1586 participants were included. The mean age of the participants was 42 years, 47% were male, mean body mass index (BMI; in kg/m2) was 26.8, median baseline fasting glucose was 5.13 mmol/L, and the median duration of interventions was 5 weeks. Replacing SFA with MUFA or PUFA had no significant effects on insulin sensitivity [standardized mean difference (SMD) SFA compared with MUFA: 0.01, 95% confidence interval (CI): -0.06 to 0.09, I2 = 0% and SMD SFA compared with PUFA: 0, 95% CI: -0.15 to 0.14, I2 = 0%]. Replacing SFA with MUFA did not significantly impact the β-cell function, evaluated by the disposition index (mean difference: -12, 95% CI: -158 to 133, I2=0%). Evidence on glucose tolerance (SFA compared with MUFA or PUFA) and on β-cell function when SFA were replaced with PUFA was scant.

CONCLUSIONS

Short-term substitution of saturated with unsaturated fat does not significantly affect insulin sensitivity nor β-cell function (the latter in the SFA compared with MUFA comparison). Future studies are needed to elucidate longer term effects of dietary fat saturation on glucose homeostasis. This trial was registered at PROSPERO as CRD42020178382.

Effects of diets rich in ghee or olive oil on cardiometabolic risk factors in healthy adults: a two-period, crossover, randomised trial

This study aimed to evaluate the cardiovascular health-related effects of consuming ghee in the usual diet. Thirty healthy men and women were studied in a free-living outpatient regimen. The participants were instructed for the isoenergetic inclusion of ghee or olive oil in their diets for 4 weeks using a randomised crossover design. At the end of run-in (baseline), 2-week wash-out and interventions, fasting blood samples were drawn. In addition, 2-h postprandial blood samples were collected after ingestion of a meal containing olive oil or ghee at week 4 of each dietary intervention. Body weight was not different between the two interventions. Compared with the olive oil, the diet with ghee increased fasting plasma apo-B (apo B) (0·09, 95 % CI 0·02, 0·17 g/l, P = 0·018), non-HDL-cholesterol (non-HDL-cholesterol) (0·53, 95 % CI 0·01, 1·05 mmol/l, P = 0·046) and LDL-cholesterol did not differ significantly between diet groups (0·29, 95 % CI -0·05, 0·63 mmol/l, P = 0·092), but had no significant effect on total cholesterol:HDL-cholesterol ratio (0·75, 95 % CI - 0·24 to 1·74 mmol/l, P = 0·118). No significant difference was observed in fasting as well as 2-h postprandial plasma TAG, glucose, insulin and plasminogen activator inhibitor-1 concentrations. This study showed that ghee that is predominantly saturated fats had an increasing effect on plasma apo B and non-HDL-cholesterol compared with olive oil, adding further evidence to the existing recommendations to replace dietary fats high in SFA with dietary fats high in unsaturated fats to reduce CVD risk.

Dairy fat intake and risk of type 2 diabetes in 3 cohorts of US men and women

BACKGROUND

Previous studies have examined dairy products with various fat contents in relation to type 2 diabetes (T2D) risk, although data regarding dairy fat intake per se are sparse.

OBJECTIVES

We aimed to evaluate the association between dairy fat intake and risk of T2D in 3 prospective cohorts. We also examined associations for isocalorically replacing dairy fat with other macronutrients.

METHODS

We prospectively followed 41,808 men in the Health Professionals Follow-Up Study (HPFS; 1986-2012), 65,929 women in the Nurses' Health Study (NHS; 1984-2012), and 89,565 women in the NHS II (1991-2013). Diet was assessed quadrennially using validated FFQs. Fat intake from dairy products and other relevant sources was expressed as percentage of total energy. Self-reported incident T2D cases were confirmed using validated supplementary questionnaires. Time-dependent Cox proportional hazards regression was used to estimate the HR for dairy fat intake and T2D risk.

RESULTS

During 4,219,457 person-years of follow-up, we documented 16,511 incident T2D cases. Dairy fat was not associated with risk of T2D when compared with calories from carbohydrates (HR for extreme quintiles: 0.98; 95% CI: 0.95, 1.02). Replacing 5% of calories from dairy fat with other sources of animal fat or carbohydrate from refined grains was associated with a 17% (HR: 1.17; 95% CI: 1.13, 1.21) and a 4% (HR: 1.04; 95% CI: 1.00, 1.08) higher risk of T2D, respectively. Conversely, a 5% calorie replacement with carbohydrate from whole grains was associated with a 7% lower risk of T2D (HR: 0.93; 95% CI: 0.88, 0.98).

CONCLUSIONS

Dairy fat intake was not associated with T2D risk in these cohort studies of US men and women when compared with calories from carbohydrate. Replacing dairy fat with carbohydrates from whole grains was associated with lower risk of T2D. Replacement with other animal fats or refined carbohydrates was associated with higher risk.

Avocado Fruit on Postprandial Markers of Cardio-Metabolic Risk: A Randomized Controlled Dose Response Trial in Overweight and Obese Men and Women

Avocados are distinctive fruits having both fats and fibers along with various micronutrients and bioactive phytochemicals. This study aimed to assess the effects of replacing carbohydrate energy in meals with half or whole avocado on postprandial indices of metabolic and vascular health. A single-center, randomized, controlled, 3-arm, 6 h, crossover study was conducted in overweight/obese middle-aged adults (n = 31). Participants consumed energy-matched breakfast meals containing 0 g (Control), 68 g (Half-A) or 136 g (Whole-A) fresh Hass avocado on 3 separate occasions. Post-meal glycemic (p < 0.0001), insulinemic (p < 0.0001) and flow mediated vasodilation (FMD) responses were reduced compared to Control meal (p < 0.01), independent of dose. Nuclear magnetic resonance analyses indicated lower concentrations of triglyceride-rich lipoproteins and higher concentrations of larger high-density lipoprotein (HDL) particles after the Whole-A vs. the Control meal (p = 0.02, p < 0.05, respectively). Race/ethnicity influenced sub-class lipoprotein concentrations (p < 0.05). Oxidized low-density-lipoproteins, monocyte chemoattractant protein-1, and interleukin-6 were not different among meals. Tumor necrosis factor-α tended to be lower after Whole-A vs. Control meal (p = 0.07). Replacing carbohydrate components with avocados in a meal improved FMD, a measure of endothelial function, and improved glycemic and lipoprotein profiles in overweight/obese adults. The study provides insight on the acute cardio-metabolic benefits of incorporating avocados into a meal.

Effects of low-carbohydrate- compared with low-fat-diet interventions on metabolic control in people with type 2 diabetes: a systematic review including GRADE assessments

Background

It remains uncertain which diet is best for people with type 2 diabetes (T2D).

Objective

We compared the effects of dietary carbohydrate restriction with fat restriction on markers of metabolic syndrome and quality of life in people with T2D.

Design

This systematic review of randomized controlled trials (RCTs) and controlled clinical trials (CCTs) compares the effects of a low-carbohydrate [≤40% of energy (%)] diet with those of a low-fat (≤30%) diet over a period of ≥4 wk in patients with T2D. Two investigators independently selected studies, extracted data, and assessed risk of bias. The GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach was used to assess the certainty of evidence. Pooled mean differences (MDs) and 95% CIs were calculated with the use of a random-effects model.

Results

Thirty-three RCTs and 3 CCTs (n = 2161) were included. Glycated hemoglobin declined more in people who consumed low-carbohydrate food than in those who consumed low-fat food in the short term (MD: -1.38%; 95% CI: -2.64%, -0.11%; very-low-certainty evidence). At 1 y, the MD was reduced to -0.36% (95% CI: -0.58%, -0.14%; low-certainty evidence); at 2 y, the difference had disappeared. There is low to high (majority moderate) certainty for small improvements of unclear clinical importance in plasma glucose, triglycerides, and HDL concentrations favoring low-carbohydrate food at half of the prespecified time points. There was little to no difference in LDL concentration or any of the secondary outcomes (body weight, waist circumference, blood pressure, quality of life) in response to either of the diets (very-low- to high-certainty evidence).

Conclusions

Currently available data provide low- to moderate-certainty evidence that dietary carbohydrate restriction to a maximum of 40% yields slightly better metabolic control of uncertain clinical importance than reduction in fat to a maximum of 30% in people with T2D. This systematic review is registered at http://www.crd.york.ac.uk/PROSPERO/display_record.php?ID=CRD42017052467 as CRD42017052467.

Effects of oils and solid fats on blood lipids: a systematic review and network meta-analysis

The aim of this network meta-analysis (NMA) is to compare the effects of different oils/solid fats on blood lipids. Literature searches were performed until March 2018. Inclusion criteria were as follows: i) randomized trial (≥3 weeks study length) comparing at least two of the following oils/solid fats: safflower, sunflower, rapeseed, hempseed, flaxseed, corn, olive, soybean, palm, and coconut oil, and lard, beef-fat, and butter; ii) outcomes LDL-cholesterol (LDL-C), total cholesterol (TC), HDL-cholesterol (HDL-C), and triacylglycerols (TGs). A random dose-response (per 10% isocaloric exchange) NMA was performed and surface under the cumulative ranking curve (SUCRA) was estimated. Fifty-four trials were included in the NMA. Safflower oil had the highest SUCRA value for LDL-C (82%) and TC (90%), followed by rapeseed oil (76% for LDL-C, 85% for TC); whereas, palm oil (74%) had the highest SUCRA value for TG, and coconut oil (88%) for HDL-C. Safflower, sunflower, rapeseed, flaxseed, corn, olive, soybean, palm, and coconut oil as well beef fat were more effective in reducing LDL-C (−0.42 to −0.23 mmol/l) as compared with butter. Despite limitations in these data, our NMA findings are in line with existing evidence on the metabolic effects of fat and support current recommendations to replace high saturated-fat food with unsaturated oils.

Recent Science and Clinical Application of Nutrition to Coronary Heart Disease

One of the greatest threats to mortality in industrialized societies continues to be coronary heart disease (CHD). Moreover, the ability to decrease the incidence of CHD has reached a limit utilizing traditional diagnostic evaluations and prevention and treatment strategies for the top five cardiovascular risk factors (hypertension, diabetes mellitus, dyslipidemia, obesity, and smoking). It is well known that about 80% of CHD can be prevented with optimal nutrition, coupled with exercise, weight management, mild alcohol intake, and smoking cessation. Among all of these factors, optimal nutrition provides the basic foundation for prevention and treatment of CHD. Numerous prospective nutrition clinical trials have shown dramatic reductions in the incidence of CHD. As nutritional science and nutrigenomics research continues, our ability to adjust the best nutrition with an individualized approach is emerging. This article reviews the role of nutrition in the prevention and treatment of CHD and myocardial infarction (MI).