Impact of dietary supplements, diet on metabolic health explored in review

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A review¹ published in the journal Molecules sought to analyze the role of food ingredients and dietary supplements in managing metabolic syndrome and non-alcoholic fatty liver disease (NAFLD) in human clinical trials. The review found that dietary supplements and foods including omega-3s, polyphenols, and vitamin D, plus fruits and vegetables, may be effective in reducing pro-inflammatory cytokines found in metabolic syndrome, cardiovascular risks, and obesity, and may also improve the body’s lipid profile.

Metabolic syndrome is an “aggregation of interconnected metabolic factors that appear to directly develop into a cardiovascular disease (CVD), increasing the risk of the development of type 2 diabetes,” the authors write in the review. Some of the agreed-upon criteria for metabolic syndrome include insulin resistance, inflammation, visceral adiposity, hyperglycemia, elevated blood pressure, and dyslipidemia, or elevated triglyceride levels and reduced levels of HDL cholesterol, among others.

The researchers sought to establish whether certain dietary supplements derived from natural products, including plants, spices, and herbs, with a variety of bioactive compounds, could affect some of these metabolic parameters in adults with metabolic syndrome and NAFLD. Previous research indicates that curcumin (Curcuma longa), resveratrol, and quercetin, one of major flavonoids found in many plants, may exert a beneficial effect on the above metabolic parameters.

Other natural products, including grape, green tea (Camelia sinensis), Aloe vera, and more, have also been shown to support metabolism. These food ingredients, the researchers note, “have been related to health promotion, chronic disease prevention, and adjunctive therapy in individuals with metabolic syndrome and NAFLD.”

Curcumin, specifically, has a polyphenolic structure with antioxidant and anti-inflammatory properties, according to a number of the studies analyzed. Inflammation and oxidative stress are key contributors to metabolic syndrome and NAFLD. Daily supplementation with curcumin (500 mg twice per day) and piperine (500 mg of curcumin plus 5 mg piperine) were found to reduce serum levels of pro-inflammatory cytokines and adipokines, increase adiponectin, and reduced leptin levels between group-comparison in a randomized, controlled trial in subjects diagnosed with metabolic syndrome. In other clinical data, curcumin was shown to possess lipid-modifying and antioxidant-boosting properties.

Resveratrol, meanwhile, is a natural polyphenolic compound occurring that has demonstrated positive effects on metabolic syndrome and NAFLD in human clinical trials. One clinical study demonstrated resveratrol’s beneficial effects on subjects’ body mass index (BMI), fat mass, waist circumference, and total insulin secretion after supplementation with 500 mg resveratrol three times per day for 90 days in individuals with metabolic syndrome. Other studies consulted showed both positive and neutral metabolic effects of resveratrol supplementation.

Quercetin may also affect parameters of metabolic syndrome, the authors write. One of the studies consulted showed that 150 mg quercetin per day reduced systolic blood pressure in overweight individuals with high cardiovascular disease risk. In that same study, quercetin also demonstrated lipid-modifying properties.

The review also found that diet plays a key role in managing parameters of metabolic syndrome. Fruits and vegetables, in particular, have a variety of antioxidants and dietary fiber, state the authors. The authors point a current randomized, controlled trial showing that 20 g of wine grape pomace flour daily improved blood pressure, glycemia, and postprandial insulin. Grape seed extract, meanwhile, demonstrated some metabolic improvements for metabolic syndrome, particularly in blood pressure.

Green tea has demonstrated health benefits including possibly lowering subjects’ BMI. Its anti-inflammatory properties have been examined in a number of studies. Elsewhere, research indicates that orange juice, hibiscus (Hibiscus sabdariffa L.), Aloe vera, bitter melon (Momordica charantia), and barberry (Berberis vulgaris), may also provide metabolic health benefits.

Finally, the researchers explored the role of vitamins and fatty acids in potentially managing metabolic health factors. Vitamin D deficiency has been associated with an elevated risk for metabolic syndrome. Among its various potential health benefits, one clinical study also suggests “a significant correlation of active vitamin D and its components with metabolic syndrome.” Vitamin E, too, may be associated with metabolic syndrome, they add, and it has been shown to have a beneficial effect on lipid profiles.

Regarding fatty acids, the authors write: “In general, the introduction of unsaturated fatty acids, both monounsaturated fatty acids and polyunsaturated fatty acids, and especially the latter, are effective at controlling and treating metabolic syndrome and NAFDL.” They add that the suggested supplementation time should be “long term,” and differences have been reported after around 12 weeks.

The authors conclude that “foods rich in polyphenols and phenolic compounds, in addition to vitamin D, fruits, and vegetables, are effective at reducing pro-inflammatory cytokines found in metabolic syndrome, reducing their signaling pathways.” Specifically, these nutraceuticals provided cardiovascular support, both by biochemical and hormonal modulation. Supplements and foods with phenolic compounds and catechins also reduced body weight. EPA and DHA fish oil improved subjects’ lipid profiles, inflammatory markers, and endothelial function.

While the review provides some clarity on the mechanisms by which these supplements and foods exert their potential metabolic health benefits, the authors also state that the dose, time of treatment, long-term supplementation, and bioavailability of these dietary supplements should be further evaluated.

References:

1. Figueiredo PS et al. “An overview of novel dietary supplements and food ingredients in patients with metabolic syndrome and non-alcoholic fatty liver disease.” Molecules. Published online April 11, 2018.