Some metabolic changes differ by race for women switching to vegetarian diet

Some metabolic changes differ by race for women switching to vegetarian diet

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Improvements in fatty acid metabolism occurred for women switching from their habitual omnivorous diet to a vegetarian diet, according to a study published in Nutrition, Metabolism & Cardiovascular Diseases.

European American and African American women switching to a vegetarian diet exhibited significant changes in diet-derived metabolites and metabolites of saturated, monosaturated and polyunsaturated fatty acids. However, changes in plasma concentrations of acylcarnitines, which reflect the completeness of fatty acid oxidation, differed by racial group.

Silver is a research professor of medicine and director of the Vanderbilt Diet, Body Composition and Human Metabolism Core at Vanderbilt University Medical Center.

“The metabolic response to switching from a predominately animal-based diet to a predominately plant-based diet may improve the ability of dietary fat to be oxidized and used as an energy source rather than be stored and contribute to excess body fat,” Heidi J. Silver, PhDRD, research professor of medicine and director of the Vanderbilt Diet, Body Composition and Human Metabolism Core at Vanderbilt University Medical Center, told Healio. “However, the individual metabolic response to a diet intervention, of any type, differs, and here we see a difference in fatty acid metabolism response by race/ethnicity. Therefore, there is no one type of diet that fits all people.”

Silver and colleagues conducted a prospective cohort study of 20 European American and 18 African American women in the Nashville, Tennessee, area. Participants were aged 18 to 40 years and had a normal-weight BMI between 18.5 kg/m2 and 24.9 kg/m2. The study was designed to evaluate the acute effects of new-onset vegetarian diet. European American and African American participants were matched by age, BMI, physical activity level and energy requirement. Each woman served as her own control to compare pre-intervention and post-intervention outcomes. One group of women was enrolled from October 2017 to February 2018 and the second group from November 2018 to February 2019. After a baseline testing visit on day 1, participants switched to a vegetarian menu with no meat, fish, poultry, eggs or dairy products from days 2 to 5. A final testing visit was conducted on day 6. Anthropometric measures, blood and urine samples were collected for all 6 days of the study.

No changes in energy intake

Participants did not have a change in energy intake or body weight with the vegetarian diet. The percentage of energy from carbohydrates increased about 10%, with no difference between European American and African American women. There was no change in the percentage of energy from total fat intake, but saturated fatty acid intakes decreased about 50% in both groups, and the ratio of saturated to unsaturated fat intake dropped 50% in both groups (P < .001 for both).

Participants had an upregulation of many fatty acids, including a 25% to 30% increase of multiple long-chain monounsaturated fatty acids and long-chain polyunsaturated fatty acids. There was also a 25% to 30% change in plasma concentrations of long-chain saturated fatty acids. The changes occurred concurrently with a 42% decrease in the ratio of stearic to oleic acid (18:0/18:1) and a 27% decrease in the ratio of palmitic to palmitoleic acid (16:0/16:1).

Fatty acid metabolite changes differ by race

Increases in circulating concentrations of the conjugated fatty acid metabolites of carnitine metabolism were observed. Changes in the concentrations of nonanoylcarnitine, hexanoylcarnitine, laurylcarnitine, decanoylcarnitine and 5-dodecenoylcarnitine differed by race. There was a trend toward significant diet by race interactions for seven other fatty acid metabolites.

“The optimal diet for any individual must be personalized, taking into account not only that individual’s demographics, but also an individual’s specific metabolic needs and an individual’s specific metabolic health problems,” Silver said. “Further, the optimal diet for any individual depends on how that individual responds to the diet with regard to the factors that may increase or decrease risk for chronic diseases like type 2 diabetes and cardiovascular disease.”

Researchers also observed changes in the circulating levels of metabolites that may result from alterations in the gut microbiome, including the downregulation of metabolites of the aromatic amino acids phenylalanine, tyrosine and tryptophan. There were also plasma and urine changes in gut fermentation products involved in aromatic amino acid metabolism. Plasma concentration of trimethylamine N-oxide was reduced by 33% with the vegetarian diet. There was a 1.2-fold increase in circulating oleoyl ethanolamide and a 1.4-fold increase in circulating N-oleoyl taurine. Further microbiome metabolite changes were observed in urine samples.

Silver said more randomized controlled trials are needed to investigate the long-term cardiometabolic effects of vegetarian and vegan diets, especially in adults with obesity and those who are attempting to lose weight or maintain weight loss.

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Heidi J. Silver, PhD, RD, can be reached at