Vegan vs omnivore diet – Diet and Health Today

This week, I review a paper that filled my inbox with ‘look at this’ requests. It was a study published in JAMA titled “Cardiometabolic Effects of Omnivorous vs Vegan Diets in Identical Twins: A randomised clinical trial” by Landry et al. The name that caught my attention was Professor Christopher Gardner from Stanford University, a veteran vegetarian with whom I’ve corresponded on previous occasions.

Professor Gardner, renowned for the DIETFITS and KETO-MED trials, is the last author on this paper, indicating his senior role. The DIETFITS study, a randomized trial involving 609 participants, compared healthy low-carb and healthy low-fat diets. Notably, Gardner’s studies stand out for their rarity in the field of nutrition – rigorous randomised controlled trials (RCTs), a focus on whole foods, and explicit attention to diet adherence.

This latest research from Gardner’s team is another RCT comparing two whole-food diets—vegan and omnivorous—enrolling 22 pairs of identical twins. Unlike population studies, RCTs typically equalise characteristics through randomisation. However, this study, though small, revealed baseline differences between groups, notably in weight, blood pressure, and lipid levels.

The trial spanned eight weeks, with the first four weeks providing meals to ensure adherence. Notably, the vegan group received fewer calories, revealing a significant flaw in the study’s design, contradicting its claim of no prescribed energy restriction. Macronutrient proportions and nutrient intake differed between groups, highlighting the main issues with the study.

The vegan group experienced a significant decrease in LDL-cholesterol, fasting insulin, and body weight compared to the omnivores. However, the predictable reduction in cholesterol due to increased plant sterol intake was not groundbreaking. Moreover, diet satisfaction plummeted among vegans, with only one expressing intent to continue the diet, while omnivores reported increased or maintained satisfaction.

Strengths of the study, such as using identical twins and ensuring adherence through a food delivery period, were acknowledged. However, there were limitations, including a small sample size, short duration, lack of follow-up, and a non-isocaloric design, which should raise concerns.

In summary, this trial appears to be a waste of time and resources and lacking in novel insights. From a research standpoint, it failed to unveil new information. Narratively, it contributes to the literature favouring plant-based diets, despite nutritional evidence suggesting the opposite is true.

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