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A Randomized Controlled Trial of 5 Different Diets, and The Biggest Loser is…

Tim Boyer's picture
Diet trial

One of the biggest problems behind dieting - and why we fail - is that it requires self-monitoring i.e. calorie counting. A new study shows that it is possible to lose weight without calorie counting based on the results of a new randomized controlled trial of 5 different diets. Find out which one proved to be the biggest loser.


A new study published in the journal Nutrition pitted the effects of 5 different diets against one another to determine how varying degrees of plant-based diets can have on weight loss. The study consisted of a broad range of overweight men and women ages 18-65 and lasted for 6 months, of which 79% (50) successfully completed the study. A non-plant based omnivorous diet was included as a comparison control.

The weight loss study participants were randomly divided into one of five dieting groups that consisted of:

Vegan― no animal products allowed
Vegetarian―dairy products allowed
Pesco-vegetarian―dairy products and seafood allowed
Semi-vegetarian―all foods allowed, but red meat only once a week and poultry five times or less a week
Omnivorous―eat whatever crosses your path

All participants were encouraged to focus on going low-fat and were allowed limited amounts of healthy fats from nuts, seeds, olives and avocadoes. Calorie counting or restriction was not required or encouraged; rather, eating until one felt full was their guideline. All participants were required to attend weekly group meetings with the exception of the omnivorous group who had monthly meetings supplemented with weekly e-mail lessons.

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The results of the 6 month long study showed that:

• The vegan group lost the most weight with an average weight loss of 7.5 pounds.
• The vegetarian group came in second with an average weight loss of 6.3 pounds.
• The pesco-vegetarian group lost an average 3.2 pounds.
• The semi-vegetarian group lost an average of 3.2 pounds.
• The omnivores lost an average of 3.1 pounds.
• The Vegan participants decreased their fat and saturated fat more than did the pesco-vegetarian, semi-vegetarian, and omnivorous groups.
• There was no significant difference in reported activity levels among the five groups.

The researchers concluded from the data that Vegan diets may result in greater weight loss than more modest recommendations where a plant-based diet allows not only dairy, but seafood, some beef and poultry. The bonus of a vegan and vegetarian diet is not only a lower-fat diet, but also may help dieters stick more positively and longer to a weight loss plan that does not require the burden of a popular calorie counting diet, but allows a dieter to eat until feeling satiated.

Image Source: Courtesy of Wikimedia Commons

Reference: “Comparative effectiveness of plant-based diets for weight loss” Nutrition Oct. 2014, G. Turner-McGrievy et al.