Food: the type of protein eaten has a significant influence on weight gain

Québec City, June 7, 2021 – The type of protein eaten has a significant influence on weight gain, insulin resistance, and the related metabolic diseases, according to an international study published today in Nature Communications. This means nutritional interventions to prevent or fight obesity and type 2 diabetes should not focus only on fats and sugars, concluded the research team led by André Marette, professor at Université Laval’s Faculty of Medicine.

The researchers looked at groups of mice fed diets rich in fats and sugars, but with different compositions of proteins. Half the mice received feed containing only one protein, casein. The other mice received feed with a composition modeled after the North American diet. “This feed contained proteins sourced from rice, soy, peas, beef, chicken, pork, milk, eggs, and fish, in proportions reflecting the average North American diet,” said Dr. Marette, who is also associated with the Québec Heart and Lung Institute Research Centre and the Institute of Nutrition and Functional Foods.

After 11 weeks, the researchers found that the mice eating the feed with the protein blend had gained 15% more weight than those eating the feed containing only casein. The weight gain came primarily from an increase in stored fat. Those mice also had a harder time keeping their blood sugar levels within normal range. 

The metabolic effects of the protein-blend diet seem to be due to the gut microbiota, said Dr. Marette: “We observed a reconfiguration of the number of bacteria species present in the intestinal tract, as well as increased production of two compounds that come from protein fermentation. The compounds, isovalerate and isobutyrate, cause insulin resistance in the liver.”

These findings suggest that the type of protein present in food can have a significant impact in a short period of time on the gut microbiota and the compounds it produces. Nutritional interventions for weight loss should take this into account, said the researcher. 

What are the best proteins to eat? “Our study showed that casein, a milk protein, is beneficial compared to a blend of all dietary proteins,” said Dr. Marette. “Now we plan to compare proteins from red meat and fish as well as plant-based proteins to determine which should be avoided or preferred, especially when the diet is already high in fats and sugars and tends to cause obesity.”

The authors of the study are Béatrice Choi, Noëmie Daniel, Vanessa Houde, Adia Ouellette, Bruno Marcotte, Thibault Varin, Cécile Vors, Perrine Feutry, Philippe St-Pierre, Angelo Tremblay, and André Marette (Université Laval); Olga Ilkayeva and Phillip White (Duke University); Marcus Stahlman and Fredrik Bäckhed (University of Gothenburg).