Scientists at Aberdeen's Rowett Research Institute have shown that a very low carbohydrate weight-loss diet results in a four-fold reduction in the numbers of certain types of bacteria in the gut of obese men.
This is a significant finding because these gut bacteria produce a substance called butyrate, which has been shown to be important for keeping the gut healthy including helping to prevent colorectal cancer. The study raises questions about the impact of the prolonged use of very low-carbohydrate weight-loss diets on gut health.
Very low-carbohydrate weight-loss diets (such as the so-called ‘Atkins-type diets) are popular with people struggling to lose weight and are used in some weight-loss clinics. Nutritionists have raised concerns about the low fruit and vegetable content of such diets as these contain nutrients that help protect against a number of diseases and cancers within the body. Less attention has been paid to the consequences of the low carbohydrate intake on the bacteria within the gut and how this might alter the release of either beneficial or harmful compounds from the food.
In this study, 19 healthy, obese men were given three diets containing different levels of carbohydrate (high, medium and low). Two of the diets also contained a high proportion of protein, as this is known to help reduce appetite and is used in a number of diets that help produce weight loss. Indeed, the volunteers lost similar amounts of weight and body fat on these two diets. Stool samples were analysed for the amount and type of bacteria, and for butyrate.