Low carb diet can compromise the gut

A study at Aberdeen’s Rowett Research Institute (Applied and Environmental Microbiology, 73:1073-8) has shown that a very low carbohydrate weight-loss diet results in a four-fold reduction of certain types of bacteria in the gut of obese men.

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 challenges the prolonged use of very low-carbohydrate weight-loss diets on intestinal health.

Very low-carbohydrate weight-loss 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. Butyrate is known as a short chain fatty acid, and is produced in the gut when the bacteria ferments carbohydrates. Studies have shown that it can prevent cancer cells from multiplying.

“If low carbohydrate diets are to be consumed for long periods of time, it may be important to ensure that there is enough of the right sort of carbohydrate in the diet which can be used by the bacteria to produce compounds such as butyrate, which are beneficial for human health. This means making sure you continue to eat plenty of sources of fibre – such as fruit and vegetables,” said Professor Harry Flint, one of the study’s authors.

One more reason to avoid extreme animal-based diets. Low-carb quick fixes (though potentially effective from a weight loss perspective) can be dangerous in the long term. We still don’t know how this will affect overall health when maintained for prolonged periods.