Fasting diets may raise risk of diabetes, researchers warn

Fasting every other day to lose weight could have damaging side effects. That is the conclusion of a group of scientists speaking this weekend at the European Society of Endocrinology’s annual meeting.

Their findings suggest that fasting-based diets may impair the action of sugar-regulating hormone insulin, and lead to increased risk of diabetes. Care should be taken before starting such programmes, say researchers.

Ana Bonassa, whose team from the University of São Paulo in Brazil carried out the study, said: “This is the first study to show that, despite weight loss, intermittent fasting diets may actually damage the pancreas and affect insulin function in normal healthy individuals, which could lead to diabetes and serious health issues.”

In recent years intermittent fasting diets have gained popularity. Participants fast for two days out of seven, or on alternate days. However, evidence of their success has been contradictory and there is debate among doctors about their potential to trigger harmful long-term effects.

Previous research has also shown that short-term fasting can produce molecules called free radicals, highly reactive chemicals that can cause damage to cells in the body and which may be associated with impaired organ function, cancer risk and accelerated ageing.

The São Paulo researchers examined the effects of fasting every other day on the bodyweight, free radical levels and insulin function of normal adult rats over three months. Although the rats’ bodyweight and food intake decreased as expected, the amount of fat tissue in their abdomen actually increased. In addition, cells of the pancreas that release insulin showed damage, while the presence of increased levels of free radicals and markers of insulin resistance were also detected.

The results also suggest that in the long-term harm may be caused and that more investigation is needed to assess how people may be affected, particularly those with existing metabolic issues.

“We should consider that overweight or obese people who opt for intermittent fasting diets may already have insulin resistance, so although this diet may lead to early, rapid weight loss, in the long-term there could be potentially serious damaging effects to their health, such as the development of type 2 diabetes,” added Bonassa.