5:2 and Other Intermittent Fasting Diets Could Raise Risk of Diabetes, Scientists Warn

Fasting diets involve calorie restrictions during specific windows of time Getty Images

Fasting diets have been hailed as a panacea for weight loss and good health in recent years, despite a lack of concrete evidence to back up such claims. Now, a new study on rats has suggested that fasting diets could increase a person's risk of developing diabetes.

A team of Brazil-based scientists have warned that fasting every other day could affect how the body releases insulin, the hormone that helps the body to process sugars, raising the risk of diabetes. The team presented their findings at the European Society of Endocrinology annual meeting.

Popular fasting diets include 5:2, where calories are restricted for two days a week; alternate-day fasting where individuals eat normally every other day; and 16:8, where food is consumed in a daily eight-hour window.

Such diets have been linked to weight loss, increased life expectancy, lower blood pressure and improved efficiency of the pancreas, the organ which produces insulin.

However, there is conflicting evidence on the benefits of such diets, and they have also been linked to the product of free radicals which have been associated with cancer, and aging.

The American Heart Association, for instance, recently said that studies indicate that intermittent fasting has short-term heart benefits, as does eating smaller, frequent meals throughout the day. But the long-term effects have not been thoroughly investigated.

To study intermittent fasting, researchers in Brazil put rats on alternate day fasting diets, and measured their body weight, insulin levels, and the presence of free radicals in their bodies over three months. While the rats lost weight overall, they developed fat tissue around their stomach and their pancreas cells showed signs of damage. The team also found markers of insulin resistance in their blood, and higher levels of free radicals.

Ana Bonassa, the lead author of the study conducted at the University of Sao Paulo, Brazil, said in a statement theirs was the first to show that, despite weight loss, intermittent fasting could damage the pancreas and affect insulin function in healthy individuals "which could lead to diabetes and serious health issues."

The scientists also expressed concerns regarding the unknown long-term effects of fasting, particularly on individuals with 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," she said.

Bonassa told Newsweek: "until we fully understand the consequences of intermittent fasting and realize if there is any risk in humans maybe there are better strategies to lose weight, like caloric restriction. Because a good diet is a diet you can keep for a lifetime, and is healthy in the long run."

Dr. James H. Catterson of the Institute of Healthy Aging at University College London, recently told Newsweek: "So far, the consensus [on intermittent fasting] seems to be 'let's wait until more rigorous studies, with larger sample sizes that adjust for confounding lifestyle behaviors, have been performed before we conclude anything prematurely'."

This piece has been updated to include comment from Ana Bonassa.