Intermittent fasting might seem like a good way to control your eating and lose weight, but new research presented at the annual meeting of the European Society of Endocrinology suggests that it could come with an unexpected risk. Diets based on temporary periods of fasting, such as intermittent fasting, could alter the body’s natural release of insulin, increasing the risk of Type 2 diabetes.

Ana Bonassa and a team of researchers from the University of Sao Paulo in Brazil investigated the effects of fasting diets on a group of rats, keeping close tabs on body weight, levels of damaging free radicals, and insulin function over three months. Fasting diets, often called intermittent fasting, involve temporary intervals of reduced eating followed by intervals of eating more regularly. These types of diets have become increasingly popular in recent years, even attracting interest from celebrities like Kourtney Kardashian. Some intermittent fasters don’t eat after a certain hour, say 7 p.m., and then delay breakfast the following morning until 10 or 11 a.m.. Others fast one day a week, or follow popular diets such as the 16:8, which consists of a 16-hour fasting window followed by an 8-hour “feasting” window during which two to three healthy meals are consumed.

The researchers noticed that the diets weren’t working. Although the rats were eating less and losing weight overall, the amount of fat tissue around their abdomens grew larger. Their pancreases, which are in charge of releasing insulin, also showed damage that pointed to growing insulin resistance. Insulin resistance is the driving factor behind many cases of Type 2 diabetes.

Citing these observations, Bonassa cautioned against recommending fasting diets to those who are considered overweight or obese. This portion of the population, Bonassa said to Science Daily, may already experience insulin resistance.

“Although this diet may lead to early, rapid weight loss,” Bonassa explained, “in the long-term there could be potentially serious damaging effects to their health, such as the development of Type 2 diabetes.”

Julie Mancuso, BA, RHN, a registered holistic nutritionist specializing in dietary interventions for various health problems, explained to The Daily Meal in an email that while intermittent fasting may work wonders for some people, others find it doesn't work at all.

Mancuso cited a number of perceived benefits of fasting diets, including a reduction of cravings, the chance to give your digestive system a rest from inflammatory foods, and a decreased appetite long-term.

“Fasting can lead to the ingestion of fewer calories,” Mancuso explained, “provided you don't overindulge and overeat during the eating period. Some people look forward to the eating period after extensive fasting with great alacrity, leading to a false sense of entitlement to food overindulgences. It’s a dangerous state of mind to be in.”

Mancuso also warned against intermittent fasting for those with hypoglycemia, those who suffer from eating disorders, and those who are in need of nutrients, such as the elderly. Now, this study suggests that another group of people should be added to this list: Those at risk of devloping diabetes.

Of course, Bonassa’s team didn’t determine exactly how the diet brought about these effects, and more research is needed; there’s likely much more we don’t already know about the relationship between diabetes and diet.