New research presented recently at the European Society of Endocrinology annual meeting is suggesting the intermittent fasting diets may actually damage the pancreas and increase a person's risk for type 2 diabetes. The research stands in opposition to many studies in recent years that have pointed to the positive health effects of intermittent fasting and experts suggest this new data should be treated with caution.
The new study, from a team at the University of Sao Paulo in Brazil, set out to investigate the effect of fasting on body weight, free radical levels and insulin function. For three months, healthy adult rats were subjected to intermittent fasting consisting of no food every other day. Although a decrease in overall body weight was recorded across the experiment period, an increase in abdominal fat tissue was identified.
Most striking is the study's finding that after three months of this diet, insulin-producing cells in the pancreas displayed damage. Markers of insulin resistance were identified, as were increased levels of free radicals.
"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," says Ana Bonassa, one of the researchers on the project.
The research was presented as part of a conference presentation, is currently unpublished and is not peer-reviewed, so caution is necessary when evaluating its conclusions. The report also stands in direct contrast to several strong studies recently suggesting that fasting can actually improve a person's health. More specifically, a study from the University of Southern California in 2017 found that mimicking a fasting diet in mice with diabetes actually repaired insulin production and stabilized blood glucose levels. These results have also been replicated in humans.
So why is this new study demonstrating such outlying data? Nicola Guess, from King's College London, suggests one major factor could be the fundamental difference between rats and humans regarding both insulin production mechanisms and relative duration of fasting.
"… it's important to bear in mind there are important differences between rodents and humans – particularly with regard to diet. For example, a high fat diet causes insulin resistance in rats but it does not appear to in humans," explains Guess. "The exact method is unclear from the abstract, but if the rats were fasted for one day, this is equivalent to an approximately three to four week fast in humans! So it's not applicable to the 24-hour or 48-hour fasts practiced by humans on common fasting diets."
Simon Cork from Imperial College London also suggests that the disease markers examined in the study do not necessarily correlate with an onset of diabetes.
"The 'diabetes' was assessed by looking at markers associated with insulin resistance, which doesn't actually mean that the animals had become diabetic; it points towards that possibility, but there are better methods to assess whether an animal has become diabetic," says Cork.
A 2017 human trial subjected 71 participants to a three-month cycle involving five consecutive 'fasting-mimicking' days each month. The fasting did not involve completely cutting all food out for five days, but rather it consisted of dramatically reducing caloric intake by around two-thirds, causing the body to enter a 'fasting-like' state. The trial found that after three months, a number of positive health effects could be identified in the human subjects, including reduced body fat, lowered blood pressure, and a decrease in a protein marker related to inflammation.
While these new results are certainly concerning, they don't negate the growing volume of evidence finding beneficial effects from controlled intermittent fasting. Perhaps the biggest take away from this new report is that dramatic fasting, for example zero calories every other day, could be damaging to one's health over a long period of time. But this is not a manageable dietary process recommended by any clinician.
The new report was presented in Barcelona at the 2018 European Society of Endocrinology Annual Meeting.
Source: ESE via EurekAlert