New research suggests that intermittent fasting, a popular diet method considered to increase lifespan and prevent cancers, may adversely affect our metabolic health by damaging the pancreas and affecting the insulin function thereby leading to health problems including diabetes. This popular diet consists of "fast" days, where one drastically restricts their calorie intake and "feast" days, where the person dieting can eat whatever they please.

Indeed, many studies have shown that intermittent fasting may lower the risk of cancer, and in certain observational studies people who fast regularly for religious concerns seems to live longer than seniors who do not fast.

But could there also be downsides to intermittent fasting? Research presented by Ana Cláudia Munhoz Bonassa and colleagues from University of São Paulo, Brazil, at the European Society of Endocrinology annual meeting, Barcelona, Spain, indicates so.The researchers based their study on older studies suggesting that fasting for a short period of time increases oxidative stress and the production of free radicals. Oxidative stress and excessive levels of free radicals can cause a range of damages to the body, can speed up the aging process, and raise the risks for cancer, cardiovascular disease, neurodegeneration etc.

Bonassa and her colleagues placed healthy, adult rats on intermittent fasting for a period of 3 months. During this time, the researchers recorded rats’ insulin levels and function, body weight, and free radical levels. At the end of the dieting period, the rats had lost weight, as expected. However, the distribution of their body fat changed unexpectedly. The amount of fat tissue in the rodents' abdomen increased, a sign deeply linked with type 2 diabetes development. Damage in the insulin-secreting pancreatic cells, as well as higher levels of free radicals and signs of insulin resistance were observed.

In conclusion, intermittent fasting diet may not be healthy to be adopted by individuals seeking rapid weight loss. Ana cautions, "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."

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