A calorie-restricted diet has long been recognized and proven as a positive contributor to longevity and better metabolic health. For more than 50 years, experiments on rodents showed caloric reduction in diet could increase their longevity. Following studies on primates also had similar findings – monkeys given a calorie-restricted diet were healthier than their standard-calorie diet counterparts. Half a century has passed by, and here we are today, facing an epidemic of non-communicable diseases including diabetes, obesity, metabolic syndrome, and others. We know what would do us good – inputting fewer calories – which could easily be achieved by eating less food. The tricky question is how.

Fasting caught our attention along our journey in search of ‘how’. From an evolutionary point of view, today’s metabolic disease epidemic occurs because our metabolism isn’t prepared for overexposure to refined carbs and abundant high-fat, high-sugar foods. On the contrary, fasting is what we have been programmed for. When our ancestors were hunter-gatherers, they could starve for days before they caught a giant animal and enjoyed a fiesta. So in theory, our metabolism should already be adapted to this fasting-fiesta cycle.

In a recent study published in Nutrition & Metabolism, Prof. Yan Chen and his co-authors at Shanghai Institute of Nutrition and Health in Chinese Academy of Sciences looked at the effect of intermittent fasting on both type 1 and type 2 diabetic mice. In their study, the type 1 diabetic mice underwent a treatment that destroyed all their β-cells. The type 2 diabetic mice were genetically modified in a way so they were lack of receptors for a key satiety hormone, leptin, to prevent them from overeating. The mice were fed 1/3 of the standard caloric intake each day for 7 days, then received 7 days of free feeding. The two diets were then alternated every 7 days. The intervention went on for 8 weeks in total. The results showed reduced level of fasting glucose, improved glucose tolerance and insulin sensitivity in type 2 diabetic mice. The most stunning finding was that insulin secretion was detected in type 1 diabetic mice that underwent fasting, and their number of β cells significantly increased.

“Our minds were blown when we saw the results on insulin secretion and β-cells.” Prof. Chen said, “you heard people talking about fasting and how amazingly helpful it was when dealing with obesity and weight problems. You’d think it had worked because the caloric intake was cut and so naturally people lost weight. This has been the first time I’ve been convinced that fasting can actually improve metabolism. Fasting worked because of the positive changes in the body’s biology.” The type 1 diabetic mice had lost their β cells at the beginning of this intervention, but after fasting they began producing functioning β cells that could produce insulin. This result suggests that intermittent fasting has the potential to reset the glucose metabolism.

If you google fasting online, you get all sorts of terms – intermittent fasting, prolong fasting, whole-day fasting, water fasting, fast-mimicking diet… There are a lot of them, mirroring the various efforts to find a practically sustainable fasting style. The researchers’ ultimate goal is to push the fasting regimen to humans. Therefore, looking for a fasting style that is easy to stick to is of practical value. In the current study, Prof Chen’s team implemented 1/3-caloric-intake level of fasting for 7 days alternating with 7 days free feeding. They have started further studies to see whether 2 day, 5 day or 7 day fasts, alternating with 1 week of free feeding, would have a similar effect on glucose metabolism. They will also study whether intermittent fasting has any positive effect on cancer and autoimmune diseases.

Prof. Chen is cautiously optimistic about pushing the research forward to humans. “I have been testing fasting on myself since I got the results on β cells,” He mentioned, “using the same fasting regimen I tested on the mice.” Serving as his own lab mouse, Prof. Chen was on the same fasting regimen for over 3 months, and ended up losing 5 kg, as well as ceasing to take lipid-lowering drugs. Although the results on himself were promising, he is very cautious about how to interpret this unpublished case report. “It’s too soon to make any recommendations as we don’t have long term large scale population studies to confirm the safety and efficacy of fasting. There are too many questions to be answered – what the optimal fasting regimen is, how sustainable it is to only feed ourselves 1/3 of our daily calorie in the long term, how safe it is for generally healthy people and people with chronic conditions to fast…”. While promising, people shouldn’t be trying out fasting without consulting professionals first.