Fasting is certainly not a new idea. Studies suggest that it is beneficial for healthy aging, including regenerating the immune system, increasing brain-derived neurotrophic factor (BDNF) levels (something akin to manure for brain cells!), and improving insulin sensitivity. Animal models also point to the likelihood of reduced toxicity to chemotherapy used for cancer treatment.
The use of intermittent fasting specifically to target weight loss, however, while a relatively new phenomena, already has more than a thousand popular books published. About 40 percent of dieters in the United Kingdom use one such version, the 5:2 diet, believing this approach provides superior results compared to less severe daily calorie restriction.
Intermittent versus continuous fasting
In intermittent fasting on two days of the week, or every other day, a person eats 70 percent less than their usual intake. In practice this means consuming approximately 500 calories for women or 600 calories for men on the fast days. Then they resume a normal diet for the rest of the week.
The effects of intermittent fasting for weight loss have been compared to continuous calorie restriction, where people eat about 25 percent fewer calories on a daily basis.
Best for the waistline?
A limited number of short-term studies show that intermittent fasting helps overweight/obese people to lose weight, because on the nonfast days they, surprisingly, do not completely compensate for their previously reduced intake. This means their daily caloric intake, on average, is reduced by about 35 percent. However, research also shows that their waistline is no better off compared to following a daily caloric restriction of similar magnitude.
While more studies are needed to assess the long-term consequences of regular fast and feast days, intermittent fasting may be a novel obesity prevention tool in Western countries, where weight gain is common as people age.