Fasting has long been viewed as a way to rid the body of toxins and give the digestive and other systems a rest. Recently, however, fasting has become a diet technique.
While most experts recommend simply eating less and getting more exercise, an increasingly popular alternative is a diet based on eating as much as you want one day and fasting the next. On each fasting day, dieters consume tea, coffee, and sugar-free gum and they drink as much water as they need. Although many people claim that this diet, called alternate-day fasting (ADF), helps them lose weight, ADF's effects on health and disease risk are not clear.
Krista Varady, PhD, a research associate in the Department of Nutritional Sciences and Toxicology at UC Berkeley and her colleagues decided to study the effects of alternate-day fasting on 24 male mice for four weeks. They not only tested mice that followed and did not follow an ADF diet, but they also studied mice that followed the diet only partially: a group of mice consumed 50 percent of their regular diet every other day (ADF-50%) and another consumed 75 percent of their regular diet every other day (ADF-25%).
What they found is reported in the October issue of the Journal of Lipid Research. Mice that were given no food on alternate fasting days (ADF-100%) lost weight showed a reduction in the size of fat cells of over 50%.
The fat cells of mice in the ADF-50% group — those who ate half their normal diet on fasting days — shrank by 35 percent.
Also, in these two groups of mice, fat under the skin — but not abdominal fat — was broken down more than in mice that did not follow the diet.
These results suggest that, at least in the short term, both complete and partial ADF diets should help protect against obesity and type 2 diabetes. Further studies will be needed to confirm whether the long-term effects of ADF regimens are beneficial for health and reduce disease risk.