The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting

by Jason Fung

The study compared the effectiveness of daily caloric reduction and intermittent fasting among 107 women. One group reduced their daily caloric intake from 2,000 calories to 1,500 calories. The other group was allowed normal caloric intake (2,000 calories) five days a week but only 25 percent of that (500 calories) on the remaining two days—this is referred to as a 5:2 fast. This means that over the course of a week, average caloric intake for the two groups was very similar: 10,500 calories per week for the reduced-calorie group and 11,000 calories per week for the fasting group. Both groups consumed similar Mediterranean-style diets with 30 percent fat. After six months, both groups had similar levels of weight loss and fat loss. But the 5:2 fasting group showed a clear, substantial improvement in insulin levels and insulin resistance, whereas the caloric-reduction group did not. Figure 5.11. A study of type 2 diabetics showed that a very low carb diet does reduce insulin compared to a standard diet, but fasting reduces it even more.