The most recent trendy U.K. import is not music or fashion but a weight-loss plan. The British bestseller The Fast Diet by Dr. Michael Mosley isn’t as popular here yet, but it is in Amazon’s health books Top 10.
The mechanics of the Fast Diet are simple. You eat your usual foods five days a week, and on two nonconsecutive days you drastically reduce your intake —to 500 calories for women, 600 calories for men. This plan is not permission to overeat on the five nonfast days.
Unlike most fad diets, the Fast Diet quickly made its way into professional journals. An article published this month in the British Journal of Diabetes & Vascular Disease reviewed years of research in support of intermittent fasting.
Extensive animal studies have found that the practice not only leads to weight loss but also preserves memory, reduces risk of cancer and neurological disorders and might even promote longevity. The animal research is strong. In humans there is an abundance of anecdotal evidence but few controlled studies.
Assuming you don’t pig out on nonfast days, intermittent fasting reduces calorie intake by at least 2,000 a week, which can translate into a loss of about a pound every 10 days. Mosley, the British author, cites studies that have found fasting also results in increased insulin sensitivity and reduced insulin resistance, oxidative stress and fatty liver disease.
If one’s diet five days a week is rich in fruits, vegetables, lean protein and whole grains, severe calorie restriction two days most probably will not cause a nutritional crisis for a healthy adult.
The bigger question is if intermittent fasting has greater benefit than traditional weight-loss strategies such as changing eating habits, reducing portion sizes and increasing activity. Even author Mosley, who trained in psychiatry but has made his career in television, admits this is a work in progress.
Sheah Rarback is a registered dietitian on the faculty of the University of Miami Leonard M. Miller School of Medicine.