Rock Doc: A light fast twice per week

By E. Kirsten Peters, College of Agricultural, Human & Natural Resource Sciences

petersPULLMAN, Wash. – It certainly sounded like a fad to me. A while ago I caught a program on public television about a medical doctor in Great Britain. Dr. Michael Mosley, like millions in both that country and in the U.S., found that in middle age he needed to lose weight and lower his blood sugar and cholesterol levels.

Mosley works as a journalist for the BBC and has decades of experience talking with scientific researchers on a whole range of topics. In connection with one of his programs, he had an MRI of his body. The scan indicated he was “thin on the outside, fat inside,” meaning he had deep-seated fat wrapped around his organs.

He was also mildly overweight. At 5 foot 11 inches, he weighed 187 pounds, giving him a body mass index of 26.4 (the recommended range is 19 to 25). In addition, his blood sugar was mildly elevated.

‘There’s always tomorrow’

After taking stock of his situation, he decided on a bold way of trying to lose weight and get his body into better shape. Instead of counting calories each day or avoiding carbs, he decided to experiment with what I’d call “light fasting.”

Mosley’s approach is described in his recent book, “The Fast Diet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting” (written with journalist Mimi Spencer).

The crux of his approach is to restrict calories a lot, but only two days per week. The days should not be consecutive.

He opted for Mondays and Thursdays, and that’s apparently a pretty common pattern for adherents of the diet. Men are allowed 600 calories on their fasting days, women 500 calories.

What made the deprivation tolerable to Mosley (and later Spencer, who has also followed the plan) is that “there’s always tomorrow.” In other words, a person is only one day away from being able to eat normally.

Lifetime commitment to maintenance

Mosley eats a small breakfast and a light supper on his fast days, with nothing in between. Spencer allows herself such things as an apple for a snack. But the plan remains the same: greatly restricting calories on two non-consecutive days of the week (or one day for maintenance).

After three months, Mosley’s weight was down to 168 pounds (a loss of almost 20 pounds). That changed his BMI to 24, a fine value. In addition, his fasting blood sugar had evolved to be in the good range.

But many a diet can work for a person in the short run. What really matters about weight loss is keeping it off.

Two things seem pretty clear to me about the fasting plan. First, people should try such a serious rearrangement of eating patterns only after consulting with their health care provider. Second, it’s worth a go only if you are willing to make the commitment to intermittent fasting for the rest of your life.


Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.