Don’t be fooled by the book title. The FastDiet (Atria, 2013), by Dr. Michael Mosley and Mimi Spencer, doesn’t call for a total fast—or eating quickly. Also known as the 5:2 diet, it has you adopt a lifelong pattern of fasting two days a week and being “gloriously free from calorie counting” for five days. On those two fasting days, you can eat 500 or 600 calories—for women and men, respectively.
The promise is steady weight loss (about a pound per week). And in theory you don’t pig out on your eat-what-you-want days because your stomach shrinks and can’t handle large volumes of food. The added benefit is better health. The science supporting fasting is growing: research findings from lab animals suggest intermittent fasting may lower your risk of cancer, delay the onset of dementia and Alzheimer’s and improve your body’s sensitivity to insulin. The science, though, is in its infancy and it’s not all promising. The downside is that fasting—even the way Mosley and Spencer recommend—isn’t easy. You barely eat two days a week. So on the days you eat ad lib, it really shouldn’t be an unhealthy foods free-for-all. Also, on those five days, it’s crucial for you to follow a healthy diet to get all the nutrients your body needs.
Bottom line: Like most diets, this is simply another way to cut calories. If you’ve thought about fasting, this diet could be a healthy guide to do it. Fasting isn’t appropriate for everyone, though, particularly if you’re pregnant or have type 1 diabetes. It’s not for children either. Also, check with your doctor first if you’re taking any prescription medication.