The 5:2 diet, also known as the “Fast Diet,” involves restricting calories two days a week to 500 calories per day (with two 250 calorie meals), while eating normally for the other five days. For example, you might eat all of your regular meals Saturday through Wednesday, and eat 500 calories per day on Thursdays and Fridays.There isn’t a ton of research to back up this diet, although it was publicized by Michael Mosley, a British journalist and doctor. Since it doesn’t completely restrict food on the fasting days, it may also be an effective way to ease into fasting without shocking your system. The Fast Diet is considered safe for men and women.
You’re consuming less food and thus spending less money. Rather than overeating to put on 1 pound of muscle and 4 pounds of fat in a week or two, you’re aiming to eat exactly enough to put on 1 pound of muscle without adding much fat on top of it. Yeah, it’s a delicate balance, but there’s far less swing involved. You are just slowly, steadily, and consistently building muscle and strength over many months.
I was very curious about this, so I asked the opinion of metabolic expert Dr. Deborah Wexler, Director of the Massachusetts General Hospital Diabetes Center and associate professor at Harvard Medical School. Here is what she told me. “There is evidence to suggest that the circadian rhythm fasting approach, where meals are restricted to an eight to 10-hour period of the daytime, is effective,” she confirmed, though generally she recommends that people “use an eating approach that works for them and is sustainable to them.”
Understanding the potential adverse effects of intermittent fasting is limited by an inadequate number of rigorous clinical trials. One 2015 review of preliminary clinical studies found that short-term intermittent fasting may produce minor adverse effects, such as continuous feelings of weakness and hunger, headaches, fainting, or dehydration. Long-term, periodic fasting may cause eating disorders or malnutrition, with increased susceptibility to infectious diseases.
There were [no statistical] differences between the low- and high- [meal frequency] groups for adiposity indices, appetite measurements or gut peptides (peptide YY and ghrelin) either before or after the intervention. We conclude that increasing meal frequency does not promote greater body weight loss under the conditions described in the present study.