According to his research and personal experience, Michael Mosley, MD, claims to have come up with the answer to every dieter's dilemma—the right recipe for losing weight and still enjoying favorite foods. Impossible, you say? Not so fast.

Mosley's new eating plan, which is garnering lots of attention in the UK is detailed in the book The Fast Diet. The strategy consists of eating regular meals five days a week, then semi-fasting (500 calories for women and 600 for men) on the other two (non-consecutive) days. For Mosley, this approach has not only helped him lose weight but has also improved his health. (The British doctor lost 20 pounds in nine weeks.)

Reducing Calories Through Fasting

"This concept of ultra-low-calorie eating days combined with eat anything and everything days, may be a strategy that could work for some people—especially those who do not want to change their current eating habits or feel deprived of foods they love," says Janet Brill, PhD, RDN, LDN, CSSD, who is a nutritionist and author of Blood Pressure Down (Three Rivers Press, May 2013). "This type of dieting may help people to eat [fewer] calories in a less painful manner."

Nutritional Concerns With The Fast Diet

While the 5:2 concept may seem appealing, Brill says there are a few things you should consider before trying this plan. "Nutrition is a concern if you do not eat wisely on the eating days," she points out. This means that even on the five regular meal days, you should still be paying attention to your food intake and make sure you are making balanced and healthy choices. "The typical American diet—high in processed foods, bad fats, and sodium and low in nutrients—can still promote disease—even if combined with weight loss," she says.

The Fast Diet Weight Loss Difference

You'll also need to keep in mind that not all weight loss is created equal. "The fact is that to lose weight, one needs to eat fewer calories and burn more through exercise," Brill says, explaining that in the ideal world, you'd want to create a long-term calorie deficit through a combination of mild calorie restriction and daily exercise in order to lose body fat (and not muscle mass). However, with two days of fasting, the severe calorie restriction will probably lead to loss of both body fat and lean body mass. "This alters metabolic rate long term, making it harder to maintain this lower body weight over the long haul." 

A More Moderate Option

For her own clients, Brill recommends taking a different approach to weight loss. "The best diet for losing weight and improving health is a plant-based, nutrient-dense, lower calorie diet combined with an active lifestyle," she says. But for people who want to try something more radical, she agrees that following Mosley's fasting diet plan is more preferable than remaining overweight and experiencing the related health conditions, such as an increased risk of heart disease, certain types of cancers, diabetes, and high blood pressure.

Janet Brill, PhD, RDN, LDN, CSSD, reviewed this article.



Brill, Janet PhD, RDN, LDN, CSSD nutritionist and author of Blood Pressure Down (Three Rivers Press, May 2013). Email interview 4 April 2013.

Mosley, Michael MD and Spencer, Mimi. The Fast Diet: Lose Weight, Stay Healthy, and Live Longer With the Secret of Intermittent Fasting. 26 Feb. 2013. Web. 7 April 2013.