Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Talk to Your Doctor First Before Trying Fasting-Mimicking Diet

Dear Doctor: I'm reading a lot about a fasting-mimicking diet, which is supposed to help you live longer. What is it? I've been planning to lose some weight and wonder whether this diet might be worth trying.

Dear Reader: The approach you're referring to falls into an ever-expanding category of dieting known as intermittent fasting. It has its roots in research that has found a correlation between periodic fasting and increased longevity, as well as positive health outcomes. We live in a culture obsessed with the notion that we're just one ingredient or rule or combination of foods away from a perfect diet, one that will keep us (no pressure) lean and fit and healthy and happy, so it's not too surprising that the fasting-mimicking diet would have its moment.

Let's start with the background. A number of studies have found that intermittent fasting can bestow a range of metabolic benefits. These include a reduction in body fat and overall body weight, lower blood pressure, improved blood lipid levels and improved regulation of blood sugar. Several methodologies fall under the intermittent fasting umbrella, including 24-hour fasts, alternate-day fasting, restricted calorie diets and time-restricted diets, which allow eating only during certain hours of the day. The downside of this approach to eating is that it is quite restrictive and can be difficult to adhere to. In addition, there is concern that intermittent fasting, which entails a certain amount of deprivation, can lead to bingeing and other extreme eating behavior.

When it comes to the fasting-mimicking diet, the food restrictions kick in for just five days out of the month. That is, the diet mimics a fast without requiring daily deprivation. During those five days, calories are limited to about 800 per day. The nutrient profile of the diet is typically high in fat, low in protein, with carbohydrates falling somewhere in the middle. Some versions of this approach, which are more extreme, allocate nutrients in accordance with the high-fat ketogenic diet. In this approach, 80 percent of daily calories come from fat, with the rest divided equally between carbohydrates and protein.

A study published in the journal Science Translational Medicine last year followed 71 individuals who either followed a fasting-mimicking diet for five days each month for three months, or else switched to the fasting-mimicking diet after first following their normal diet for three months. Among both groups, researchers saw a drop in both body weight and body fat, as well as beneficial effects to blood pressure, fasting blood glucose and markers of inflammation. Interestingly, these benefits were more pronounced among individuals at greatest risk for disease than in those who were not at risk. And while the authors of this study concluded that the five-day fasting-mimicking diet is both safe and feasible for healthy adults, they also point out that larger studies are needed to see whether these results can be replicated.

As for whether this particular approach is one you should try, we believe that's a discussion you should have with either a dietician or your family physician. While the benefits of this approach to diet are appealing, it requires both discipline and consistency for optimal results.

(Send your questions to, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)