Fasting Mimicking Diet: What Is It & What Are The Benefits?

Odds are you’ve heard about fasting. Defined as "abstinence from eating," the potential medical benefits have increasingly been substantiated in animal and medical research projects and now extend to enhance cognitive function. But is there a way to reap the benefits of fasting without, well, fasting? The answer—maybe.

I have been using a form of periodic fasting called a fasting mimicking diet (FMD) in my clinic with my patients, which has some pretty great benefits (similar to those from fasting). Here are some general and brain-specific data on the FMD and why you might be interested in trying it, plus how to take part in this eating plan.

The FMD is the evolution of decades of pioneering work on longevity by Valter Longo, M.D., and his team at the University of South California. Longo is recognized as a leading expert on longevity, and has done great work in describing the basic biochemical pathways by which cells age. The FMD program was patented by Longo after years of basic and preliminary research in yeast and animal models.

The diet decreases calories to 1,100 on the first day and then to around 800 the next four days for five days overall. The nutrients are key and include plant-based whole foods like nuts, olives, teas, and soup mixes that contain 55% calories from fat, 35% from carbohydrates, and 10% from protein.

During the five days of restricted calories, exercise and alcohol are prohibited and coffee is limited to zero or one cup a day. The program is also rich in nuts—so it’s not appropriate for those with a nut allergy—and requires eating whole olives (something to note if you dislike olives).

What is so special about the FMD? The science behind its success.

After years of experimenting with FMD in animal models and showing its benefits on metabolism and life span1, Longo’s team analyzed the effects in a human clinical trial. One hundred healthy subjects participated in this study; half of them followed a Prolon FMD five days a month for three months, and the other half ate their usual diet. Profound differences were seen in terms of weight loss, visceral fat loss, drops in blood pressure, blood sugar, blood cholesterol, and markers of inflammation2 in the FMD group.

Even more profound was a drop in insulin-like growth factor 1 (IGF-1), which is a biomarker for cancer growth, and an increase in stem cell production, which is a marker for regeneration of cells. In fact, the Prolon FMD program is marketed by Longo’s teams at USC as a program that promotes regenerative and rejuvenating changes, which is unique from all other data published for fasting programs.

There are even provocative data suggesting that combining this FMD with cancer chemotherapy may lead to improved success and fewer side effects3. While much more research is needed before we can make those definite claims, the data we do have sure looks promising.

In preliminary studies with FMD, fairly remarkable brain changes4 were identified on this diet. FMD fed to mice four days in a row twice a month extended longevity, lowered visceral fat, reduced cancer incidence and skin lesions, rejuvenated the immune system, and delayed bone mineral density loss.

In old mice, FMD cycles also promoted brain growth (hippocampal neurogenesis), which would be a nice thing to have happen in humans! Researchers were able to demonstrate improved cognitive performance4.

Overall, these preliminary data are encouraging. It seems the best brains may result from the least calories, at least for five days a month.

The FMD requires a ProLon Fasting Mimicking Diet kit, a commercialized product comprised of everything you'll eat in a five-day period. Included in the kits, there are nut bars for breakfast, soups and crackers for the other 2 meals, vitamins, a drink, and a cacao snack for a tiny sweet. All of the food is in the program is non-GMO, gluten-free, and plant-based.

As mentioned, the program provides three meals a day, with about 1,100 calories for the first day and around 800 calories from days two to five.

In terms of how long you should do the FMD, the specific research states to use it five days in a row, then repeating that cycle two more times a month apart. So, to match the research, it's a 3 month program.

After that, Longo has said you can repeat the Prolon FMD monthly as often as you like. For most, a few times a year to capture the benefits is reasonable. I advise my patients that if they want to achieve the published results, they might want to do three cycles chosen at times that they do not have conflicting events, like weddings. Although not studied, a few patients of mine have done it back to back over 10 days, but not at my recommendation. While those patients did fine, it's always best to follow the guidelines on the website and research. 

While the health benefits can be profound, there are some groups of people who should probably not do this eating program (in addition to people who don't like olives). The website for Prolon FMD has clear guidelines on who should not participate in the program, and I endorse those recommendations with my patients. They include:

As always, it's best to consult a doctor before starting any restrictive diet before deciding if it can work for your lifestyle.

The FMD could be a great way to reap the benefits of fasting, while still sustaining yourself with a modest amount of calories. This program uses nutri-technology to achieve similar metabolic and anti-inflammatory results of a complete water fast, is backed by huge NIH research grants and publications, and has safely been used by tens of thousands of people.

After three consecutive months, many of my patients choose to do the program monthly or every other month for long-term health optimization. If you're interested in trying this diet out for yourself, consult your primary care physician and keep these tips in mind before embarking on your FMD journey.

Want to learn more from Joel Kahn? Check out the first-ever functional nutrition training, where he teaches classes on heart health and veganism.