The Fasting Mimicking Diet

Dr. Aaron Hartman

August 23, 2022


With all the talk about fasting, you may have heard of the Fasting Mimicking Diet (FMD), as a popular fasting method with impressive results. In this article, let’s talk about the FMD, what it is, some of the benefits, and some suggestions I have for a successful implementation of the Fasting Mimicking Diet.

What is the Fasting Mimicking Diet?

The FMD is a very low-calorie diet designed to be used for about 5 days, no more than once a month, in order to mimic a fasted state. The FMD was designed to be used for only 5 days at a time followed by a balanced, healthy diet which is resumed for at least 25 days in between each FMD cycle. In the research, done by Valter Longo at the University of Southern California, the participants were on the low calorie FMD for 5 days on, then 25 days off and this cycle is repeated 3 times.

During the 5 day FMD, between 700 to 1000 calories per day are consumed within very specific macronutrient (protein, fat, carbohydrate) ratios. During these days, about 40% of calories come from fat, 10% from protein, and 50% from carbohydrates, much from fiber-rich vegetables.

Benefits of the Fasting Mimicking Diet

Whether it’s done using the Prolon diet, as designed by the University of Southern California, or as an on-your-own, low-calorie, cyclical diet, there can be many benefits. Using calorie restriction, combined with targeted macronutrient ratios, activates certain cell pathways in a similar way to fasting. The FMD does not generally induce full-blown ketosis or a full fasting state, but it does promote healthy changes including a reset of the gut bacteria as well as some of the similar signaling patterns seen in a full five-day water fast.

Since the FMD allows a person to eat during the “fast”, it seems to be more accessible to people and avoids some of the problematic side-effects of water fasting.

The FMD has become popular with elite athletes in order to slim down and improve performance, as well as with executives who want improved cognitive function. The research shows that 3 cycles of the FMD provides a significant metabolic reset. Dr. Longo’s work in using the FMD has achieved impressive results involving weight management, diabetes, cardiovascular disease, Alzheimer’s, autoimmune disease, and more.

Suggestions for Implementing the Fasting Mimicking Diet

There are several ways to have a more successful, pleasant fast whether it be an FMD or water fast. First, and most importantly, any fast should be cleared with your physician ahead of time. Second, proper hydration with mineral support during the entire fast is a key to success. Finally, planning ahead can make or break your fast. Writing down what you will (or won’t) eat or drink during the specified time can help you stand your ground in moments of indecision. Also, letting your family or roommates know what you’re doing and why will allow them to support you along the way.

Just remember to stop the fast if you feel unwell at any point. Feeling tired and a little cranky is normal, but blood pressure drops, low blood sugar episodes, or feeling faint or unable to function, are signs that you may not be metabolically ready for such a significant fast.

To prepare your metabolism, I often recommend that people work their way up to a fast by starting with a 12 hour a day fast for a few weeks. This would mean consuming no calories from say 7pm to 7am, depending on when you eat dinner. Ideally, you could also work up to a 14 or 16 hour interval fast before you do something like a fasting mimicking diet.

Finally, if you need help getting started, find yourself a good Functional Medicine Practitioner to work with, or ask your health coach if they can help walk you through this. Check out our website for more articles on the topic of fasting and metabolic health.

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