How to Use the Fasting Mimicking Diet



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I’ve been interested in fasting and related concepts for a long time because of the potential for major health improvement. Research continues to show promising benefits. For years I’ve been fascinated by the work of Dr. Valter Longo on the topic of fasting and how to use it to increase our odds of a long, healthy life.

I had the honor of interviewing him on the Wellness Mama podcast (listen here), so today I thought I’d share all I’ve learned about his method of fasting called the Fasting Mimicking Diet.

His approach allows you to get the benefits of fasting, without skipping meals. Interested? Read on!

Dr. Valter Longo and the Fasting Mimicking Diet

Dr. Longo is the Director of the Longevity Institute and a professor who studies how aging affects the body and biological sciences at the University of Southern California. His research has focused on longevity, fasting, aging, and metabolic disease. Based on his extensive research, he created a protocol known as the Fasting Mimicking Diet or FMD. Today we’re going to discuss what it is and the benefits it might have to offer you.

The Fasting Mimicking Diet came out of Dr. Longo’s research of nearly two decades. The diet focuses first on the genes that control how the body ages and responds to disease. The concept is that lifespan and healthspan can be increased by supporting the expression of these genes.

First, let’s review some of the different types of fasting before we try to understand how FMD works and why it is different.

Different Types of Fasting: The Basics

There is a lot of misinformation on the internet and elsewhere about fasting: what it is, what it isn’t, and how to go about it. As fasting has gained popularity, it has also become less correctly understood. Dr. Longo is one of the world’s top experts on the subject of fasting.

Dr. Longo’s biggest fasting truth is that “fasting” in and of itself doesn’t mean anything. You can say “eating” and it doesn’t actually tell anyone anything about your diet. The same is true for fasting because there are so many different ways and types to go about it.

Fasting in many forms almost always means calorie restriction in some way. Many types of fasting will induce ketosis due to lower caloric intake and often lower carbohydrates.

Some types of fasting include:

  • Water fasting: the name pretty much says it all… you just drink water for a period of time. You can read about my experience (and cautions) about water fasting here.
  • Alternate day fasting: not eating any food every other day (but still drinking water)
  • 16/8: time-restricted fasting: eating is limited to only 8 hours during the day, sometimes known as intermittent fasting
  • 5:2 fasting: a fasting approach where 2 days a week only 500 calories are consumed
  • Fasting mimicking diets: a protocol where, for 3-7 days, anywhere from 300 to 1,100 calories are eaten on a specific protocol to mimic the benefits of fasting without total deprivation

Dr. Longo explains that, as with many things, there are positives and negatives about all types of fasting. Not all types are good for everyone, so it’s never a good idea to just do something on your own without personalized advice from your healthcare provider.

Note: Lengthy water fasts should only ever be done under clinical supervision and have more serious risks. Even under clinical supervision, water fasting can still produce strong symptoms. These can include fatigue, gastrointestinal symptoms, thyroid problems, and glucose imbalances, not to mention more serious issues like infection or inflammatory problems. Please do your own research and only do one under the guidance of your doctor.

Why Fasting Mimicking?

Dr. Longo’s research focuses on Fasting Mimicking plans because, unlike water fasting, they’re broadly safer and can be as effective without the risks or deprivation.

I personally find Fasting Mimicking to be fascinating. Total deprivation from food sounds like torture to many people (although I’ve had positive experiences, and it sounds worse than it really is). Still, a protocol that accomplishes many of the same benefits without having to completely skip food can be a great starting point for many people.

Enter the Fasting Mimicking Diet. But how does it work?

FMD provides guidance on macronutrients, like protein, because it contains amino acids. Amino acids are known as the building blocks of protein, and it’s how the body literally repairs and restores cells and tissues. They also control growth hormone levels and insulin-like growth factor 1, both of which are highly involved in the speed at which the body ages and develops disease processes.

FMD also modulates sugar intake to support blood glucose, because that controls another gene known as PKA, which influences aging and disease, too.

Health Benefits of a Fasting Mimicking Diet

Fasting Mimicking can influence genes in a powerful way by providing the fuel and conditions the body needs to implement some protective changes. It’s so impactful that it has an influence on gene expression long after the Fasting Mimicking Diet has ended. After just five days of FMD, protective benefits can be shown for months afterward.

These are the demonstrated benefits of following an FMD, according to research.

Cell Protection with Autophagy

Autophagy is the body’s internal protective mechanism for getting rid of cells that are broken or damaged. Cells replicate at different rates, depending on where they are in the body. Skin cells are replaced every 2 weeks, while red blood cells are replaced every 2.5 to 4 months. The epithelial cells that line the intestinal walls are replaced every 5 days.

Cells are always replicating. In that process, they transfer DNA. Sometimes information gets lost or cells are damaged. If the body is allowed to continue with broken or damaged cells, or ones missing crucial information, the body would rapidly deteriorate! Autophagy is the body’s built-in system for cleaning house of broken, damaged, or old cells with bad information.

A study by Dr. Longo and colleagues from 2015 showed that the FMD plan helped to optimize the process of autophagy. As a result, it has a protective effect on cells and may even help to slow cellular degeneration and aging. Autophagy is also shown to ramp up in nerve cells in response to short-term fasting.

Cancer and Chemotherapy

Cancer is the second leading cause of death in the United States (behind heart disease). While chemotherapy has been able to treat and bring many types into remission, the immune suppression of chemotherapy presents a danger in and of itself. Immune system malfunction is also a trigger of cancer, when the body fails to destroy damaged cells through autophagy.

A 2015 study in mice showed that prolonged fasting could increase stress resistance in cells, as well as the ability for them to renew and regenerate. Multiple rounds of fasting were also able to decrease immune suppression and mortality associated with chemotherapy.

A 2018 review found that FMD, when paired with chemotherapy or immunotherapy, was able to increase how well the treatments worked while reducing side effects.

Cardiovascular Health

There are many factors that affect heart health. In a 2019 randomized trial of 100 subjects, those who followed the Fasting Mimicking Diet compared to a normal diet experienced weight loss, fat loss, decreased blood pressure, and lower levels of fasting blood sugar, triglycerides, LDL cholesterol, and C-reactive protein (an inflammatory marker).

This beneficial picture of FMD on factors that can influence heart health demonstrates the positive effects it can have on people at risk for diseases related to inflammation and aging.

Body Weight

In the same trial of 100 randomized subjects who followed either a normal food plan or the Fasting Mimicking Diet for three months (3 different 5-day FMD cycles), those who were on the FMD plan lost weight and body fat. Having excessive body weight can increase the risk of many types of chronic and age-related diseases, so finding a method to support ongoing and extended healthy weight is essential.


The benefits of Fasting Mimicking also extend to autoimmune conditions like multiple sclerosis and irritable bowel disease (IBD) like Crohn’s and ulcerative colitis.

Multiple sclerosis (MS) is a neurological degenerative disease with roots in autoimmunity. Past research has shown that, overall, specific diets haven’t been very successful at treating or reversing MS symptoms.

Animal research from 2016 showed that periodic 3-day cycles of the Fasting Mimicking Diet were able to address the root cause of MS—attack on the myelin sheath of the spinal cord by the immune system. FMD was able to reduce the severity of the condition in all mice and was even able to reverse symptoms in 20 percent of those studied. A Fasting Mimicking Diet can promote immune system balance as well as help to repair the myelin sheath. FMD is found to be safe and effective for treating relapsing remitting MS.

In animal studies, FMD was also able to reduce inflammation in the intestines and increase the amount of protective good bacteria in the gut. Three rounds of FMD was able to lower systemic inflammation and improve immune and stem cell levels, showing potential for eliminating IBD inflammation.

Who Can Follow a Fasting Mimicking Diet Plan?

It’s clear that a Fasting Mimicking Diet has a lot of potential benefits! Whether or not it is right for you depends on several factors. Checking with your personal healthcare provider is step one.

If your doctor gives the all-clear, following a Fasting Mimicking diet plan might help:

  • Lose weight
  • Reduce risk for heart disease, diabetes, autoimmunity, or other chronic health problems
  • Manage a condition that FMD has been shown to be helpful for
  • Live a long life and promoting healthy aging

A Fasting Mimicking Diet is more of a lifestyle shift with two parts: the 3-7 day fasts where you’re taking in fewer calories for a set amount of time, and the other days where you should be eating with health in mind.

Dr. Longo isn’t a legalist when it comes to this. As he explains, it’s about the majority of what you’re doing. If you want a small bit of sugar in your coffee, it’s such a small amount that it’s not going to rewrite your genetic code. But the cumulative effect of several sugary sodas, desserts, and high-carb, refined foods on a daily basis—those will add up to negatively impact the longevity of your genes.

How to Follow a Fasting Mimicking Diet Plan

One of the main principles of an FMD plan is to eat low protein and high unsaturated fat, and to overall reduce calories during the fasting period. Plans should still be customized with a healthcare provider, but the average FMD plan will include around 1,100 calories the first day, and just 800 or less the next few days.

Protein restriction combined with the fasting-mimicking protocol is what gives the diet plan its beneficial effects. So, no, you can’t just eat high-protein (or whatever you want) for your allotted calories during the fast. Healthy fats are also important for the diet’s benefits.

How to start? Read Dr. Longo’s book The Longevity Diet to get started. Dr. Longo says that the FMD can be done anywhere from a few times a year to once a month, depending on your current state of health and age.

If you do follow a fast mimicking diet, make sure that you follow proper refeeding techniques at the end. Breaking a fast by rushing headlong into eating high-calorie, high-carb, and high-fat meals will make you feel sick and can be dangerous.

This article was medically reviewed by Dr. Shani Muhammad, MD, board certified in family medicine and has been practicing for over ten years. As always, this is not personal medical advice and we recommend that you talk with your doctor or work with a doctor at SteadyMD.

Have you ever tried a Fasting Mimicking Diet? If you have, share in the comments how it went. If you haven’t, what drawbacks or questions do you still have?


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