The Science Behind the Fasting Mimicking Diet

Our ancestors, thousands of years ago, lived a hunter-gatherer lifestyle that was largely dependent on fasting and feasting. Whenever there was bounty (think: a successful hunt or coming across an abundance of ripe fruits and nuts), they would feast and store the surplus for times of scarcity. 

When there was nothing to be found, they would fast for days or weeks, surviving on whatever reserves they had stored, then feast again when a new resource was discovered.

This cycle of fasting and feasting triggered an evolutionarily conserved metabolic state that allowed our ancestors to survive periods of famine (5). 

In recent years, scientists have realized the benefits of this evolved state and have been able to use this metabolic state to improve health outcomes.

Unfortunately, modern lifestyle has changed the way we eat and live; instead of a cycle of feasting and fasting, we tend to eat three square meals plus snacks throughout the day. Food, often unhealthy and processed, is readily available so there are rarely periods of fasting (unless you intentionally plan it).

You might wonder—can staying in this constant state of eating be harmful? The answer is yes! Especially when you’re not eating the right foods. 

Studies have shown a correlation between modern lifestyles, unhealthy food choices, and various metabolic diseases such as type 2 diabetes, obesity, and cardiovascular diseases (13).

And while hunger might not be the first solution you think of, science is now showing that fasting can bring many health benefits (6) (18). The goal is to achieve a metabolic state similar to our ancestors’, where the body switches from a “fed” state to a “fasting” state.

But you may worry that trying to fast for long periods of time is too difficult and could lead to adverse health outcomes. 

The good news is, there’s a way to reap the benefits of fasting without having to fast for days at a time: the fasting mimicking diet (FMD). Below, we delve into the science behind FMD, its potential benefits and how you can incorporate it into your lifestyle to improve your overall health. 

What, Pray Tell, is the Fasting Mimicking Diet?

The fasting-mimicking diet (FMD) is a dietary pattern that closely mimics the physiological effects of fasting, but without the need for long periods of no food. It was developed by Dr. Valter Longo and his team at the University of Southern California.

This diet is designed to take advantage of the metabolic benefits of fasting while providing all the essential nutrients you need to stay healthy (1). 

Here’s how it works: instead of abstaining from food altogether, you’re cutting back on calories and switching up your macronutrient profile (the ratio of carbs, fat, and protein) for five days out of the month. 

During this time period, you’ll consume foods like soups, nuts, and bars formulated for the FMD to provide complete nutrition while still triggering a fasting-like state.

How Does the Fasting Mimicking Diet Work?

The FMD works by pushing your body into a metabolic state similar to fasting. 

By drastically reducing your calorie intake and switching up the macro-nutrient profile of what you eat, your body is tricked into thinking that it’s in a period of starvation, and it responds by activating the same metabolic processes that occur during a period of fasting. 

These processes include burning fat reserves for energy, reducing inflammation, and resetting the body’s metabolic pathways (16). For example, when you fast, your body naturally shifts from burning sugar to burning fat, which is beneficial for weight loss and metabolic health. 

By triggering these same processes without the need to fast for days at a time, the FMD can provide as many of the same health benefits as longer fasts. 

Read More: Carve Out A Fasting Schedule To Meet Your Fitness Goals 

Breakdown of the FMD Protocol

The FMD protocol consists of five consecutive days when you follow the diet and then you have 25 days off to eat however you normally would. During the five days: 

• You reduce your calorie intake by 34–50% (on day one, you’ll eat the most and then gradually reduce it).
• You consume 1,100 calories on day one (of these, 11% come from protein, 46% from fat and 43% from carbohydrates). 
• You consume 725 calories on days two to five (of these, 9% come from protein, 44% from fat and 47% from carbohydrates). 
• You consume only plant-based foods such as nuts, legumes, vegetables, and fruits.
• You shift your macronutrient profile from high carb/low fat to low carb/high fat 
• You consume foods specifically designed for the FMD, such as soups, bars and nutritionally balanced snacks 
• You avoid strenuous exercise. Walking, low impact exercise, such as yoga and tai chi, is encouraged. 
• You drink at least 1.5 liters of water every day 

These five days are followed by 25 days off, during which you can eat normally and resume your regular exercise routine. For optimal results, repeat the FMD cycle once a month for at least three consecutive months. 

How Is the Fasting Mimicking Diet Different from Intermittent Fasting?

Intermittent fasting (IF) is an increasingly popular way to get the benefits of fasting without going long periods of time without food. This involves abstaining from food for certain periods of time, usually 16-24 hours at a time (10). 

There are many different forms of IF, from alternate day fasting to 16:8 intermittent fasting.

Consequently, this type of fasting has gained a lot of traction in recent years. It’s relatively well studied; researchers have identified potential anti-aging and anti-inflammatory effects, as well as a myriad of other benefits (12).

The fasting-mimicking diet is different from intermittent fasting in several ways:

Food Abstinence

IF involves complete abstention from food for long periods of time, usually 16-24 hours. FMD does not require you to fast completely; instead you are provided with food that still triggers a fasting-like metabolic state. 

Calorie and Macros

IF does not involve a predetermined calorie or macros profile; you simply abstain from food for set periods of time. The FMD is designed to meet your nutritional needs while still promoting a fasting-like state. 

Length of Time

IF usually involves short term periods of fasting, lasting 16-24 hours. The fasting mimicking diet is a longer term protocol, lasting for 5 days before you return to your regular diet. 

Origins

IF has been around for centuries; it’s an ancestral practice that we have adapted to the modern world. The FMD is a more recent development, patented by Dr. Valter Longo and his team at the University of Southern California.

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Research

While IF has been researched extensively, the FMD is still relatively new. More research needs to be done in order to get a better understanding of its potential health benefits. 

Accessibility

IF is easy to incorporate into your lifestyle and free; the FMD requires an investment in special products, making it less accessible.

Flexibility

With IF, you can adjust your fasting protocol to suit your lifestyle. The FMD requires a more rigid adherence to the 5 day protocol.

Why Mimic Fasting?

You might be asking yourself why you would want to mimic fasting, rather than just fast for real? The purported benefits below, some of which have scientific backing, suggest that the FMD is at least worth a try. 

1. Give Your Body a Boost

Autophagy is your body’s natural process of getting rid of old and damaged cells, which can slow aging and help reduce inflammation (2). Research suggests that the FMD can help trigger autophagy and its associated benefits (15).

2. Keep Your Metabolism Humming

Fasting has been found to reduce insulin levels and other hormones, which can help maintain the body’s metabolic balance (11). The FMD is designed to mimic these effects without completely cutting off food intake. 

3. Protect Your Brain

Research suggests that fasting can help protect the brain against neurodegenerative diseases by promoting neurogenesis (the growth of new neurons) (4). The FMD may be able to replicate this effect while still providing nutrition. 

Read More: 16:8 Intermittent Fasting 7-Day Meal Plan

4. Rejuvenate Your Body

This is actually the main, and most researched, benefit of the FMD. It is believed that the diet triggers a process called cellular rejuvenation that helps reset and repair cells to keep the body functioning optimally (1) (8). 

5. Shed Some Pounds

By cutting out the majority of calorie intake for five days, it’s reasonable to assume that you would shed some weight during the FMD. However, this is not a long-term solution; you will need to make sustainable changes to your diet and lifestyle in order to keep the weight off. 

Note that the creators of the FMD do not promote it as a weight loss solution. Rather, they suggest that its primary purpose is to reset and repair cells in order to promote overall health and longevity. 

6. Beat the Clock

The FMD has been found to have anti-aging benefits. By triggering autophagy and cellular rejuvenation, it may help slow down the aging process and promote longevity (17). Furthermore, it can help reduce inflammation, which has been linked to aging and a variety of diseases. 

7. Reverse Disease

By promoting autophagy and cellular rejuvenation, the FMD may be able to help reverse many of the chronic diseases associated with aging. Studies have shown promising results in terms of reducing the risk of cardiovascular disease, diabetes, and cancer (7). 

8. Skip the Hunger

Unlike regular fasting, the FMD involves consuming a specific set of products (available online), which means no feelings of hunger. You will still be consuming calories, though in a limited amount. 

If you’ve unsuccessfully tried traditional fasting, or just want to experience the purported benefits of mimicking a fast without having to commit fully, the FMD could be worth a try. 

9. Skip Unpleasant Side Effects

Hunger isn’t the only unpleasant side effect associated with fasting. It can also cause headaches, dehydration, and dizziness (14). Since the FMD involves consuming a limited amount of calories, it may help minimize these side effects. 

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Is It Fasting Mimicking Diet Too Good To Be True?

The FMD has certainly gained a lot of traction, but there’s still not enough scientific evidence to back up its claims. Furthermore, we still don’t know about the long-term effects of this type of fasting. 

Here are some reasons why the FMD may not work for everyone: 

It’s a Product-Driven Diet

Even though it’s based on research, the core concept of the FMD is to consume a specific set of products to mimic the effects of fasting. Therefore, its scope may be limited in terms of adapting to individual needs. 

There is not much advice on how to customize the diet for different needs, or even experiment with alternative approaches.  

It’s Not Free

The cost of any product-driven diet will definitely be a factor to consider. The FMD is no exception; if you want the full package, it comes with a price tag that depending on your budget may be too steep. 

Compared to IF which offers more flexibility and can be done for free, this could be a factor that makes the FMD less appealing. 

It Can Trigger Unhealthy Eating Habits

Although it’s based on scientific research, the FMD is still a strict diet. It may trigger unhealthy eating habits such as an obsession with calorie counting (3). 

Anyone who’s prone to emotional eating, binge eating, or disordered eating should definitely be aware of this. The best approach is to consult with a healthcare professional before starting the diet. 

Allergy Considerations

The FMD involves consuming specific products that may contain allergens. People with allergies or sensitivities should pay attention to the ingredients list before consuming any of the products. 

Safety Considerations

The FMD is contraindicated for the following individuals: pregnant women, breastfeeding mothers, people with liver or kidney disease, those under the age of 18, and anyone with a chronic health condition such as type 1 or 2 diabetes and heart disease (9). 

In addition, it’s important to be aware of any potential interactions between the FMD and any medications you may be taking. It’s wise to consult with a healthcare professional before starting the diet. 

Sustainability Concerns

The FMD is designed to be a one-time event, rather than a long-term lifestyle. It’s unclear whether it can be sustained over a long period of time without adverse effects. 

Chances are, like most restrictive diets, it would eventually become unsustainable. This is more likely because you leave the program with no real knowledge on how to continue a healthy lifestyle. 

Conclusion

For some, mimicking a fast without having to commit for an extended period of time may seem like the perfect solution. And there’s some evidence that the FMD could offer some of the purported benefits of fasting. 

But it’s important to consider the risks and limitations associated with this diet before attempting it. Consult with a healthcare professional to determine if the FMD is right for you.