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The Fasting-Mimicking Diet Guide: How To + Potential Benefits

Our nutrition coach investigates the effects of caloric restriction.

The fasting-mimicking diet, also called a fast-mimicking diet, is a type of intermittent fasting that involves a five-day low-calorie diet repeated periodically with a specific macronutrient breakdown to follow.

So what is the Fasting-Mimicking diet program like? Is this short-term five-day diet good for weight loss? What can you eat on the Fasting-Mimicking diet plan? 

In this diet guide, we will discuss what the Fasting-Mimicking diet plan involves, the principles behind it, how to follow it, and potential Fasting-Mimicking diet benefits and drawbacks.

Let’s jump in!

A nutritionist putting together a meal plan for the fasting-mimicking diet.

What Is the Fasting-Mimicking Diet Plan?

The fasting-mimicking diet, also called a fast-mimicking diet (FMD), is a type of intermittent fasting or an approach to intermittent fasting rather than one specific meal plan.

This means that there are different ways to practice the fasting-mimicking diet, but the most common approach is a 5-day plan.

There is also a commercial ProLon 5-day fasting-mimicking program, created by Dr. Valter Longo, head of the Longevity Institute at the University of Southern California and author of the Longevity Diet.

Like other types of intermittent fasting, the fasting-mimicking diet dictates when you can and cannot eat rather than what you can and cannot eat.

For example, with a traditional time-restricted intermittent fasting diet, the 24-hour day is divided into a designated fasting window and a designated eating window.

For example, the 16/8 intermittent fasting diet plan requires fasting for 16 hours and allows you to eat all your meals within the remaining eight-hour window.

Alternate-day fasting is another form of intermittent fasting that generally involves having a full day of fasting and then resuming your normal diet the next day.

A notebook that says intermittent fasting, a clock, plate and utensils.

With any type of intermittent fasting, the fasting windows are true fasts, which means that you are not supposed to consume any caloric foods or beverages.

You can drink water, plain herbal or caffeinated tea, or black coffee, but you are not even supposed to have milk, sugar, or low-calorie beverages or foods for strict fasting on an intermittent fasting diet or some other fasting practice.

As a risk factor or side effect of intermittent fasting, it can be physically and mentally difficult to abstain from all food and caloric beverages on a fasting diet.

Additionally, if you like to perform high-intensity or long endurance exercise, intermittent fasting diets may not work well with your workout schedule.

This will depend on how long you are fasting and when you need to exercise because it might be impossible to fuel well before or after your workout.

Fasting-mimicking diets offer a less restrictive approach to fasting than strict fasting.

Basically, fasting-mimicking diet plans allow you to have some calories during the “fasting“ so that you toe the line between keeping your caloric intake low enough to derive the benefits of fasting while still consuming enough calories not to feel starving or to provide your body with some energy for what you need to be doing in the day.

In this way, the fasting-mimicking diet approach is a low-calorie diet that aims to “trick“ your body into thinking you are fasting without actually having to perform a complete fast.

A monthly calendar with a circle around the 5th day.

How Do You Follow the Fasting-Mimicking Diet?

In addition to being a low calorie intake diet plan, the ProLon fasting-mimicking diet program has a specific macronutrient breakdown.

The fasting-mimicking diet plan lasts five days and is outlined in terms of calories and macros as follows:

Day 1

You can eat 1,100 calories, of which 11% should come from protein, 43% from carbohydrates, and 46% from fat. 

Based on the number of calories per gram of protein, carbohydrates, and fats, this works out to the following:

  • Protein: 0.11 x 1100 = 121 calories. Since there are about 4 kcals (net) in a gram of protein, 121 / 4 = 30.25 grams of protein.
  • Carbs: 0.43 x 1100 = 473 calories. Since there are 4 kcals per gram of carbohydrates, 118 / 4 = 30.25 grams of carbs.
  • Fat: 0.46 x 1100 = 506 calories. Since there are 9 kcals in a gram of fat, 121 / 4 = 56.2 grams of fat.

You are also supposed to drink a minimum of 70 ounces of water, which is a little more than half a gallon.

Fruits and vegetables.

Days 2 to 5

You consume only 725 calories per day, with a macronutrient split of 9% protein, 47% of the calories from carbohydrates, and 44% of your calories from fat.

Based on the number of calories per gram of protein, carbohydrates, and fats, this works out to the following:

  • Protein: 0.09 x 725 = 62.5 calories. Since there are about 4 kcals (net) in a gram of protein, 121 / 4 = 16 grams.
  • Carbs: 0.47 x 725 = 340.75 calories. Since there are 4 kcals per gram of carbohydrates, 118 / 4 = 85 grams.
  • Fat: 0.44 x 725 = 319 calories. Since there are 9 kcals in a gram of fat, 121 / 4 = 35.44 grams.

Again, you are supposed to drink at least 70 ounces of water per day on each of these days.

This 5 day fasting-mimicking diet routine is supposed to be repeated once a month for 3-4 months and then once every 3 months to maintain the purported metabolic benefits of ProLon fasting-mimicking or twice a year for healthy aging.

A person snacking.

What Can You Eat On the Fasting Mimicking Diet Plan?

Like other types of intermittent fasting, there are no specific foods you can and cannot eat.

However, unlike standard time-restricted intermittent fasting, the five-day fasting-mimicking diet for weight loss and health gives specific macronutrient ratios that you are supposed to hit.

Because of the prescribed macros, you will need to be mindful of what you are eating on your 5 day fasting mimicking meal plan.

Particularly on days two through five, you have very few calories to work with, and throughout this diet protocol, the protein intake is notably low, and likely much lower than most people generally consume relative to carbs and fat.

This is one of the more surprising aspects of the 5 day fasting mimicking diet program because many weight loss diets are higher in protein than the standard American diet or the protein recommendations set forth by the 2020–2025 Dietary Guidelines for Americans.1Dietary Guidelines for Americans | health.gov. (2022). Health.gov. https://health.gov/our-work/nutrition-physical-activity/dietary-guidelines

‌This is because evidence suggests that protein tends to be a particularly satiating nutrient, helping control appetite and fewer calories.

Healthy fats.

Some studies have found that a high-protein diet tends to promote weight loss, and when comparing a high-protein meal versus a high-carb meal, eating more protein tends to curb appetite for longer.2Moon, J., & Koh, G. (2020). Clinical Evidence and Mechanisms of High-Protein Diet-Induced Weight Loss. Journal of Obesity & Metabolic Syndrome29(3), 166–173. https://doi.org/10.7570/jomes20028

‌For example, studies that have looked at different breakfast choices have found that dieters report feeling fuller for a longer after eating a high-protein egg breakfast versus a high-carb breakfast of oatmeal or cereal.3Grech, A., Sui, Z., Rangan, A., Simpson, S. J., Coogan, S. C. P., & Raubenheimer, D. (2022). Macronutrient (im)balance drives energy intake in an obesogenic food environment: An ecological analysis. Obesity30(11), 2156–2166. https://doi.org/10.1002/oby.23578

‌Needless to say, the five day fasting mimicking meal plan is a high-fat, high-carb, low-protein diet while also being a low-calorie diet for weight loss.

Therefore, while technically no foods are totally off-limits (unless they exceed the total daily caloric intake or the macro ratios), you will have to choose low-protein foods and foods that are higher in fat, such as avocado, coconut, and nuts.  

It is also ideal to have plenty of fruits and vegetables since they are lower in calories and will give you the carbs that you need for the macro ratios prescribed by this diet plan.

A plate of food and an alarm clock.

What are the Health Benefits of the Fasting Mimicking Diet?

Numerous studies4Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition Reviews73(10), 661–674. https://doi.org/10.1093/nutrit/nuv041 have found many benefits of intermittent fasting,5Bhutani, S., Klempel, M. C., Berger, R. A., & Varady, K. A. (2010). Improvements in Coronary Heart Disease Risk Indicators by Alternate-Day Fasting Involve Adipose Tissue Modulations. Obesity18(11), 2152–2159. https://doi.org/10.1038/oby.2010.54 such as supporting fat loss, reducing oxidative stress and chronic inflammation,6Johnson, J. B., Summer, W., Cutler, R. G., Martin, B., Hyun, D.-H., Dixit, V. D., Pearson, M., Nassar, M., Tellejohan, R., Maudsley, S., Carlson, O., John, S., Laub, D. R., & Mattson, M. P. (2007). Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radical Biology and Medicine42(5), 665–674. https://doi.org/10.1016/j.freeradbiomed.2006.12.005 decreasing LDL (“bad”) cholesterol and triglycerides levels,7Bhutani, S., Klempel, M. C., Berger, R. A., & Varady, K. A. (2010). Improvements in Coronary Heart Disease Risk Indicators by Alternate-Day Fasting Involve Adipose Tissue Modulations. Obesity18(11), 2152–2159. https://doi.org/10.1038/oby.2010.54 promoting autophagy,8Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Research Reviews47, 183–197. https://doi.org/10.1016/j.arr.2018.08.004 improving blood sugar regulation, and reducing the risk of diseases.9Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research164(4), 302–311. https://doi.org/10.1016/j.trsl.2014.05.013

‌However, these clinical trials have looked at real fasting, not fasting-mimicking diets.

The ProLon Fasting-Mimicking Diet Program makes a lot of claims about the metabolic and anti-aging benefits of this approach to fasting.

It does seem that some research is demonstrating benefits of the fasting-mimicking diet approach for a variety of anti-aging and health benefits

However, as with all types of fasting diets, it is very important to speak with your healthcare provider before trying it, as it is extremely low-calorie, and therefore, is generally not safe nor recommended for most people.

If you are looking for a diet for weight loss or weight management, consider speaking with a nutritionist or a registered dietitian to help find which eating plan will work best for you and your needs.

A nutritionist holding out a salad.

References

  • 1
    Dietary Guidelines for Americans | health.gov. (2022). Health.gov. https://health.gov/our-work/nutrition-physical-activity/dietary-guidelines
  • 2
    Moon, J., & Koh, G. (2020). Clinical Evidence and Mechanisms of High-Protein Diet-Induced Weight Loss. Journal of Obesity & Metabolic Syndrome29(3), 166–173. https://doi.org/10.7570/jomes20028
  • 3
    Grech, A., Sui, Z., Rangan, A., Simpson, S. J., Coogan, S. C. P., & Raubenheimer, D. (2022). Macronutrient (im)balance drives energy intake in an obesogenic food environment: An ecological analysis. Obesity30(11), 2156–2166. https://doi.org/10.1002/oby.23578
  • 4
    Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition Reviews73(10), 661–674. https://doi.org/10.1093/nutrit/nuv041
  • 5
    Bhutani, S., Klempel, M. C., Berger, R. A., & Varady, K. A. (2010). Improvements in Coronary Heart Disease Risk Indicators by Alternate-Day Fasting Involve Adipose Tissue Modulations. Obesity18(11), 2152–2159. https://doi.org/10.1038/oby.2010.54
  • 6
    Johnson, J. B., Summer, W., Cutler, R. G., Martin, B., Hyun, D.-H., Dixit, V. D., Pearson, M., Nassar, M., Tellejohan, R., Maudsley, S., Carlson, O., John, S., Laub, D. R., & Mattson, M. P. (2007). Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radical Biology and Medicine42(5), 665–674. https://doi.org/10.1016/j.freeradbiomed.2006.12.005
  • 7
    Bhutani, S., Klempel, M. C., Berger, R. A., & Varady, K. A. (2010). Improvements in Coronary Heart Disease Risk Indicators by Alternate-Day Fasting Involve Adipose Tissue Modulations. Obesity18(11), 2152–2159. https://doi.org/10.1038/oby.2010.54
  • 8
    Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Research Reviews47, 183–197. https://doi.org/10.1016/j.arr.2018.08.004
  • 9
    Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research164(4), 302–311. https://doi.org/10.1016/j.trsl.2014.05.013
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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