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What is The Fasting Mimicking Diet

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What is The Fasting Mimicking Diet

Fasting has been practiced for religious and spiritual purposes for millennia, but only recently has it come to the forefront because of the research backing some of its vital health benefits.

Those who have tried a true fast (stopping eating for a defined period of time) know that it can be mentally and physically challenging. Not to mention, it can be socially tricky. The fasting mimicking diet allows you to eat while still reaping the benefits of traditional fasting.  

This article will explore the concept of a fasting mimicking diet and discuss the potential health benefits.


What is The Fasting Mimicking Diet?

Fasting is often undertaken for weight loss, disease concerns, spiritual practices, or discipline. Fasting may improve metabolic health, cardiovascular health, and cancer.

The complete restriction of calories for a defined period, as is required during a true fast, may be challenging for many of us. A fasting-mimicking diet is purported to give many benefits of fasting without having to forego food intake altogether. A fasting mimic is performed by consuming fewer calories than usual in a specific ratio of carbohydrates, protein, and fat. This tricks the body into thinking it is fasting; hence it mimics a fasted state.

Emerging research also investigates mechanisms like autophagy that can be upregulated in a fasted state. Autophagy is the process of the body clearing out cellular debris and recycling cellular components. It is thought that autophagy helps rid the body of damaged DNA and other poorly functioning cellular components, etc.

How to Follow The Fasting Mimicking Diet?

A fasting mimicking diet is usually performed for five consecutive days per month. It can be repeated monthly or less frequently, depending on factors such as BMI and the severity of conditions being treated or prevented. Specific foods that are low in calories, sugar, and protein but high in unsaturated fats are consumed during the fasting mimic.

The five-day period provides adequate time for the body to shift into a state of ketosis, promote autophagy, and allow for subsequent health benefits. Once the five-day period is over, a regular diet is resumed.

On day 1 of the diet, approximately 1100 calories are consumed, consisting of 11% protein, 46% fat, and 43% carbohydrate. On days 2 through 5 of the diet, approximately 700 calories are consumed, consisting of 9% protein, 44% fat, and 47% carbohydrate.

Side Effects of a Fasting Mimicking Diet

Mild-to-moderate unpleasant side effects of a fasting mimic can occur in up to 46% of participants. The most common side effects are fatigue, weakness, headache, dry mouth, and memory impairment.

Research Backing The Fasting Mimicking Diet

Much research regarding the cellular mechanisms of how the fasting mimicking diet works has been performed in yeast, mice, and other animals. However, new research is emerging from human clinical trials demonstrating that the fasting mimicking diet may benefit metabolic health, cancer prevention, and autoimmune disease.

Metabolic Health

To date, the best evidence for the fasting mimicking diet is regarding metabolic health. Markers like blood sugar, hemoglobin A1c, BMI, lipid panels, and blood pressure have improved in clinical studies.

A phase 2 clinical trial of 100 participants randomized to fasting mimicking diet or control diet demonstrated that markers associated with weight and body habitus (such as BMI and waist circumference) were significantly reduced compared to the control group. Remarkably, lean body mass was preserved in the fasting mimicking group (see more below).

Systolic blood pressure was also significantly lower in the fasting mimicking group. Of interest, patients who were at greater risk for disease, for example, those with higher BMI, higher blood pressure, or unfavorable cholesterol panels, showed the most benefit from the three cycles of the fasting mimicking diet.

Results from another clinical trial using fasting mimicking diet intervention in patients with Type 2 diabetes showed significant improvements in hemoglobin A1c, fasting blood glucose, BMI, waist circumference, and blood lipids compared to the control group.

Kidney damage is a serious complication for patients with type 2 diabetes and might also be improved with a fasting mimicking diet. A small proof-of-concept clinical trial evaluated 40 patients having both type 2 diabetes and kidney damage (determined by an increased albumin-to-creatinine ratio). The patients who were in the fasting mimicking diet arm of the study and had baseline microalbuminuria experienced a significant improvement in their albumin-to-creatinine ratio at the end of the study.


Cancer is another disease state being researched to evaluate possible anticancer effects of the fasting mimicking diet. A phase 2 clinical trial evaluated the blood marker insulin-like growth factor-1 (IGF-1) and its response to fasting mimicking diet. Elevated IGF-1 levels are associated with several cancers (colorectal, breast, prostate) and possibly associated with malignant melanoma, multiple myeloma, and thyroid cancer. The participants in the clinical trial who underwent three rounds of the fasting mimicking diet had significantly lower levels of IGF-1 compared to controls.

Many clinical trials are underway to evaluate the possibility of fasting mimicking diet enhancing anticancer therapies. This topic is beyond the scope of this article but will be important to follow in the future.

Retention of Muscle Mass

A concern about fasting is the possibility of decreased muscle mass accompanying weight loss. A recent randomized study evaluated young men who underwent three cycles of a fasting mimicking diet compared to young men who ate standard diets. Despite a significant decrease in body mass in the participants who did the fasting mimicking diet, there was no appreciable difference in muscle force and muscle volume between the two groups at the end of the study.

Medical-Based Fasting Mimicking Diets

To date, the only commercially available fasting mimicking diet is Prolon by L-Nutra. This plant-based program provides the food necessary for 5-days. Vitamins, supplements, and herbal teas are also provided.

Before beginning a fasting mimicking diet, speak with your healthcare provider about your individual risks and benefits. Caution is advised for:

  • Patients with food allergies (allergens in the Prolon program include soy and nuts, among others)
  • Patients with type 2 diabetes or hypertension who are on medications that lower blood sugar or blood pressure
  • Medications will likely need to be adjusted with the help of a healthcare provider during a fasting mimic

According to the Prolon website, certain populations should NOT participate in fasting mimicking diet. These include:

  • Pregnant or breastfeeding women
  • Children under age 18
  • Adults over age 70
  • Patients with an active or recurrent infection
  • Patients with an eating disorder
  • Patients who are underweight
  • Patients who are malnourished or have a history of protein deficiency


Fasting has many health benefits but can be an arduous undertaking. The concept of being able to eat and still gain health benefits from a “fasting mimic” is appealing. A fasting mimicking diet has evidence for improving many metabolic and cardiovascular risk factors, including blood sugar, insulin resistance, BMI, and blood pressure. Many clinical trials are ongoing to evaluate fasting mimicking diet as an adjunct to anticancer therapies. Those at risk of specific cancers that are associated with elevated IGF-1 levels (like colorectal, breast, and prostate cancer) might benefit from fasting mimicking diet. Much more human research is needed to evaluate the benefits of a fasting mimicking diet for longevity, autoimmune diseases, and other health conditions.

*Dr. DePorto has no financial affiliation with Prolon. She is receiving no monetary or product compensation for this article.

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