Fasting-Mimicking Diet Reduces IGF-1, Body Fat, and Disease Risk Markers: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

Researchers at the University of Southern California wanted to know whether a periodic fasting-mimicking diet (FMD) — done for just five consecutive days once a month — could reduce biological markers linked to aging, cancer, diabetes, and heart disease in healthy adults without requiring continuous calorie restriction.

The FMD is a carefully calibrated plant-based, low-calorie protocol designed to trigger the cellular effects of fasting — including IGF-1 reduction and autophagy — while still providing some nutrients. It differs from water fasting in that participants eat small, controlled amounts throughout each of the five days. For background on how fasting activates these cellular processes, see how intermittent fasting promotes autophagy and intermittent fasting and longevity: what the science says.

Who Was Studied

Participant profile: Healthy adult men and women, average age approximately 40, with a mean BMI around 25 (non-obese). Participants spanned a range of baseline metabolic profiles, allowing the researchers to detect differential effects by baseline risk level. Individuals with significant health conditions or on medications that would confound metabolic measurements were excluded.

How the FMD worked in this study: Participants received a commercially prepared FMD kit for each of their three monthly cycles:

• Day 1: ~1,090 kcal (10% protein, 56% fat, 34% carbohydrate) — plant-based soups, an energy bar, drink concentrates, herbal teas, and a supplement
• Days 2–5: ~725 kcal per day (9% protein, 44% fat, 47% carbohydrate) — similar plant-based items in smaller quantities

Days 6 through the end of each month: participants ate their normal, unrestricted diet. The total fasting-modified period was therefore only 15 days out of each 90-day study period — roughly 17% of the time.

What the Researchers Found

IGF-1: The Key Aging Biomarker

IGF-1 (Insulin-like Growth Factor 1) is one of the most studied biological markers of aging. Chronically elevated IGF-1 is associated with accelerated cellular aging and increased risk of several cancers. The FMD produced a statistically significant reduction in circulating IGF-1 while simultaneously raising IGFBP-1 — a protein that binds free IGF-1 and reduces its activity. This combination is considered a favorable longevity signal in aging research.

Body Composition

The preservation of lean body mass is the most clinically important finding in this table. Very low calorie diets typically cause muscle loss alongside fat loss. The FMD's carefully calibrated macronutrient composition — particularly the protein and fat ratios — prevented this.

Blood Pressure

• Systolic blood pressure: Significantly reduced in the FMD group vs. control
• Diastolic blood pressure: Significantly reduced in the FMD group vs. control

These reductions were clinically meaningful, particularly for participants with elevated baseline readings.

Metabolic and Cardiovascular Markers

• Total cholesterol: Reduced, most significantly in those with elevated baseline
• Triglycerides: Reduced, most significantly in those with elevated baseline
• Fasting glucose: Significantly reduced in participants who began the study with above-normal fasting glucose; minimal change in those already in normal range

Inflammatory Markers

• CRP (C-reactive protein): Significantly reduced in participants with elevated baseline; minimal change in those with normal baseline CRP

What Did Not Change

• Lean body mass (successfully preserved by the protocol design — a deliberate outcome)
• Blood markers already within the normal reference range showed minimal change — the FMD appeared to be corrective rather than a uniform suppressor

What the Researchers Concluded

Three monthly cycles of the 5-day FMD produced meaningful reductions across multiple markers linked to aging, metabolic disease, and cardiovascular risk — all while preserving muscle mass and without requiring continuous dietary restriction. The researchers noted that effects were most pronounced in participants who began the trial with the highest risk profiles, suggesting the FMD has a corrective or normalising action.

What This Means If You Fast

• Short periodic fasting cycles can produce lasting metabolic benefits. The FMD was applied for just 5 days per month — 15 days out of every 90. That 17% of modified eating produced significant, measurable changes across aging and disease markers. You do not need to fast continuously.
• IGF-1 reduction is a key longevity signal. Lower IGF-1 is consistently associated with longer lifespan in multiple species. Periodic fasting is one of the few confirmed tools to reduce it in healthy, non-calorie-restricted humans.
• Muscle is protected during the FMD. Despite meaningful fat loss, lean body mass was fully preserved. This directly addresses the concern many people have about fasting destroying muscle — at least when the protocol is properly designed.
• Benefits concentrated where they were most needed. People with elevated blood pressure, glucose, or CRP saw the largest improvements. Those already in normal ranges experienced smaller changes — a reassuring safety finding.
• Blood pressure can improve without medication. The reductions in both systolic and diastolic blood pressure were clinically significant. For context on fasting and blood pressure more broadly, see can intermittent fasting lower blood pressure.
• The unrestricted days matter. Participants ate normally for roughly five sixths of the study period. This demonstrates that periodic fasting — not permanent calorie restriction — can achieve meaningful metabolic benefits.

Study Limitations

• The randomized phase had 100 participants total, split unevenly (71 FMD vs. 29 control) — this is relatively small for a definitive RCT and results need replication in larger trials
• The control group was not matched in size to the FMD group, which can introduce statistical imbalance
• The FMD used was a commercially prepared kit from a company with ties to the research group — a conflict of interest that should be noted and does not invalidate the findings but calls for independent replication
• Three months is a short follow-up; it is not known whether benefits persist with continued monthly cycles or if effects diminish over time
• Participants were predominantly healthy adults; findings may not translate directly to people with significant chronic conditions
• Some participants were unable to complete all three FMD cycles due to compliance challenges — an adherence consideration for real-world application
• The study design did not allow blinding of participants to their group assignment, which is inherent in dietary trials

Source

Wei M, Brandhorst S, Shelehchi M, Mirzaei H, Cheng CW, Budniak J, Groshen S, Mack WJ, Guen E, Di Biase S, Cohen P, Morgan TE, Dorff T, Hong K, Michalsen A, Laviano A, Longo VD. (2017). Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Science Translational Medicine, 9(377):eaai8700. PMID: 28202779

Frequently Asked Questions

What is a fasting-mimicking diet (FMD)?

An FMD is a structured low-calorie, plant-based eating protocol — approximately 1,090 kcal on day 1 and 725 kcal on days 2–5 — designed to trigger fasting-like cellular effects (IGF-1 reduction, autophagy, ketone production) while still providing some nutrients. Unlike water fasting, you eat small amounts throughout the five-day period.

How much did IGF-1 drop in this study?

The study found a statistically significant reduction in serum IGF-1 after three monthly FMD cycles. Lower IGF-1 is linked to reduced cancer risk and slower biological aging. The exact percentage reduction varied by individual baseline level, with larger reductions in those who started higher.

Did participants lose muscle on the FMD?

No. Lean body mass was preserved despite a significant reduction in total body weight and body fat. The macronutrient composition of the FMD — around 9–10% of calories from protein, structured around plant-based sources — was calibrated specifically to prevent muscle breakdown while restricting total calories.

Do you need to use the commercially prepared FMD kit?

The study used a specific commercial kit. The research group at USC has published the nutritional parameters of the protocol in the paper itself, and some practitioners use these as a guide for home preparation. However, the exact ratios matter — consult the published protocol and a healthcare professional before attempting a home version.

How does the FMD differ from standard daily intermittent fasting?

Standard intermittent fasting (like 16:8 or OMAD) restricts eating to a daily time window. The FMD is a periodic protocol — five consecutive days of very low calories once a month, with completely unrestricted eating for the remaining weeks. Both activate fasting-related cellular pathways, but through different mechanisms and timescales.

Related Research and Articles

• Intermittent fasting benefits: the complete science-backed guide
• How intermittent fasting promotes autophagy
• Intermittent fasting and longevity: what the science says
• Does intermittent fasting slow aging?
• Can intermittent fasting lower blood pressure?
• Does intermittent fasting destroy muscle? myth vs. fact
• Intermittent fasting and inflammation: the research explained

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