Fasting-Mimicking Diet and Metabolic Syndrome

What Is Metabolic Syndrome?

Metabolic syndrome is a cluster of risk factors (elevated waist circumference, elevated triglycerides, low HDL cholesterol, elevated blood pressure, and elevated fasting glucose) that together raise cardiometabolic risk more than any one factor alone. Clinicians typically diagnose it when a person has at least 3 of these 5 components. It is a risk-factor cluster, not a single disease.

Because metabolic syndrome touches several systems at once (weight, blood sugar, blood pressure, and lipids), researchers have studied periodic fasting-mimicking cycles as a non-drug way to move several of these markers together, rather than targeting just one.

What a 2025 Review of Human FMD Trials Found

A 2025 narrative review of human FMD studies in people with metabolic syndrome or some of its components, including type 2 diabetes and obesity (Popa et al., 2025) [1], reports reduced BMI and waist circumference, preserved lean mass, and an improved metabolic profile overall. The review also notes a pattern worth reading carefully: people with a higher starting BMI or a greater number of metabolic-syndrome components appeared to derive greater benefit from the intervention. That pattern comes from a small set of trials, not a dosed or individually predictive response, so it should not be read as "the worse your metabolic syndrome, the more this will help you." A pooled analysis discussed below points the other way on one of those cuts: in its subgroup of participants with a BMI of 30 or more, no risk factor changed significantly (Mohammadzadeh et al., 2025) [5].

The review states its own limit in the same breath as its benefit claim: high dropout rates, small sample sizes, and methodological constraints restrict the generalizability of current findings. Its conclusion describes the human trial results as "encouraging but still conflicting" and calls for further large-scale studies to confirm these effects before FMD can be established as what the review calls "a viable non-pharmacological strategy for managing MetS."

The Individual Trials Behind That Review

This page covers fasting-mimicking diet research on metabolic syndrome and its components in people without cancer; trials of the diet alongside cancer treatment are a separate area and are not summarised here.

A 2-month trial of 60 women with obesity who were otherwise metabolically healthy compared FMD cycles against continuous calorie restriction. There was no significant difference in weight loss between the two approaches (calorie restriction -2.29 kg vs. FMD -1.13 kg, p=0.06), but FMD showed more favorable fat-mass and muscle-mass preservation (Sadeghian et al., 2021) [2]. Both halves of that finding matter: FMD did not beat ordinary calorie restriction on the scale, even where it did better at protecting lean tissue.

A 4-month trial in 100 people with type 2 diabetes tested an FMD-based meal-replacement regimen. Fasting glucose, HbA1c, blood lipids, blood pressure, BMI, and waist circumference were all more favorable than in the comparison meal-replacement group after 4 months (all p<0.05) (Tang and Lin, 2020) [3].

A 12-month randomized controlled trial added a monthly FMD cycle to usual primary care for 100 people with type 2 diabetes managed with metformin alone or with diet alone. It reduced the need for glucose-lowering medication (adjusted treatment effect -0.3, 95% CI -0.4 to -0.2, p<0.001), improved HbA1c (-3.2 mmol/mol, p=0.04), and reduced weight (-3.6 kg, p<0.001). It found no treatment effect on systolic blood pressure (-0.4 mmHg, 95% CI -6.0 to 5.1, p=0.87) or diastolic blood pressure (-0.5 mmHg, 95% CI -3.2 to 2.2, p=0.74), and mean changes in blood lipids did not differ between groups apart from a slightly larger rise in HDL cholesterol in the FMD group (0.1 mmol/L, p<0.001). Eighteen of the 100 participants were lost to follow-up, and the trial excluded people treated with insulin or a sulfonylurea, so it has no data on them (van den Burg et al., 2024) [4].

A 2025 systematic review and meta-analysis pooled 11 qualified studies (12 sub-studies, 761 participants) and found significant reductions in HbA1c, IGF-1, systolic blood pressure, and diastolic blood pressure. Stated with the same weight as those positive results: the pooled analysis found no significant effect on body weight, waist circumference, BMI, fat mass, fasting glucose, insulin resistance, blood lipids, or C-reactive protein. In the authors' subgroup analyses, body weight, waist circumference, and BMI did fall significantly in the trials of people with diabetes, while in the subgroup of participants with a BMI of 30 or more no risk factor changed significantly. In the authors' own sensitivity analyses, the IGF-1 reduction was no longer significant once either a breast-cancer trial (not cited on this page) or Wei et al., 2017 was removed from the pool, and the blood-pressure reductions were no longer significant once Tang and Lin, 2020 was removed (Mohammadzadeh et al., 2025) [5]. Two of the four positive findings in this analysis depend on a single trial each.

Where the Evidence Falls Short

Most trials behind this picture are small: the largest in the review's own tables enrolled 100 people, and the review reports dropout rates ranging from 2.3% to 30%. The longest trial in those tables ran 12 months, so durability beyond that window is untested. The review organizing this page states plainly that further large-scale studies are needed and calls its results encouraging but still conflicting, conclusions it reaches on its own, not hedges this page is adding on top.

Who Should Not Try This Without a Clinician

People managing diabetes or blood pressure with medication, people with kidney or liver disease, anyone pregnant or under 18, and anyone with a history of an eating disorder should talk to a clinician before trying an FMD cycle. The full list and the trial evidence behind it is on the FMD overview page; it is not repeated in full here.

Safety and Cautions

This is general information, not medical advice. Talk to a clinician before trying an FMD if you are pregnant, under 18, have a history of an eating disorder, manage diabetes or blood pressure with medication, or have kidney or liver disease. Most human FMD research to date is short-term and small-scale; treat specific numbers from any single trial as evidence to weigh, not a guarantee of your own result. None of the citations on this page support a cures, treats, or prevents framing for metabolic syndrome.

Authors and Funding of the Cited Studies

• Popa et al., 2025 [1]: no Longo author. The paper's own statements: "This research received no external funding" and "The authors declare no conflict of interest." No L-Nutra tie found. The review does summarise trials that have Longo authors and L-Nutra ties.
• Sadeghian et al., 2021 [2]: no Longo author and no L-Nutra funding tie found.
• Tang and Lin, 2020 [3]: no Longo author and no L-Nutra funding tie found. The paper states it "was financially supported by the Hubei Province health and family planning scientific research project (grant no. WJ2018H0037)" and that "there is no conflict of interest regarding the publication of this paper."
• van den Burg et al., 2024 [4]: Longo is a co-author, not the senior author. Funding statement: the trial "was co-funded by Health~Holland, Top Sector Life Sciences & Health, the Dutch Diabetes Foundation and L-Nutra." The paper's funding section adds that "L-Nutra contributed the formula diet and a small part of the funding" and that the funders "had no role in study design, data collection, data analysis, data interpretation, writing of the report, approval of the manuscript or the decision to submit the manuscript for publication." Longo "is a founder and shareholder of L-Nutra (his shares are assigned to the Create Cures Foundation and other charitable and research organisations), owns patents licensed to L-Nutra, receives support for travel expenses from L-Nutra and is on the advisory board of L-Nutra."
• Mohammadzadeh et al., 2025 [5]: no Longo author. The paper's own statements: "There is no fund for this study" and "The authors declare no competing interests." The trials it pools include ones with Longo authors and L-Nutra ties, among them Wei et al., 2017 and van den Burg et al., 2024 [4].
• Disclosures are listed where the full text of the paper was available to us; a study not listed here is not a statement that its authors have no ties.