Ketogenic Diets Lower IGF-1 Without Fasting: What It Means

You do not have to fast to lower circulating IGF-1, at least in the short-term human trials reviewed so far. A 2024 meta-analysis found that ad libitum ketogenic diets reduced serum IGF-1 by an average of 24.9 ng/mL. That is a real, statistically significant biomarker change. It is not proof that keto prevents cancer, extends life, or belongs on every prediabetic person's menu.

The distinction matters. IGF-1 helps regulate growth, repair, and metabolism. Lowering it may reduce signaling through the insulin/IGF-1 and PI3K/Akt/mTOR pathways, which draws interest in cancer and aging research. But biology rarely rewards a single-number optimization contest. Low IGF-1 can also carry risks, particularly when viewed alongside its binding proteins and a person's metabolic health.

Keto lowered IGF-1 by about 25 ng/mL

The best direct evidence comes from a 2024 systematic review and meta-analysis of ketogenic diets and IGF-1. Across 10 human trials, 236 people completed ketogenic diet interventions. The pooled mean difference in serum IGF-1 was −24.9 ng/mL, with a 95% confidence interval of −31.7 to −18.1 ng/mL. The result was statistically significant, and heterogeneity was low at I²=27%, which suggests that the observed reduction did not depend on one unusually positive trial.

The analysis also found statistically significant average reductions in fasting insulin of 2.57 mU/L and fasting glucose of 7.30 mg/dL. Those changes fit the basic metabolic logic of carbohydrate restriction: less circulating glucose and insulin can alter the hormonal environment that influences hepatic IGF-1 production.

Still, the mechanism is not settled in humans. Lower insulin may matter, but lower protein intake could also lower IGF-1. The included trials did not standardize or consistently report protein intake well enough to separate the effect of ketosis itself from changes in protein consumption. Ketones may have direct effects on hepatic IGF-1 production, but the current human evidence does not quantify that contribution.

What the meta-analysis can—and cannot—tell us

These were ketogenic diet studies designed without fasting or explicit calorie-restriction protocols. The review excluded fasting and calorie-restriction interventions, so the result supports dietary composition as a practical route to lower IGF-1 without prescribed caloric deprivation.

It does not show that keto lowers IGF-1 more than fasting, prolonged fasting, protein restriction, or conventional calorie restriction. No included trial made those comparisons within the same participants. "No fasting required" is supported by the intervention design; "better than fasting" is not.

The size of the average reduction also needs context. Adult serum IGF-1 reference ranges span roughly 100 to 400 ng/mL, and the meta-analysis did not provide individual trial baseline values that would allow a precise percentage change for each group. A 24.9 ng/mL decline could be meaningful for someone near the lower end of that range and less consequential for someone starting higher. Numbers need a baseline before they acquire a personality.

Why cancer researchers care about the IGF-1 axis

Higher circulating IGF-1 has epidemiologic relevance in breast cancer. A 2025 case-cohort analysis in postmenopausal women found that higher IGF-1 was associated with greater risk of estrogen receptor-positive breast cancer. That supports IGF-1 as a risk biomarker. It does not establish that lowering IGF-1 with a ketogenic diet prevents breast cancer.

The intervention gap remains wide. A randomized clinical trial of ketogenic metabolic therapy in patients with breast cancer reported metabolic effects consistent with reduced anabolic and growth signaling. It provides clinical context and feasibility data for keto as an adjunctive metabolic strategy, but it cannot establish an effect on tumor outcomes by itself.

Binding proteins further complicate the picture. In a phase III tamoxifen trial analysis, IGFBP-3 had predictive value for low-dose tamoxifen efficacy in women with noninvasive breast cancer. This does not show that keto changes treatment response. It shows that the broader IGF signaling system has clinical relevance, and that total IGF-1 alone is not the whole story.

Diet timing and exercise also move the signal

Keto is not the only dietary strategy that interacts with this pathway. An exploratory 2024 randomized trial of time-restricted eating in adults with obesity found changes in IGFBP-1 and IGFBP-2. The publication does not provide an extractable absolute IGF-1 change suitable for a numerical comparison with the keto meta-analysis. So it would be premature to declare either approach the better IGF-1 tool.

Exercise may also change the outcome. A 2025 randomized trial in older adults with obesity undergoing caloric restriction found that aerobic exercise, resistance exercise, or both modified IGF-1 and related endocrine markers. This matters for older adults: reducing growth signaling may appeal on paper, while preserving muscle mass and physical function remains an immediate concern. Resistance training belongs in that conversation, although this study did not test whether it offsets keto-induced IGF-1 reductions.

The diabetes caveat is not optional

Lower IGF-1 is not automatically healthier. In a 2022 prospective study of people with prediabetes, low IGF-1 combined with high IGFBP-1 predicted later diabetes onset. This was an observational finding, so it does not prove that lowering IGF-1 causes diabetes. But it directly weakens the claim that chronic IGF-1 suppression is a universal longevity target.

Ketogenic diets often improve glucose and insulin measures, as the meta-analysis showed. Yet no ketogenic trial in that evidence base prospectively sorted participants by this low-IGF-1/high-IGFBP-1 risk profile. Prediabetes is therefore a reason for clinical context and monitoring, not for treating a lower IGF-1 result as a trophy.

A 2025 comparative study in metabolic dysfunction-associated steatotic liver disease adds another warning against simplistic conclusions. It examined tirzepatide combined with a low-energy ketogenic diet versus a low-calorie diet, with liver steatosis, stiffness, and metabolic outcomes. In clinical practice, diet, medication, weight loss, insulin resistance, and liver health often move together. One hormone rarely explains the whole result.

Adherence and long-term safety remain open questions

The IGF-1 meta-analysis enrolled 522 people, but only 236 completed ketogenic interventions. About 55% did not complete them. That attrition raises the possibility that the pooled estimate reflects people who could tolerate and sustain the diet better than the average person who starts it. The effect in an intention-to-treat population may be smaller.

The studies also varied in duration, leaving durability uncertain. No evidence here establishes whether a lower IGF-1 level persists for years or whether sustained suppression affects bone density, immune function, wound healing, cancer incidence, all-cause mortality, or lifespan. The subgroup analysis by oncological status was non-significant, but with only 236 total completers, that result cannot establish equivalence between people with and without cancer.

A ketogenic diet can lower IGF-1 without prescribed fasting. The evidence supports that biomarker effect; it does not yet support a cancer-prevention or longevity claim.

The practical verdict

For someone who wants to modulate IGF-1 without fasting, ketogenic eating is a validated dietary lever. The average reduction of 24.9 ng/mL is consistent across the available trials and arrived alongside lower fasting insulin and glucose.

That makes keto a reasonable option to discuss for selected adults, especially when carbohydrate restriction already fits their metabolic goals. It is not a mandate to drive IGF-1 as low as possible. People with prediabetes, older adults at risk of sarcopenia, and anyone managing cancer should weigh the biomarker change against their full clinical picture with a qualified clinician. We have a measurable hormonal shift. We do not yet have proof of a longer life or fewer cancers.