A claim you hear on longevity podcasts

Does protein increase IGF-1?

Leaning for. Of 8 studies that test it, 5 agree, 2 partly agree and 1 disagrees.

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The claim checked: Protein, particularly from animal sources, raises IGF-1 Hear it at 29:07

What do the studies say?

Leaning for

Five of eight studies found that more protein, or more milk and dairy, went with higher IGF-1. Two found it only for some foods or groups, and one small whey trial found no rise.

Computed from 8 studies that test this point, each judged by two readers, in full. 13 more studies are waiting for a full read and do not count yet.

The study behind the claim tested something else. See what it tested

What was said on the podcast?

“protein particularly from animal sources spikes levels of a hormone called igf-1 which can help build muscle support brain health it enhances muscle repair but high igf-1 levels also come with potential downsides like promoting the survival of pre-cancerous cells and potentially allowing them to form cancer”
Rhonda Patrick, FoundMyFitness · The Science of Protein and Its Role in Longevity, Cancer, Aging, and Building Muscle · 29:07 on YouTube
Comes up in 6 episodes of the show.
The study behind the claim The retelling overstates it

What did the study actually test?

On tape: young adults under 50 put on high, medium and low protein diets, with IGF-1 tracking protein, and no difference at 65 and older. The study matches the IGF-1 pattern, but the people were aged 50 to 65 and 66 and over, and they reported their usual intake; only the mice were put on diets. Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metab, 2014. Observational: NHANES III respondents' single 24-hour diet recall, 18 years of mortality follow-up, serum IGF-1 in a random subsample; separate mouse diet experiments, 6,381 US adults aged 50 and over; IGF-1 measured in 2,253 (1,125 aged 50-65, 1,128 aged 66+).

What was saidWhat the study did
What was given Differs Adults put on a high, medium or low protein diet Usual protein intake from one 24-hour recall (low under 10%, high 20% or more of calories); diets were fed only to mice
Compared with Matches High against low protein High and moderate against low protein intake groups
What was measured Matches IGF-1 (and mTOR) tracking protein intake Serum IGF-1; mTOR was not measured in people
Who took part Differs Adults younger than 50, and people 65 and older Adults aged 50 to 65 and 66 and over

What it found

“Adjusted mean IGF-1 levels were positively associated with protein consumption for both age groups (Fig. 2).”

PMID 24606898

How the authors extend it

“Overall, our human and animal studies indicate that a low protein diet during middle age is likely to be useful for the prevention of cancer, overall mortality, and possibly diabetes through a process that may involve, at least in part, regulation of circulating IGF-1 and insulin levels.”

PMID 24606898

Not stated in the text we read. The senior author declares equity in L-Nutra, a company that develops medical food. Two readers agreed on the label, and the paper was read in full.

The point checked Leaning for

Protein, particularly from animal sources, raises blood levels of IGF-1

Agree 5

pooled analysis · 2017 · landmark

“Of the 31 data points (from 28 studies) included in the main IGF-I analysis, 29 data points showed positive associations of milk and dairy intake with IGF-I levels compared to two data points that showed negative or null associations.”

Does milk intake promote prostate cancer initiation or progression via effects on insulin-like growth factors (IGFs)? A systematic review and meta-analysis. Cancer Causes Control
Who: human studies (RCTs, non-randomized trials, cohorts, cross-sectional) of milk, dairy product or dairy protein intake and serum/plasma IGFs, participants aged 2-86 years, mostly Caucasian; plus a separate IGF-prostate cancer arm
PMID 28361446

controlled trial · 2008 · landmark

“In addition, our data suggest that chronic protein intake is more powerful than calorie intake in modulating circulating IGF-1 concentration in humans.”

Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3 concentration in humans. Aging Cell
Who: 46 non-obese adults aged 50-60 in a 1-year CR/exercise RCT; a cross-sectional comparison of 28 Calorie Restriction Society members, 28 low-protein vegans and 28 Western-diet controls (about age 52); and 6 CR practitioners in a 3-week protein reduction
PMID 18843793

trial or observed group · 2021

“Comparing participants in the highest quintile with participants in the lowest quintile of intake for total protein, protein from animal sources, and protein from milk, IGF-I concentrations were 1.72 nmol/L (95% CI: 1.40, 2.03), 1.19 nmol/L (95% CI: 0.88, 1.50), and 1.18 nmol/L (95% CI: 0.87, 1.49) higher, respectively”

Associations of circulating insulin-like growth factor-I with intake of dietary proteins and other macronutrients. Clin Nutr
Who: UK Biobank adults aged 37-73 (mean 56.7 years) who completed four or five 24-h dietary assessments and had serum IGF-I measured at recruitment; cross-sectional, with a secondary analysis of IGF-I measured about 4 years later
PMID 34237695

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other primary study · 2022

“Higher animal protein intake was associated with higher IGF-1 and lower IGFBP-1 and IGFBP-2, whereas higher plant protein intake was associated with higher IGF-1 and IGFBP-1.”

Association of animal and plant protein intakes with biomarkers of insulin and insulin-like growth factor axis. Clin Nutr
Who: US women from the Nurses' Health Study and men from the Health Professionals Follow-up Study who gave a blood sample and were free of major disease at blood draw; cross-sectional analysis
PMID 35504170

other primary study · 2014 · landmark · cited on tape

“Adjusted mean IGF-1 levels were positively associated with protein consumption for both age groups (Fig. 2).”

Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metab
Who: US adults aged 50 and over from NHANES III (mean age 65), with IGF-1 measured in a random subsample; plus mouse and yeast experiments
PMID 24606898

Partly agree 2

trial or observed group · 2014

“This study supports evidence from clinical trials and observational studies of a specific relationship between milk consumption and IGF-I; albeit, in our study this relationship was only statistically significant for free IGF-I.”

Associations of serum insulin-like growth factor-I and insulin-like growth factor-binding protein 3 levels with biomarker-calibrated protein, dairy product and milk intake in the Women's Health Initiative. Br J Nutr
Who: 747 postmenopausal women aged 50-79, randomly selected controls from the Women's Health Initiative Observational Study, cross-sectional
PMID 24094144

trial or observed group · 2000

“Mean serum insulin-like growth factor-I was 9% lower in 233 vegan men than in 226 meat-eaters and 237 vegetarians (P = 0.002).”

Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men. Br J Cancer
Who: 696 white men from the Oxford arm of EPIC (226 meat-eaters, 237 lacto-ovo-vegetarians, 233 vegans), cross-sectional
PMID 10883675

Disagree 1

controlled trial · 2025

“The present findings do not support either hypothesis, in which insignificant decreases were observed in both the CON (~3%) and PRO (~1%) groups, with no difference between the groups over the twelve weeks.”

Post-Exercise Whey Protein Supplementation: Effects on IGF-1, Strength, and Body Composition in Pre-Menopausal Women, a Randomised Controlled Trial. Nutrients
Who: healthy, untrained, normally menstruating pre-menopausal women aged 18-50 (mean about 33 years) in Dunedin, New Zealand, doing combined upper-body resistance and interval training; double-blind RCT
PMID 40573144

What else was said but not tested?

  • High IGF-1 may help pre-cancerous cells survive and form cancer, and studies link elevated IGF-1 with several cancers
  • Lowering IGF-1 too far has its own risks

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