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.
Level 3 - non-randomized controlled study
Prospective epidemiological cohort follow-up combined with mechanistic mouse models
PubMed 24606898 · doi:10.1016/j.cmet.2014.02.006
What was done
The authors analyzed epidemiological data tracking mortality over an 18-year follow-up period based on reported dietary protein intake (distinguishing animal versus plant protein) in respondents aged 50–65 and over 65. They also conducted mouse studies to test the effects of protein restriction and growth hormone receptor/IGF-1 signaling on tumor incidence, tumor progression (breast and melanoma), and longevity across age groups.
What was found
In participants aged 50–65, high protein intake was associated with a 75% increase in overall mortality and a 4-fold increase in cancer mortality over 18 years; these associations were attenuated or abolished when protein was plant-derived. Conversely, in respondents over age 65, high protein intake was associated with reduced cancer and overall mortality. Across all age groups, high protein intake was associated with a 5-fold increase in diabetes mortality. Mouse experiments confirmed that high protein intake and intact GHR/IGF-1 signaling increased tumor progression in younger animals but found detrimental effects of low-protein diets in older animals.
Why it matters
This study suggests that optimal protein requirements may shift dynamically with age, pointing toward low protein intake during middle age and moderate-to-high protein intake in older adults to support longevity.
Limits
The abstract does not report the total human sample size, baseline health characteristics, or exact quantitative confidence intervals. Dietary intake was based on self-report, and observational findings are susceptible to residual confounding. Key findings rely on subgroup analyses stratified by age.
Cited by
- supports A study by Valter Longo found that higher protein intake was correlated with higher all-cause and cancer mortality in middle-aged adults, but was inversely correlated with mortality in adults above a certain age.