Cross-sectional studyindependent cross-checkabstract checked★ key study I-LIFE-104 in-depth review

Do we burn less energy in modern life?

Energy expenditure and obesity across the economic spectrum.

Overview

McGrosky A et al.. Proc Natl Acad Sci U S A 2025 · PMID 40658837 · DOI 10.1073/pnas.2420902122

People in industrialised countries burn about as much energy as hunter-gatherers; eating more, not moving less, explains most weight gain.

Does the study support the specific claim? No · Methodological quality: high

Study explained simply

What did the researchers want to find out?: Compare energy expenditure across lifestyles.
How was the study done?: Doubly labelled water in 4,213 adults from 34 populations.
How many people, animals or samples were studied?: 4,213 adults worldwide.
What was actually found?: Expenditure explains ~10% of excess fat; intake/UPF much more.
How large was the observed effect?: Size-adjusted TEE 6-11% lower with development.
What do the results mean in everyday life?: Movement is healthy, but diet drives most weight gain.
What are the study's limitations?: Cross-sectional.
What does it say about Elawady's specific claim?: Contradicts the claim.
Do the results apply to Germany and Europe?: Applies; same physiology.
What can explicitly not be concluded from this study?: Individual-level causes.

Authors: McGrosky A et al.
Journal: Proc Natl Acad Sci U S A
Year: 2025
Identifier: PMID 40658837 DOI 10.1073/pnas.2420902122
Verification: verified – PubMed efetch 2026-10-26; Crossref update-to/updated-by check
Retracted: no
Corrections: none
Extent checked: abstract only
Conflicts of interest and funding: No competing interests.

Is obesity with economic development explained more by reduced energy expenditure or by increased intake?

Study design: Cross-sectional study – Cross-sectional comparison of doubly-labelled-water energy expenditure across 34 populations
Population: Adults from hunter-gatherer, pastoralist, farming and industrialised populations
Country: 34 populations on six continents
Period: not stated in abstract
Sample size: 4,213 adults
Inclusion and exclusion criteria: not stated in abstract

Results: Development associated with greater body mass, BMI and body fat but also greater total, basal and activity energy expenditure; size-adjusted TEE and BEE decreased about 6-11% with development; adjusted TEE accounted for roughly one-tenth of the elevated body fat and BMI; estimated intake greater in developed populations; % ultra-processed food associated with body fat (25 populations).
Absolute risks: not reported
Authors' conclusion: Dietary intake plays a far greater role than reduced energy expenditure in obesity related to economic development.

Expenditure explains about 10% of the development-related fat excess.

Directly contradicts 'lack of movement is the origin of weight gain': lower activity explains only a small share of population obesity.

Universal biology; applies in Europe and Egypt.

Strong contradicting evidence for the single-cause claim.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	high
Risk of bias	some concerns
Precision of results	moderate
Directness	direct
Reproducibility	partly replicated
Consistency with the overall evidence	consistent
Regional transferability	moderate
Adequacy of the interpretation (by the archive)	not applicable