In men with overweight or obesity, eating a lower-protein diet for 5 weeks did not change their resting metabolism compared with a higher-protein diet.
See the scientific wording
In men with overweight or obesity, 5 weeks of an isocaloric protein-reduced diet (0.9 g/kg body weight per day with increased carbohydrate intake) does not change resting metabolic rate compared with a habitual higher-protein isocaloric diet (1.8 g/kg body weight per day).
Indication only — weak evidence
Randomized trialsOne low-scoring study points this way, but the evidence is still early.
What the research says
1 study reviewedSupporting (1)
Randomized Controlled TrialHuman2026
Resting metabolic rate was measured weekly by indirect calorimetry and did not change in either group. This null finding rules out a detectable increase in resting energy expenditure as the explanation for the weight loss.
Contradicting (0)
No contradicting studies found yet
That doesn't mean it's settled — it just means no study has tested the opposite.
Quality-weighted scoring: we follow the GRADE framework — each study is rated High, Moderate, Low, or Very Low based on study design, methodology rigor, and risk of bias. A single high-quality RCT can outweigh several weaker observational studies.
Scores reflect study quality, not just count.
When men eat less protein but the same calories, their liver releases more of a hormone called FGF21. This hormone usually tells the body to burn more energy. But in fat tissue, the receiver for this hormone does not change, so the extra burning signal does not fully turn on. At the same time, the body breaks down less muscle protein and wastes fewer protein building blocks. This saves energy that would have been used to process protein. Because the saved energy balances out the hormone signal, the resting metabolic rate stays the same even though they lose some weight.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting study
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In men with overweight or obesity, eating a lower-protein diet for 5 weeks did not change their resting metabolism compared with a higher-protein diet.
Mechanism
1 studyWhen you eat less protein but same calories, your liver makes more of a hormone that usually burns energy. But the parts of the body that respond to that hormone do not change, so they do not burn more energy at rest. At the same time, your body stops breaking down as much muscle protein and wastes fewer protein building blocks. This saves energy. The saved energy cancels out the hormone's effect, so your resting metabolism stays the same even though you lose weight.
When men eat less protein but the same calories, their liver releases more of a hormone called FGF21. This hormone usually tells the body to burn more energy. But in fat tissue, the receiver for this hormone does not change, so the extra burning signal does not fully turn on. At the same time, the body breaks down less muscle protein and wastes fewer protein building blocks. This saves energy that would have been used to process protein. Because the saved energy balances out the hormone signal, the resting metabolic rate stays the same even though they lose some weight.
Reduced dietary protein intake lowers amino acid availability and decreases amino acid oxidation, which reduces plasma urea concentrations.
The liver increases production and secretion of fibroblast growth factor 21 (FGF21) into the bloodstream in response to protein restriction.
FGF21 binds to the FGFR1c/β-klotho receptor complex on target tissues such as adipose tissue and the central nervous system; in subcutaneous adipose tissue, receptor expression and downstream ERK1/2 phosphorylation remain unchanged, indicating no increase in adipose thermogenic signaling.
The body decreases muscle protein breakdown and maintains total and individual plasma amino acid concentrations, conserving lean body mass during weight loss.
Reduced protein turnover and amino acid oxidation lower the energy expended on protein synthesis and degradation; this energy saving offsets the FGF21-mediated drive for energy expenditure.
Resting metabolic rate remains unchanged despite reductions in body weight and fat mass.
Evidence from Studies
Supporting (1)
Community contributions welcome
Dietary Protein Reduction During Isocaloric Conditions Reduces Body Weight in Men With Overweight or Obesity.
Contradicting (0)
Community contributions welcome
Score Breakdown
No multi-axis breakdown available yet. The overall Pro / Against score above is the best signal.
- No clinical evidence is available; the score reflects mechanistic plausibility only.
What Would Prove This
Per GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this claim, ordered from strongest to weakest.
Systematic Review and Meta-Analysis of Isocaloric Protein-Reduced vs Higher-Protein Diets on Resting Metabolic Rate in Overweight or Obese Men
Systematic search of randomized controlled trials in men with overweight or obesity (BMI ≥25 kg/m²), comparing isocaloric protein-reduced diets (0.9 g/kg/day protein, increased carbohydrate) with higher-protein isocaloric diets (1.8 g/kg/day protein) for at least 5 weeks, with resting metabolic rate measured by indirect calorimetry.
Randomized Controlled Trial of 5-Week Isocaloric Protein-Reduced vs Higher-Protein Diet on Resting Metabolic Rate in Overweight or Obese Men
Parallel-group or crossover randomized controlled trial in men with overweight or obesity, isocaloric diets providing 0.9 g/kg/day protein with increased carbohydrate versus 1.8 g/kg/day protein, lasting 5 weeks, with resting metabolic rate measured by indirect calorimetry before and after the intervention.
Prospective Cohort of Habitual Protein Intake and Resting Metabolic Rate in Overweight or Obese Men
Prospective cohort of men with overweight or obesity, measuring habitual dietary protein intake and resting metabolic rate at baseline and after 5 weeks or longer, adjusting for energy intake, body composition, and physical activity.
Cross-Sectional Comparison of Resting Metabolic Rate by Habitual Protein Intake in Overweight or Obese Men
Cross-sectional study measuring resting metabolic rate by indirect calorimetry and habitual protein intake in men with overweight or obesity, comparing groups consuming approximately 0.9 g/kg/day versus 1.8 g/kg/day protein.
Controlled Feeding Study in Diet-Induced Obese Male Rodents: Isocaloric Protein-Reduced vs Higher-Protein Diet and Resting Metabolic Rate
Male diet-induced obese rodents randomized to isocaloric diets with protein reduced to 0.9 g/kg/day equivalent and increased carbohydrate versus 1.8 g/kg/day protein for 5 weeks, with resting metabolic rate measured by indirect calorimetry.