The Study
Dietary Protein Reduction During Isocaloric Conditions Reduces Body Weight in Men With Overweight or Obesity.
This study is like a fair test where two groups of guys ate different diets, but both ate the exact same number of calories. One group ate less protein and more carbs, and they lost weight. So we can say this diet probably helped them lose weight—but only because they were randomly assigned, not because they chose it.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Scientists gave men with extra weight two different diets with the same calories: one with normal protein, one with much less protein and more carbs.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 568 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Losing 2 kg of fat without cutting calories is meaningful — it suggests your body might burn more energy just from changing what you eat, even if you eat the same amount.
- 2The low-protein, high-carb group lost 2 kg (about 4.4 lbs) in 5 weeks, mostly fat (1.1 kg).
- 3Their blood FGF21 went up, and the more FGF21 rose, the more weight they lost.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Obesity
Year
2026
Authors
A. E. Lyster, A. S. Frederiksen, Jacob K Jensen, Annemarie Lundsgaard, N. R. Andersen, K. S. Jørgensen, D. Weber, Lukas Nachtigall, Erik A. Richter, A. Fritzen, Bente Kiens
Related Content
Claims (4)
In men with overweight or obesity, eating less protein and more carbohydrates while keeping total calories the same causes an average weight loss of 2.0 kg over five weeks, mostly from fat loss, without changing resting metabolic rate or energy lost in feces.
In men with overweight or obesity, eating less protein and more carbohydrates raises levels of the protein FGF21 in the blood, and the greater the rise in FGF21, the less weight is lost.
In men with overweight or obesity, eating a 5-week diet with less protein and more carbohydrates, while keeping total calories the same, leads to a loss of about 1.1 kg of fat mass, with little to no change in muscle mass.
In men with overweight or obesity, eating 0.9 grams of protein per kilogram of body weight per day for five weeks does not change resting metabolic rate, the ratio of oxygen to carbon dioxide exchanged during breathing, or the levels of proteins involved in mitochondrial energy production in muscle.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.