Protein2026-08

Dietary Protein Reduction During Isocaloric Conditions Reduces Body Weight in Men With Overweight or Obesity.

Lyster Aslak E, Frederiksen Amalie S, Jensen Jacob K, Lundsgaard Annemarie et al. — Obesity (Silver Spring, Md.)

Summary

A recent study found that men who are overweight or obese could lose weight by reducing their protein intake, even if their total calorie consumption remained the same. Participants who ate less protein, with carbohydrates making up the difference, experienced an average weight loss of about 2 kilograms over five weeks. This suggests that the balance of macronutrients, not just total calories, can influence body weight.

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Key points

Reducing dietary protein, while keeping total calories constant, led to weight loss in men with overweight or obesity.
Participants on a lower-protein diet lost an average of 2 kilograms over five weeks.
This weight loss was primarily due to a reduction in fat mass.
The study suggests that macronutrient balance can impact weight independent of total calorie intake.

What the study looked at

This study investigated whether reducing protein intake, while keeping total calories the same, could lead to weight loss in men who are overweight or obese. Previous research had shown similar effects in lean individuals, and this study aimed to see if those findings applied to a population struggling with weight. Researchers recruited seventeen men with overweight or obesity and randomly assigned them to one of two highly controlled diets for five weeks. Both diets provided the same total number of calories. One group followed a protein-reduced diet (0.9 grams per kilogram of body weight per day), with the difference in calories made up by increased carbohydrates. The other group consumed a habitual protein intake (1.8 grams per kilogram per day). The study found that men on the protein-reduced diet lost an average of 2 kilograms of body weight, primarily from fat mass, compared to the higher-protein group, even though both groups consumed the same total calories. They also observed an increase in a hormone called FGF21, which was linked to the weight loss.

Dietary takeaway

This study suggests that for men with overweight or obesity, adjusting the balance of macronutrients by reducing protein and increasing carbohydrates, even without cutting total calories, might be a strategy for modest weight loss. While protein is essential, this research indicates that extremely high protein intake might not always be optimal for weight management in all contexts. Remember, this is one small study, and dietary changes should always be discussed with a healthcare professional.

Abstract

OBJECTIVE: Dietary protein reduction increases plasma fibroblast growth factor 21 (FGF21) and energy requirements in lean men under eucaloric conditions. Whether these metabolic effects translate to weight loss during isocaloric conditions in men with overweight or obesity remains unclear. METHODS: Seventeen men with overweight or obesity were randomly allocated to two different highly controlled, isocaloric diets for 5 weeks, receiving either a protein-reduced diet (0.9 g kg BW day) substituted with increased carbohydrates or a habitual diet (1.8 g kg BW day). RESULTS: Protein reduction induced a 2.0 ± 0.6 kg weight loss and increased plasma FGF21 concentration compared with higher protein intake, without caloric restriction. Changes in plasma FGF21 concentration were inversely associated with changes in body weight (r = -0.59, p = 0.02). Expression of key components in the FGF21 receptor complex, FGFR1 and β-klotho, and downstream targets in subcutaneous adipose tissue remained unchanged. Markers of skeletal muscle mitochondrial oxidative phosphorylation were also unaltered. Fat mass decreased significantly, whereas this level of protein reduction only tended to lower lean body mass. CONCLUSIONS: These findings suggest that reducing protein intake (0.9 g kg BW day), substituted with increased carbohydrates, compared with a habitual protein intake (1.8 g kg BW day), can induce weight loss without restricting total energy intake in men with overweight or obesity. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT06263725.

View on PubMed →DOI: 10.1002/oby.70248