When people with excess body fat eat very few carbs and more fats, they lose about 4-5% of their muscle mass within a month, and this muscle loss continues for the full 12 weeks of the diet.
Scientific Claim
Very low-carbohydrate high-fat diets cause significant decreases in total lean body mass by approximately 4-5% within 4 weeks in overfat adults, which persists throughout the 12-week intervention period.
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design supports claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
While the study shows association between VLCHF diet and lean mass loss, the authors note that DXA may interpret body water loss as lean mass loss due to accelerated sodium and water excretion with low-carb diets. The causal claim should be qualified.
More Accurate Statement
“Very low-carbohydrate high-fat diets are associated with significant decreases in total lean body mass by approximately 4-5% within 4 weeks in overfat adults, which persists throughout the 12-week intervention period, though this may partly reflect body water loss.”
Source Excerpt
“Total lean mass significantly decreased after 4 weeks by 4.7 [3.9; 5.7] % and 3.9 [3.1; 5.1] % in the VLCHF and VLCHF+HIIT groups, respectively. These changes remained stable over the 8 and 12 week measurements (4.2 [3.1; 5.2] % and 4.9 [3.8; 6.5] %, respectively)”
Evidence from Studies
Supporting Evidence (1)
The RCT design shows consistent lean mass decreases in VLCHF groups compared to control and HIIT groups. The study measured lean mass using DXA, which has high reliability for body composition assessment, and found significant decreases starting at 4 weeks that persisted throughout the intervention.
⚠️ Overstated
While the study shows association between VLCHF diet and lean mass loss, the authors note that DXA may interpret body water loss as lean mass loss due to accelerated sodium and water excretion with low-carb diets. The causal claim should be qualified.
More accurate phrasing:
“Very low-carbohydrate high-fat diets are associated with significant decreases in total lean body mass by approximately 4-5% within 4 weeks in overfat adults, which persists throughout the 12-week intervention period, though this may partly reflect body water loss.”