Macro partitioning
The proportion of fat-free mass lost during weight reduction increases with the magnitude of the weight loss, meaning large weight losses (such as those from bariatric surgery) result in a disproportionately higher loss of lean tissue compared to modest weight losses.
If you are losing a large amount of weight (e.g., through bariatric surgery or extreme dieting), expect to lose a higher proportion of your lean muscle mass compared to someone losing a small amount of weight. This is a physiological reality of large energy deficits, not necessarily a failure of your effort. Monitoring body composition rather than just scale weight is crucial to accurately assess progress in these scenarios.
The new equation predicts that the composition of weight change depends on both the direction and magnitude of the weight change... for large weight changes, such as the massive weight losses found in patients following bariatric surgery, Forbes’s original equation consistently underestimated the fat-free mass loss.
Why this rating
The model is validated against multiple human experimental datasets (underfeeding, overfeeding, bariatric surgery), showing favorable comparison, though it remains a mathematical derivation rather than a new primary clinical trial.
Source
Body fat and fat-free mass inter-relationships: Forbes's theory revisited
Kevin D. Hall · British Journal Of Nutrition · 2007
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →