Lean and obese people have very different weight loss responses regarding body composition. The initial ratios of lean body mass to fat mass can alter how a person responds to a diet. As a diet continues, lean mass and fat mass decrease, resulting in a decline in metabolism. A lean individual starting a diet has less body fat.
Body fat serves to buffer the severity of protein breakdown that occurs in a calorie restriction. There is an inverse relationship between body fat and protein breakdown (i.e., the more body fat, the less protein breakdown).(1) Kevin Hall recently developed a modification of the Forbes equation. The proportion of weight loss accounted for by lean body loss was affected by the magnitude of the weight loss and the initial fat content. (2)
YOU CAN USE A GREATER CALORIC DEFICIT WITH MORE BODYFAT
An obese person can have a much larger caloric deficit and lose less mass due to excess body fat. Thus, a lean person may lose more lean muscle mass than an obese person on the same diet. Women who have more body fat than men of similar body weight lose weight more slowly for an energy deficit. (3) Thus, the higher the initial body fat, the greater the energy deficit required to produce optimal weight loss. In a study of bodybuilders dieting for a show, those who had the lowest body fat and lost the greatest amount of weight also lost the most lean muscle mass. (4) The losses in lean muscle mass were suggested to be caused by the decreased insulin and IGF-1 levels. No significant changes in testosterone or cortisol occurred during the diet.
SLOW AND STEADY IS BETTER THAN RAPID WEIGHT LOSS
Many dieters often desire a rapid loss of weight. It’s rewarding to see a drop in scale weight, which can be positive feedback that the diet is working, despite the psychologically rewarding benefits of seeing rapid weight loss. Some rapid weight loss studies, but not all, have found suboptimal decreases in lean mass compared to gradual weight loss. (5,6) A recent review found that slow weight loss is better for long-term body composition. The review article found the following benefits for a slower weight loss compared to faster weight loss:
1. Gradual weight loss was associated with greater body fat loss and % body fat loss.
2. Gradual weight loss was associated with greater preservation of RMR.
3. Rapid weight loss resulted in a 2.2 pound greater lean mass loss than gradual weight loss.
RAPID WEIGHT LOSS: LOSE MORE FAT.. BUT ALSO MUSCLE KEY POINTS:
· People with more body fat can use a greater caloric deficit, whereas lean individuals will need a lower caloric deficit to minimize muscle loss.
· Gradual weight loss is better for preserving lean muscle loss.
1. ‘Effect of Starvation and Very Low Calorie Diets on Protein-Energy Interrelationships in Lean and Obese Subjects’ <https://archive.unu.edu/unupress/food2/UID07E/UID07E11.HTM> [accessed 26 January 2022].
2. Kevin D. Hall, ‘Body Fat and Fat-Free Mass Inter-Relationships: Forbes’s Theory Revisited’, The British Journal of Nutrition, 97.6 (2007), 1059–63 <https://doi.org/10.1017/S0007114507691946>.
3. Kevin D. Hall, ‘What Is the Required Energy Deficit per Unit Weight Loss?’, International Journal of Obesity (2005), 32.3 (2008), 573–76 <https://doi.org/10.1038/sj.ijo.0803720>.
4. Jarek Mäestu and others, ‘Anabolic and Catabolic Hormones and Energy Balance of the Male Bodybuilders during the Preparation for the Competition’, Journal of Strength and Conditioning Research, 24.4 (2010), 1074–81 <https://doi.org/10.1519/JSC.0b013e3181cb6fd3>.
5. Damoon Ashtary-Larky and others, ‘Rapid Weight Loss vs. Slow Weight Loss: Which Is More Effective on Body Composition and Metabolic Risk Factors?’, International Journal of Endocrinology and Metabolism, 15.3 (2017), e13249 <https://doi.org/10.5812/ijem.13249>.
6. Roel G. Vink and others, ‘The Effect of Rate of Weight Loss on Long-Term Weight Regain in Adults with Overweight and Obesity’, Obesity (Silver Spring, Md.), 24.2 (2016), 321–27 <https://doi.org/10.1002/oby.21346>.