Without exercise, inducing weight loss in the general population will generally result in fat loss and muscle loss, lean body mass loss *could* be as high as 60-80% if subjects are sleep deprived and psychologically stressed. Meta-analyses in overweight and obese subjects still show muscle losses in the range of 22-29% in the abscence of a physical activity arm.

This really is not that interesting of a finding and the more overfat you are the less relevance this actually has as “when calorically restricted, protein and fat free mass losses are relatively smaller in the obese who have a large baseline fat mass than are those of normal weight subjects.” –Heymsfield et al. 2014

It just means it is unethical to induce weight loss in a sleep-deprived and psychologically stressed population without some form of exercise.

What is interesting is the peasantry level and type of exercise that can maintain muscle mass while in a caloric deficit.

Aerobic exercise can do it.

Two days of circuit training

1-2 sets of 8-10 exercises can do it.

Body pump classes can do it.

Exergaming can probably do it.

y hunch is that swimming probably cannot do it.

So if you are trying to lose weight get out there and do whatever something you like and can adhere to.

Relevant quotes…

“During the 4-week period the average training for all subjects per week was as follows: 90 minutes resistance training (body pump, circuit, weight training), 110 minutes aerobic training (running, cycling, aerobics) and very low aerobic training (brisk walking, vacuuming) for 280 minutes.” One group lost 4.4 lb in four weeks and the other group lost 8.4 lb and both maintained LBM. -Mero et al. 2009

“Modest weight loss from calorie restriction reduces total and lower extremity lean mass and absolute aerobic capacity. In contrast, the same amount of weight loss induced by exercise did not alter lower extremity lean mass and increased aerobic capacity.” -Weiss et al. 2017

“There is a strong support for the notion that resistance is at least as effective as aerobic endurance in reducing some major cardiovascular disease risk factors. Findings demonstrate that resistance training may be an effective alternative to improve body composition and maintain reduced fat mass in obese patients after exercise training or energy intake restriction.” -Strasser and Schobersberger 2011

“The proportion of weight loss as lean tissue varies over time and is determined by multiple factors including level of energy intake, diet composition, sex, baseline adiposity, the presence of inactivity or type and level of added activity, and potentially the subject’s metabolic state or hormonal response.” -Heymsfield et al. 2014

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