Key Points
- Overall, exercise results in improved body composition and improved metabolic profile
- The largest effects are likely to be from higher-intensity exercise and resistance training.
Overall, in studies of people who are categorised as overweight or with obesity, exercise reduces body weight and visceral fat, 1 reduces overall fat mass and increases lean mass.2 However, one review has suggested that exercise does not significantly increase lean body mass.1 This is likely to be because the exercise interventions used (mostly moderate intensity and skewed towards aerobic-type activities) were not conducive to stimulating muscle for hypertrophy and muscle retention.
There is no difference between diet and exercise, surgery, or weight-loss drugs in how much visceral vs subcutaneous fat is lost.3 However, when comparing a hypocaloric diet to exercise, while diet elicited greater reductions in weight, there was a trend towards larger reductions in visceral fat with exercise.4
There was a trend towards larger reductions in visceral fat with exercise
The role of exercise in fat loss is often downplayed, but weight is an inexact measure and has little effect on metabolic health independent of adiposity (fat mass). Visceral fat is especially hazardous with respect to metabolic and overall health. Therefore, exercise is a key part of ensuring optimal metabolic health. Exercise (and diet plus exercise) are also more effective for reducing body fat than thermogenic weight-loss supplements.5
In children with obesity, both diet and diet + exercise results in significant reductions in weight and improvements in metabolic profile. The addition of exercise leads to greater improvements in HDL cholesterol, blood glucose, and insulin. Interestingly, in the studies reviewed, diet-only interventions caused greater reductions in triglycerides after 6 months (which were not significant after 1 year) which might have been related to poorer dietary adherence or increased consumption in the diet + exercise groups.6
In another review of trials conducted on adults (one year or more), adding exercise to diet, or diet and behaviour therapy, resulted in improved weight loss and improvements in HDL cholesterol, triglycerides, and blood pressure.7 In post-menopausal women with obesity both diet and exercise resulted in significant reductions in weight and diet combined with exercise resulted in greater fat loss than diet alone.8
Adding exercise to diet, or diet and behaviour therapy, resulted in improved weight loss and improvements in HDL cholesterol, triglycerides, and blood pressure
Adding exercise to energy-restricted diets also results in improved cardiovascular fitness, strength, fat loss, and muscle retention (vs diet-alone) with the greatest benefits seen from resistance training.9
Diabetes
Exercise is known to improve glucose and insulin homeostasis in diabetes and it has now been shown that exercise specifically improves the size and function of β-cells of the pancreas, resulting in improvements in insulin content of those cells, and the subsequent response to a glucose stimulus.10 In type 2 diabetes, both behavioural interventions and structured exercise programs, increase physical activity with structured exercise programs having a larger effect on long-term physical activity.11
In people with type 1 diabetes, exercise improves cardiovascular fitness, blood glucose control (demonstrated by reduced HbA1c) and as a result, reduces insulin use. These effects are strongest in children and adolescents, those exercising at least 3 times per week, and those including resistance training in their exercise regimen.12
Exercise is known to improve glucose and insulin homeostasis in diabetes
References
1. Lee HS, Lee J. Effects of Exercise Interventions on Weight, Body Mass Index, Lean Body Mass and Accumulated Visceral Fat in Overweight and Obese Individuals: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. International Journal of Environmental Research and Public Health. 2021;18(5).
2. Shin Y-A, Choi M-D, Kim I-Y. Review on Exercise Intervention Methods for Weight Loss in Obese Individuals. Exerc Sci. 2016;25(4):219-29.
3. Merlotti C, Ceriani V, Morabito A, Pontiroli AE. Subcutaneous fat loss is greater than visceral fat loss with diet and exercise, weight-loss promoting drugs and bariatric surgery: a critical review and meta-analysis. International Journal of Obesity. 2017;41(5):672-82.
4. Verheggen RJHM, Maessen MFH, Green DJ, Hermus ARMM, Hopman MTE, Thijssen DHT. A systematic review and meta-analysis on the effects of exercise training versus hypocaloric diet: distinct effects on body weight and visceral adipose tissue. Obesity Reviews. 2016;17(8):664-90.
5. Clark JE, Welch S. Comparing effectiveness of fat burners and thermogenic supplements to diet and exercise for weight loss and cardiometabolic health: Systematic review and meta-analysis. Nutrition and Health.0(0):0260106020982362.
6. Ho M, Garnett SP, Baur LA, Burrows T, Stewart L, Neve M, et al. Impact of Dietary and Exercise Interventions on Weight Change and Metabolic Outcomes in Obese Children and Adolescents: A Systematic Review and Meta-analysis of Randomized Trials. JAMA Pediatrics. 2013;167(8):759-68.
7. Avenell A, Brown TJ, McGee MA, Campbell MK, Grant AM, Broom J, et al. What interventions should we add to weight reducing diets in adults with obesity? A systematic review of randomized controlled trials of adding drug therapy, exercise, behaviour therapy or combinations of these interventions. Journal of Human Nutrition and Dietetics. 2004;17(4):293-316.
8. Cheng C-C, Hsu C-Y, Liu J-F. Effects of dietary and exercise intervention on weight loss and body composition in obese postmenopausal women: a systematic review and meta-analysis. Menopause. 2018;25(7):772-82.
9. Miller CT, Fraser SF, Levinger I, Straznicky NE, Dixon JB, Reynolds J, et al. The Effects of Exercise Training in Addition to Energy Restriction on Functional Capacities and Body Composition in Obese Adults during Weight Loss: A Systematic Review. PloS one. 2013;8(11):e81692.
10. Curran M, Drayson MT, Andrews RC, Zoppi C, Barlow JP, Solomon TPJ, et al. The benefits of physical exercise for the health of the pancreatic β-cell: a review of the evidence. Experimental Physiology. 2020;105(4):579-89.
11. Haghighi MM, Mavros Y, Singh MAF. The Effects of Structured Exercise or Lifestyle Behavior Interventions on Long-Term Physical Activity Level and Health Outcomes in Individuals With Type 2 Diabetes: A Systematic Review, Meta-Analysis, and Meta-Regression. Journal of Physical Activity and Health. 2018;15(9):697.
12. Wu N, Bredin SSD, Guan Y, Dickinson K, Kim DD, Chua Z, et al. Cardiovascular Health Benefits of Exercise Training in Persons Living with Type 1 Diabetes: A Systematic Review and Meta-Analysis. Journal of Clinical Medicine. 2019;8(2):253.
