More on the Fat Family: Exercise Can Change Body Fat
Young Ju, Ph.D.
Exercise training is one of many strategies used to maintain healthy weight as well as lose weight. However, weight loss does not always mean body fat loss. Current research supports the positive changes that exercise can make to both body fat and health.
Body Fat
Body fat (called adipose tissue) is distributed throughout the body. Body fat contains fat cells, lipids, nerves, immune cells, and connective tissues. Although excess body fat is not appreciated, body fat has many essential bodily functions including storing energy, generating heat, maintaining body temperature, secreting hormones that control metabolism and appetite, and contributing to immune function, etc. Body fat is highly vascularized (provided with blood vessels) to maintain its metabolic functions. There are different types of body fat. The two major types are white fat (white adipose tissue) and brown fat (brown adipose tissue) (1, 2, 3).
White fat, the most abundant body fat type, stores fat and secretes hormones, enzymes, and growth factors. White fat can be further divided into subcutaneous (between skin and muscle: waist, hips, buttocks, and thighs), and visceral (around internal organs in the abdominal cavity). Subcutaneous fat makes up most body fat. Too much subcutaneous and visceral fat can increase the risk of disease, but visceral fat’s impact is greater than subcutaneous fat. A higher amount of visceral fat is correlated with a higher risk of cardiovascular disease, diabetes, and certain cancers. Visceral fat also secretes inflammatory chemicals.
Brown fat makes up ~2-5% of body weight at birth and gradually declines throughout your lifespan. Brown fat is specialized to burn carbohydrates and fats to generate energy and heat and help maintain body temperature. In order to carry out these metabolic functions, brown fat cells contain more mitochondria (“fuel batteries”) than white fat cells. Mitochondria contain high amounts of iron, which gives brown color. During infancy, brown fat is located in the back, neck, and shoulders. In adults, it is located around the neck, kidneys, adrenal glands, and heart. Brown fat mass is not affected by the amount of calorie intake. A higher brown body fat mass is correlated with a lower body weight, higher physical activity level, and younger age.
Fat cells can expand in both size and number (3, 4). The number of fat cells in the body is determined from infancy to adolescence and stays steady throughout adulthood if body weight remains stable. But long-term excess calorie intake can increase the size and number of fat cells. Enlarged fat cells become resistant to insulin, which increases the risk of type 2 diabetes and cardiovascular disease. Weight loss can reduce the size of fat cells but not the number.
Exercise and Body Fat
Numerous research studies have investigated how exercise affects body fat (5, 6, 7, 8). The effects of exercise on white fat cells include consistent findings that exercise:
reduces the size of white fat cells and fat mass. (It is important to note that exercise can reduce total fat mass and visceral fat mass without reducing body weight.)
reduces the lipid content.
increases mitochondrial activity.
decreases inflammation.
reduces hypoxia. (Hypoxia induces insulin resistance.)
stimulates blood vessel development.
decreases fibrosis which is also associated with insulin resistance.
improves hormonal regulation.
increases insulin sensitivity.
Changes in brown fat are less clear, but studies consistently show that exercise:
does not change the size and number of brown fat cells.
does not change the capability to burn calories.
increases communication with other tissues, e.g., signals to muscles to use more energy.
reduces glucose uptake to burn calories and generate heat which may not be a priority during exercise.
Type and Intensity of Exercise
Researchers have also investigated whether different types and intensity of exercise training have different effects on body fat. Tennis is considered to be a high-intensity interval training workout.
When comparing moderate amounts of cardio/aerobic training with strength/resistance training, both exercise types reduced body fat with no difference between them (9). (Moderate here is defined as a 20-60 minute/session, 3 days/week.)
When high-intensity and low-intensity trainings were compared, the higher intensity exercise showed greater reduction in total body fat, visceral fat, and subcutaneous fat compared with lower intensity exercise (10, 11, 12). (High intensity is considered to be ~70-85% of maximum heart rate, moderate is ~50-60% of maximum heart rate, and low intensity ~40-50% of maximum heart rate.)
When high-intensity and moderate-intensity trainings were compared, both intensity types reduced body fat with no difference between the two intensity types (13).
These findings suggest that maintaining a healthy body fat percentage can reduce the risk of many
chronic health conditions, and high- or moderate-intensity aerobic or resistance exercise can contribute to beneficial changes in body fat. However, the effect of exercise on body fat function and dysfunction still needs to be more thoroughly investigated.
Dr. Young Ju is a Ph.D and Associate Professor of Human Nutrition, Foods, and Exercise at Virginia Tech.
REFERENCES
Cleveland Clinic. Adipose Tissue. https://my.clevelandclinic.org/health/body/24052-adipose-tissue-body-fat
Harvard School of Public Health. Body Fat. https://www.hsph.harvard.edu/nutritionsource/healthy-weight/measuring-fat/
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Irving BA, Davis CK, Brock DW, Weltman JY, Swift D, Barrett EJ, Gaesser GA, Weltman A. Effect of exercise training intensity on abdominal visceral fat and body composition. Med Sci Sports Exerc. 2008; 40(11):1863.
Rugbeer N, Constantinou D, Torres G. Comparison of High-Intensity Training Versus Moderate-Intensity Continuous Training on Cardiorespiratory Fitness and Body Fat Percentage in Persons With Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Phys Act Health. 2021;18:610.
Always seek the assistance of a medical or health and fitness professional for personal program guidance in reducing or managing body fat. As always, this information is provided for your reference and you use at your own risk; you should rely on your medical professional for medical advice.
