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New Research Explains How Lifting Heavy Reduces Body Fat

A recent study shows that on a cellular level, your favorite form of exercise can provide a boost to both your body composition and overall health.

Image of man performing a lat pull-down exercise at heavy load in connection to study showing reduced body fat
  • A new study examined molecular changes in the body during heavy resistance training.
  • Researchers found that during heavy resistance training, muscle contractions can initiate viceral fat breakdown, which may have a significant effect on your body composition and overall health.
  • This finding is supported by a recent meta-analysis that found resistance training reduced body fat percentage, body fat mass (the total weight made up of fat), and visceral fat in healthy adults.
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Resistance training is well-known to boost strength, reduce body fat, and improve health. But exactly how your favorite workout accomplishes these results has yet to be explored until now. New research published in The FASEB Journal looked at molecular changes in both mice and humans during strength training. Researchers found that on a cellular level, muscle contractions can trigger fat breakdown, which may explain why resistance work improves body composition.

In the study conducted at the University of Kentucky College of Medicine, human participants underwent blood tests and muscle biopsies both before and after four sets of leg extensions and leg presses set at a heavy load. The results showed that muscle cells seem to release a type of mRNA that instructs fat (or adipose tissue) to break down in response to resistance training.

“Previous research on resistance training tended to focus on improvements in muscle function,” said John McCarthy, PhD, Researcher and Associate Professor of Physiology at the University of Kentucky. “This is the first to demonstrate that there are metabolic adaptations in fat tissue, and those changes are seen throughout the body, not just in the muscles being used.” 

McCarthy added that aerobic exercise like cardio also stimulates fat-burning to a degree, but resistance training seems to be more powerful for creating these adaptations at the cellular level. That’s because when you are on a fat-loss program, exercise helps maintain your muscle mass, explains Brad Schoenfeld, PhD, hypertrophy expert and Tonal advisory board member. Maintaining this fat-free mass can help prevent a modest loss in metabolic rate, or the rate at which you burn calories even when at rest.

The idea that resistance training cues changes in body composition is further supported by a recent meta-analysis, which examined 54 studies in Sports Medicine and excluded any that involved calorie restriction. It found that resistance training reduced body fat percentage, body fat mass (the total weight made up of fat), and visceral fat in healthy adults. In terms of creating lean muscle mass and reducing fat mass for healthy adults, these results suggest that resistance training can spark better results than aerobic or cardio exercise.

It’s important to note that resistance training reduced visceral fat in these studies. That’s the fat that parks itself around your midsection as opposed to the fat that sits right underneath your skin, covering your muscles.

Visceral fat is linked to a number of health issues such as metabolic syndrome, cardiovascular disease, and several types of cancer. The muscle-induced fat breakdown seen in McCarthy’s study specifically targeted visceral fat, indicating potential long-term health benefits of resistance training. 

If you’re not incorporating resistance training during a fat-loss phase, Schoenfeld adds, you’ll actually end up losing muscle mass which isn’t advantageous for aesthetics, function, or health. Schoenfeld says resistance training is “essential for weight maintenance and for the preservation of lean muscle mass.”