How Do Our Bodies Burn Fat? Scientists Offer New Answer

How does the body burn fat? According to scientists, a special molecule could play a key role.

The authors of the paper published in the journal Cell Metabolism wanted to understand why exercise seems to cut levels of visceral adipose tissue in our bodies. Visceral adipose tissue is the name for the fat that can wrap around the internal organs in the abdominal area, such as the liver and the intestines.

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More specifically, they wanted to investigate whether a signaling molecule called interleukin-6 helped to regulate this tissue by studying belly fat. A signaling molecule works by sending information about its environment to help cells do their jobs properly. The body gives off interleukin-6 during exercise, and the molecule is known to help us process fats. It also helps to keep the metabolism ticking along correctly.

Past studies have linked excess fat around the abdomen to poor physical and mental health, including life-threatening conditions such as cancer, dementia, cardiometabolic disease, as well a higher overall risk of premature death. What's more, fat around the abdomen can also indicate whether a person has potentially dangerous visceral adipose tissue.

The study's authors noted that some past research has suggested a hormone called epinephrine could explain how exercising appears to attack visceral fat tissue. But they argued the role of interleukin-6 in this has been under researched.

To test its hypothesis, the team recruited 53 participants with excessive fat around their bellies for a 12-week study. They measured their internal body fat levels using an MRI scanner at the start and finish of the study.

The volunteers were randomly split into four groups. Some were assigned intravenous doses of tocilizumab every four weeks. Tocilizumab is a drug that is usually prescribed for patients with rheumatoid arthritis, which is known to stop the interleukin-6 molecule from sending out its signals. Others were given a placebo of saline solution at the same four-week intervals. The participants were either asked not to exercise, or were told to complete three 45-minute cycling sessions per week.

The study authors found that the participants who were given the placebo and who exercised lost 225 grams of visceral fat when compared with those who didn't work out. And those who took tocilizumab and exercised put on 278 grams of visceral fat by the end of the study, compared with those who cycled but were dosed with the placebo saline.

Taking tocilizumab also appeared to be linked to higher levels of cholesterol against those who took the placebo, regardless of whether the participants exercised.

Anne-Sophie Wedell-Neergaard, first author of the study at the University of Copenhagen, said: "To our knowledge, this is the first study to show that interleukin-6 has a physiological role in regulating visceral fat mass in humans." However, she cautioned that the results don't prove interleukin-6 is the panacea for body weight management.

The take home message from the study is "do exercise," she said. "We all know that exercise promotes better health, and now we also know that regular exercise training reduces abdominal fat mass and thereby potentially also the risk of developing cardio-metabolic diseases."

And Wedell-Neergaard had some words of encouragement for those looking to amp up their exercise levels.

"It is important to stress that when you start exercising, you may increase body weight due to increased muscle mass," she explained. "So, in addition to measuring your overall body weight, it would be useful, and maybe more important, to measure waist circumference to keep track of the loss of visceral fat mass and to stay motivated."

The paper is the latest to investigate the fat that lurks inside our bodies. Research published in the journal Clinical Interventions in Aging in July indicated that having low muscle mass and high levels of body fat—known as skinny fat or sarcopenic obesity—could raise an older person's risk of developing dementia.

Doug Brown, chief policy and research officer at the U.K.-based charity Alzheimer's Society, who did not work on the paper, told Newsweek at the time: "This study suggests people struggling with midlife obesity and muscle loss due to aging are more likely to experience some impairment to their brain and thinking abilities."

He said the study should provide the public with further motivation to keep fit but that more study was needed to uncover how muscle strength affects brain health.