This study challenges the narrative that body mass index (BMI) alone should be used as a marker to assess risk for cardiometabolic disease. Previous studies have shown visceral fat (fat build up on your internal organs, such as the liver) is an independent risk factor for cardiometabolic disease while BMI is not. The issue with BMI is it does not discern body composition. Muscle weighs more than fat, so if I pack on muscle in the gym, I increase my BMI. You have to add a substantial amount of muscle to be in the overweight and obesity categories, but it’s often accomplished (many professional body builders are in the categories, albeit steroid assisted).
If we zoom out and look at populations, BMI works well to assess trends and gather a snapshot of one health marker. If we want to gather more actionable data, visceral fat is likely the target.
The researchers wanted to know if diet or exercise could reduce visceral fat in overweight or obese adults. They pulled data from 26 studies exploring the effects of exercise and 16 exploring the effects of caloric restriction. In total, 983 people were in the exercise groups, 394 in the calorie restriction groups, and 813 in the control groups (no change in calories or activity levels). Some studies included people with comorbidities such as type 2 diabetes, metabolic syndrome, dyslipidaemia and non-alcoholic fatty liver disease.
The pooled data showed both exercise and caloric restriction are effective for reducing weight loss, providing moderate effect sizes. On the surface, it appears caloric restriction may be superior as the effect sizes were larger but the dose response analysis favored exercise. Per 1000 calorie deficit, exercise had a greater influence on visceral fat.