Wednesday, November 18, 2009
Peter and I have often discussed the links between visceral fat and metabolic risk. Visceral fat is the fat which surrounds the internal organs, and is thought to mediate much of the risk between obesity and disease. For example, individuals with excess body weight tend to have more visceral fat, which is likely responsible for the relationship between body weight and numerous chronic diseases. However, as Peter discussed on Monday, subcutaneous fat (the fat beneath the skin) does not seem to have these same negative associations with health. This means that regardless of body weight, individuals with excess visceral fat tend to be at increased health risk, while those with low amounts of visceral fat tend to be at low risk. This probably explains why up to 30% of obese individuals are metabolically healthy - these individuals are likely to have lots of subcutaneous fat, but not much visceral fat.
Given this link between visceral fat and chronic disease, it is interesting that exercise preferentially reduces visceral fat. In other words, even when exercise does not result in reductions in body weight, it still results in reductions in visceral fat (which is likely one reason that exercise results in dramatic health benefits even without a change in body weight). Perhaps just as importantly, a new study in the journal Obesity suggests that even small amounts of exercise can prevent the accumulation of visceral fat, even when total body weight is increasing.
In this new study, Dr Gary Hunter and colleagues at the University of Alabama followed a group of women for 1 year after completing an intervention which resulted in significant weight loss (~25 lbs). The authors divided the women into three groups - those that were to perform aerobic exercise twice a week, those that were to perform resistance exercise twice a week, and a control group which performed no exercise at all. As is often the case, body weight gradually increased following the intervention in all three groups. However, among the exercisers, body weight increased by much less than in the non-exercisers (~7.5 lbs vs ~13.5 lbs). What is even more interesting (and probably much more important from a health perspective), is that visceral fat levels increased by over 20% in the non-exercise group during the 1-year follow up, while there was no change in visceral fat levels in individuals who performed resistance or aerobic exercise.
I find these results to be very encouraging. Individuals in this study performed just 80 minutes of exercise per week, which is well below most recommendations, and frankly isn't much exercise at all. And yet, these individuals still prevented any increase in visceral fat. So while 80 minutes of exercise may not be enough to completely prevent weight gain (although it did dramatically reduce it), it might still be enough to prevent the accumulation of visceral fat, which is likely to also help prevent the accumulation of metabolic risk factors. These results are also a reminder that exercise can have dramatic effects on body composition and metabolic health, regardless of what is happening with your body weight. So whether your body weight is increasing, decreasing, or holding steady, if you are exercising regularly, you are likely reducing your visceral fat levels, as well as your health risk.
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Hunter, G., Brock, D., Byrne, N., Chandler-Laney, P., Del Corral, P., & Gower, B. (2009). Exercise Training Prevents Regain of Visceral Fat for 1 Year Following Weight Loss Obesity DOI: 10.1038/oby.2009.316
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