Wednesday, July 08, 2009
Photo by Sylvar.
Last week I discussed sex-differences and obesity related metabolic risk among elderly men and women. This week I'd like to stay on the topic of obesity related sex-differences, focusing on a paper by Drs Jen Kuk and Bob Ross (not that Bob Ross) which was published recently in the International Journal of Obesity. In this new study, Drs Kuk and Ross examined the influence of sex on regional fat loss in overweight/obese men and women in response to diet and/or exercise interventions.
Interestingly, they report that for a given amount of weight loss, men lost more visceral fat (fat surrounding the internal organs in the abdomen), while women lost more lower body subcutaneous fat (the fat you can pinch on your legs, hips, and buttocks). That may seem trivial, but it's important to note that visceral fat is closely associated with disease risk and even mortality, while lower body subcutaneous fat often has no relationship with health risk at all (while in some situations it is even protective). Theoretically (and I stress that it is theoretical), this suggests that for a given amount of weight loss, men may actually experience more health benefits than women.
I found this study very interesting, so I thought this would be a great opportunity to do another Obesity Panacea interview. Not only is Dr Kuk an excellent researcher, but she is also a close friend of both Peter and I. She was a lab-mate, mentor, and roommate (briefly) at Queen's University, and has co-authored several papers with us (mostly with Peter, but my first formal collaboration with Jen was accepted for publication earlier this week, and will be featured on the blog in the very near future!). She was kind enough to take the time out of her busy schedule as an Assistant Professor at York University to answer a few questions on the study, why she feels waist circumference is a better measure than the waist-to-hip ratio, and what she thinks is the most important message of her research to date.
TS: You found that for a given amount of weight loss, men and women lost the same amount of body fat, but men lost more visceral fat, while women lost more lower body subcutaneous fat. Why do you think that is?
JK: In part, some of the sex differences are because of how much regional fat men and women begin with. Men tend to have more visceral fat than women, whereas women have more subcutaneous fat, particularly in the hip and gluteal regions. So it makes sense that you would able to lose more of a specific tissue that you have an overabundance of. Other reasons could be due to differences in hormones or the way fat is mobilized in men and women. So in other words, it could be a difference in genetic programming.
TS: Given that your previous work has suggested that visceral fat is an independent predictor of mortality, does this suggest that women may need to lose more weight to experience the same metabolic benefits as men? Do you know if men and women experience similar metabolic improvements for a given amount of weight loss?
JK: That's a great question. There is some work suggesting that men and women have the same cardiometabolic profile for a given level of visceral fat (see Lemieux et al. Diabetelogia 1994). This means that if a man and woman have the same amount of visceral fat, then you would expect they would have similar levels of glucose, lipids and blood pressure. If this pattern holds true with weight loss, then it would suggest that men may have a greater metabolic benefit from a given weight loss, but this has yet to be shown in a study. That said, this study should not deter women from trying to lose weight, as weight loss will improve your health and qualtiy of life regardless of whether you are a man or woman. So in the end it doesn't really matter who has the advantage.
TS: Do these findings have clinical implications?
JK: As I said above, it doesn't really matter in the end who has the advantage with weight loss, both men and women should lose weight. So in a sense, no...this study has no clinical implications ;)
[Travis' Note: For more on the clinical implications of the study, please see this post by Dr Arya Sharma on his blog earlier this week]
TS: Given the associations between visceral fat and disease, is there any way that people can "target" visceral fat specifically in their weight loss program?
JK: Like all fat depots, there is no way to target a specific fat depot, but exercise has been shown to increase the amount of visceral fat loss expected for a given amount of weight loss as compared to dieting. In fact, you can lose visceral fat with exercise without losing weight.
TS: You also report that waist-to-hip ratio is not a good predictor of long-term changes in body composition. Could you briefly explain why a measure like waist circumference is a more useful longitudinal marker of body fat distribution?
JK: Essentially, the waist-to-hip ratio is not good particularly in women because you are comparing two things that are changing. With weight loss, people will loss inches (fat) both from their waist and hip/gluteal region. And so if you are coming your waist to your hip, you are kind of aiming at a moving target. In men it is not as bad, as they generally do not lose very much from their hip and gluteal region, so the waist-to-hip ratio is more of a function of changes in waist. Since waist alone is a better predictor of changes in visceral fat, and it's simpler to measure, just use waist.
TS: If people could take one message from your research to date, what would it be?
JK: Watch your waistlines, and walk yourself to a healthier you.
Thanks Jen for taking the time to answer our questions!
For more information on Dr Kuk and her research, please visit her York University page here.
1. Public transit and physical activity - an Obesity Panacea interview.
2. Sex differences in obesity related metabolic risk in elderly men and women.
3. Is losing fat from your thighs bad for your health?
Kuk, J., & Ross, R. (2009). Influence of sex on total and regional fat loss in overweight and obese men and women International Journal of Obesity, 33 (6), 629-634 DOI: 10.1038/ijo.2009.48
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