Mitochondria and Obesity Revisited

Several months ago I blogged about the results from a Finnish twin study that found lower mitochondria numbers and disturbed mitochondrial energy metabolism activity in fat cells from identical twins who were leaner than their genetically identical co-twins. These impairments correlated with critical clinical measures of obesity including liver fat accumulation, reduced whole-body insulin sensitivity, hyperinsulinemia, hypoadiponectinemia and adipocyte hypertrophy. In this month’s issue of OBESITY, Tomas Gianotti and colleagues from the University of Buenos Aires, Argentina, report a significantly lower mitochondrial-to-nuclear DNA ratio (mtDNA/nDNA) in insulin resistant (IR) adolescents recruited out of a subset (n=175) of a cross-sectional, population-based study of 934 high school students. In this study, the mtDNA/nDNA ratio was also inversely correlated with HOMA index, a crude but simple measure of insulin resistance. This study is very much in line with the notion that obesity-prone individuals may have impaired mitochondrial number and/or function resulting in increased risk for obesity. From the aforementioned twin study, we know that the decreased number and function is not corrected by weight loss. Indeed the question is whether or not mitochondrial number and function can be increased by prescribing higher activity levels? If yes, how much activity will be needed to reverse these changes? And most importantly, will people with impaired mitochondrial function actually be able to enjoy exercise enough to actually stick with this prescription? Perhaps it is not obesity that causes impaired mitochondrial function but rather impaired mitochondrial number and/or function that predisposes to obesity. This impairment could be genetic but also due to intrauterine programing or perhaps simply luck of the draw (remember – all mtDNA comes from your mom). Of course this is not an “excuse” for obesity as is often misinterpreted when data on the genetics and biology are presented. However, it is clear that if you have impaired mitochondrial number and/or function you are much more likely to become obese in an environment that promotes sedentariness than if you were dependent on physical activity to meet your basic needs for survival. Remember, there were times, not too long ago, when people were actually paid to be physically active. Today, choosing to be physically active actually costs money (not to mention time). AMSEdmonton, Alberta

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Lifestyle not a Determinant of Obesity in Teens?

Now here is a counter intuitive finding from Catherine Sabiston, of McGill University, and P.R.E. Crocker, of the University of British Columbia (UBC) published in the Journal of Adolescent Health earlier this year. In their study of 900 Vancouver-area 16-18 year-old teenagers in Grades 10 through 12, neither was there a link between body mass index (BMI) values and levels of physical activity nor did the physically active teens eat a markedly healthier diet than their less-active counterparts. If anything, the heavier teens were actually the ones making healthier food choices while the teens with “healthier” BMI values were no more likely to be physically active than those with higher, “unhealthier” values. According to Dr. Sabiston (quoted in a press release from McGill University) “A lot of people are surprised, but when you think about it, BMI doesn’t have a huge impact on physical activity. And in terms of diet, it actually makes sense that someone who is not happy with their body might try to eat more healthily. What this study really says, is that one cannot assume that someone who is physically active necessarily eats a healthy diet – or the reverse, that someone who is more sedentary or has a high BMI by definition eats a diet of junk food.“ To me the findings aren’t all that surprising. I have always maintained that health cannot be simply deducted from the number on your scale and that for every overweight kid who eats mostly junk food and spends every spare minute on his Xbox, there’s a skinny kid out there who’s no better. The simple truth is that eating healthy and exercising is important at any weight! On the other hand, just as simply eating poorly and not exercising by no means guarantees weight gain – simply eating healthy and exercising does not guarantee a so-called “healthy” weight. When everyone eats too much and no one moves, it’s likely the poor kids with the “wrong” genes that pack on the pounds – the kids with the “right” genes are simply lucky and can apparently get away with their lousy lifestyles – who says life has to be fair! Of course, the words “wrong” and “right” in the previous sentence refer to these genes in today’s world. Until not all too long ago in the history of mankind, the “wrong” genes would have been just “right” and vice versa… Read More »

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