This 2013 review assesses the links between exercise, weight loss, and the function of skeletal muscle mitochondria. As outlined in a previous post on CrossFit.com, defects in skeletal muscle mitochondrial function are associated with (and may in fact contribute to the development of) insulin resistance observed in individuals suffering from obesity and Type 2 diabetes. In particular, the paper proposes a pathological pathway through which obesity and improper lipid regulation lead to fat accumulation within the liver and skeletal muscle. This fat accumulation then disrupts mitochondrial function in these tissues, thereby affecting their ability to process energetic fuels (i.e., lipids and glucose).
The authors provide evidence that these mitochondrial defects are reversible with weight loss and especially exercise training, which leads to substantial increases in skeletal muscle mitochondrial function and content in obese and diabetic subjects. These mitochondrial improvements often correlate with improvements in insulin sensitivity, though it is not precisely known whether changes in mitochondrial status directly cause changes in insulin sensitivity or are correlated through other yet undetermined factors.
The authors note that aging, like obesity and diabetes, is associated with impaired energy metabolism and decreased muscular mitochondria content and function. Exercise in the elderly has been shown to improve mitochondrial function, though the impact of these improvements on insulin sensitivity is not discussed.
In sum, the authors conclude the mitochondrial dysfunction frequently present in obese and diabetic individuals can be consistently reversed at least in part through exercise, though the implications for insulin resistance remain uncertain.
Comments on The Role of Weight Loss and Exercise in Correcting Skeletal Muscle Mitochondrial Abnormalities in Obesity, Diabetes and Aging
Exercise is part of the solution, not for balancing calories but for hormonal health!
There are two specific nuggets of importance in this paper:
1. Skeletal muscle insulin resistance - and so whole-body insulin resistance - seems to be tied to fat accumulation, specifically because fat accumulation in the muscles leads the muscles to become insulin resistant;
2. If this insulin resistance has developed, exercise seems to be able to specifically reverse it, at least partially.
It's too much of a stretch to say exercise would play a role in reversing the sort of whole body insulin resistance we see in diabetes by itself - in fact, the data I'm aware of seems to suggest it can't. But I would expect, given this information, that if the right exercise program is added to the right diet, we might see glycemic control, and so the other downstream effects of insulin resistance, begin to reverse more quickly.
The Role of Weight Loss and Exercise in Correcting Skeletal Muscle Mitochondrial Abnormalities in Obesity, Diabetes and Aging
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