Controlling for obvious differences such as weight and muscle mass, the predominant theory is that some people are more efficient at utilizing caloric energy than others due to differences in the efficiency of their mitochondria. These you may remember as the ‘power-plants’ of the cell: they take glucose and fats from the bloodstream and convert it to ATP for the muscles to use as energy.
It now appears that this theory is incorrect.
A new study by researchers at the Karolinska Institute and the University of Southern Denmark shows that individual differences in mitochondrial efficiency cannot explain overall efficiency. Instead, they say, the efficiency must be accounted for by how the muscles use this ATP.
Work efficiency, they found, was correlated to a protein called UCP3. Higher levels of this protein meant lower levels of efficiency. Previous studies (PDF alert) in mice have shown over-expression of UCP3 leads to lower levels of subcutaneous, visceral, and intermuscular fat.
So, how can you make yourself more inefficient? It appears that this UCP3 protein is more prevalent in fast twitch muscle fibers than slow twitch. This would suggest that sprint or speed training should have the largest benefit by recruiting and building those muscles. Unfortunately, training — both endurance and high intensity — actually lowers UCP3 expression. (Why can’t it just be simple?) But on the whole, it still appears sprint and speed training are the best bet.
[tags]weight, fat, muscle, genetics [/tags]