While in a fasting state, the metabolic fuel our body uses is primarily determined by our body’s carbohydrate balance. For example, when carbohydrate stores are empty our bodies tend to burn mainly fat, and in contrast, when carbohydrate stores are full our bodies tend to burn less fat. Environmental factors like stress and sleep deprivation can shift our body’s fuel towards carbohydrate or fat usage.
Note that all of the above only applies to individuals who are considered healthy. Not sure if that's you? Check out this article.
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