Energy Management

Our body uses sugars (glucose) and fats for energy. The brain alone uses 125-150 grams of glucose per day. Sugars (glucose) are constantly transported in the blood, which is referred to as "blood sugar". If the blood is satiated with sugar, the body will convert the excess sugar into glycogen.

Glycogen is mainly stored in the liver (about 400 kcal) and the skeletal muscles (about 1200 kcal). Skeletal muscles account for about 50% of the energy use in a resting person, up to 90% during high physical activity. In resting muscles the basic energy comes from fatty acids and ketone bodies, and moderately active muscles will use blood sugar in addition to that. Glycogen can be reconverted into glucose whenever needed, for instance when muscles are maximally active. Glycogen from the liver can be used for different purposes, but that from muscles can only be used for muscle activity.

If those glycogen depots are full, the body converts glucose into body fat. When needed, body fat can be made (by intracellular lipase) to release fatty acids, which then bind to serum albumin and are carried to the skeletal muscles and the heart, which use most of the fatty acids. If the body fat accumulated is not used up, which means energy intake is greater than energy output, bodyweight will increase.

When our glycogen depots are full and the blood sugar level is maximal, we are at the peak of our energetic potential. In order to keep near this peak and avoid unnecessary insulin secretion - insulin is secreted more when glucose needs to be converted into glycogen and/or body fat - we only need to replenish the blood sugar when needed. If the body is used to this system, it will signal when it needs more energy, by a slight energy dip or hunger feeling.

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