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Mitochondria have many roles in the body. A mitochondrion is an organelle that is the powerhouse of a cell. It acts like a digestive system, breaking down nutrients and producing a ton of energy in the form of ATP. Mitochondria are found in all cells. Muscles have a lot of them because of the energy demand during exercise. Endurance athletes have and need more of these than power athletes.

There are three groups of carbohydrates: monosaccharides, oligosaccharides, and polysaccharides. Monosaccharides are the simplest form of carbohydrates; these include glucose, fructose, and galactose (fruits and starchy carbs have these simple sugars in them). Oligosaccharides are chains of two or three monosaccharides, such as sucrose (sugar), maltose, and lactose (sweet potatoes and cheese are examples of foods containing oligosaccharides). Polysaccharides are long chains of monosaccharides, such as starch, glycogen, and fiber (whole-grain bread and legumes contain these). All sugars are eventually broken down to glucose in the bloodstream. In the stomach, carbs are the first to be passed through, which is why you may not feel full if you eat a high-carbohydrate meal. Around 20 grams of glucose circulates in the bloodstream every hour. If your blood sugar drops, either the liver will dump glucose into the bloodstream or you will have to eat something to supply new glucose. Only glycogen in the liver can provide glucose. Muscle cell glycogen is reserved for glycolysis in that muscle cell. If there is excess glucose in the blood, the liver and muscle cells will take up what they can, and then the rest gets stored as fat.