Nutrition Pt 2

So I said I would deal with Carbs - this is the most versatile supplier of ATP and supplies vertually every metabolic process in the body. Everything we do needs energy, even sleeping and thinking. Sugar is the most basic form, but there are various sugars (Glucose, Sucrose, Fructose) and combining carb molecules creates complex carbs such as bread and pasta.

The body can store carbohydrate as glycogen, which is formed through the combination of thousands of glucose molecules and whose primary store is the liver. So whenever the body needs carbohydrate liver glycogen is broken down into glucose and released into the bolldstream. Glycogen that is stored in muscles is only used in that particular muscle to fuel its needs.

The only carbohydrate that the body can metabloise for energy is glucose. Once carbs are absorbed from the intestine they are carried to the liver where conversion takes place. Different carbs areabsorbed in different ways from the intestine. So-called glucose carriers in the intestine wall attach to the glucose molecules on the inside of the intestine and carry them through to the outer wall where they get into the bloodstream. During this process the carrier molecule also carries a water molecule. This mechanism aids in water absorption and is an important factor in making sports drinks. There is no such carrier molecule for fructose which has to pass through the intestine passively.

Fats are made up from triglycerides which in turn are made from a glycerol molecule attached to 3 long carbon chains called fatty acids. In digestion the fatty acids are separated from the glycerol and absorbed as free fatty acids. They are taken to the liver where they combine with cholesterol and are re-released into the bloodstream for transport to storage - body fat.

Unlike carbs fats are digested and absorbed slowly. Fat metabolism is also much more complex than for carbs, meaning that fats do not provide such quick energy. Also fat burning requires more oxygen than carb burning, so fat is only used sparingly during high intensity exercise, when the body needs oxygen most. This is why medium intensity exercise is best for fat burning - long bike rides!

The advantage of fat is that it stores immense amounts of energy. When full to the brim, the body can store about 2,000 to 2,500 calories (what an average man uses in a day) as glycogen . In contrast, even the leanest cyclist has roughly 30,000 calories in his fat tissue (so I have a great deal more). 1 gram of carb provides 4 calories but 1 gram of fat provides 9. Similarly 1 molecule of carbohydrate can produce 36 ATP molecules, whereas 1 free fatty acid molecule can produce about 130 ATP molecules. Thus, although fat cannot fuel high intensity activities it can provide many of the calories needed during the long medium intensity effort of a long ride, leavind the limited carb stores for sprints. Remember Ranulph Fiennes and his loony Antarctic walking friends eat lumps of butter - because it contains the most energy. Yuk.

Protein is made up from amino acids. There are some, known as essential amino acids, which the body cannot make, but otherwise the body can deconstruct protein into other amino acids and make the specific proteins required. These substances perform a number of functions in the body including providing building blocks for muscle tissue.

Protein can provide the same calorific content as carbohydrate but honestly not much is known about the metabolism of protein during exercise, but afterwards, protein is needed to repair damaged muscle and to replace protein used as fuel.

Here endeth the lesson - for now!