Understanding the role of nutrients in sports is important since nutrients are fuel for energy systems and having more energy aids in optimizing performance on the court.
The body uses nutrients to grow, restore body tissue, and provide energy to perform work. The body requires some nutrients in large quantities, called macronutrients, and other nutrients in smaller quantities, called micronutrients.
Macronutrients provide energy, whereas micronutrients do not yield any energy directly but they assist in the transfer of energy (e.g. B-vitamins).
Micro Nutrients: Non-Energy Yielding
- Water (2nd simplest form; made of hydrogen & oxygen)
- Minerals (simplest form; each is a chemical element)
- Vitamins (made of hydrogen, oxygen, and carbon –> organic): vitamin B & C are water-soluble, vitamin A & D & E & K are fat-soluble
Macro Nutrients: Energy Yielding
The primary energy yielding nutrients used during exercise are:
- Carbohydrates (CHO) (made of hydrogen, oxygen, and carbon –> organic): yield 4kcal/g
- Lipids (made of hydrogen, oxygen, and carbon –> organic): yield 9kcal/g
- Protein (made of hydrogen, oxygen, and carbon –> organic): yield 4kcal/g; only minor contribution (2-5%)
Nutrients containing carbon are called organic (=alive)! Which nutrient predominantly provides the energy during exercise depends on:
- exercise intensity (low intensity = fat; high intensity = carbs)
- exercise duration (long duration=fat; short duration=carbs)
Carbohydrates predominantly provide energy for high intensity/short duration activities, whereas lipids (fat) provide the energy for moderate intensity/long duration activities.
When exercise intensity increases, the body will use more carbohydrates and less fat. The cross-over point, where more carbohydrates are being used than fat, occurs when exercise intensity increases steadily. At – and beyond the cross-over point, carbohydrates become the dominant source of fuel.
There are two factors, with respect to high exercise intensity, that cause the shift from fat to carbohydrates (fat -> carbs):
- recruitment of fast-twitch muscle fibers
- an increase in blood levels of epinephrine
More and more fast-twitch fibers are being recruited when exercise intensity is high. Fast-twitch fibers are better equipped to metabolize carbohydrates than fat!
Therefore, the more fast-twitch fibers an athlete has, the more carbohydrates are being used compared to fat.
With high intensity exercise, blood levels of epinephrine increase and this increase in epinephrine levels is responsible for higher glycogen breakdown, carbohydrate metabolism, and higher lactate production.
Lactate production is a byproduct of anaerobic metabolism, which increases with exercise intensity. High levels of lactate inhibits fat metabolism, which means less fat is being used during high-intensity exercise.
Therefore, the more lactate that is being produced, the less fat is metabolized, which leads to an increased usage of carbohydrates during high-intensity exercise.
Factors that control the rate of fat metabolism during prolonged exercise are the enzymes that control lipolysis (lipases). The lipases activity is stimulated by the hormones:
During prolonged low-to-medium intensity exercise, epinephrine levels in the blood rise, which leads to better lipase activity, which in turn promotes lipolysis and lipolysis promotes fat metabolism.