IB Sports, exercise and health science A.2.2.1 Macronutrients as Energy Sources and the Factors Influencing Their Use Notes

Macronutrients as energy sources

1. The three primary macronutrients carbohydrates, proteins, and lipids contribute differently to energy metabolism based on factors such as exercise intensity, duration, and an individual's physiological state.
2. They support growth, rest, and physical activity, with each macronutrient playing a unique role.

Carbohydrates are the main fuel for high intensity exercise

1. Carbohydrates serve as the primary fuel source for most bodily functions and physical activities, particularly during high-intensity exercise.

Carbohydrates are classified by the number of sugar units

Monosaccharides

1. The simplest form of carbohydrate, consisting of a single sugar molecule.
2. Easily absorbed by the body.
3. Examples include glucose, fructose, and galactose.

Disaccharides

1. Composed of two monosaccharides linked together.
2. Examples include sucrose (glucose + fructose) and lactose (glucose + galactose).

Oligosaccharides

1. Carbohydrates that contain 3 to 9 sugar units.
2. An example is maltodextrin, often used in processed foods and sports drinks for quick energy release.

Polysaccharides

1. Long chains of monosaccharides, such as starch and glycogen, that provide long-lasting energy.
2. Broken down into glucose during digestion.

Dietary Fiber

1. Some polysaccharides, like cellulose, cannot be digested by the human body and are considered dietary fiber.
2. Although not a direct energy source, fiber is crucial for digestive health.

Energy yield

1. Carbohydrate energy density: ~1,760 kJ per 100 g.
2. Storage capacity: Limited to about 400 g muscle glycogen + 100 g liver glycogen in a healthy adult.
3. Other functions: Contribute to cell membrane structure and to DNA/RNA synthesis, but the dominant role is fuel.

Carbohydrates are digested to glucose and stored as glycogen

1. Digested carbohydrates are broken down into glucose, which enters the bloodstream.
2. Excess glucose is stored in the liver and muscles as glycogen through a process called glycogenesis.