Which macromolecule is the primary source of long-term energy storage?

Which macromolecule is the primary source of long-term energy storage?

• A. Carbohydrates
• B. Proteins
• C. Lipids
• D. Nucleic acids

Answer: (C)

Lipids provide the body's longest-lasting energy reserve. They pack about 9 kilocalories per gram, more than twice the energy per gram of carbohydrates, which give around 4 kcal/g. Because lipids are stored as triglycerides in adipose tissue with little associated water, they store energy very densely by weight, whereas carbohydrate stores (as glycogen) are hydrated and bulky. When energy is needed, triglycerides are mobilized, fatty acids are released and oxidized to generate ATP for extended periods, such as fasting or sustained activity. Proteins can be used for energy but are mainly for tissue maintenance, and nucleic acids store genetic information rather than energy. So lipids are the primary source of long-term energy storage.

Lipids provide the body's longest-lasting energy reserve. They pack about 9 kilocalories per gram, more than twice the energy per gram of carbohydrates, which give around 4 kcal/g. Because lipids are stored as triglycerides in adipose tissue with little associated water, they store energy very densely by weight, whereas carbohydrate stores (as glycogen) are hydrated and bulky. When energy is needed, triglycerides are mobilized, fatty acids are released and oxidized to generate ATP for extended periods, such as fasting or sustained activity. Proteins can be used for energy but are mainly for tissue maintenance, and nucleic acids store genetic information rather than energy. So lipids are the primary source of long-term energy storage.