NBEO Biochemistry Practice Exam 2026 - Free Biochemistry Practice Questions and Study Guide

Lipids generate the highest amount of calories per gram compared to proteins, carbohydrates, and fiber. This is primarily due to their molecular structure. Lipids, which include fats and oils, contain long hydrocarbon chains that are rich in energy-dense C-H bonds. When metabolized, lipids yield approximately 9 calories per gram.

In contrast, proteins and carbohydrates provide about 4 calories per gram. Although fiber is technically a type of carbohydrate, it is not fully digestible by the body and generally does not provide significant caloric value, typically yielding less than 2 calories per gram due to its complex structure and the way it's processed by the digestive system.

This energy density of lipids makes them a crucial component of the diet, especially in terms of providing a substantial amount of energy for bodily functions, cellular processes, and overall metabolism. Understanding the caloric content of these macronutrients emphasizes the role of lipids in energy storage and nutritional planning.