Macronutrients are the chemical compounds which provide the bulk of dietary energy. The three primary macronutrients are carbohydrates, protein and fat. Some also consider fibre to be a macronutrient. Fat provides 37 kJ/g (9 kcal/g) of energy compared to 17 kJ/g (4 kcal/g) for both carbohydrates and protein. More recent dietary guidelines have increased focus on patterns of eating, reducing emphasis on individual nutrient intake. This approach may improve public implementation of dietary guidance through easier comprehension and practical translation. Scientific understanding of the physiological and health effects of nutrients is likely to be enhanced by considering nutrients individually, potentially improving our understanding of the associations between overall eating patterns and chronic diseases.
The benefit of understanding the physiology of individual nutrients is illustrated by considering the energy balance hypothesis of obesity. In the late 19thand early 20thcenturies, the energy balance model of obesity was promoted, largely based on the technology of calorimetry available at the time(15, 16). This model, while correctly based on the premise that weight gain occurs in the setting of positive energy balance, neglected the hormonal influences of different macronutrients. While our understanding of hormonal and biochemical impacts of varying macronutrient composition is still incomplete, it is now well understood that different macronutrients can have varying impacts on fat storage, even for iso-caloric intakes. Macronutrients must therefore be considered not solely as a source of energy, but also as substances that have biochemical and hormonal impacts.