The primary function of macronutrients is to provide energy, with carbohydrates, proteins, and fats each contributing to this role. They also support other functions such as brain development and blood sugar regulation, but energy provision is the core purpose. Therefore, the correct answer is 'Provide energy.'
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Macronutrients' primary function is to provide energy, with carbohydrates, proteins, and fats serving this role. They are also involved in other functions like supporting brain development and regulating blood sugar, but energy provision is fundamental. Therefore, the answer to the question is 'Provide energy.' ;