Of which of the following nutrients do infants require extra servings?

The answer

Infants require extra servings of fatty acids — dietary fat. In the first year of life, a baby's brain and nervous system grow faster than at any other time, and fat is central to that growth. Roughly half of an infant's daily calories come from fat, which is why breast milk and infant formula are far higher in fat as a percentage of calories than a healthy adult diet. Fat is the most energy-dense nutrient (about 9 calories per gram versus 4 for protein or carbohydrate), so it packs the fuel a rapidly growing baby needs into a small stomach.

Beyond energy, specific fatty acids are structural. DHA (docosahexaenoic acid), an omega-3 fatty acid, is a major building block of the brain and the retina of the eye. Fat also carries the fat-soluble vitamins A, D, E, and K and supports the development of the myelin sheaths that insulate nerve cells. For all these reasons, fat intake that would be considered high for an adult is exactly right for an infant.

Why the other options are wrong

Typical distractors on this question are protein, carbohydrates, and vitamins or fiber. Each matters, but none is the nutrient infants need in extra proportion the way fat is:

• Protein — babies do need protein for tissue growth, but their protein needs per calorie are modest, and too much protein actually stresses immature kidneys. Breast milk is notably low in protein compared with the milk of many other mammals, precisely because human infants do not need an outsized protein share.
• Carbohydrates — lactose provides energy, but carbohydrate is not the nutrient requiring special extra emphasis for brain development, and infants are not fed high-carbohydrate diets.
• Vitamins / fiber — vitamins are essential in tiny amounts, but they are not "servings" and are not required in extra bulk. In fact, high-fiber diets are discouraged for infants because fiber fills the stomach and can crowd out the calorie- and fat-dense foods they actually need.

Fat stands alone as the nutrient infants require in a proportionally larger amount than older children and adults.

Infant needs vs. adult needs

The content gap in most answer pages is that they never contrast infant and adult needs. The pattern reverses what we consider "healthy" for grown-ups:

• Adults are told to limit fat to roughly 20–35% of calories; infants get about 50% of calories from fat, and this is desirable.
• Adults benefit from high fiber; infants should have little to no added fiber.
• Adults can handle higher protein; infants thrive on the lower protein share found in breast milk.

This is why you should never put an infant on a low-fat or "heart-healthy" adult diet. Restricting fat in the first two years can impair brain and nervous-system development.

The bigger picture

Breast milk is the model: it is naturally rich in fat and DHA, which is why it is recommended as the primary food for the first six months, and infant formulas are fortified with DHA and ARA to mimic it. As solid foods are introduced, full-fat dairy and other fat sources remain important through toddlerhood. The takeaway for exams and for real life is the same — infancy is the one stage where a high-fat diet is not just acceptable but necessary.