What Exactly Is Baby Fat?

Few things are cuter than a hearty baby with those adorable rolls, which people often affectionately call "baby fat." Having noticeable baby fat is often associated with being well-nourished, happy, and healthy. But many people may wonder what exactly "baby fat" is and what function it serves.

Essentially, baby fat provides crucial warmth and sustenance for babies and toddlers, explains Mollie Greves Grow, MD, MPH, an associate professor of pediatrics at the University of Washington/Seattle Children's Hospital. While baby fat is crucial for babies to thrive, there is a natural range in how much each child has. Learn more about baby fat, when kids start to "lose" it, and why having enough of it is crucial for optimal health, growth, and development. 

Those Cute "Rolls," Explained

Newborns quickly put on weight in the first few weeks and months of life. Much of that is added as fat, which is technically called adipose tissue. Those adorable rolls on their legs and arms get bigger as more of this crucial tissue accumulates, While every baby is different, and there is a big range of what is considered "normal," babies and toddlers have a much higher percentage of body fat than older kids, teens, and adults.

Baby fat is made up of two kids of fat, explains Dr. Grow. There is "brown" fat, which helps regulate body temperature, and "white" fat, which stores energy. Brown adipose tissue accumulates on the back and shoulders and makes up about 5% of an infant's body mass. White fat makes up an even larger percentage of a baby's body weight (around 15%) and contributes more to those cute rolls.

Infants put on weight so quickly due to the high-fat content in their diets. "Breast milk...contains 50% of calories as fat. Fat is needed for infants to promote brain growth," says Amy Reed, MS, RD, CSP, LD, a pediatric dietitian at Cincinnati Children's Hospital Medical Center and spokesperson for the Academy of Nutrition and Dietetics.

Body proportions are another reason for the visible prominence of fat on a baby's body, explains Ari Brown, MD, a pediatrician in Austin, Texas, and author of the Baby 411 book series. "The reason why babies look like that is because body proportions change as we grow up. For instance, a baby's head is about 1/4 of their body length and by adulthood, it's about 1/6. Leg-to-trunk proportions also change drastically from babyhood to adulthood. That's why they look chubby."

Why "Baby Fat" Is Important

Having enough adipose tissue is crucial to keep a baby warm and developing properly. "The appropriate amount of body fat helps to encourage development because it helps to provide the energy needed for this rapid period of growth. The fat consumed and stored by infants can also help in the development of their immune system," explains Reed.

Human babies have a higher percentage of body fat at birth and early childhood compared with other mammals, says Dr. Grow. "Historically, human babies need to survive with less access to food, especially when transitioning from a human milk diet to a food diet. This extra fat helps to protect for survival."

A diet rich in fat is key for brain development and other important functions, too. "Many people don't realize that our brains are composed mostly of fat. We need fat to develop nerve tissue, hormones that our bodies produce, as well as utilize fat for energy," says Dr. Brown.

Because babies and young children's brains are developing so rapidly in the first two years of life, pediatricians actually recommend that babies get more (healthy) fat into their diets, says Dr. Brown. "Breast milk and infant formula are fat-rich. And then we advise whole milk until age 2. But once they turn 2, the party's over and kids should have a diet lower in fat just like adults."

When Do Children Lose "Baby Fat?"

After age 2, babies start to eat a diet with less fat, and by kindergarten, they will have shed much of the "baby fat" we associate with babies and toddlers. Increased physical activity and independence also play a role. "As babies start to move and become more active in the toddler years, they tend to become leaner," says Reed. 

A child's body fat percentage usually starts to decrease at around 1 year of age, then continues to decrease until its lowest body mass index, around age 4 to 5. Kids tend to be the leanest at that age, says Dr. Grow. "At that point, it's normal for kids' ribs to show, and then they'll begin to see an increase in body fat again when they start puberty, around age 9 to 12."

Can a Child Have Too Much "Baby Fat?"

One of the primary purposes of well-child check-ups is for your baby's pediatrician to monitor growth and weight gain. Generally speaking, a baby can't have too much fat. In fact, typically, the biggest concern is not putting on enough weight rather than too much, says Dr. Grow. "We don't measure baby fat or put babies on restricted diets." There is a wide range of "normal" when it comes to how much adipose tissue a baby has.

More important than the number of a baby's weight is that they are maintaining steady growth. When a baby has a lack of weight gain or slowed weight gain, they are at risk of being underweight.

"Being underweight is concerning because there is rapid brain growth during the first year of life and a lack of key nutrients can affect this growth," says Reed. "If a parent is concerned about their infant's weight, it is encouraged that they talk with their healthcare provider and they can ask for a referral to a pediatric dietitian."

It's important to emphasize some babies and toddlers will have more body fat than others—and these differences in size and body fat percentage can all be healthy. "What we know from population norms is that some babies will be bigger," says Dr. Grow. For example, parents who are physically smaller will typically have smaller babies, and larger parents may have bigger babies. Additionally, breastfed babies tend to be leaner than bottle-fed babies.

A Word From Verywell

"Baby fat" or adipose tissue creates those super cute baby rolls—but it also plays a crucial role in helping babies thrive. Warmth, energy storage, and brain development are among the most important functions of baby fat. Your child will keep their baby fat through toddlerhood and then begin to get leaner until puberty when their bodies will start getting fuller again.

Some babies will have lots of rolls on their legs and arms and others will be leaner, but both body types are healthy. Rather than worrying if your baby has enough or too much "baby fat," look for consistent weight gain and development of skills. Your child's pediatrician will be monitoring their growth and is a good resource if you have any questions or concern's about your child's weight or diet.