September 29, 2020

A Dietitian’s Best Advice If Your Child Is Underweight

Insights and healthy tips for parents to help your child achieve their recommended weight

A child eating

As a parent, of course you’re trying to keep your child happy and healthy. You’re focused on providing the right amount of nutrients to help them grow and be strong.


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But despite your best efforts, some children still may not achieve the recommended weight. This leaves you asking “is my child underweight for their age or size?”

So what makes a child underweight? How can you get an underweight child to gain weight they need to grow? You may also wonder “when should I worry about my child’s weight?” if the things you do as a parent don’t seem to be helping.

Pediatric registered dietitian, Jennifer Hyland, RD, answers some common questions about weight, and how healthcare providers can help families get on track and help their underweight child gain in a healthy way.

Q: What qualifies as ‘underweight’ for a child?

A: A child is underweight if they’re in the bottom 5th percentile for weight compared to their height. Underweight is not only classified compared to other children their age, but to their height as we clinically look for a child to be proportionate.

The way pediatricians and dietitians monitor children is on a weight-to-length measurement for children from birth to age 2.

After age 2, we use the Centers for Disease Control growth charts to look at weight, height and BMI (body mass index) for age. BMI for this age range compares a child’s weight to their height. A BMI for age less than the 5th percentile indicates a child is underweight.


Q: How can I tell if my child is underweight?

A: There are several signs that parents should watch for:

  • Every kid has their own optimal weight. But if your child’s weight percentile declines on the growth charts at annual pediatrician visits, that’s cause for concern.
  • At home keep an eye on how clothes fit your child. If a younger child doesn’t begin to outgrow her clothes each season, you should meet with your pediatrician.
  • At bath time or at the swimming pool or beach during warm months, watch to see whether you can see your child’s ribs. Ribs that stick out or are prominently visible are a sign that your child may be underweight.

Q: Are there medical issues that cause this problem?

A: Children born prematurely are often underweight because their growth needs to catch up with peers. But a common reason older children are underweight is inadequate food intake.

This may or may not be a result of picky eating. There are also several medical issues that can suppress appetite or block nutrient absorption. These include:

  • Medications: Those used in attention deficit-hyperactivity disorder (ADHD), which can suppress appetite.
  • Food allergies: These can make getting enough calories a challenge. The more food allergies, the greater the challenge.
  • Hormonal or digestive problems: These or other issues of inadequate nutrient absorption can sometimes keep children from gaining weight as they grow.

Q: Are there daily situations that might keep my child from maintaining a healthy diet?

A: When a pediatrician finds that your child is underweight, they may schedule a one-day consultation with a dietitian. The goal is to rule out poor food intake as the issue, and if so, the dietitian can offer recommendations.

You’ll usually be asked to keep a food record that examines your child’s eating habits. The dietitian will also look at other possibilities:

  • For daycare-aged kids: Some centers are better than others at documenting that your child is consuming enough calories during the day.
  • For older kids: Sports and other school activities often create a hectic schedule where kids just don’t eat enough. If active, they may also have a higher caloric need but may not be making up for it.
  • For children who stay with multiple households: When parents are separated or divorced, that could cause kids to miss meals without either parent communicating or knowing.

Q: What eating habits should children avoid?

A: There are some common trends that many parents should focus on preventing or avoiding to help their child gain weight properly.

  • “Grazing” or excessive snacking: This is one of the most common pitfalls. Families should set meal and snack times so that the child has time to get hungry before sitting down to a nutritionally balanced dinner. “Grazing” will fill the child up on foods with low energy density. They’ll actually get more calories if they wait for meals.
  • Use of electronics: Where to eat is just as important as what to eat. Healthy snacks are encouraged but children should eat them at the table — not mindlessly in front of the television, phone or computer screen.
  • Avoid fruit juices: Especially those with added sugar. Juices and other sugary beverages will fill kids up without providing them with any energy, fat or protein.
  • Protein powders: These aren’t recommended since even underweight kids still seem to get enough protein in their diet (and these powders don’t provide a balance of nutrients needed for weight gain).

Q: How can families help children gain weight in a healthy way?

A: Believe it or not, the goal is to incorporate more fats into the child’s diet — not just any fats like saturated fats from fried foods, but healthy fats like those from oils and nut butters. Here are some suggestions:

  • Add nut butters. For example, encourage kids who like raw fruits and vegetables to eat celery sticks or apple slices with peanut butter.
  • Sneak in healthy oils. It is also beneficial to sneak in some olive oil or other heart healthy oils by adding it to foods, which can help even the pickiest eaters.
  • Try oral supplements. Ask to speak with a registered dietitian about if an oral supplement is right for your child.

The overall goal is to instill sustainable, healthy eating habits. That’s why it’s important to meet with a dietitian who will also help monitor your child’s progress and offer tips and recipes.

Q: What if my family has special dietary needs or beliefs?

A: Dietitians work closely with parents and families to aid their understanding of why food intake is inadequate and make a plan that fits each families goals and beliefs.

“Dietitians focus on working one-on-one with families to help children gain weight in a way that is consistent with the family’s dietary preferences,” Hyland says. “They can work with all sorts of preferences and varieties of food, including organic foods, whole foods, vegan diets, or diets influenced by religious or cultural beliefs.”

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