Poor weight gain in infants and young children

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Read about poor weight gain, which is when a child does not grow or gain weight as expected. Learn about the causes and management of poor weight gain in infants and young children.

Key points

  • Failure to thrive is an older term used to describe a child’s weight gain or growth that is slower than expected.
  • The best way to diagnose poor weight gain is to carefully measure and plot a baby’s weight, height, and head circumference over time and then compare the measurements to standardized growth charts.
  • There are many reasons that growth and weight gain may be slower than expected in infants and young children, and treatment will depend on the cause.

Failure to thrive is an old term used to describe a child’s weight gain that is slower than expected. A more commonly used term is poor weight gain. Not all infants or children who are small have poor weight gain. A premature infant, for example, who is small at birth but gains weight steadily does not have poor weight gain. On the other hand, a previously healthy child who stops gaining weight or gains slower than expected, may be at risk for undernutrition.

It is the rate of weight gain in comparison to expected growth patterns for infants or children of similar ages that is key to diagnosing a problem with poor weight gain. A child’s height is related to their weight gain and your health care team will also monitor your child’s growth. Children with certain genetic conditions, for example, Down Syndrome, will gain weight at different speeds than other children and can be followed according to their own expected growth patterns.


Causes of poor weight gain

Most newborns lose weight in the first few days after birth. Typically, newborns regain the weight that was lost by 2 weeks of age and are then expected to gain weight steadily. How fast a child is expected to gain weight changes as they move from being infants to toddlers, and into the school years. The pattern, however, is similar in most children and can be predicted using a growth chart. Most causes of poor weight gain fall into one of these four categories with some overlap. Many conditions affect growth in various ways and may fit under more than one of these categories.

Insufficient nutrient intake

Infants and children need calories and nutrients to grow. Conditions that lead to reduced intake can cause slow weight gain. Some examples include:

  • Babies who are breastfed need to feed regularly, latch well and transfer enough breastmilk effectively to gain weight. Problems with any step can lead to poor weight gain.
  • Formula-fed infants need to have formula prepared according to the instructions on the can. Formula that is too dilute will not provide adequate calories for growth.
  • Illnesses, such as viral infections, may lead to reduced intake of breastmilk or formula while infants are sick. Sometimes children with breathing difficulties, such as bronchiolitis, may be breathing too quickly to feed well. Poor weight gain from these causes should be short lived.
  • Infants with gastroesophageal reflux disease may vomit significant volumes of each feed and may not gain weight well.
  • Infants who have cleft lift and palate, swallowing difficulties or congenital heart disease may tire out when trying to feed and may not feed adequate volumes to gain weight.
  • Infant and young children who experience discomfort while eating may develop an aversion to feeding and be unable to feed adequate volumes to gain weight.
  • Infants or children who lack reliable and consistent access to food due to financial limits, being underhoused, or if they are living in areas of conflict may have poor weight gain.

Increased nutritional needs

Some infants and children have underlying conditions that require more calories and nutrition than other children to gain weight. Some examples include:

  • Infants with some congenital heart conditions breathe quickly and have hearts that need to work harder. This extra work requires more calories. They may also tire out while feeding and have difficulty drinking the amounts that are required.
  • Chronic illnesses including prolonged infections and conditions associated with inflammation are associated with increased caloric needs.
  • Infants and young children who have had a prolonged illness that has prevented them from gaining weight often need extra calories for a period of time for catch-up growth.

Problems with absorption of nutrients

Infants and young children with inflammation in their gut (intestines) may not be able to digest and absorb the nutrients in their milk or food and won’t gain weight as expected. Some examples include:

  • Infants with cows’ milk protein intolerance can develop inflammation in their intestines and bloody or mucousy stools when exposed to the protein in cow’s milk.
  • Infants and young children with cystic fibrosis are missing digestive enzymes that help them absorb fat.
  • Some infections in the gut, including parasites, bacteria and viruses, can cause diarrhea and temporary inflammation that prevents nutrients from being absorbed.
  • Children with inflammatory bowel disease experience inflammation in different parts of the gut. They may also have increased nutritional needs, increased losses (through diarrhea and vomiting) and reduced appetite, all of which can also affect weight gain.

Problems with utilization of nutrients

Once food is digested, each cell in the body needs to be able to use nutrients for energy. Some conditions affect the way some nutrients are used and often are associated with poor weight gain (and sometimes weight loss). Some examples include:

  • Infants who are born with rare inherited conditions called inborn errors of metabolism lack specific enzymes that allow their cells to use certain nutrients such as sugar, fat and protein.
  • Young children who have developed diabetes lack insulin, which is needed to use sugar are energy.

Diagnosing problems with weight gain

Infants and young children typically gain weight and grow following expected patterns. Part of well-baby and child check-ups focuses on regularly weighing and measuring your child’s length and head circumference and plotting those measurements on standardized World health Organization (WHO) growth charts. Growth charts are essentially graphs of weight gain and growth in infants and children and have been used to monitor health and well-being in children for over 200 years. Your child’s health-care provider can compare your child’s weight gain and growth over time on their growth chart to ensure that their pattern of growth is following an expected rate.

If the rate of weight gain slows, health-care providers will do several things to figure out why. This may include:

  • a detailed history
  • a physical examination
  • review of your child’s growth charts
  • a detailed feeding history
  • observation of feeding
  • nutritional screening measurements and/or blood tests
  • understanding the feeding environment and how it might impact eating
  • understanding a caregiver’s financial needs to ensure proper supports can be put in place


The first step in managing poor weight gain is to identify the underlying cause. Some children first need tests to determine the cause of their poor weight gain or to evaluate their nutritional status before a treatment plan can be established. Other children need a change in their diet or in their eating routine. Some families need assistance accessing healthy food due to cost. Each child with poor weight gain benefits from an individualized approach to understand their specific nutritional needs. Your child’s health-care provider may enlist the help of feeding specialists, including a paediatrician, a lactation consultant, an occupation therapist, and/or a dietitian. Every young child with poor weight gain needs regular growth measurements to monitor their progress.

Helping your child

Understanding why your child is not gaining weight as expected is key to establishing a plan to help them grow. Keeping track of your child’s intake and following the instructions that your child's health-care team provides is helpful. It is also important that you and your child enjoy the bond that feeding creates and that feeding remains a positive experience for both you and your child. Ask your child’s health-care team for suggestions to make feeding as relaxing and as effective as it can be.

Last updated: April 2nd 2024