A child’s weight is one of the biggest reasons why families are referred to see a paediatric dietitian. In my last post, I discussed about overweight children, and today I will cover the opposite end of the spectrum – the underweight child. This is the first part of a three-part series where part 1 will focus specifically on slow growth in infants
We have all seen children who appear underweight and wondered what might be wrong. Is the child not eating? Are the parents not feeding them properly? It is easy to make judgments from the outside, but my experience working with families of underweight children tells a different story. Most of these families are just like any others and they want the best for their child.
Common reasons a child might be underweight:
- Underlying medical conditions – Conditions that increase metabolism, malabsorption, or cause frequent illness and reduced appetite.
- Severe fussy eating – Some children eat a highly limited range of foods where parents can list the exact number of foods their child will eat, e.g., “My child only eats 12 foods and nothing else.”
- Complex social issues – such as domestic violence, food insecurity, parental mental health challenges, child abuse, or neglect. These cases require careful navigation and multidisciplinary support is essential.
- Dietary restrictions due to medical conditions – Children placed on restricted diets for various reasons such as to diagnosed food allergies or intolerances, coeliac disease, low FODMAP diet or inborn errors of metabolism
- Nutritionally incomplete diets – Lack of parental knowledge about balanced nutrition, such as improperly planned vegan diets or misinformed parents around fad diets to improve behaviour, sleep, or mood.
- Eating disorders – Emerging in children as young as pre-teens, impacting their ability to maintain adequate nutrition.
- Unknown causes – Despite thorough assessments, some cases remain unexplained.
Effects of slow growth at different life stages:
- Infants (0-12 months)
- Toddlers (1-3 years old)
- Preschoolers (3-5 years old)
- Primary school aged (5-11 years old)
- Pre-teens and teenagers (12-18 years old)
Infants (0-12 months)
Infants experiencing slowed growth should be assessed by a health professional as soon as possible. Infants should not lose any weight, as they are going through a period of rapid growth.
Did you know? A baby nearly triples their birth weight in the first year of life! There are no other life stage that will experience such rapid growth.
A common misconception among parents are the fact that their baby is still putting on weight, so what is the concern? As mentioned earlier, an infant is expected to grow rapidly and while a baby may be gaining weight, they might not be gaining enough for their age. A health professional will plot your baby’s weight, length, and head circumference over time to assess their growth trajectory. If an infant’s growth slows significantly, urgent intervention is required to prevent faltering growth. If left unaddressed, a baby’s length and head circumference may also drop in percentiles over time, a condition known as stunting.
What happens if an infant has poor growth?
If there is no medical explanation for slow growth, a referral to a paediatric dietitian is typically the next step. Dietitians conduct a thorough assessment of the baby’s nutritional intake and output. Given that milk remains the primary source of nutrition for infants, dietitians will ask questions such as:
- How often and how much does the baby drink?
- How is formula or expressed breastmilk prepared?
- For babies around 4 months of age: Has the baby started solids? If so, what foods are being offered versus what is actually eaten? How much food is eaten? How are foods prepared? How often are foods offered through the day?
A less expected but equally important part of the assessment involves monitoring the baby’s nappy output. Parents can expect questions around:
- How many wet nappies per day?
- How many bowel movements?
- What is the colour and consistency of the baby’s stools?
These details help identify possible malabsorption issues, hydration and nutrition status, and potential medical conditions such as food allergies or intolerances. While minor regurgitation is normal in infants, severe reflux may prevent adequate milk intake, affecting growth.
What to do with infant with poor growth
If a medical issue is identified, addressing it is the first priority. In cases where no obvious cause is found, infants under six months of age may require a specialised and tailored recipe devised by a paediatric dietitian to concentrate milk feeds.
A very small number of babies struggle with bottle feeding. This may require a referral to a paediatric speech pathologist with expertise in infant feeding. Speech pathologists can observe feeding sessions and make recommendations on:
- Optimal feeding positions
- Adjusting bottle flow rates and teat sizes to help with swallowing of milk
- Techniques to support more effective bottle feeding
- How to read baby’s cues around bottle feeding
Force feeding in infants who are not on solids (usually <6 months old)
Force-feeding may provide short-term gains to get babies to drink more milk. However, I find families who force feed their babies at a very young age may lead to long term feeding issues such as:
- Vomiting after feeds
- Bottle refusal
- Feeding aversion (resisting anything near their mouth)
- Babies learning to clamp their mouth shut and refuse feeding of food or milk
- Babies learning to spit food or milk out
- Increased stress at every bottle feeds and mealtime
Should a baby develop severe feeding aversions whereby they completely refuse bottles, they may require a nasogastric (NG) tube to maintain adequate nutrition intake. A paediatrician will assess the pros and cons of NG feeding, the expected duration of NG feeds, and long-term feeding plans for the child.
Cue based feeding
Responsive feeding where you follow your baby’s hunger and satiety cues will help create positive feeding experiences and reduces the need for NG feeding. Since babies cannot communicate verbally, recognising their body language is essential. The Raising Children Network has some excellent videos on how to read your baby cues.
Some infants refuse bottles but may accept milk via alternative feeding methods, including:
- Open cups
- Sippy cups
- Straw cups
- Syringes
- Spoons
This is particularly useful for babies who associate bottles with negative feeding experiences and has developed bottle aversions.
This is a photo of me needing to feed my son a bottle on his first day of childcare after refusing all his bottles through the day. My youngest son was a difficult feeder and would only take a bottle from me or my husband. I believe this was because I understood his cues better than others, and I respected his needs and followed his cues on when he was ready for a bottle and when he needed a break.
Older infants (usually >6 months old)
Once a baby shows signs of readiness for solids (see my previous post on signs of readiness), maintaining a positive mealtime environment is crucial. In some cases, doctors may recommend introducing solids slightly earlier (from 4 months old) to avoid the need for NG feeding. Underweight infants starting solids should be offered high-energy, high protein foods to promote catch up growth, alongside standard solids introduction guidelines.
A paediatric dietitian can provide ongoing support with both bottle feeding and solid feeding strategies.
To summarise, the key to management of infants with poor growth include:
- Identify and address any underlying medical conditions
- Conduct a detailed nutritional intake assessment
- Assess nappy output (urine, stool frequency, and consistency)
- Evaluate feeding environment and mealtime interactions
- Monitor growth regularly (every one to two weeks initially and gradually reducing the frequency of follow ups) and adjust recommendations accordingly
In my next blog post, I will explore slow growth in toddlers and preschoolers in greater detail.
