Signs of Overfeeding and Underfeeding in Infants: How to Tell the Difference

"Is she eating enough?" and "is she eating too much?" are competing first-month worries that often coexist in the same parent. Both are reasonable concerns. The reassuring fact: babies have a much more sophisticated appetite regulation system than adults give them credit for, and the things that genuinely indicate intake is off are concrete — weight curves, wet nappies, growth — rather than the harder-to-interpret signals (fussiness, possits, gas) that parents tend to over-interpret.

This piece covers what the actual signs are, how to interpret them, and when to ask for help. The aim is to reduce the bandwidth that intake worry takes up in the early months, not to add to it.

The Healthbooq app lets you track feeds, nappies, and weights in one place — particularly useful for showing a health visitor a real pattern rather than a remembered one.

Babies Are Better at This Than Adults

Healthy newborns come pre-loaded with appetite regulation. They feed when hungry, stop when full, and show satiety with relaxed limbs, drowsy attention, and release of the breast or bottle. This system is observable from the first 24 hours of life and is well-documented across feeding research traditions.

The classic body of work on this is Leann Birch's research at Penn State (1980s–2010s) on the development of food regulation. Birch showed repeatedly that overriding infant satiety — offering more after the baby signals "done" — disrupts long-term appetite regulation and is associated with greater obesity risk later in childhood. Amy Brown at Swansea has extended this to UK feeding practice (responsive vs schedule, bottle vs breast) and shown similar patterns.

The implication for parents: trust the baby unless something concrete indicates a problem. The list of "concrete" things is short:

• Weight curve
• Wet nappies
• Stool pattern
• Behaviour pattern over the day, not the moment

These are reliable. Possits, fussiness, gas, frequency of wanting to feed — these are not, individually, reliable signs of either over- or underfeeding.

What "Normal" Feeding Looks Like in the First Weeks

Day 1–3: small, frequent feeds, often every 1–3 hours. Colostrum (the early breast milk) comes in small volumes (5–15 ml per feed); newborns aren't designed to take large volumes immediately. Formula-fed babies in this window typically take 30–60 ml per feed.

Day 3–7: breast milk volume increases, formula intake gradually increases to ~60–90 ml per feed. Wet nappies should reach at least 6 per 24 hours by day 5–6. Yellow stools begin to appear (replacing meconium).

Week 1–4: feeds settle into a more recognisable pattern (8–12 feeds in 24 hours typically), with cluster feeding episodes — usually evenings — being normal. Formula intake by 1 month: typically 90–150 ml per feed, around 750–900 ml total per day.

By 6 weeks: most babies have regained birth weight (should have done so by day 14), are following their birth centile, having ~8 feeds per 24 hours, and producing 6+ wet nappies and at least one substantial stool daily.

Throughout the first year: intake gradually increases by volume but not by total of body weight — older babies and weaning babies become more efficient feeders. Total daily milk intake at 6 months is around 800–1,000 ml; this drops as solids increase and is around 500–700 ml by 12 months.

Why Overfeeding Is Mostly a Bottle Problem

Direct breastfeeding makes overfeeding genuinely difficult. The baby controls flow (by sucking, pausing, or releasing), the milk doesn't continue to flow when they pause, and breast milk fat content rises across a feed (the "hindmilk" effect) signalling fullness. Overfed breastfed babies do exist but are uncommon and usually have an underlying issue (overactive let-down combined with constant comfort feeding, for example).

Bottle feeding — whether formula or expressed breast milk — changes the dynamics. Gravity drives a more or less continuous flow. Pausing requires the baby to actively stop sucking and disengage from the teat. Visual cues — a half-finished bottle, the parent's awareness of how much was prepared — pull toward "finishing" rather than "responding to baby." All of this can override the baby's natural pacing.

The fix is paced bottle feeding, the technique that mirrors breastfeeding rhythm:

• Slow-flow teat (newborn flow even past the newborn stage if pace is too fast)
• Hold the bottle horizontal, not tipped down — the baby has to actively suck to draw milk out
• Sit the baby upright, not lying flat, head supported
• Pause every 20–30 seconds. Tip the bottle down slightly so milk drains away from the teat. Let the baby breathe and decide whether to continue.
• Switch sides halfway through, like changing breasts
• Watch satiety cues — turning away, slowing sucks, relaxed hands, milk dribbling out — and stop. Don't encourage finishing.
• Allow 20 minutes for a feed if possible; bottle feeds finished in 5 minutes are likely too fast and will lead to overfeeding.

This technique is the single biggest intervention against bottle-driven overfeeding and is now standard advice from infant feeding teams in UK NHS Trusts.

What Genuine Overfeeding Looks Like

The reliable indicator: weight gain that consistently runs above the baby's birth centile trajectory on the WHO/UK growth chart. Centile crossing upward of two centile lines (e.g. from the 50th to the 91st) over weeks is meaningful and warrants a feeding review with a health visitor or GP.

Ancillary signs that may suggest overfeeding (in conjunction with weight, not alone):

• Frequent large possits — more than a small posset (less than a tablespoon) after most feeds
• Visible abdominal distension that doesn't settle
• Discomfort after feeds (drawing legs up, prolonged crying)
• Wanting to feed very frequently and taking large volumes each time

Things that don't indicate overfeeding:

• Hiccups
• Small possets after feeds
• Gas
• Wanting to feed often (frequent feeding is normal, especially in cluster periods)
• Taking a full bottle quickly (a hungry baby with an over-fast teat will do this; check teat flow first)

The weight curve is the diagnostic. Don't restrict feeds based on possits or fussiness alone.

What Genuine Underfeeding Looks Like

The early markers, in roughly order of usefulness:

• More than 10% loss from birth weight in the first week (a weight loss check is part of the routine day 5 visit)
• Failure to regain birth weight by day 14
• Subsequent failure to follow the birth centile trajectory
• Centile crossing downward of two centile lines

• Fewer than 6 wet nappies per 24 hours from day 5–6
• Strongly concentrated, dark yellow urine
• A nappy that feels light when removed (a wet disposable nappy is heavier than parents tend to expect — practise feeling the difference)

• Persistent meconium (black/dark green) past day 3–4
• Few or no stools after day 5 in a young baby
• Persistent dry, crumbly stools

• Frantic feeding cues after a feed ends, repeatedly
• No periods of contentment between feeds
• Lethargy, hard to wake for feeds, very weak suck
• Increasingly reluctant to wake for feeds in a baby who has lost weight (warning sign — get reviewed urgently)

• Sunken fontanelle
• Dry mouth, no tears
• Loose folds of skin where there was previously roundness
• Cool extremities

If multiple signs above are present, especially weight loss + low wet nappies, contact your midwife (in the first 28 days), health visitor, or GP same day. Severe dehydration in a young baby is a 999 / A&E situation.

What's Normal That Looks Like a Problem

Hiccups. Common, harmless, no intervention needed.

Small possets after feeds. A teaspoon to a tablespoon of milk reappearing after a feed is normal. The baby gains weight; gravity does its thing.

Frequent feeding. Newborns can feed 10–14 times in 24 hours. Cluster feeding (multiple short feeds in close succession, especially evenings) is normal in the first 6–8 weeks.

Crying after feeds. Could be wind, overstimulation, tiredness, normal evening fussiness, reflux discomfort — not automatically hunger and not automatically overfeeding.

Variable feed volumes. Babies eat different amounts at different feeds, just as adults do. A 90 ml feed followed by a 150 ml feed is normal.

Growth spurts. Days of unusually frequent feeding around 2–3 weeks, 6 weeks, 3 months, 6 months are common. Resist the urge to "supplement" — the system is designed to ramp up production through the increased demand.

Possit while crying. Crying babies swallow air, which comes back up with stomach contents. Not a sign of overfeeding.

Reflux: When Possits Become a Problem

Some babies do have clinical gastroesophageal reflux (GOR) or, less commonly, gastroesophageal reflux disease (GORD) requiring intervention. Features that suggest GOR/GORD rather than benign possetting:

• Possets so frequent and large that nappies and clothes are repeatedly soaked
• Faltering growth despite adequate apparent intake
• Pain on feeding or after — arching, refusing the bottle/breast despite being hungry
• Recurrent chest infections from aspiration
• Distress out of keeping with normal newborn fussiness

Most physiological reflux improves on its own by 6–9 months as the lower oesophageal sphincter matures and the diet thickens with weaning. Position (upright after feeds for 20–30 minutes), smaller more frequent feeds, and paced bottle feeding all help. GP review for evaluation if features above are present; thickeners (Carobel, Gaviscon Infant), proton pump inhibitors (omeprazole), or specialist input may be needed.

The UK Weight Monitoring Schedule

Routine weight checks under the Healthy Child Programme:

• Birth
• Day 5 (midwife)
• Day 10–14 (midwife or health visitor; should be back to birth weight)
• 6–8 weeks (health visitor or GP review)
• 8–12 months (developmental review)
• 2 years (developmental review)

Additional weighing as needed if there are concerns. Most clinics will weigh weekly or fortnightly during a feeding concern; this should be on the same scales each time, with the baby naked or in a clean dry nappy, ideally at the same time of day.

The UK Personal Child Health Record (red book) plots weights on the WHO growth charts. Looking at the trend matters more than any single point.

When to Get Help

• Baby has lost more than 10% of birth weight or hasn't regained it by day 14
• Fewer than 4 wet nappies in 24 hours after day 5
• Lethargic baby, hard to rouse for feeds
• Sunken fontanelle, dry mouth, loose skin folds
• Persistent green vomiting (suggests obstruction; A&E)
• A breastfeeding mother in significant pain or with breast infection

• Centile crossing upward or downward by two lines
• Persistent feeding distress (pain, refusal, crying)
• Recurrent large possits
• Concerns about latch, supply, or feeding pattern (breastfeeding) — IBCLC or NHS infant feeding team
• Recurrent fussy feeding pattern that's wearing the family out

• NHS infant feeding teams (most Trusts have one)
• IBCLC (International Board Certified Lactation Consultant)
• Local breastfeeding peer support — La Leche League, NCT breastfeeding counsellors, BfN
• National Breastfeeding Helpline 0300 100 0212 (free, 9.30 am–9.30 pm daily)

What Helps Long-Term

The single most useful framing: trust the baby unless concrete signals say otherwise. Concrete signals are weight, wet nappies, stools, energy, and demeanour — not possits or fussiness.

In bottle feeding, the technique is paced feeding with slow-flow teat, horizontal bottle, frequent pauses, response to satiety. This technique alone prevents most bottle-driven overfeeding.

For weight monitoring, the trend matters more than the point. Variations between feeds, days, and weeks are normal. Two weeks of trend on the same scales tells you more than one weight on a busy clinic morning.

And for parents who feel unsure — the routine weight check is genuinely the right place to raise concerns. Health visitors are trained for this, and a worried parent who turns up at the baby clinic is exactly who the service is for.

Babies are born with the ability to regulate their own intake — what disrupts it is usually how the milk is delivered, not the baby. Overfeeding is rare in breastfed babies and meaningfully more common in bottle-fed ones, because gravity and a constant teat flow override the baby's pacing. The UK red-book weight checks (birth, day 5, day 10–14, then 6–8 weeks and at developmental reviews) are the reliable signal of whether intake is adequate. Wet nappies — at least 6 in 24 hours from day 5 onward — are the earliest practical home check. Possits, gas, and fussiness are not, on their own, signs of overfeeding. Centile crossing in either direction is the clinical signal, and should be discussed with a health visitor or GP rather than acted on unilaterally.