Breastfeeding Nutrition Guide: What to Eat While Nursing

Breast milk is nutritionally complete for infants under six months and remains nutritionally important through the first year and beyond. The body prioritises breast milk production at the expense of the mother's own nutritional reserves: if dietary calcium is insufficient, calcium is drawn from the mother's bones; if dietary iodine is low, iodine is extracted from the mother's thyroid. This protective mechanism for the infant means the breastfeeding mother's nutrition affects her own health more directly than her breast milk composition in most micronutrient cases, but several specific nutrients, particularly omega-3 fatty acids and vitamin D, are passed through in quantities that directly reflect maternal dietary intake. Eating well while breastfeeding is primarily about protecting the mother's health, and secondarily about optimising specific nutrients in breast milk.

Calorie and Macronutrient Needs During Lactation

Producing breast milk requires approximately 500 kilocalories per day above pre-pregnancy maintenance requirements. The NHS and ACOG both recommend that breastfeeding mothers do not restrict calories significantly during the first six months of exclusive breastfeeding; the body draws from fat stores for some of the energy, but dietary restriction below 1,800 to 2,000 kilocalories per day is associated with reduced milk supply in some women.

• Protein: The UK recommended intake increases from 45g/day pre-pregnancy to 51g/day during lactation. In practice, most women eating a balanced diet meet this through their normal food intake without specific planning.
• Fat: The fatty acid composition of breast milk reflects maternal dietary fat intake. A diet higher in omega-3 fatty acids (from oily fish, flaxseed, walnuts) produces breast milk with a more favourable DHA:omega-6 ratio, which is associated with better infant neurodevelopmental outcomes. Saturated fat in the maternal diet does not significantly affect breast milk saturated fat content (the body regulates this independently).
• Carbohydrates: No specific requirement change; adequate carbohydrate supports energy levels and milk production.

Critical Micronutrients During Breastfeeding

Iodine

Iodine is one of the most critical and most commonly deficient nutrients during lactation in the UK. Breast milk iodine concentration directly reflects maternal iodine intake. Infant iodine deficiency affects thyroid hormone production and is associated with impaired cognitive development; the consequences of severe deficiency are irreversible. The UK recommended intake increases from 140mcg/day pre-pregnancy to 200mcg/day during breastfeeding. The main dietary sources are dairy products (a 240ml glass of cow's milk provides 40 to 60mcg), white fish, and eggs. Seaweed (particularly nori and wakame) is a concentrated source but is variable and potentially excessive. The UK Scientific Advisory Committee on Nutrition (SACN) recommends that women who eat little or no dairy consider an iodine supplement during pregnancy and breastfeeding.

Vitamin D

Vitamin D concentration in breast milk is low unless the mother has sufficient vitamin D status: breast milk from vitamin D-deficient mothers contains 5 to 80 IU/L, which is insufficient for the exclusively breastfed infant's requirements (400 IU/day). The NHS recommends that all breastfed babies receive vitamin D drops (8.5 to 10mcg/day) from birth, regardless of maternal vitamin D status. Breastfeeding mothers themselves should supplement with 10mcg (400 IU) vitamin D daily, increasing to 25mcg (1,000 IU) in winter months or for those with limited sun exposure.

Calcium

Approximately 200 to 300mg of calcium is transferred into breast milk per day. The body compensates partly by increasing intestinal calcium absorption during lactation (from approximately 30% to up to 60% efficiency) and partly by mobilising calcium from bone. Bone mineral density typically decreases by 3% to 5% during lactation and fully recovers after weaning in most women. The UK recommended intake during breastfeeding is 1,250mg/day (higher than the 700mg/day for non-pregnant adults). Three to four servings of dairy or calcium-fortified alternatives typically meet this requirement.

Choline

Choline is essential for infant brain development, particularly the hippocampus (memory) and the cholinergic system. Breast milk is a rich source of choline, but choline concentrations reflect maternal intake. Eggs (147mg per large egg) and meat are the most concentrated dietary sources; dairy contributes moderate amounts (35mg per 240ml milk). The UK has not established a specific reference nutrient intake for choline, but the Institute of Medicine (US) recommends 550mg/day for breastfeeding women.

Foods to Limit or Avoid While Breastfeeding

Caffeine

Caffeine passes into breast milk at approximately 1% of the mother's blood caffeine concentration. At moderate consumption (one to two cups of coffee per day), the amount transferred is small and unlikely to affect most infants. The NHS recommends limiting caffeine to 200mg per day while breastfeeding (the same limit as during pregnancy). Newborns and premature infants metabolise caffeine very slowly; some mothers of newborns who are sensitive to stimulants choose to eliminate caffeine temporarily.

Alcohol

Alcohol passes into breast milk at concentrations approximately equal to blood alcohol concentration. The safest approach is to avoid alcohol entirely during breastfeeding, or to wait 2 hours per unit of alcohol consumed before nursing (the time required for the body to clear one unit from the blood). Expressing and discarding milk ("pumping and dumping") after drinking does not speed alcohol clearance from the blood and therefore does not change when it is safe to breastfeed again.

High-Mercury Fish

The same mercury restrictions that apply during pregnancy (avoiding shark, swordfish, marlin, and raw tuna; limiting fresh tuna to two servings per week) apply during breastfeeding. Mercury passes into breast milk and accumulates in infant tissue. Tinned tuna has lower mercury than fresh tuna and is not restricted by the NHS during breastfeeding.

Diet and Milk Supply

The most important determinant of milk supply is breast stimulation through nursing or pumping frequency: the more the breast is drained, the more milk is produced (supply and demand). No specific food reliably increases milk supply in women with normal lactation physiology. Galactagogues (foods traditionally believed to increase milk supply, including fenugreek, oatmeal, brewer's yeast, and fennel) have limited clinical evidence; a 2018 Cochrane review found insufficient high-quality evidence to support any specific galactagogue for increasing milk volume. Adequate hydration is important: dehydration reduces milk production, and breastfeeding increases fluid requirements by approximately 500ml per day.

Related: Baby Formula Guide: Types, Ingredients, and When to Use It | Dairy and Bone Health: What the Research Shows