What Not to Eat When Breastfeeding: The Evidence-Based Australian Guide

Mercury-Rich Fish: The One Non-Negotiable

This is the clearest and most universally supported dietary restriction during breastfeeding. Methylmercury accumulates in certain large, predatory fish, passes into breast milk, and can affect a developing infant’s nervous system. Unlike most dietary concerns, the evidence here is strong and the guidance is consistent.

Fish to avoid or strictly limit while breastfeeding:

• Shark (flake)
• Swordfish
• King mackerel
• Tilefish
• Orange roughy
• Bigeye tuna (limit to one serve per fortnight)

Fish that are safe and encouraged (2–3 serves per week):

• Salmon — also an excellent source of DHA for infant brain development
• Sardines
• Light canned tuna (not albacore or bigeye)
• Prawns and shrimp
• Tilapia
• Catfish

Fish is a valuable source of omega-3 fatty acids, protein, and iodine — all important during breastfeeding. The goal is not to avoid fish but to choose the right types.

Caffeine: Limit, Don’t Eliminate

Caffeine does pass into breast milk in small amounts, and very high intake can cause infant irritability and disrupted sleep. However, moderate caffeine consumption is considered safe by Australian and international health guidelines.

The recommended limit is 200–300 mg of caffeine per day, which is approximately:

• 2–3 cups of brewed coffee
• 3–4 cups of tea
• 5–6 cans of cola (though cola is not recommended as a daily drink for other reasons)

Caffeine peaks in breast milk at approximately 60–120 minutes after consumption. If you’re concerned about your baby’s response, timing feeds to occur before consuming caffeine rather than just after is a practical strategy. Caffeine sensitivity varies between infants — some show no response at all; others are more sensitive, particularly in the newborn period when caffeine clearance is slower.

Note that caffeine is also present in green tea, black tea, matcha, chai, energy drinks, and some medications. Herbal teas are generally caffeine-free — though their own ingredient safety varies.

For a complete guide to which herbal teas are safe — and which to avoid — during breastfeeding, see the article on herbal teas for breastfeeding.

Alcohol: Timing Is the Key Variable

Alcohol passes readily into breast milk, reaching approximately the same concentration as in the mother’s blood. The safest approach is to avoid alcohol entirely while breastfeeding, particularly in the newborn period. However, occasional, moderate consumption — managed with appropriate timing — is not considered to cause harm by most health authorities.

The key guideline: alcohol clears from breast milk at approximately the same rate it clears from the bloodstream — roughly one standard drink per two hours for an average adult woman. Pumping and discarding milk (pump and dump) does not speed this process, as alcohol clears through metabolism, not milk removal.

One standard Australian drink = 10g of alcohol = 375mL mid-strength beer, 150mL wine, or 30mL spirits.

If you choose to drink occasionally, feeding or pumping immediately before drinking and then waiting at least two hours per standard drink before the next feed is the evidence-based approach.

High-Dose Herbal Supplements: Caution Required

While many herbal teas at normal food and tea quantities are safe during breastfeeding, concentrated herbal supplements are a different consideration. Several herbs commonly found in supplements can reduce milk supply (including sage, peppermint in high doses, and parsley in large quantities), and others have not been adequately studied for safety in lactation.

The general principle: whole food and tea-quantity amounts of culinary herbs are usually safe. High-dose supplements of the same herbs may not be. Always check with a healthcare provider or pharmacist before starting any new herbal supplement while breastfeeding.

Highly Processed Foods: Not Forbidden, But Worth Limiting

There is no specific food in this category that is directly harmful to breastfed babies. However, heavily processed foods high in added sugars, refined fats, and artificial additives contribute to blood sugar instability, poor energy management, and nutritional gaps in the maternal diet. During breastfeeding — when caloric and nutritional demands are elevated — the opportunity cost of choosing nutritionally empty foods is higher than usual.

This is less about restriction and more about crowding out. The energy that goes into a processed snack is energy that could have gone into whole foods supporting recovery, supply, and sustained energy.

If you follow a particular way of eating — vegan, dairy-free, gluten-free, or low-carb — breastfeeding is manageable on all of these diets with appropriate planning. The key is understanding which nutrients require extra attention.

Dairy-Free Breastfeeding

Whether you’re avoiding dairy because your baby shows signs of cow’s milk protein sensitivity, or because of your own dietary preferences, a dairy-free breastfeeding diet is entirely achievable. The primary nutrient to monitor is calcium.

Breastfeeding increases calcium requirements significantly. Without dairy, reliable sources include:

• Fortified plant milks (oat, almond, soy) — choose calcium-fortified varieties with at least 120mg per 100mL
• Tahini and sesame seeds
• Canned sardines and salmon with bones
• Tofu set with calcium sulphate
• Almonds
• Leafy greens including kale, bok choy, and broccoli (note: spinach is high in oxalates which reduce calcium absorption)

A calcium supplement may be appropriate if dairy is fully excluded and dietary sources are inconsistent. Discuss with your healthcare provider or an Accredited Practising Dietitian.

For mothers managing a baby with suspected cow’s milk protein allergy or eczema triggered by dairy, the article on whether breastfeeding helps or affects eczema covers the elimination diet decision in detail, including when and how to do a systematic trial.

Vegan Breastfeeding

A well-planned vegan diet can support healthy breastfeeding. The nutrients that require active attention are:

• Vitamin B12: Found almost exclusively in animal products. Deficiency in breastfed infants of B12-deficient mothers can cause serious neurological harm. Supplementation is essential for vegan breastfeeding mothers — this is not optional.
• DHA (omega-3): Important for infant brain development. Plant sources provide ALA, which converts poorly to DHA. Algae-derived DHA supplements are the recommended source for vegan mothers.
• Iodine: Important for infant thyroid function and brain development. Plant foods are generally low in iodine except seaweed (which varies widely in iodine content and should be used cautiously). A supplement is usually recommended.
• Iron: Plant-source iron (non-haem) is less bioavailable than animal-source iron. Consuming vitamin C-rich foods alongside iron-rich plant foods improves absorption. Iron status should be monitored.
• Vitamin D: Not reliably obtained from plant foods or fortified sources alone. Sunlight exposure and/or supplementation is the standard recommendation for most Australians, including vegan mothers.
• Zinc: Plant sources include legumes, seeds, and wholegrains, though absorption is lower than from animal foods. Varied intake usually meets needs.

The CDC specifically notes that healthcare providers should work with vegan and vegetarian breastfeeding mothers to determine individual supplementation needs. A consultation with an Accredited Practising Dietitian (APD) is a worthwhile investment.

Low-Carb or Keto While Breastfeeding

A strict ketogenic diet during breastfeeding requires caution. The main concerns are:

• Caloric adequacy: Breastfeeding requires an additional 330–400 calories per day above pre-pregnancy needs. Strict carbohydrate restriction can make adequate caloric intake harder to achieve and may compromise supply.
• Ketosis and breast milk: Mild ketosis is unlikely to affect milk composition significantly, but severe or prolonged ketosis has not been well studied in lactating mothers. Some case reports suggest a risk of ketoacidosis in breastfeeding mothers following very low carbohydrate diets, though this is rare.
• Electrolyte losses: Low-carb diets increase urinary excretion of sodium, potassium, and magnesium. Combined with the electrolyte demands of breastfeeding, this increases the risk of depletion.

A moderate low-carbohydrate approach — rather than strict keto — is a more practical and lower-risk strategy during breastfeeding. Prioritising complex carbohydrates (oats, legumes, sweet potato, wholegrains) alongside adequate protein and fat supports both supply and energy without the risks associated with extreme restriction.

Gluten-Free Breastfeeding

For mothers with coeliac disease or gluten intolerance, a gluten-free diet is safe and appropriate during breastfeeding. Gluten proteins do not transfer into breast milk, so there is no evidence that a mother’s gluten intake affects a breastfed baby’s coeliac risk or tolerance.

The nutritional consideration for gluten-free mothers is ensuring adequate B vitamins (particularly B1, B2, B3, and folate), iron, and fibre, which are often lower in processed gluten-free products. Choosing naturally gluten-free whole foods — oats (certified gluten-free), rice, quinoa, legumes, and root vegetables — rather than relying on packaged gluten-free alternatives is the better nutritional approach.

If your breastfed baby consistently shows symptoms — unsettled behaviour, eczema flares, mucusy or bloody stools, or significant digestive distress — after you eat a particular food, a supervised elimination trial may be appropriate. The key word is supervised.

An evidence-based elimination approach:

1. Identify the specific food(s) suspected — based on consistent timing of symptoms after maternal consumption, not general fussiness or colic
2. Eliminate fully for two to four weeks — reading ingredient labels carefully, as common allergens like dairy appear in many products under various names
3. Monitor symptoms objectively — keeping a simple food and symptom diary helps identify genuine patterns versus coincidental changes
4. Reintroduce — if symptoms resolve, cautious reintroduction of the eliminated food confirms whether it was the cause
5. Seek professional guidance — particularly if eliminating a major food group like dairy, as nutritional replacement planning is important

The most commonly implicated foods in breastfed infant reactions are cow’s milk protein, soy, eggs, wheat, peanuts, and tree nuts. Cow’s milk protein is by far the most common, affecting an estimated 0.5–2% of breastfed infants.

For mothers managing eczema in a breastfed baby, the guide on choosing between breastfeeding and formula for eczema babies covers the specific decision framework around dairy elimination versus formula change in detail.

The most useful dietary focus during breastfeeding is not a list of things to avoid — it’s a framework for eating enough of the right things.

• Eat enough calories: Breastfeeding requires 330–400 extra calories per day. Undereating is more likely to affect supply than anything on the “avoid” list.
• Prioritise nutrient density: Protein, iron, calcium, iodine, vitamin D, omega-3s, and B vitamins all have elevated requirements during breastfeeding. Varied whole foods cover most of these; targeted supplementation fills gaps.
• Stay hydrated: Breast milk is approximately 87–90% water. Drink to thirst, and more during hot weather or physical activity.
• Eat diverse flavours: Breast milk takes on the flavours of the maternal diet. Varied eating during breastfeeding may support your baby’s willingness to accept diverse foods at solids introduction.

For the full picture of what to eat to support milk supply and breastfeeding nutrition, the article on foods that may increase breast milk supply covers the positive nutritional framework in detail.

For evidence on specific foods and galactagogue ingredients, the article on do lactation cookies work reviews the research on oats, fenugreek, and fennel honestly.

• Unnecessary restriction based on myths: Eliminating foods like broccoli, spicy food, or citrus without specific evidence of a reaction in your baby adds dietary stress without nutritional benefit.
• Eliminating dairy without proper nutritional replacement: If dairy is removed from the diet, calcium and other nutrients need to be replaced from other sources. Elimination without replacement creates gaps.
• Restricting calories to lose weight: The early postpartum period is not the right time for caloric restriction. Supply, energy, and nutritional recovery all depend on adequate intake.
• Following cultural rules rather than evidence: Every culture has lists of foods breastfeeding mothers should avoid. Many of these contradict each other internationally. Evidence-based guidelines, not cultural convention, should guide your choices.

Starting a strict elimination diet without professional support: If multiple foods are suspected, working with an Accredited Practising Dietitian ensures the process is systematic, nutritionally adequate, and reaches a clear conclusion.

For the complete framework on breastfeeding nutrition — including what to prioritise, how much to eat, and evidence on specific foods — return to the Breastfeeding Nutrition & Milk Supply: Evidence-Based Guide for Australian Mothers.

If you’re looking for convenient, whole-food breastfeeding support that works with any dietary pattern — including dairy-free and vegan options — the Nella Vosk lactation cookie range is formulated without dairy, eggs, nuts, and brewer’s yeast, making it accessible to mothers managing food sensitivities or following special diets.

The breastfeeding tea range is caffeine-free, vegan, and formulated with herbs that have a well-regarded safety profile in lactation.

→ Also in this cluster:

→ Foods to increase breast milk supply: what the evidence says

→ Do lactation cookies work? What the evidence actually says about galactagogues