Nobody Told Me That Pregnancy Had Literally Borrowed from My Brain

This article is part of the Nella Vosk Postpartum Nutrition & Recovery: Complete Guide for New Mothers — your comprehensive resource on rebuilding your body and mind after birth.

This article is part of Nella Vosk’s Nobody Told Me series — a growing collection of posts about the information gap that too many mothers encounter after birth. Every article in this series starts from a moment a mother wasn’t told something she needed to know, and works back through the clinical truth behind it. You can find the full series at nellavosk.com.au/pages/nobody-told-me.

Nobody told me that pregnancy had literally borrowed from my brain.

I don’t mean this metaphorically. I mean it in the specific, documented, neurological sense: docosahexaenoic acid — DHA, the long-chain omega-3 fatty acid that is the primary structural fat of the human brain — is transferred from the mother to the developing baby preferentially during the third trimester and through breast milk. The mother’s brain gives up DHA to support the baby’s neurological development. And in Australia, where dietary intake of the oily fish that provide the richest food sources of DHA is among the lowest in the developed world, many mothers enter the postpartum period already meaningfully depleted in the nutrient their own brain most depends on.

The fog. The flatness. The sense that your thoughts are arriving more slowly than they used to. The irritability that sits underneath the tiredness and feels different from simple exhaustion. These are not just sleep deprivation. They are, in part, the neurological expression of a brain that has been running low on its primary structural fat for months.

This post explains what DHA is, why pregnancy and breastfeeding deplete it so significantly in Australian mothers specifically, what the evidence says about omega-3 and postpartum depression, how much you need, and the best food-first and supplementation approach to addressing the depletion.

What DHA Is and Why the Brain Depends on It

DHA (docosahexaenoic acid) is a long-chain omega-3 polyunsaturated fatty acid. It is the most abundant fatty acid in the human brain, comprising approximately 97% of the omega-3 fatty acids in brain tissue and around 25% of the total fat content of the brain overall. It is also the primary structural fat of the retina.

DHA is not synthesised efficiently by the human body from shorter-chain omega-3 precursors. The conversion of alpha-linolenic acid (ALA, found in flaxseed, chia seeds, and walnuts) to DHA through the body’s own conversion pathways is slow and limited — research suggests that less than 5% of dietary ALA is converted to DHA in most people, and this rate is further reduced by high dietary omega-6 intake, which is characteristic of most modern Western diets including Australia’s.

This means that the primary reliable source of DHA is preformed DHA from the diet — principally from oily fish, with smaller amounts from eggs (particularly from hens fed DHA-enriched feed) and from algal oil supplements (the original marine source from which fish accumulate their DHA).

DHA is critical for neuronal membrane fluidity, synaptic signalling, neurotransmitter regulation, inflammatory modulation in brain tissue, and the production of neuroprotective compounds called protectins and resolvins. When DHA is low, all of these processes are affected. The brain can continue to function — but not at the same level of efficiency, resilience, or mood stability.

How Pregnancy and Breastfeeding Deplete Maternal DHA

The human foetus has an extraordinarily high demand for DHA in the third trimester, when rapid brain development requires large quantities of the fatty acid for neuronal membrane construction. The placenta actively transports DHA from the maternal circulation to the foetus against a concentration gradient — meaning the foetus receives DHA preferentially, even when the mother’s own DHA levels are not optimal.

This preferential transfer means that the mother’s DHA stores are drawn down significantly over the course of pregnancy — and further drawn down by breastfeeding, as DHA appears in breast milk at concentrations that reflect maternal dietary intake, with the baby’s needs again prioritised over the mother’s own reserves.

Research on maternal DHA status before and after birth consistently finds significant reductions in maternal erythrocyte DHA concentrations postpartum. A landmark paper by Hornstra (2000) documented the progressive reduction in maternal DHA with each successive pregnancy in women who did not actively replenish between pregnancies — a finding that helps explain why the cognitive fog and mood vulnerability of the postpartum period is often more pronounced in second and third pregnancies than in first.

Australian mothers face a compounding challenge. Research on DHA status in Australian adults consistently finds lower levels than in populations with higher oily fish consumption. The Australian dietary pattern is lower in the oily fish that provide preformed DHA — salmon, sardines, mackerel — and higher in the omega-6 fatty acids from vegetable oils, processed foods, and grain-fed meat that compete with and reduce DHA utilisation. An Australian mother entering the postpartum period begins at a lower DHA baseline than her counterparts in Japan, Scandinavia, or Mediterranean countries — and has further to fall.

Omega 3 and Postpartum Depression: What the Research Shows

The relationship between omega-3 status and postpartum depression is one of the more consistently studied areas in perinatal nutrition research, and the picture that has emerged is meaningful — even if it is not yet definitive.

The epidemiological evidence

Cross-national comparisons have consistently found that countries with higher dietary fish consumption — Japan, Hong Kong, Norway, Portugal — have lower rates of postpartum depression than countries with lower fish consumption, including the United Kingdom, the United States, and Australia. While these associations cannot establish causation — many other factors differ between countries — they provide a consistent ecological signal that dietary omega-3 intake may play a protective role.

A large Belgian cohort study (2019) found a significant negative association between maternal erythrocyte DHA concentrations in early pregnancy and the risk of postpartum depression — meaning that higher DHA levels in early pregnancy were associated with lower PPD risk at one year postpartum. This was independent of other risk factors.

The biological mechanism

DHA plays several roles in brain function that are directly relevant to mood and depression risk. These include:

• Modulation of serotonin and dopamine signalling — both neurotransmitter systems implicated in mood regulation and both dependent on adequate membrane DHA for efficient receptor function

• Regulation of the hypothalamic-pituitary-adrenal (HPA) axis — which governs the stress cortisol response. Research in animal models shows that DHA depletion in postpartum females leads to augmented HPA responses to stress, meaning the cortisol response to stressors is more pronounced and takes longer to resolve

• Reduction of neuroinflammation — DHA-derived compounds called resolvins and protectins are anti-inflammatory in brain tissue. Low DHA is associated with increased neuroinflammation, which is independently associated with depression risk

• Support of hippocampal BDNF (brain-derived neurotrophic factor) — a protein critical for neuroplasticity, learning, and mood regulation that is reduced in DHA-depleted postpartum animals

The intervention evidence

A 2020 meta-analysis of eight randomised placebo-controlled trials found that omega-3 fatty acids significantly improved depressive symptoms in perinatal women, with the response linked particularly to a higher EPA proportion in the omega-3 formula used. This is an important nuance: DHA is the primary structural brain fatty acid, but EPA appears to be more directly mood-active in the context of depression treatment, with the optimal supplementation approach for mood support combining both rather than providing DHA alone.

A 2025 review in the European Journal of Psychiatry confirmed this picture: omega-3 PUFAs show a potential preventive role in postpartum depression, with higher EPA:DHA ratios showing the most consistent mood benefit.

It is important to be honest about what the evidence does and does not show. Omega-3 supplementation is not a treatment for clinical postpartum depression — which requires professional assessment and may require medication, therapy, or both. What the evidence supports is that adequate omega-3 status, particularly DHA, is one nutritional factor in the postpartum mood picture that is worth addressing as part of a broader recovery approach. It is not a substitute for professional care when professional care is needed.

If you are experiencing persistent low mood, anxiety, or emotional difficulty in the postpartum period, please speak with your GP. Nutritional support is one piece of the picture, not a replacement for clinical care. PANDA (Perinatal Anxiety & Depression Australia) — 1300 726 306 — provides support for mothers experiencing perinatal mental health challenges.

DHA in Breast Milk: What Breastfeeding Mothers Need to Know

DHA concentration in breast milk is not fixed — it directly reflects the mother’s dietary DHA intake. Studies measuring DHA in breast milk across populations consistently find that Australian breast milk has lower DHA concentrations than milk from Japanese, Norwegian, or Portuguese mothers, reflecting the lower oily fish consumption of the Australian diet.

This matters for the baby because DHA in breast milk supports the continued neurological development and visual maturation of the infant outside the womb. A baby whose mother is significantly DHA-depleted receives less DHA through breast milk than a baby whose mother has a DHA-replete diet.

It also matters for the mother, because the body’s priority is to maintain milk DHA concentration at the expense of maternal stores. A breastfeeding mother who is not consuming adequate dietary DHA will deplete her own reserves to supply the baby — the same preferential transfer mechanism that operated during pregnancy continues through lactation.

For breastfeeding mothers, this makes DHA one of the highest-priority nutritional areas to address actively, both for the baby’s developmental benefit and for the mother’s own neurological and mood recovery.

How Much DHA Do Postpartum and Breastfeeding Mothers Need?

The NHMRC does not currently set a specific recommended dietary intake for DHA separately from total omega-3 fatty acids. International expert groups vary in their recommendations, but a commonly cited target for breastfeeding women is 200 to 300mg of DHA per day, with some experts suggesting higher doses of 500mg or more in the context of clear deficiency or elevated risk.

For context:

• A 100g serving of Atlantic salmon provides approximately 1,000 to 1,800mg of DHA

• A 100g serving of canned sardines provides approximately 700 to 1,100mg of DHA

• A 100g serving of mackerel provides approximately 800 to 1,200mg of DHA

• A 100g serving of canned tuna provides a more modest 100 to 300mg of DHA depending on the variety (skipjack tuna is lower than albacore)

• Two eggs from DHA-enriched hens provide approximately 120 to 200mg of DHA

Eating oily fish two to three times per week is the most practical food-first strategy for meeting DHA requirements during breastfeeding. For mothers who do not eat fish — whether by preference, allergy, or dietary pattern — algal oil supplements (derived from the marine algae that fish consume to accumulate their DHA) are the most appropriate supplemental source and are safe during breastfeeding.

Fish Safety and Mercury During Breastfeeding

The mercury content of fish is a legitimate consideration during breastfeeding, as methylmercury passes into breast milk and can affect infant neurological development. However, the risk is specifically associated with high-mercury fish consumed in large quantities — not with the low-mercury oily fish that provide the best DHA sources.

Fish to limit or avoid during breastfeeding (due to high mercury):

• Orange roughy — limit to one serve per fortnight

• Catfish, shark (flake), broadbill, marlin, and swordfish — limit to one serve per fortnight

• Do not eat any other fish in the fortnight you consume these species

Fish that are low in mercury and high in DHA — safe to eat two to three times per week during breastfeeding:

• Atlantic salmon (farmed or wild): excellent DHA, very low mercury

• Sardines (fresh or canned in olive oil or water): high DHA, low mercury, also high in calcium

• Mackerel (Atlantic or Pacific, not King mackerel which is high mercury): excellent DHA

• Herring: very high DHA, low mercury

• Canned pink or sockeye salmon: good DHA, low mercury, convenient

• Anchovies: high DHA, low mercury, versatile in cooking

The FSANZ (Food Standards Australia New Zealand) guidelines for fish consumption during pregnancy and breastfeeding provide the most current Australian-specific advice and are worth checking if you have specific questions about particular fish species.

Omega-3 Supplements While Breastfeeding: What to Know

Fish oil and algal oil omega-3 supplements are considered safe during breastfeeding and will increase breast milk DHA concentrations in proportion to the dose consumed. Supplementation is appropriate for mothers who:

• Do not eat fish or eat it less than once per week

• Are vegetarian or vegan (algal oil is the appropriate form)

• Have a suspected or confirmed low DHA status

• Are experiencing mood symptoms that may have a nutritional component

• Had a previous postpartum period characterised by significant brain fog or low mood

Choosing a supplement

Look for a product that provides combined EPA and DHA rather than DHA alone, as the meta-analysis evidence for postpartum mood support is strongest for formulas with a higher EPA proportion. A product providing at least 200mg of DHA and a similar or higher amount of EPA is a reasonable starting point.

Algal oil supplements are equivalent to fish oil in their effect on DHA status and are appropriate for mothers who prefer a non-fish source. They are also free of the contamination concerns (mercury, PCBs) associated with poorly sourced fish oils.

Store omega-3 supplements in the refrigerator once opened — they are prone to oxidation, and rancid fish oil provides no benefit and may cause harm. If your supplement smells strongly fishy or "off", it may be oxidised.

A Practical Food-First Approach to DHA Postpartum

For most mothers, the most reliable and enjoyable path to adequate DHA is a combination of regular oily fish consumption and a supplement to fill any gaps. Here is a practical framework:

• Aim for two to three servings of low-mercury oily fish per week: salmon, sardines, mackerel, herring, anchovies

• Include eggs from DHA-enriched hens where possible (labelled as omega-3 eggs in most Australian supermarkets)

• Use walnuts, chia seeds, and flaxseed regularly — these provide ALA (the omega-3 precursor) which contributes modestly to DHA status even at low conversion rates, and they provide additional nutritional benefits beyond their omega-3 content

• Consider a daily DHA + EPA supplement of 500 to 1,000mg combined, particularly if fish consumption is less than twice weekly

• Reduce the omega-6 fatty acids that compete with DHA utilisation: vegetable oils high in linoleic acid (sunflower, safflower, corn oil), processed snack foods, and grain-fed rather than grass-fed or pasture-raised meat where possible

For the broader nutritional picture of what a breastfeeding mother’s diet should include, the guide to best foods for lactation covers the complete food-first framework. For ideas that make consistent nourishment practical with a baby in the picture, the article on best postpartum snacks for energy and milk supply gives one-handed, accessible options that can be prepared in advance.

Keep Reading

These posts connect to the postpartum depletion picture:

Signs of Postpartum Depletion (And What to Do)

Nobody Told Me That Zinc Was Quietly Running Low

Iron-Rich Foods for Postpartum Recovery

Postpartum Nutrition & Recovery: Complete Guide for New Mothers

Breastfeeding Nutrition & Milk Supply: Evidence-Based Guide

Best Postpartum Snacks for Energy and Milk Supply

Postpartum Allergies: Why They Happen & What to Do

Your brain gave a significant amount of itself to grow and feed your baby. The Nella Vosk postpartum recovery range is formulated by a Certified Postpartum Nutrition Professional to address the specific nutrient depletion profile of the postpartum body — including the nutrients most critical for maternal neurological recovery that standard postnatal supplements often overlook.

ABOUT THE AUTHOR

Kelly Northey is a Certified Postpartum Nutrition Professional (CPPNP) and founder of Nella Vosk, an Australian maternal and family wellness brand. She specialises in postpartum nutritional recovery, breastfeeding nutrition, and the evidence behind maternal brain and mood health after birth.
Learn more about Kelly.