By Hilary Metcalfe 

When my milk first came in, I thought breastfeeding would be all about the breast: positioning, latch, supply. That’s what everyone told me. No one mentioned my digestion, my bloating, the antibiotics I’d taken after delivery, or the constant swings between constipation and diarrhoea. And yet, quietly, these gut struggles were shaping my energy, my hormones, even the milk I was making for my baby.

Science now confirms what many mothers sense intuitively: the gut and the breast are deeply connected. Breastmilk is not just water and fat, it’s a living fluid, carrying nutrients, immune cells, and even microbes that originate in the mother’s gut. This process, called the entero-mammary pathway, allows bacteria and immune information from the gut to seed the mammary gland and flow into the milk.

At the same time, the gut is the body’s nutrient gatekeeper. If absorption is compromised by inflammation, dysbiosis, or stress, then the raw materials for milk, iron, calcium, B vitamins, omega-3s, simply don’t get through. And when the gut–brain axis is disrupted by chronic cortisol, both digestion and let-down can falter.

Put simply: a mother’s gut health may be one of the hidden determinants of breastfeeding success.

1. Nutrient Absorption: Feeding Milk at the Source

Breastmilk is a reflection of the mother’s diet, her nutrient stores, and how effectively her gut absorbs them.

• Iron and Zinc: Critical for infant neurodevelopment and immune function. Iron deficiency in mothers reduces milk iron concentration, especially if absorption is impaired.
  

• Vitamin D: Maternal gut absorption directly influences breastmilk levels. Without supplementation or optimal gut absorption, milk often contains insufficient vitamin D for infant needs.
  

• Omega-3s: DHA in milk is entirely dependent on maternal intake and absorption. Gut inflammation can impair fat uptake, lowering DHA delivery to infants.
  

For mothers with gut disorders, IBS, IBD, post-antibiotic dysbiosis, absorption can be compromised, leaving them depleted and anxious about supply. Supporting digestion isn’t cosmetic; it’s central to milk quality.

2. The Entero-Mammary Pathway: Microbes in Transit

Breastmilk is alive. It carries up to 700 bacterial species that help seed the infant gut microbiome.These aren’t random contaminants, they originate in the mother’s gut. Immune cells pick up microbes in the intestine, travel through the bloodstream, and deliver them to the mammary gland.

This means maternal diet and microbiome health shape not only the mother’s wellbeing but also her baby’s foundational gut ecosystem.

• A mother consuming a diverse, fibre-rich diet passes on more diverse bacteria, linked to healthier infant microbiomes.
  

• Conversely, antibiotics, low-fibre diets, or dysbiosis can reduce diversity, potentially raising the risk of allergies, asthma, and obesity later in life (Lyons et al., 2020).
  

The gut, then, is the baby’s first teacher. Every bite a mother eats, every microbe she nurtures in her own gut, informs what her baby inherits through milk.

3. Immune Education: How Gut Inflammation Shapes Milk

The maternal gut is a training ground for immune cells that later migrate into breastmilk as antibodies, especially secretory IgA. These antibodies coat the infant’s gut, protecting against pathogens and shaping immune tolerance.

If the mother’s gut is inflamed, by processed foods, infections, or chronic stress, immune education may be altered. Studies show mothers with healthier gut microbiota produce milk with higher antibody levels and more anti-inflammatory factors.

This isn’t just about protecting the baby from colds. It’s about laying the foundation for an immune system that knows the difference between friend and foe, reducing risks of autoimmunity and allergies.

4. Stress and the Gut-Brain-Breast Axis

Every breastfeeding mother knows stress can stall let-down. But few realise this is mediated through the gut.

• Stress elevates cortisol, which alters gut permeability (“leaky gut”), reduces beneficial bacteria, and increases inflammation (De Palma et al., 2015).
  

• A disrupted microbiome produces fewer short-chain fatty acids (like butyrate), which normally calm inflammation and support oxytocin release.
  

• The result: a double hit of poor digestion and impaired let-down.
  

Supporting the gut, with prebiotic fibres, fermented foods, and calming herbs, is therefore also supporting the hormonal reflexes of breastfeeding.

5. Practical Gut-Supporting Strategies for Breastfeeding Mothers

• Fermented Foods: Kefir, kimchi, sauerkraut, and live yoghurt provide live microbes that may transfer through the entero-mammary pathway.
  

• Prebiotic Fibres: Oats, apples, garlic, and asparagus feed beneficial gut bacteria, increasing production of butyrate.
  

• Hydration and Minerals: Nettle and oat straw, included in Breastfeeding Herbata, replenish depleted mineral stores while feeding gut flora.
  

• Gentle Herbal Support: Tulsi and vervain calm the nervous system, reducing cortisol’s impact on both the gut and the let-down reflex.
  

• Caution with Antibiotics: Sometimes necessary postpartum, but always worth pairing with probiotics or fermented foods to rebuild diversity.
  

Why This Matters

We tend to view breastfeeding as isolated to the breast: a matter of ducts, nipples, supply, demand. But the science of the gut–breast axis tells a different story. The success of breastfeeding is influenced just as much by what happens in the intestines as by what happens at the nipple.

When a mother’s gut is thriving, she absorbs nutrients efficiently, passes on beneficial microbes, produces richer immune factors, and maintains a calmer hormonal environment for let-down. When her gut is struggling, milk supply, quality, and infant health can all be quietly affected.

This isn’t about adding one more pressure to mothers,  it’s about broadening the conversation. Because when we see breastfeeding not just as a breast issue but as a whole-body system, we can better support mothers where they need it most: with real food, microbial nourishment, and care for the gut that sustains both her and her baby.

ABOUT HILARY

Hilary is the Co-Founder of the SABI, a Holistic Nutritionist, natural, whole foods Chef, product developer and advocate for women getting to know their bodies, cycles and selves better. Born in Los Angeles, California and raised in Baja California, Mexico, she now lives in Los Cabos with her partner Kees, a curly-tailed rescue dog from Curacao, Flint and her rainbow babies Paloma and Bea.  

HORMONAL & PROUD

Created as a brand to help women navigate the toughest moments in pregnancy, childbirth, postpartum — and practically every stage of life –– The SABI is changing the narrative around our hormones from one of taboo, embarrassment, and loneliness to awareness and even, pride. As more than a wellness brand, The SABI offers a carefully-crafted line of products to carry you through your hormonal journey, including rituals, supportive tools, and ancient herbal remedies that have been tested time and time again by women and now come backed by medicine. The SABI is a blend of science and nature conceived by women who have experienced the joys and deep struggles of bringing a child into the world, the pains of a heavy, difficult period, miscarriage, and difficulty conceiving.

We invite you to get to know your body and its cycles better –– to really understand what is going on inside. Learn to use your hormones to your advantage no matter your stage of life, and know that you can support and balance your hormone levels. We are here to help with the information, understanding and natural tools to support your body and the emotional process along with it.

DISCLAIMER

The SABI blog and articles are not meant to instruct or advise on medical or health conditions, but to inform. The information and opinions presented here do not substitute professional medical advice or consultations with healthcare professionals for your unique situation.

References

1. Fernández L, et al. The human milk microbiota: origin and potential roles in health and disease. Pharmacol Res. 2013.
   
   

2. Cabrera-Rubio R, et al. The human milk microbiome changes over lactation. Am J Clin Nutr. 2012.
   
   

3. Lyons KE, et al. Breast milk, the infant microbiome and immune system development. Front Immunol. 2020.
   
   

4. Allen LH. Nutritional influences on lactation. Adv Nutr. 2012.
   
   

5. Hollis BW, Wagner CL. Vitamin D requirements during lactation. Am J Clin Nutr. 2015.
   
   

6. De Palma G, et al. The microbiota–gut–brain axis in stress and neuropsychiatric disorders. Trends Mol Med. 2015.