Bifidobacterium

Bifidobacteria live mostly in the large intestine and ferment complex fibres that the small intestine can't digest. The end products are acetate, lactate, and indirectly butyrate (when other species cross-feed on bifido outputs). They train the immune system, lower colonic pH, and crowd out pathogens. They also produce folate, which is absorbed in the colon.

• Bifidobacterium infantis 35624 (sold as Align): improves bloating, gas and bowel habit in IBS in randomised trials.
• Bifidobacterium longum BB536: reduced influenza infection and fever in a trial in elderly adults; supports gut transit.
• Bifidobacterium breve M-16V: reduces eczema risk and severity in some infant trials.
• Bifidobacterium animalis subsp. lactis BB-12: improves bowel regularity, common in yoghurts.
• Bifidobacterium bifidum: foundational species, present in healthy breastfed infant guts.

Healthy breastfed infants typically have a gut microbiome dominated by Bifidobacterium, often around 70% of bacteria on average. Human milk contains specific oligosaccharides (HMOs) that bifidobacteria are uniquely efficient at using, though some other gut bacteria can also consume them. This dominance trains the immune system, protects against pathogens, and influences long-term metabolic and allergy outcomes. Formula-fed and C-section infants have lower bifidobacteria, which is why some formulas now add HMOs and bifido strains directly.

• Niche: bifidobacteria mostly colon, lactobacilli mostly small intestine.
• Outputs: bifidobacteria produce acetate and lactate; lactobacilli mostly lactic acid.
• Oxygen: bifidobacteria are strict anaerobes (oxygen kills them); some lactobacilli tolerate oxygen.
• Both are common in probiotics; many products combine strains from both genera.
• Bifido strains are usually freeze-dried with stabilisers because they're so oxygen-sensitive.

1. Eat prebiotic fibres: inulin (onion, leek, garlic, asparagus, chicory), GOS (galacto-oligosaccharides, in legumes), and resistant starch (cooled cooked potato or rice).
2. Eat polyphenols: berries, dark chocolate, green tea, red onion. Bifidobacteria thrive on these.
3. Avoid frequent antibiotics. Bifidobacteria are particularly sensitive and can take months to recover.
4. Breastfeed if possible. Human milk oligosaccharides selectively feed infant bifidobacteria.
5. Targeted supplements (e.g. B. infantis 35624 for IBS, B. lactis BB-12 for regularity) when there's a specific reason.

Bifidobacteria decline across life, from dominance in infancy to a small fraction in older age, and diet quality is the one lever you keep. A fibre-and-polyphenol pattern sustained over years slows that decline, and every year the colony stays fed is a year of acetate and cross-fed butyrate quietly doing maintenance work on the gut lining.