Buttermilk, yoghurt and the gut

Fermented dairy occupies a defined place in Ayurvedic dietetics. Yoghurt and buttermilk are treated as distinct foods with distinct properties, and the texts give specific instructions about each.

The classical positions

Buttermilk — takra, made by churning yoghurt with water and removing the butter — is described favourably, particularly for digestive conditions, and is recommended in a range of situations.

Yoghurt — dadhi — is treated more cautiously. The texts describe it as heavy and as increasing kapha, and give instructions about when it should be avoided: at night, in certain seasons, and in certain conditions. Eating it plain and cold is discouraged in several sources; it is generally recommended diluted, spiced, or as buttermilk.

This differentiation is interesting because the two products differ genuinely — buttermilk is more dilute, lower in fat, and its preparation alters the composition.

What is known about fermented dairy

Lactose content. Fermentation reduces lactose, and the live bacteria assist its digestion in the gut. Yoghurt is generally better tolerated than milk by people with reduced lactase activity, which is well documented and clinically useful.

Live cultures. Yoghurt contains living bacteria, though whether they survive transit and colonise is a separate question — most do not establish permanently, and effects, where present, are largely transient and dependent on continued consumption.

Cardiovascular associations. Observational studies have generally found neutral or favourable associations between fermented dairy consumption and cardiovascular outcomes, which is somewhat at odds with what the saturated fat content alone would predict. The explanations proposed involve the food matrix and fermentation products, and this remains an area of active investigation rather than settled science.

Probiotics: what the evidence actually supports

The probiotic field has generated enormous commercial activity and the clinical evidence is narrower than the marketing.

Where evidence is reasonably good, it is strain-specific and indication-specific.

Antibiotic-associated diarrhoea. Certain strains have reasonable evidence for reducing incidence. This is among the better-supported applications.

Acute infectious diarrhoea in children, where some strains have evidence for modest reduction in duration, though large trials have produced more equivocal results than earlier studies.

Irritable bowel syndrome, where some evidence exists for symptom improvement with particular strains, with inconsistency between studies.

Necrotising enterocolitis in preterm infants, where specific probiotics have evidence in a clinical setting.

Where evidence is weak or absent: general immunity, mood, weight, skin conditions, and most of the broad wellness claims.

Crucially, effects are strain-specific. Evidence for one strain does not transfer to another, and products frequently do not specify strains or contain what they claim. Independent testing has repeatedly found discrepancies between labelled and actual content.

Safety, which is not zero

Probiotics are safe for most people and there are exceptions that matter.

Cases of infection caused by probiotic organisms have been reported in people who are severely immunocompromised, critically ill, have central venous catheters, or have compromised gut barriers.

Anyone in these categories should not take probiotics without medical advice.

What supports gut health with better evidence

Dietary fibre and dietary diversity. The best-supported dietary influence on gut microbial composition. Fibre from a range of plant sources, in quantity, has more evidence than any supplement.

Fermented foods generally, where some interventional evidence exists for effects on microbial diversity, and where the evidence base is developing.

Avoiding unnecessary antibiotics, which have substantial and sometimes prolonged effects on the gut microbiota.

The classical recommendation of buttermilk with a meal, alongside a diet containing vegetables, legumes and whole grains, produces most of what the evidence supports without any product being purchased.

The microbiome hype problem

Gut microbiome research is genuinely exciting and it is at an early stage.

Associations between microbial composition and a wide range of conditions have been reported. Causation is largely unestablished — the direction of the relationship is frequently unclear, and disease can alter the microbiota as readily as the reverse.

Commercial microbiome testing services offering dietary recommendations based on a stool sample are ahead of the science. There is no established mapping from a microbiome profile to a personalised diet with demonstrated outcomes.

Treat claims in this area with the same scepticism you would apply anywhere, and note that a field's genuine promise is not the same as its current clinical applicability.

The practical version

Eat fermented foods if you enjoy them. Buttermilk with a meal is pleasant, well tolerated by most people who react to milk, and traditional practice for good reasons.

Eat a lot of plants of many kinds, which is the intervention with the best evidence.

Do not buy a probiotic for a general purpose. If you have a specific indication with strain-specific evidence, use the strain that was studied.

Do not take probiotics if you are immunocompromised, critically ill or have a central line, without medical advice. Persistent digestive symptoms require assessment.