Fermentation of milk through addition of Lactobacillus bulgaricus and Streptococcus thermophilus bacteria produces yoghurt. Yoghurt can be used as a source of dairy by those with lactose intolerance because the lactose content is not as high as milk. This is because the bacteria in yoghurt digest the lactose into lactic acid and thus the lactose content is greatly reduced. The high lactic acid content gives the yoghurt its characteristic flavour. Endogenous bacteria also contain lactase (β-galactosidase) that converts some of the lactose into galactose and glucose in the human gut. In the Mediterranean region, genetic defects of lactase cause a high incidence of lactose intolerance, but yoghurt is a staple food of such populations. This ability of yoghurt to be more easily digested than milk has also been demonstrated in the nutritional research. In fact, yoghurt is as well tolerated as pre-treated milk designed to remove the lactose (here).
However, there exists variation between yoghurt brands and how they are tolerated by subjects. This is thought to arise because of variation in the endogenous lactase activity. For example, one group of researchers1 investigated the effects of different brands of commercially available yoghurt on the intolerance in 20 human subjects. The yoghurts tested were the brands Borden, Danone and Royal Maid, and intolerance was assessed through a questionnaire for symptoms, and a hydrogen breath test that is used to reflect the fermentation of lactose in the colon. The results showed that the Danone and Royal Maid yoghurts showed significantly less hydrogen production when compared to a lactose control, suggesting that they were better tolerated. However there was no such difference for Borden. The authors stated that the symptoms reported by the subjects did not correlate with the hydrogen production.
These results therefore suggest that variation exists in the tolerance of subjects to brands of yoghurt. This may relate to the amount of fermentation by the bacteria Lactobacillus bulgaricus and Streptococcus thermophilus. Alternatively, endogenous lactase is able to aid in the digestion of lactose present in the yoghurt because it is protected from the stomach acid by the buffering capacity of yoghurt and because it is contained within the bacteria. However, for this to happen the bacteria must be added after pasteurisation so that the yoghurt contains live cultures. The degree that the endogenous lactase is able to survive the transit through the stomach may have an influence in the degree of subsequent intolerance to the yoghurt. Those with lactose intolerance may therefore find that different brands of yoghurt affect their lactose intolerance symptoms to varying degrees and this necessitate experimentation in order to find the best source.
RdB
