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This summary is adapted from ‘Comparison of the Bifidogenic Effects of Goat and Cow Milk-Based Infant Formulas to Human Breast Milk in an in vitro Gut Model for 3-Month-Old Infants’ by Gallier et al. 2020
The microbial communities that live in the human gastrointestinal tract carry out a range of functions, including processing substances that have not been absorbed from the gut. The human microbial composition is established soon after birth and thereafter is strongly affected by diet. This includes breast-feeding compared to formula feeding. There is also a definitive change when solid food is introduced. This means that early life is very important for providing infants with a healthy microbiome going forward. Prebiotics are defined as foods which cannot be digested and benefit the host by having beneficial effects on bacterial species in the colon. In the infant diet, this includes human milk oligosaccharides (HMOs). They are not broken down in the stomach and therefore make it intact into the lower gastrointestinal tract. Here they can exert a prebiotic effect, encouraging the growth of beneficial bacterial species. One species of bacteria that they encourage, bifidobacteria, is thought to encourage a healthy immune system and may protect against the development of allergies in infants1.
Plant-based or manufactured oligosaccharides are often added to infant formulas in an attempt to mimic the effects of HMOs. Both cow milk and goat milk contain oligosaccharides, but at a lower concentration than in human milk. In terms of the specific molecules, goat milk oligosaccharides are closer in composition to HMOs than those found in cow milk2. Goat milk also has 4 times the amount of oligosaccharides present in cow milk. Therefore, it is thought that goat milk-based formula may have a greater prebiotic effect than cow milk-based infant formula. Some studies have confirmed this in animal models3, but it has yet to be seen in human studies. The study summarised here aimed to study the effects of whole goat milk-based and whey-adjusted cow milk-based infant formula, compared to human milk, in a simulation model for 3 month old babies.
This was based on the Simulator of the Human Intestinal Microbial Ecosystem (SHIME®) which was altered to reflect the infant gut. This was extensively tested for efficacy prior to the investigation of different feeding options. Breast milk, goat milk based infant formula and cow milk based infant formula were tested in this system. Oligosaccharides were profiled to assess their absorption and degradation in this gut model. The microbial composition was also assessed for the development of a microbiome in these models in response to the milk exposure.
It was found that when human milk and goat infant formula were broken down in the gut simulation, a significantly greater amount of gas was produced compared to cow infant formula. This indicates a similar degree of microbial activity. However, human milk produced increases in some chemical products which indicate specific microbial activity that was not seen with either cow or goat infant formula. Lactate levels were highest when goat milk infant formula was broken down in the gut, which acts as an antimicrobial agent4. With regards to microbial composition, all of the milk tested increased the beneficial Bifidobacteriaceae family of bacteria and reduced species richness, but no specific differences were seen between the breast milk and infant formulas. The highest amount of non-digestible oligosaccharides after passing through the synthetic gut was found in human milk, consistent with the much higher concentrations of oligosaccharides present in human milk compared to the two formulas.
Bacteria which produce lactate are the primary bacteria which colonise the infant gut. This lactate is taken up and used by other bacteria, which in turn produce hydrogen gas. This gas can contribute to infantile colic symptoms such as bloating and cramping5. As in this study, goat milk based formula produced increased lactate and gas in this digestion model, it would be interesting to investigate whether this causes symptoms in infants.
This study was limited by its use of an in vitro digestive model. This model did not contain all of the elements present in the infant gut, such as the exact structure of the gut wall, and enzymes present to break down some substances. However, this model did give the opportunity to investigate the effects of the different types of milks without any external factors such as environment and supplementary feeding which both impact the infant microbiome.
In conclusion, there was little difference in the microbial activity stimulated by breast milk, cow milk based infant formula and goat milk based infant formula. This may be explained by the presence of naturally-occuring oligosaccharides within the formulas, even if they are not exactly the same as those in breast milk. Further research in a clinical setting may unveil differences in the impact of goat milk based formula on the infant microbiome.
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