According to the world food program, 1 out of every 6 children on the planet suffers from malnutrition, and this is responsible for over half of deaths in children under 5 years old. The normal way to measure whether a child is malnourished is through weight - there are certain "normal" ranges of healthy weight for children of different ages, and if a child falls under some threshold, he or she would be considered unhealthy. A more detailed analysis might look at the nutrition of young children - are they getting the right amounts of carbs, proteins, fats and vitamins necessary for human development?
I don't think anyone would deny that looking at milestones of human development during childhood is important for public health, but what about milestones of microbial development? After all, just like the rest of us, young humans are hosts to a menagerie of microbial life, and it turns out that the microbiome develops just as surely as children do. As part of Cells special issue on food science this week, Jeffry Gordon's lab published a paper that asks us to consider the development of the microbiome in public health, and makes a plausible case that the development of our microbial ecosystem may be just as important (if not more) as calories and vitamins in post-natal child health.
This paper is a review of other work, but nicely synthesizes a great deal of current research on microbiome development.
The first point made by Subramanian et. al. is that the microbiome develops according to certain milestones, and that malnutrition of the human host also negatively impacts that development.
According to a paper published by the same group last year, healthy children have predictable microbiome development, but malnourished children tend to have a microbiome that looks "younger" than healthy children at the same age. The microbes that characterize early stages of development are more capable of metabolizing nutrients associated with breast feeding, while the later stages can help to digest more adult foods. What this means is that malnourished children may be doubly impacted - they're putting less food down their throats, and less of the food they do get is broken down into usable nutrients.
Quoting the paper:
"These observations raise a critical question: is microbiota immaturity a cause or an effect of childhood undernutrition? Many studies have shown that, although current protocols for treating children with (acute) undernutrition reduce mortality, they do not rescue its long-term morbidities, including stunting, immune dysfunction, and neurodevelopmental abnormalities."
In other words, getting undernourished kids more calories is not enough - maybe we need to get them better microbes too.
The authors go on to address how we might integrate microbial studies into current clinical investigation. There are a lot of research questions about early post-natal care that might benefit from a microbial mindset. What is the role of breast feeding vs formula? What about if the mother herself is undernourished?
These questions are not only relevant with respect to too few calories - what about in the case of obesity? We know that the microbiome can dramatically effect weight loss and gain, and alterations in gut microbes may start very early in life. While malnourished kids have under-developed microbiomes, kids that have microbial ecosystems that look too old for their age tend to have more adipose (fat) tissue than those of their healthy peers, and this could be observed as early as 18 months of age.
In adults, the causal relationship between certain microbiome configurations and obesity is a bit unclear. In other words, do microbes cause obesity, or does over-eating change the microbiome? The most likely answer is that it swings both ways; high fat diets alter the microbial inhabitants of the gut, and these different inhabitants promote increase weight gain and obesity. What this means is that dietary choices very early in a child's life might have lasting impacts on their health. Considering the obesity crisis in the US in particular, this cannot just be an academic concern.
Fittingly, the authors end with several paragraphs on starting a discussion around microbial development and human health:
"For public acceptance and societal benefit, a thoughtful proactive, science-based, educational outreach is needed with an understandable vocabulary tailored to targeted consumer populations and respectful of their cultural traditions. The goal would be to objectively describe the extent to which the nutritional value of food is related to a consumer’s microbiota and how food ingredients, food choices, and the microbiota are connected to health benefits.
We suggest that one way of framing a public discussion regarding the impact of human gut microbiome research on the nexus of food, agriculture, and nutrition is to divide it into three “sectors”: science and technology, ethics, and policy and governance."
It won't be easy, but it's worth it.