1. Undernutrition
2. Micronutrient related malnutrition
3. Overweight.
1. Undernutrition - If you don't have enough nutrients, you are malnourished. It is not always the lack of food, but the lack of quality food. Undernutrition means that you have a shortage of calories and most often of essential nutrients (when the access to food is denied). This is a specific type of malnourishment. As a result, you are being underweight, wasted, growth is stunted, happening usually after a weight loss event such as infectious disease associated with diarrhea. Stunting means that a person has a low height for age, and it is the result of a long term undernutrition during childhood, holding the child back from achieving their physical and intellectual potential. being underweight is a child with a low weight for age, and you can also be stunted or wasted.
There are clear differences in the gut of the undernourished people compared with healthy individuals. Most of the researches on undernutrition are focused on children, because they need fast growth for their optimal development. Undernutrition in children can have long term health implications: reduced growth rate, immune and cognitive development.
In the same time, the gut microbiota of the undernourished children remains immature. But we do not know if this is a cause or a consequence. In a mice study, after transferring the gut microbiota of a malnourished infant donor, the mice will gain less weight than the ones receiving microbiota from a healthy donor. Undernourished infants often miss bacteria from Ruminococcus and Clostridium group. All those bacteria are the ones producing the short chain fatty acid called butyrate (which is an energy source for the host cells). The microbiota can contribute to the caloric value of your food. This is useful especially when food is scarce, and any part is needed as usable energy.
Ruminococcus bacteria
Another type of malnutrition is Anorexia Nervosa (which is characterized by distorted body image, extreme dieting and the anxiety of becoming obese as main underlying factors). All these symptoms will lead to severe weight loss. Even if it seems different that the undernourishment in children, the common element is the nutrient shortage. And similar changes are noticed in the composition of the microbiota. Anorexia patients will have lower amounts of total bacteria and obligate anaerobic bacteria. In addition, they will also have lower amounts of butyrate producing bacteria and higher amounts of mucin degrading bacteria.
The undernutrition is affecting the microbiota and plays a role in the severity of the undernutrition by releasing less energy from food. The manipulation of the gut microbiota could be a helpful solution for undernourished children.
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