Prior posts, often in the context of assessments that need to be considered in the context of toxic tort litigation, have described the amazing impacts, both beneficial and adverse, that can derive from the intestinal bacterial flora. [And remember my favorite factoid..there are 10 bacteria in the human body for every one cell. Arguably (okay, facetiously) we are a transportation and housing vehicle for bacteria.]
It would seem rather obvious that malnutrition derives from a lack of food, or the proper type of food. But, it is not so simple. Malnutrition comes in two forms: marasmus (chronic, progressive wasting) & kwashiorkor (the symptoms of which include skin and liver problems and edema [swelling caused by fluid in your body's tissues]). For simplicity, researchers looked at kwashiorkor only.
Researchers looked at 317 pairs twins in Malawi during their first 3 years of life. Despite eating the same diet, one twin remained healthy; the other became malnourished (43% became discordant [showing a marked difference in size, usually around 10% by definition], and 7% manifested symptomology of acute malnutrition). After ruling out genetic differences, the difference was associated with the intestinal bacteria.
Using DNA sequencing, the researchers were able to identify various species of gut bacteria in each group. The microbiome of the children with kwashiorkor differed from those without. So far so good. But, was the difference cause or effect? To answer the question, feces from each group was transferred into mice that were born germ-free. The bacteria of the children with kwashiorkor did cause the disease (as shown by the tests with mice), but only in combination with the diet eaten in Malawi (basic, but not adequate). Mice implanted with feces from children with kwashiorkor did not manifest the disease when fed ready-to-use therapeutic food (RUTF), a peanut based food used to fatten malnourished children.
Again, using the mouse model, the researchers looked at what was causing the malnutrition at the enzymatic level. First, the bacteria from the children without kwashiorkor produced more essential amino acids. Second, several of the enzymes from bacteria taken from children with kwashiorkor interfered with the Krebs Cycle. [If you want a detailed understanding of the role of the Krebs Cycle in cellular metabolism, check out the excellent lessons at the Kahn Academy. Alternatively, view the animation at http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html.] Both of these effects lead to the symptoms of malnutrition.
The researchers also found the microbiome of those with kwashiorkor is resilient. Feeding RUFT to the mice with the "bad" bacteria fattened them up, but did not dislodge the bacteria. Some other process is necessary to break the cycle. Adding or subtracting bacteria is a strategy used to treat individuals with a potentially lethal intestinal bacterial infection called Clostridium difficile. Fecal transplants are also being used to address other major intestinal disorders, such as colitis, constipation, and irritable bowel syndrome. See http://en.wikipedia.org/wiki/Fecal_bacteriotherapy. It may be applicable here, or some variation on the concept of transplanting particular "good" bacteria that are sufficiently fit that they can outcompete the "bad" bacteria (Darwinian competition amongst bacteria).
Prior posts have noted the long-term influence on the microbiome of food types. The so-called Western diet produces microbiomes that can cause or aggravate numerous serious diseases and disorders. A healthy, but more "primitive" diet can create a microbiome that helps avoid many such diseases and disorders. However, unlike the short-term use of RUFT in this study, such dietary strategies require major permanent life-style changes.
The study can be found at http://www.sciencemag.org/content/339/6119/548.