The Good Gut is a book written by a married couple of PhD's that specialize in microbiology and immunology. They work at Stanford and the department of microbiology and immunology specifically studying the human intestinal microbiota. Their approach in their book can be described as more academic rather than practical but based on the evolving evidence of the role of the intestinal flora and barrier and overall health, I felt it prudent to do a deep dive evaluation on current evidence regarding gut health.
There is a collective project called The American Gut Project that will analyze your gut bacteria breakdown. They are using this data to evaluate populations for associations of diet and diversity of bacteria in the gut (generally thought of as good).
Some interesting results they found so far:
· The more different plant types a person eats, the higher the microbial diversity of the gut. Persons who ate 30 or more different plant types a week, had microbiomes that were more diverse than those of people who ate only 10 plant types or less per week.
· The administration of antibiotics lowered the microbial diversity of the gut, as expected. One surprising result was, that the diversity of the molecules found in people who had taken antibiotics, was much higher than in people who haven´t taken antibiotics for more than a year. These molecules found seem to be linked to the exposure to antibiotics. This is one mystery that has to be explored now.
· Another unexpected result was the detection of agricultural antibiotics in people who claimed that they haven?t taken antibiotics in the year prior to their sample collection. This means that with the meat we eat, we still might take up antibiotics which harm our microbiome.
· Comparison of two distinct Western populations revealed significant differences in the diversity of the samples: people in the UK seemed to have a higher microbial diversity than people form the US.
· The researchers discovered a link between the composition of the microbiome and people with depression. Although taken from two different sides of the Atlantic, the samples proved to be consistent in the US and UK populations. This shows that the microbiome and disease strongly influence each other, independent of the environment the person lives in.
In infants, Proteobacteria associated with colic and Lactobacillus and Bifidobacteria is protective. This may confer to adults.
Study of children's gastrointestinal illness showed that children who consumed probiotics were 24% less likely to have infections compared to children not receiving probiotics.
Prebiotics are discussed and the benefit of such prebiotic as inulin which is actually a polymer of fructose. Unlike the negative effects of fructose such as high fructose corn syrup, inulin does not breakdown until it reaches the large colon and bacteria utilize this as fuel source for the microbiome. As they ferment inulin short-chain fatty acids are produced and this protects our gut from inflammation. Natural sources of inulin include foods like onion garlic and artichokes.
In the middle portion of the book, the authors speculate on different types of bacteria but without clear practicable advice. They do discuss using fermented foods as the source of bacteria over probiotic supplements with the exception of during gastrointestinal illness, these experts believe an extra boost of bacteria through probiotics will improve the vulnerable state of the gut during infection. Natural inoculation suggested by author include foods such as yogurt pickles sauerkraut kimchi and kombucha as well as environmental bacteria that you are exposed to having a garden and pets. The experts advise against sterilizing your house.
The authors discuss dietary fiber and uses more specific term that they state is more appropriate and that is microbiota accessible carbohydrates or MACs. The overall summary of what these carbohydrates or dietary fiber do is passed through the small intestine without absorption and provide the bacteria in the large colon fuel source. The fermentation product produced is short-chain fatty acids and although these have calories it is noted that those consuming high-fiber short-chain fatty acid producing diets actually lose weight. The authors discuss the effects of starches such as Pasta white bread potatoes and white rice. These type starches get converted to simple sugar glucose before reaching the large intestine. These are defined as polysaccharides whereas oligosaccharides are found in beans whole grains and many fruit and vegetables. Oligosaccharides are not digested well in the small intestine. Mono sac rides are absorbed such as glucose or fructose and disaccharides such as sucrose and lactose are also digested in the small intestine. The goal is to maximize oligosaccharides and cellulose which is not absorbed at all as a polysaccharide in the gut. Recommendation for fiber intake is 38 g from males and 29 g for females but average Americans consume half this.
The authors point to having a poor microbiome and several studies is associated with obesity insulin resistance and pro carcinogenic compounds. The authors point to a meat rich diet being detrimental to health in the sense that small chain fatty acids are not produced to the same degree and TMAO is produced by large consumption of red meat (this finding was through Cleveland Clinic evaluation of heart patients noting high levels of TMAO predicted impending heart attack and stroke as well as CAD). Gut bacteeria that are regularly exposed to red meat seem to upregulate TMAO production (l carnitine gets metabolite of TMAO by specific gut bacteria and oxidized TMA becomes the TMAO of concern). while a vegan that eats red meat will not show upregulation. This data on pages 148 and 149 suggest that red meat consumption in someone that is a primarily plant based eater does NOT have the same negative effect as one red meat meal in a regular red meat eater. The authors concur with many other experts and that they stay away from produced packaged foods and refined flours. The authors discuss the lack of knowledge as to the many chemical molecules that are produced from gut bacteria and the functions that are somewhat drug like in nature. The authors speculate that these may be related to mutations of bacteria and at times these molecules may provide some type of evolutionary advantage. An example was given that citrus pectin metabolizing bacteria may produce a byproduct which stimulates the house to eat more citrus and this would be an advantageous byproduct that with us be beneficial to the bacteria and in essence select that mutated bacteria as being the preferred.
Regarding brain function, the authors point to a double blinded UCLA study in which yogurt use twice a day for 4 weeks showed functional MRI differences in the brain in the double-blind study. Although this is highly suggestive of a gut brain correlation, it did not specify in what way the addition of the yogurt based bacteria changed mental status. Fecal transplants are discussed to rehabilitate life threatening cdiff infections. I personally like the comparison to a forest fire when antibiotics are used and the forest looks very different after the fire with either healthy regrowth or growth of non-desirables that previously could not succeed in the presence of the competition.
The authors mention that in the elderly there is 3 different clusters of bacterial composition of the bowels. 1 was in the elderly living in the community and their composition reveals similar to younger participants. The elderly that are in hospitals or long-term care facilities have a different cluster that is most likely related to a change in diet to a lower fiber diet. The authors mention antibiotic load affecting the ability of the body to fight tumor cells as shown in mouse studies.