Genetics of Food Intolerance

Food intolerance is based on missing bacteria in the the gut rather than inadequacy of human enzymes, e.g. lactase, or altered immune system.

I make the extreme statement that food intolerance is not genetic, to emphasize that the vast majority of intolerance can be cured by changing the bacterial composition of the gut's microbiological community, the gut flora, rather than attempting to accommodate a permanent deficiency. The two common "intolerances" that are offered by my readers to invalidate my sweeping statement are lactose and gluten (celiac) intolerance.

Lactose Intolerance is Not Due to Inadequate Lactase
Everybody has the same gene for lactase, but some people have altered upstream control elements and continue to express lactase in their intestinal cells after infancy, whereas others don't. The racial pattern of adult lactase expression is an interesting note on human evolution, but is irrelevant with respect to an individual's ability to tolerate the lactose sugar in dairy products.

Lactose is the major sugar present in milk and the ability of the intestines to utilize lactose directly like glucose is a selective advantage for human evolution. Absent that ability, lactose would just pass through the gut without impact. However, bacteria in the colon also have lactose digesting enzymes. These bacteria produce hydrogen and methane gases, and these products in turn can feed other bacteria. If all of the products are consumed, then the lactose has been treated as a soluble fiber and the result is more gut bacteria and a happy gut. If some of the bacteria are missing, then the lactose acts as a laxative, e.g. lactulose, and the bowels are not so happy.

All that is needed to cure lactose intolerance, as in all food intolerances, is to provide the gut bacteria that are missing to fully metabolize the offending sugars or polysaccharides. Just continuing to eat dairy without also eating or introducing new species of bacteria into your gut, will just provide more symptoms, but eating yogurt still containing live probiotic bacteria (Read the label. Any live bacteria listed will work.) that have the enzymes to ferment lactose, will lead to a rapid cure. (See reference below.) As the fermenting bacteria grow in the gut, they transfer their genes to gut bacteria in the biofilms lining the gut and these new species of bacteria keep the lactose out of trouble.

The point is that having a food intolerance means that the aggregate of all of the genes in all of your gut microorganisms is lacking the genes/enzymes needed to completely digest a food component. In the case of lactose intolerance, the missing genes are present in typical probiotics, bacteria that grow on milk/lactose.

Celiac is not a Typical Food Intolerance
Celiac is a complex interaction between major toxic proteins in wheat (gliadin), detox gut enzyme (tissue transglutaminase, tTg) and antibodies. Gliadin is a wheat protein adapted to attack the intestines of herbivores. Herbivores, such as insects and humans, can in turn protect themselves from gliadin and other polyglutamine proteins with the enzyme transglutaminase. tTg binds to glutamines in gliadin and converts them to glutamic acids. Unfortunately, while the gliadin is bound to the tTg, inflammation can predispose the gut to present these proteins to the immune system for processing to trigger antibody production. This is the start of the autoimmune disease.

The major histocompatibility antigens (MHAs) code for the proteins that display fragments of proteins on cell surfaces for antigen presentation and immune response. There is a lot of MHA variation and evolutionary adaptation. Some MHAs favor antibody production to gliadin and tTg. This just shows that celiac and grain/gluten intolerance is not a typical food intolerance, which will be remedied by simply altering gut bacteria, even though establishing gut bacteria that metabolize gliadin or that reduce autoimmunity, may be part of the cure.


Enhancing Gut Flora is Part of the Cure for all Autoimmune Diseases
There are rare food allergies, even though the majority are misdiagnosed intolerances. The production of antibodies to food antigens is a symptom of the breakdown in communication between the gut immune system and gut flora. Particular species of bacteria are responsible for the development of both the aggressive and suppressive components of the immune system, which occurs in the lining of the gut. Loss of the suppressive cells, Tregs, can result from unhealthy diets and exposure to antibiotics, and results in autoimmune disease, in which the aggressive immune system is out of control and attacks self antigens.

Symptoms of all autoimmune diseases can be improved by reestablishing normal control of the aggressive part of the immune system via healthy gut flora. Clostridium species of bacteria normally induce healthy development of the suppressive immune system and these types of bacteria are common in soil clinging to fresh vegetables prior to extensive washing. Which of the bacteria that are eaten become established in the gut flora is unpredictable, because the bacteria interact with each other, food and cells lining the gut. The only safe and simple procedure currently available is the fecal transplant. Some experimental fecal transplants are facilitated by the use of encapsulated freeze-dried gut flora. There is great resistance to this simple, safe, cheap approach from the medical industry.

Reference:
Almeida CC, Lorena SL, Pavan CR, Akasaka HM, Mesquita MA. 2012. Beneficial Effects of Long-Term Consumption of a Probiotic Combination of Lactobacillus casei Shirota and Bifidobacterium breve Yakult May Persist After Suspension of Therapy in Lactose-Intolerant Patients. Nutr Clin Pract., 27(2):247-51.

Contagious Health

Healthy gut flora: bacteria from family, friends, Fido and food provide the foundation for the complex microbial community of the intestines, which controls the immune system.  Antibiotics and hygiene are detrimental to gut flora and health.

Gut Flora Are Complex

Recent studies of the gut flora, e.g. the human gut biome, show that each individual maintains more than 150 different species of bacteria.  Worldwide, that means that about a thousand different bacterial species are common residents of the human gut and together those gut bacteria use more than 1 million different genes.  Many of those genes code for the enzymes used by gut bacteria to digest plant polysaccharides, i.e. soluble fiber.

Hygiene Isolates People from Healthy Sources of Gut Flora

Every time we speak, we release a mist of bacteria from our lungs, mouth and GI tract.  These bacteria are on our skin, clothes and personal items, and provide a source of the bacteria that make us healthy.  Parents and older siblings pass these bacteria on to younger children.  These donated bacteria are essential for the development of a healthy immune system and children growing up with healthy relatives and exposed to soil bacteria via pets, farm animals, etc. are healthier than children who are more isolated.  

In this sense, hygiene is unhealthy, because an individual is isolated from new sources of bacteria that could replace those lost by limited diets, antibiotics, etc.  Otherwise, health is contagious, since gut bacteria from healthy individuals can spread among the population.  Washing hands and food is unnatural and unhealthy.

Few Bacteria Make You Sick, but Many Are Essential for Good Health

Food intolerance can result from “good” family hygiene, limited diets and exposure to antibiotics.  A common intolerance results from the absence of bacteria that produce an enzyme to digest dairy lactose, i.e. lactose intolerance.  Lactose intolerance can be readily cured by eating a dairy product, such as yogurt, that contains both lactose and live bacteria (probiotics) that can digest the lactose.  Simply eating moderate amounts of live yogurt daily for a couple of weeks resupplies the gut flora with bacteria that can digest lactose, and the intolerance is gone.

Soluble Fibers Are Plant Polysaccharides that Are Digestible by Bacterial Enzymes

Humans only produce enzymes to digest one polysaccharide, starch.  All of the other hundreds of polysaccharides present in plants are only digestible by bacterial (and fungal) enzymes of the gut flora.  If the bacteria and enzymes needed to fully digest a particular food polysaccharide are absent, then digestive problems ensue and the polysaccharide can act as a laxative.  Continual eating of the problem food with a new source of diverse bacteria, e.g. lightly rinsed vegetables right from the garden, then the gut flora will incorporate new bacteria that can digest the problem polysaccharide and the gut is happy.  

Soluble fiber feeds the gut bacteria that convert it into short chain fatty acids that nourish the colon. Constipation results from the absence of the bacteria needed to digest dietary fiber and to produce the large volume of bacteria that make up well hydrated stools. 

Gut Bacteria Are Needed for Healthy Immunity

Cells of the human immune system are stored predominantly in the lining of the intestines.  Intensive study of the interaction of the gut bacteria with the gut has revealed that both the aggressive half of the immune system that attacks pathogens and the suppressive half that protects the body itself from attack, develop in the gut in response to particular types of bacteria.  Thus, the absence of one type of bacteria can cripple responses to infection, while other bacteria are needed to block autoimmune diseases and allergies.  Most diseases are caused by disruption of the normal interactions between gut bacteria and the immune cells developing in the gut.

Antibiotics Lead to Autoimmunity

Antibiotics have dramatic and lasting impact on gut flora.  Cattle treated with antibiotics and a high carbohydrate diet have an altered metabolism (obesity) that leads to rapid fat accumulation in their tissues.  This is good for making tasty beef, but the same approach in people produces the suite of diseases in affluent societies.  

Children treated with an antibiotic for a simple ear infection, are much more likely to return to pediatricians for treatments of subsequent obesity, infections and diseases.  Compromised gut flora can take years to return to normal function after antibiotic treatment.  Loss of the appendix, which is the normal source of bacteria to replenish gut flora after diarrhea, results in an increased risk of abnormal gut flora and numerous autoimmune diseases.  It is likely that most autoimmune diseases are preceded by prior treatment with antibiotics that disrupted normal gut flora and permanently altered the immune system.

Interventions to Treat Disease:  the Anti-Inflammatory Diet and Fecal Transplants

It should be obvious that a disrupted or unhealthy gut flora will compromise the immune system and contribute to disease.  Treatment of diseases is complicated by the use of drugs that also impact the gut flora and produce additional side effects.  An alternative approach would be to support the healthy gut flora and normal development of the gut immune system.  As always, the answer is a supportive diet and a source of gut bacteria.  The diet is obviously the Anti-Inflammatory Diet that provides support for almost anything that ails you.  Probiotics are not retained in the gut, but they can contribute a few of the genes needed for a healthy gut flora. The source of bacteria for a  healthy gut flora may range from minimally washed garden vegetables, to the more aggressive total replacement of gut flora with a fecal transplant from a healthy donor.