In medical school I learned some fundamental concepts about nutrition and digestion that turn out to be wrong. For example, we were taught that proteins in our diet are completely broken down into single amino acids in the gut, then absorbed through the wall of the intestine as individual amino acids. Turns out that not all proteins are completely digested in this manner and that fragments of proteins that are several amino acids long can be absorbed through the gut and enter our blood. Examples of such proteins include wheat gluten and bovine serum albumin (found in cows milk and whey protein) to name a few. The problem with absorbing such nutrients into our bloodstream is that these protein fragments are “foreign” and can be recognized by our immune systems as foreign, triggering an immune (inflammatory) response.
Some peptides (short chains of amino acids) in bovine serum albumin have structural similarity to peptides in human tissues. This foreign protein has been implicated in autoimmune diseases such as Multiple Sclerosis, Rheumatoid Arthritis and Type 1 Diabetes.
Other substances such as bacterial endotoxin similarly can be absorbed into the blood and cause trouble. Endotoxin, also called LPS or Lipopolysaccharide, is a major component of the outer membranes of certain kinds of bacteria (gram negative bacteria such as E-coli) that live in the Lumen of our gut. High levels of endotoxin circulating in the blood occur during septicemia and can result in death from septic shock. Lower levels of circulating endotoxin have been demonstrated to contribute to alcoholic and non-alcoholic liver disease, both of which can cause liver failure and death.
Intestinal wall permeability is governed by many factors. There are regulatory proteins that open and close the gaps (tight junctions) between the cells that line the walls of our intestines, thereby allowing more and larger foreign substances to enter our blood. This mode of entry is referred to as “paracellular” since it does not involve the usual absorption mechanism through the walls of the cells that line the intestines.
Substances regularly consumed by Americans known to increase intestinal permeability include gluten (the sticky protein found in wheat, barely, rye, oats), alcohol, non-steroidal anti-inflammatory drugs like ibuprofen (Motrin, Advil), naprosyn (Alleve), and aspirin. Refined “vegetable oils” that are high in a specific Polyunsaturated fatty acid called linoleic acid (examples of these vegetable oils include corn oil, soy oil, cottonseed oil) have also been demonstrated to increase intestinal permeability.
Vegetable oils have also been found to enhance the liver inflammation and destruction caused by alcohol which is at least in part mediated by absorption of endotoxin and ultimately also caused by oxidative stress.
The same applies to non-alcoholic liver fatty liver disease. (Progression of alcoholic and non-al… [Drug Metab Pharmacokinet. 2011] – PubMed – NCBI)
Interestingly, consumption of saturated fat (as found in beef tallow, coconut oil, butter and cocoa butter-the oil of dark chocolate) protects the liver from inflammation and destruction caused by alcohol, while polyunsaturated fat consumption (vegetable oils) do the opposite. (References above and below)
There is growing evidence for a link between auto-immune disease and Alterations in intestinal permeability. Increased intestinal permeability (IP) has been observed in a substantial percentage of individuals with Type I diabetes. It is commonly observed in populations at high risk of developing Crohn’s disease and has been observed in patients who subsequently develop Crohn’s disease. Patients with ankylosing spondylitis have increased IP and although these patients are typically treated with NSAIDs which increase IP, the effects of NSAIDS have been isolated from a primary defect in IP which is shared by relatives without the disease.
“increased intestinal permeability is observed in association with several autoimmune diseases. It is observed prior to disease and appears to be involved in disease pathogenesis.”
A paleolithic diet avoids all sources of gluten (paleo is grain-free) and it also avoids refined “vegetable oils”. These food items present a double hit relative to inflammation. First, they increase IP which increases circulating levels of various “foreign” proteins and other foreign macromolecules which can stimulate the immune system. The second hit from these food items represents their direct inflammatory effects once absorbed into the body. I have previously discussed the inflammatory response to excess omega six fats here.
An excellent review of the importance of the ratio of omega six fats found in “vegetable oil” to omega three fats found in fish oil can also be found here , here and here.
The potential inflammatory response and anti-nutrient effects of cereal grains and in particular the gliadin portion of wheat gluten has been discussed and reviewed in multiple papers including:
Do dietary lectins cause disease?
Non-Celiac Gluten Sensitivity: The New Frontier of Gluten Related Disorders
BMC Medicine | Full text | Spectrum of gluten-related disorders: consensus on new nomenclature and classification
BMC Medicine | Abstract | Divergence of gut permeability and mucosal immune gene expression in two gluten-associated conditions: celiac disease and gluten sensitivity
Bioactive antinutritional peptides derived from cere… [Nahrung. 1999] – PubMed – NCBI
Antinutritive effects of wheat-germ agglutinin and… [Br J Nutr. 1993] – PubMed – NCBI
This discussion just scratches the surface of the effects of intestinal permeability and health. Future discussion will address how the micro-flora (bacteria and viruses that live in our GI system) affect intestinal permeability, our brains, our immune system and our health.
Avoiding foods that we have not evolved to eat will result in decreased inflammation and will often reduce the symptoms of auto-immune and other inflammatory diseases. Many present day diseases are considered by evolutionary biologists to represent a mismatch between our culture, food, and our evolutionary biochemistry. These diseases were likely rare or non-existent before the advent of agriculture and the subsequent industrialization of society with highly processed foods.
Eat only pastured meat, free range poultry and eggs, wild seafood, fresh vegetables, fruit and nuts and you will avoid the problems discussed above as well as a host of other problems to be discussed in future posts.
Bob Hansen MD