Saturday, April 9, 2011

Paleo Diet, Part II - Cereal Grains Are Bad?

I.   Introduction
II.  Vitamin Deficiency
III. Toxins
     3.1 - Gluten
     3.2 - Lectins
IV. Conclusion
V.  Bibliography
I.  Introduction

     Cereal grains (wheat, rice, maize, millet, barley, rye, oats, sorghum) are the greatest source of the world’s food supply.  They provide 56% of the food energy consumed on earth with wheat, maize, and rice comprising 75% of the world’s grain production [1].  While cereal grains have become a huge staple of developed civilizations around the world, there is a large amount of evidence suggesting that cereal grains are not an ideal food source for the genetic make-up of humans, which was established prior to the agricultural revolution.
II.  Vitamin Deficiency [1]

     One shortcoming of cereal grains is their lack of vitamins.  Cereal grains are poor sources of vitamins A, B, and C.  This can usually overcome by the addition of fruits, vegetables, and lean meats in the modern diet.  However, diets high in cereal grains (and low in fruits and veggies) put individuals at greater risk for vitamin deficiencies (vitamin A, B, C deficiency) and the health disorders associated with them (greater childhood mortality and morbidity, cancer, cognitive dysfunction, coronary heart disease.  Even though cereal grains have a decent vitamin B content, their vitamin B bioavailability (amount that is absorbed and utilized in the body) is quite lowCereal grains are also low in calcium, zinc, copper, magnesium, essential fatty acids, amino acids, protein and can impair the absorption of iron.  As more cereal grains are included in a diet, less room is available for foods rich in vitamins and minerals.  Therefore, it is important to include significant amount of fruits, vegetables, and lean meats to counteract some of these vitamin deficiencies.  However, there are other significant drawbacks from the consumption of cereal grains that can not be avoided.
III.  Toxins

     3.1 - Gluten
     Cereal grains have proven to be the main cause of celiac disease and Dermatitis herpetiformis (skin disease characterized by stinging, itchy rash).  The major component that causes these diseases is wheat gluten (found in wheat, rye, and barley).  Proteins in wheat gluten (gliadin and glutenin) induce an immune response that damages the lining of the small intestineGliadin has been shown to increase gut permeability through the upregulation of zonulin, which disrupts the tight junctions in the gut [2].  This zonulin-caused gut permeability can cause antigens to escape the gut and flow throughout the body, thus causing immune cells to become reactive.  Furthermore, this immune response to antigens has the potential to become chronic and lead to the development of autoimmune disorders.  Therefore, gut permeability has been linked to causing autoimmune disorders such as celiac disease, inflammatory bowel disease, multiple sclerosis, and type 1 diabetes [2].  The damaged tight junctions also play a role in cancer development, infections, and allergies [2]. 

     One VERY important note is that you can have gluten sensitivity without having celiac disease!!  This condition is known as non-celiac gluten intolerance (NCGI).  Symptoms of celiac disease and NCGI are very similar.  However, the severity is usually much higher with celiac disease.  Symptoms may include abdominal discomfort, diarrhea, lactose intolerance, excessive gas, headaches, bloating, or othersThe difference with celiac disease is that gluten induces a much larger response from immune cells, resulting in greater damage to the gastrointestinal lining.  

     A recent study by Sapano et al. (2011) showed that individuals with gluten sensitivity do not have the same molecular responses to gluten intake as those with celiac disease (less pro-inflammatory cytokine activity, less upregulation of immunoglobulins, less gut permeability).  However, 57% of the NCGI patients were positive for human leukocyte antigen (HLA) DQ2 or DQ8, both of which are strongly associated with celiac disease as an upregulator of immune cells [5].  Also, 48% of NCGI patients were positive for anti-gliadin antibodies (AGA), which is produced in response to gliadin consumption [5].  Interestingly, high levels of AGA in the blood are also implicated in other disorders, such as autism and schizophrenia.  While these percentages are lower than with celiac disease, they are higher than the normal population.  So even though the damage being done to your gastrointestinal tract is not as bad as with celiac disease, damage is still being done if you are sensitive to gluten.  

My educated guess is that celiac disease is a chronic form of NCGI.  As an individual ignores subtle symptoms of NCGI and consumes large amounts of gluten products, a threshold of immunological activity is reached, resulting in the severe symptoms that are common amongst those suffering from celiac disease.  Many people still don't pay attention to their response to gluten consumption.  So you may have one of these conditions and not even realize the damage you are doing.  Be aware of the symptoms of celiac disease or NCGI...or just follow the Paleo way and don't eat it!  

     3.2 - Lectins
     As seeds of grass, cereal grains contain secondary metabolites that are used for defense from pathogens and herbivores, protection from the environment, attract pollinators, store nutrients, and provide structural support.  Depending on the animal that consumes these grains, these secondary metabolites can be harmless, anti-nutritional, or toxic.  One such secondary metabolite is a lectin.

     Lectins are carbohydrate binding proteins found in most plants and in seeds such as cereals and beans.    These proteins can bind onto carbohydrate functional groups on the surface of cells in the body, such as red and white blood cells, which may cause agglutination (clumping).  Lectin activity has been shown in wheat, rye, barley, oats, corn, and rice, but not in sorghum or millet [1].  Lectins, such as wheat germ agglutinin (WGA – found in wheat) and phytohemmagglutinin (PHA – found in beans), can bind to and damage epithelial cells in the gut, interfere with digestive and absorptive activities, and cause an inflammatory response.  In vitro studies have shown that WGA can bind to cells in the mouth, stomach, intestines, pancreas, musculoskeletal system, kidney, skin, nervous system, and reproductive organs, as well as platelets and plasma proteins [3].  It is also believed that by binding to and damaging the intestinal wall, lectins increase the permeability of the intestinal wall, allowing lectins to enter the bloodstream.  This belief has been validated through the finding of lectins in the blood of normal, healthy humans following the consumption of tomato juice and roasted peanuts, respectively [4].

Once in the bloodstream, lectins can potentially bind to many cells in the body.  WGA has been shown to bind to both insulin and leptin receptors in vitro [1, 4], which could potentially cause insulin or leptin resistance if enough WGA is eaten.  Lectins from lentils, kidney beans, peas, and wheat have also been shown to increase inflammatory cytokine production in vitro.  It must be stated that no human studies have been conducted to definitively show that lectins cause insulin or leptin resistance, or increase inflammatory cytokine production.  However, by contributing to gut permeability and increasing inflammatory cytokine production, lectins may also contribute to the development of autoimmune diseases. 
IV.  Conclusion

Studies investigating the effect of cereal grains on the human body and autoimmune disorder development are still in their infancy.  However, there is A LOT of interest in this topic, with many resources available online.  This is by no means a thorough review, but just a starting point for those looking to dig a littler deeper.  Due to the lack of clinical studies currently available, some may dispute all of this evidence altogether.  However, based on the some of the current data, it is believed that future studies may provide clearer evidence toward the relationship between cereal grain intake and “diseases of civilization”.  

Dr. O 
"I don't live to eat...I eat to live!"
V.  Bibliography

1.       Cordain, L., Cereal Grains: Humanity's Double-Edged Sword. World Rev Nutr Diet, 1999. 84: p. 19-73.
2.       Fasano, A., Zonulin and Its Regulation of Intestinal Barrier Function: The Biological Door to Inflammation, Autoimmunity, and Cancer. Physiol Rev, 2011. 91: p. 151-175.
3.       Freed, D.L.J., Lectins in food: Their importance in health and disease. J Nutr Med, 1991. 2: p. 45-64.
4.       Carrera-Bastos, P., et al., The western diet and lifestyle and diseases of civilization. Res Rep Clin Cardio, 2011. 2: p. 15-35.
5.       Sapone, A., et al., Divergence of gut permeability and mucosal immune gene expression in two gluten-associated conditions: celiac disease and gluten sensitivity. BMC Medicine, 2011. 9(23).


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