Science behind the SCD

The Specific Carbohydrate Diet™ is predicated on the understanding that Ulcerative Colitis, Crohn's Disease, Irritable Bowel Syndrome, and gluten therapy resistant Celiac are the consequence of an overgrowth and imbalance of intestinal microbial flora. By altering the nutrition we take in, we can affect the constitution of our intestinal flora and bring it back into balance, healing our digestive tracts and restoring proper absorption.  

The intestinal tract forms a rich ecosystem, comprised of over 400 bacterial species. Some are harmless, and others not. In the gut of a healthy person, these various communities of microbes compete with each other for scarce nutritional resources. Consequently, they exist in a state of balance, and the stomach and small intestine harbor only a sparse population of microbial flora. In the large intestine, each type inhibits an overabundance of the others, and this prevents the waste products and toxins of a particular type of microbe from overwhelming the body. The stomach and upper intestine are also protected by high acidity, and the action of peristalsis.  

The Vicious Cycle  

When the balance in the gut is disturbed, an overgrowth of intestinal flora can result. Microbes migrate to the small intestine and stomach, inhibiting digestion and competing for nutrients. The gut then becomes overloaded with the byproducts of their digestion. This bacterial overgrowth can be triggered by overuse of antacids, reduced stomach acidity due to aging, weakening of the immune system through malnutrition or poor diet, and alteration of the microbial environment through antibiotic therapy.  

The components of our diet, particularly carbohydrates, play an enormous role in influencing the type and number of our intestinal flora. When carbohydrates are not fully digested and absorbed, they remain in our gut and become nutrition for the microbes we host. The microbes themselves must digest these unused carbohydrates, and they do this through the process of fermentation. The waste products of fermentation are gases such as methane, carbon dioxide and hydrogen,  lactic and acetic acids, as well as toxins. All serve to irritate and damage the gut. There is evidence that increased acidity in the gut due to malabsorption and fermentation of carbohydrates may lead common, harmless intestinal bacteria to mutate into more harmful ones. Further, lactic acid produced during the fermentation process has been implicated in the abnormal brain function and behavior sometimes associated with intestinal disorders. The overgrowth of bacteria into the small intestine triggers a worsening cycle of gas and acid production, which further inhibits absorption and leads to yet more harmful byproducts of fermentation. The enzymes on the surface of the small intestines are destroyed by the now present bacteria, and this further disrupts the digestion and absorption of carbohydrates, leading to further bacterial overgrowth. As both the microbial flora and their byproducts damage the mucosal layer of the small intestine, it is provoked to produce excessive protective mucus, which further inhibits digestion and absorption.  

Damage to the mucosal layer involves injury to the microvilli of our absorptive cells. These microvilli act as the last barrier between the nutrition we take in and our bloodstream. As our absorption is inhibited, folic acid and vitamin B12 deficiency can lead to impaired development of microvilli, while an abnormally thick layer of mucus prevents contact between microvilli enzymes and the carbohydrates we ingest. The small intestine responds to this spiraling irritation by producing more goblet (mucus-making) cells, creating yet more mucus. Finally, as the goblet cells become exhausted, the intestinal surface is laid bare and is further damaged and possibly ulcerated. As more carbohydrates are left in the gut, they cause water and nutrients to be pulled from the body into the colon, resulting in chronic diarrhea. Absorption is further hindered as diarrhea increases the rate with which food travels through the gut.  

The Diet 

The Specific Carbohydrate Diet is based on the principle that specifically selected carbohydrates, requiring minimal digestive processes, are well absorbed and leave virtually none to be used for furthering microbial overgrowth in the intestine. As the microbial population decreases due to lack of food, its harmful byproducts also decrease, freeing the intestinal surface of injurious substances. No longer needing protection, the mucus-producing cells stop producing excessive mucus, and carbohydrate digestion is improved. Malabsorption is replaced by absorption. As the individual absorbs energy and nutrients, all the cells in the body are properly nourished, including the cells of the immune system, which then can assist in overcoming the microbial invasion. The simpler the structure of the carbohydrate, the more easily the body digests and absorbs it. Monosaccharides (single molecules of glucose, fructose, or galactose) require no splitting by digestive enzymes in order to be absorbed by the body. These are the sugars we rely on in the diet. They include those found in fruits, honey, some vegetables and yogurt.  Double sugar molecules (disaccharides: lactose, sucrose, maltose and isomaltose) and starches (polysaccharides) are primarily avoided on the diet. Some starches have been shown to be tolerated, particularly those in the legume family (certain dried beans, lentils and split peas). However, they must be soaked for 10-12 hours prior to cooking and the water discarded since it will contain other sugars which are indigestible, but which are removed in the soaking process. Small amounts of legumes may only be added to the diet after about three months. The starches in all grains, corn, and potatoes must be strictly avoided. Corn syrup is also excluded as it contains a mixture of short-chain starches. 

Yogurt  

Finally, the SCD relies on properly fermented yogurt, and in some cases, acidophilus supplements, to help repopulate the gut with healthy intestinal flora. By increasing the population of  "good" bacteria in the gut, the overgrowth of harmful bacteria is put in check.  As the competition for nutrition between the various strains of bacteria resumes, the variety of intestinal flora is brought back into balance. Yogurt must be properly prepared by fermenting it for 24 hours. This allows enough time for the bacteria in the yogurt culture to break down the lactose (disaccharides) in milk into galactose (a monosaccharide). All SCD yogurt is homemade, as commercially available yogurts are not properly fermented.