Gluten Exposed: The Science Behind the Hype and How to Navigate to a Healthy, Symptom-free Life. Rory Jones

stored for later use—primarily as body fat.

      Transport

      Once the intestinal wall absorbs the fully digested food, it is transported into the bloodstream and made available to cells throughout the body. Carbohydrates, protein, and fat are transported across the epithelial cell membranes by different mechanisms, with some foods requiring specialized chemical “porters” that literally bind to the components and carry them across the cells of the villi.

       Carbohydrates

      Carbohydrates supply the body with the fuel it requires for immediate and long-term muscle function and energy. Complex carbohydrates (starches) are usually broken into simple carbs (sugars) in the small intestine. The simple sugars are usually readily transported across the villi into the bloodstream. But some sugars such as lactose or fructose are not absorbed by some people and arrive in the large intestine (colon) mostly undigested. It is these carbohydrates that are thought to cause many of the symptoms of IBS, and their digestive results are often mistaken for gluten intolerance.

       Proteins

      Proteins are large and complex molecules that are an essential part of every cell, organ, and body system. They are made up of hundreds of amino acids bound together in chemical chains that must be broken down to be used by the body. This is done by enzymes secreted by the pancreas and from the brush border (microvilli), which split these chains into smaller and smaller molecules and amino acids that can then be absorbed.

      The Problem Protein

      Protein is not just found in meat, fish, eggs, and cheese; it is an essential part of many foods. It is the protein portion of wheat—both the gluten and nongluten parts—that gives the small intestine of many people the most trouble. For those with celiac disease, the troublemaker is gliadin, the protein portion of wheat and several other grains. It contains one fraction that is not readily digested. So despite all the grinding, churning, mixing, and battering of digestion, some proteins remain intact. Gluten is a major culprit in this scenario.

      But scientists are learning that for those with IBS and other gluten sensitivities, it may be the nongluten portion of wheat contributing to the problem. (See chapter 11, “Gluten and Nongluten Grains.”)

       Fat

      Fat is one of the major building blocks of the body. It provides long-term energy stores and needed cholesterol. While many people take statins to lower their cholesterol, it is the main component of cell membranes and is needed to maintain the integrity of every cell in the body and to make many hormones.

       Mineral and Vitamin Digestion

      Specific minerals and vitamins are crucial to body growth, function, and metabolism. Even minor deficiencies disrupt body chemistry.

      Vitamins are either water or fat soluble. Water-soluble vitamins, the B family and C, move across the watery chyme quite easily either on their own or assisted by special carriers. Fat-soluble vitamins must be emulsified to make the trip. Sodium (salt), calcium, iron, water, potassium, and other trace minerals are readily absorbed in different parts of the small intestine, but if the villi are damaged, minerals and vitamins cannot be absorbed.

       The Colon (Large Intestine)

      Whatever is left of the chyme in the small intestine is then pushed by peristalsis into the colon or large intestine. For many people, this is the part of the digestive tract where painful problems occur.

      The digestive process that starts in the mouth culminates in the colon, which is about 6 feet long, shorter than the “small” intestine.

      The colon is home to a huge population of bacteria (the microbiota) that have colonized your intestine throughout your lifetime. They feast on everything the small intestine has discarded and digest much of the unused fiber in our diet through fermentation—the bacterial version of chemical conversion. This reduces the chyme into feces and releases folic acid and vitamins B1, B2, B6, B12, and K (the clotting vitamin).

      In fact, while the main function of the colon is the absorption of water, approximately 98 percent of the fluids entering from the small intestine—as well as a small but significant percentage of our calories—is actually absorbed in the large intestine. It is the fermentation process that produces carbon dioxide and methane gas, which often translates into flatulence (gas).

      As the food is pushed through the colon, the fecal matter becomes more and more concentrated and then stored until it is eliminated through the rectum. The longer it takes to expel feces, the more water is absorbed, making the stool harder and, in turn, more difficult to expel. Diets high in fiber (raw fruits and vegetables, high-fiber cereals) or supplemented with drugstore fiber (e.g., Metamucil or FiberCon) create more fecal bulk that goes largely unabsorbed and creates larger stools.