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The GI tract (a.k.a. the gut) starts at the mouth and ends at the anus. This is one long tube, around 25 feet in length, that contains bacteria and its own nervous system known as the enteric nervous system. When you think about it, at the most basic level, you are a walking tube, with a brain to help make decisions on how to protect this tube and what to put in it. Weird, eh? Let’s use a delicious food as an example of how food is processed as it moves through the body. How about a red, juicy, sweet-smelling strawberry? The pathway of digestion starts here, with the scent of the food. Your mouth begins to water at the scent and the anticipation of the texture and taste. The saliva comes from this anticipation of digesting the food.

RECIPES FOR DIGESTION

•Chicken Bone Broth

•Beef Bone Broth

•Kimchi

The mouth. The digestive process starts in the mouth, with chewing actions and the production of saliva. The strawberry is formed into a bolus and then swallowed and passed through the esophagus and into the stomach. The chewing action of the mouth triggers the secretion of bile, mucus, acids, and enzymes in the stomach to jump-start digestion. The floor of your mouth under your tongue has an abundance of blood vessels, where certain starches and drugs can be absorbed. Interestingly, some scientists are testing drug absorption through the mouth because it bypasses the gut and goes directly into the bloodstream, which means you would potentially need much less of the drug to feel the same effects. So far it’s only certain types of drugs, vitamins, and sugars that can do this. During moderate athletic endurance efforts—such as sport and traditional (trad) climbing or mountain biking—if you need a quick burst of energy but don’t want to drink or eat anything, rinse your mouth quickly with a carbohydrate and spit it out.

The esophagus. As long as everything went well during swallowing, this strawberry bolus travels down the esophagus. There is an important feature at the end of the esophagus called the lower esophageal sphincter, which has two critical roles. One is to act as a bouncer at the door, controlling food entry into the stomach, and the second role is to serve as an emergency exit, preventing food and stomach juices from coming back up into the esophagus (unless there is an emergency). Gravity plays a huge role in the function of the esophageal sphincter, so if you suffer from acid reflux at night, it helps to sit upright until the burning sensation subsides. If you have acid reflux regularly, it could be a sign that you are overeating, are eating too fast, or have a possible food intolerance (we go into more detail on GI dysfunction and food intolerances later in this chapter). For better athletic performance regardless of your preferred mountain sport, see your doctor and get any symptoms checked out.

The stomach. The stomach is where the digestive party happens. It’s the first major stage of digestion, but not much is absorbed here except certain drugs, alcohol, water, and vitamins. The stomach is made up of several layers of tissue that secrete hydrochloric acid (HCl), which partly breaks down the strawberry bolus to prepare it for absorption later. HCl also kills any bacteria that may be on the strawberry. A diet that includes a lot of processed foods and sugar, and not enough whole foods with vegetables, fiber, and minerals, can cause inflammation in the stomach, decreasing the acidity it needs to do its job. The stomach should have a pH of somewhere between 1.5 and 3.5 (very acidic). If the pH increases too much, it becomes too alkaline, making it tough to absorb vitamins and prepare the bolus for more digestion. To maintain a healthy level of acidity, eat a lot of fruits and vegetables and fermented foods, such as kimchi, sauerkraut, and kefir. If necessary, you can supplement with digestive HCl.

The small intestine. The partially digested strawberry moves fairly slowly from the stomach to the small intestine. It takes one to four hours for the food to empty into the small intestine; the length of time depends on the composition of the meal. For example, carbs leave first because of their ease of digestion, and often the body (the brain and muscles) needs carbs faster than any other macronutrient. Then proteins and finally fiber and fats are passed through. The small intestine, especially the first two sections of it, is where most of the nutrient absorption occurs. The last part of the small intestine absorbs vitamin B12 (essential for feeling energetic during your mountain pursuits), bile salts, and any other leftovers. The mostly digested strawberry travels roughly 1 centimeter per minute through these sections, making the total travel time around four to eight hours.

The growling in your stomach is actually coming from your small intestine and is caused by smooth muscle contractions occurring when there is nothing in the gut.

The large intestine/colon. Next, the strawberry is passed to the large intestine/colon, so named because of its diameter. It is actually quite short, yet the strawberry takes even longer to pass through this section, where the travel time is 12 to 25 hours until excretion. Sodium, potassium, acids, gases, and any remaining water are absorbed here. What’s left is a semisolid waste colloquially known as poop. Poop is partly dead bacteria, inorganic material, and fat. The remainder is fiber, bile, pigments, and proteins. Total food travel time from mouth to anus can range from 18 to 72 hours, a speed determined largely by the amount of fiber present in your meals. In general, those who eat more vegetables and plant-based foods have more bowel movements, so keep those plants coming!

SWEET TASTE BUDS

The mouth has taste buds that pick up the five primary tastes: sweet, salty, bitter, sour, and umami. These tastes often trigger protein binding and other molecular secretions elsewhere in the body to prepare it for these foods. What’s even cooler is that sweet taste buds have also been found in the GI tract, in the pancreas, and in the brain! What does this mean? The body is preparing for the rush of glucose into the body by starting to secrete insulin, even when artificial sweeteners are present. The resulting spikes in insulin aren’t good for the ambitious athlete trying to keep a decent body fat percentage for performance or for those who might be prone to type 2 diabetes (see chapter 6, How Fuel Provides Energy, for more on insulin and blood sugar levels).