Proteins, Carbs & Fats: How They Break Down in Your Body

           Food is Fuel, What Fuel Are You Filling Up With? 

     Bite, Chew, Swallow. So, you think that's how digestion works, right? Well, there's a lot more to it than that. The autonomic nervous system is responsible for how the digestive system works, which means that humans do not have to think about it or make anything happen, until the end. Essentially, the human digestive system is on autopilot; food goes in, waste goes out. Let's take a look at how your body digests what you take in and maybe it will help you understand how carbohydrates, fats and proteins are broken down in your body and used as fuel. Just like a car, if you put in cheap, low grade gas, you are going to get less mileage and gunk build up in your engine, whereas when you put in Supreme Unleaded, you get more mileage and your engine does not build up gunk. Your body is like a car, you can choose foods that make you feel sluggish and tired (less mileage) or foods that optimally nourish your body and give you energy (more mileage). After all, you eat to fuel your body and you want to make sure you are putting in Supreme Unleaded versus Regular for optimum mileage. 

     
     We take a bite of food, let's say a hamburger, and because I know you are good at fueling your body well, it has a whole grain bun (carb), lean ground beef or turkey (protein and fat), lettuce, tomato and avocado (fiber, healthy fat). Instead of fries (bad carbs), you have a side salad (carbs) with dressing on the side and water or unsweetened iced tea. Mm-mm, that burger sure tastes good, you chew it and while you are chewing, your body is starting the digestion process in your mouth! Chewing breaks up the food as we all know, but it also activates a little motion called peristalsis, which is the series of squeezing waves that starts with your tongue's movements. (Sizer & Whitney, 2013) Saliva is the first chemical reaction in your body to soften and moisten the food to prevent it from tearing the esophagus (that thing in your next that is a tube to your stomach). Saliva also breaks down starches. 
     Once food passes to the stomach, your stomach is churning and mashing into a paste with digestive juices such as enzymes and acids that can be passed down into the small intestine, this paste is called chyme. The acid is your stomach is very powerful, therefore, your stomach needs a strong lining of mucus to coat and protect it. The stomach is also where protein is broken down, this is the stomach's main job. Bet you didn't know that!  
     There's a little thing called the pyloric valve that only allows out little bits of chyme at a time to go into the small intestine. (Sizer & Whitney, 2013) The small intestine is responsible for most of the digestion processes. "The small intestine is the organ of digestion and absorption." (Sizer & Whitney, 2013, p. 86. The gallbladder squirts bile into the small intestine and pancreatic juice from the pancreas in released which contains bicarbonate (you've probably seen this on the Rolaids and Tums ingredients list by the way!) to neutralize the stomach acid. Thus, the protein, carbs and fats you just ate are absorbed by the small intestine while water and fiber remain for the final journey. 

     
     From the small intestine to the large intestine the remaining food travels. The large intestine reabsorbs the water from the contents and the fiber moves on and the end result is, well you know, waste. 

     How are proteins, fats and carbs used by the body?

     Protein is the building blocks for muscles and tissues and come in the form of meats and dairy. Proteins also contain amino acids which are necessary for building proteins. Not all proteins are the same and as most proteins come with fat, it can be a double whammy. It is important to keep proteins lean such as fish and chicken. That is not to say that you cannot enjoy a steak, but limit how often and the portion size. 

     Carbohydrates come in the forms of sugars and fibers, are used for energy especially by the brain and nervous system, and comes from plants. Carbohydrates are turned into glucose which is how the body uses it. The problem with carbohydrates is that there are many that are not good for us as they contain too much sugar and are overly processed. Some come in the form of drinks such as juice, soda, alcohol and energy drinks. Good carbohydrates have high fiber density like leafy greens, whole grain breads and pastas and brown rice. 

     Fats are used for energy, some now and some later, so it makes sense that when the body stores too much fat, we are not using it or consuming too much of it. Fats come from meats, dairy and plants. While we need fats so our bodies can function, there are bad fats that have high cholesterol levels, and many prepackaged foods have trans-fats. Healthy fats are monounsaturated and polyunsaturated fats which are better for you. Foods that contain healthy fats are avocados, olives, canola oil and fish.

     It is interesting to see how these can work together. The protein molecules are like little vehicles that fat molecules travel on and proteins help fat move and get absorbed by the body. Protein requires help from carbohydrates in certain aspects and if there is not enough carbohydrates (as in the Atkin's Diet) the body diverts protein from it's own critical functions, such as maintaining a healthy immune system. (Sizer & Whitney, 2013).  

     I hope you have enjoyed reading about your body's digestive process and the break down process of protein, carbs and fats. It is also my hope that you think about what you are putting into your body. As you read some of my other posts, you will see the importance food has on disease, weight and lifespan needs. Please feel free to share this or leave a comment. 
     References: 
     Sizer, F. & Whitney, E. (2013).  Nutrition: Concepts and Controversies (13th ed.).  
          Mason, OH: Cengage Learning
     Hamburger photo courtesy of tripadvisor.ca retrieved from      
     http://www.tripadvisor.ca/LocationPhotoDirectLink-g155004-d3651691-i117666930-Original_Burger_Joint-Ottawa_Ontario.html
     Digestive System Figure 3-9 from Sizer, F. & Whitney, E. (2013).  Nutrition: Concepts and Controversies (13th ed.).  
          Mason, OH: Cengage Learning, p. 83.