Macronutrients: What happens after when we eat them?

So we learned during my previous post that macronutrients are essential to our body. But how does our body process them? Let's start with carbohydrates. In order to digest carbohydrates, our body must first "render the starch and disaccharides from the food into momsaccharides that can be absorbed through the cells lining the small intestines" (that sounds exhausting). Starch (the largest of the carbohydrate molecules) needs the biggest breakdown while disaccharides need to only be split once before absorbtion can be acheived. Digestion of starch starts in the mouth with an enzyme in saliva begins to break it down. Once you begin chewing, disaccharides seperates from the starch. Starch digestion stops once it gets to the stomach but starts again when it arrives at the small intestine. The starch is then brokedown into disaccharides and polysaccharides. It also breaks down Sugars (sucrose and lactose) from  the food and maltose and polysaccharides from the starch into monosaccharides for absorbtion. Once the monosaccharides are created, they are then picked up by our blood stream and sent to the liver. The liver can convert fructose into galactose and galactose into glucose. The circulatory system then transports glucose to our cells. Fibers, however, are fermented by the bacteria in the colon. Is any one else impressed by the human body? And we haven't even gotten to proteins or fats yet (Sizer & Whitney, 2013).

Unlike carbohydates, protein digestion does not begin in the mouth. It begins in the stomach. Once in the stomach, acid breaksdown the protein strands and an enzyme splits amino acid strands into ploypeptides and a few amino acids. Once in the small intestine, enzymes from the pancreas and intestine split the protein strands into tripeptides, dipeptides, and amino acid strands. Enzymes on the lining of the small intestine and in the cells then split tripeptides and dipeptides. The intestinal cells then absorb and transfer amino acids to the bloodstream. Once in the bloodstream, amino acids are transported to all the cells in the body (Sizer & Whitney, 2013).

For fats, not much digestion takes place in the mouth and stomanch. Once in the small intestine, digestive enzymes perform most of the digestion. Bile mashes the fat, and then enzymes split triglycerides into fatty acids, glycerol, and monoglycerides. Then the parts are absorbed by intestinal villi. Glycerol and short-chain fatty acids go directly into the bloodstream. The cells of the intestinal lining then change large lipid fragments back into triglycerides and mix them with protein which forms chylomicrons that journey through the lymph vessels into bloodstreams. In the large intestine, a small amount of cholesterol stuck in the fiver leaves our body with feces. (Sizer & Whitney, 2013).

Before taking this nutrition class, I can honestly say that I had no idea that our body did so much work every day! Simply amazing.

http://www.divavillage.com/images/Oct05/digestion_eating_web1017.jpg

 

Reference:

Sizer, F. & Whitney, E. (2013).  Nutrition: Concepts and Controversies (13th ed.).  Mason, OH: Cengage Learning