Starch digestion begins in your mouth.
Sure, you may have heard that carbs are your body's preferred source of energy (and the sole source of energy for your brain), while fats provide tons of fuel. But how do you get from that plate of creamy whole-grain pasta or that bahn mi rice bowl to energy? Through a digestive process that takes place in your mouth and continues throughout your digestive tract.
Digestion Begins in the Mouth
Various enzymes throughout the digestive tract do the heavy work when it comes to breaking down foods, but they're not effective on large particles of food. For this reason, chewing is the first step toward the healthy digestion of lipids and starches. The mechanical process of breaking food into smaller pieces enables enzymes to do their jobs and also makes it easier for the stomach to churn the food into a semifluid mass.
Starches are complex carbohydrates made from many molecules of sugar connected together. They must be digested into individual sugar molecules before they can be absorbed into your bloodstream. Their chemical digestion begins in your mouth. Saliva contains an enzyme called amylase, which begins the process by breaking bonds that hold the sugars together. This is only the first step because starches aren't completely broken into simple sugars until they reach your small intestine, where amylase secreted from the pancreas finishes the job. Then they're absorbed through the intestine wall and head straight to your bloodstream.
Breakdown of Lipids
Lipids, or fats, are not digested by enzymes until they enter the small intestine. Here, the liver secretes bile, which emulsifies them into smaller droplets, while the pancreas secretes the enzyme lipase. Lipase breaks lipids down into their constituent molecules: fatty acids and monoglycerides. Because lipids aren't soluble in water they must go through a few extra steps before they can enter your bloodstream. In the lining of the small intestine, they're packaged together with proteins to create structures called lipoproteins. The lipoproteins carry fats through your blood.
Good and Bad Lipoproteins
Lipids are packaged into several different types of lipoproteins. The roles filled by each type explains how you can have good and bad cholesterol. Low-density lipoproteins stay circulating in your bloodstream as they carry cholesterol and other lipids to cells that need essential fats. As these LDLs circulate, they're responsible for the cholesterol that sticks to artery walls, so they're the so-called bad cholesterol. Another type called high-density lipoprotein is considered to be good cholesterol because HDL carries cholesterol back to the liver for disposal.