A healthy diet contains the widest possible variety of natural, whole foods. It provides you with a balance of fats, carbohydrates -- particularly fiber, and protein, as well as vitamins and minerals. In general, the amount of food energy, measured in calories, supplied by your diet, should not exceed the amount of energy you need for daily activities. This simple formula will keep your weight relatively constant. Improving your diet does not always mean cutting out these macronutrients, it simply means cutting back on excess.
Beginning of Digestion
As fats, carbohydrates and proteins are broken down in the stomach, and eventually in the small intestine, the process is aided by secretions from the pancreas, the liver, by way of the gallbladder and the intestine itself. The enzymes that break down food in the small intestine can function only in alkaline conditions. Food leaving the stomach is highly acidic, so the small intestine must first reduce the acidity of the partially digested nutrients. Glands secrete the hormone secretin, which reduces the production of stomach acid as food enters the small intestine. Secretin also stimulates alkaline secretions from the pancreas and liver, which also reduces the acidity.
Fats
One of the major dietary problems for individuals living in the United States is consuming more food than the body needs. Very little fat appears in the feces because the absorption of fat from the diet is usually rapid and complete. Fat from your diet is broken down by bile, which is produced by the liver and stored in the gallbladder. Through the process of digestion, bile travels to the small intestine, where bile salts break down large fat droplets. This process increases the surface area of the droplets and speeds up their digestion by the pancreatic enzyme lipase. Lipase breaks down fats into glycerol, a sugar alcohol and fatty acids.
Carbohydrates
Sometimes, you can indulge in foods without drastically affecting your health. However, when you consistently indulge in some foods, it can cause significant health problems. Humans cannot digest all forms of carbohydrates, which is a good thing. Some of the more complex carbohydrates, such as cellulose, remain undigested because we don't produce the enzyme needed to break them down to simple sugars. These insoluble fibers pick up and transport toxins from the body through feces. Glands within the small intestine also secrete maltase, sucrase and lactase, which split double sugars into single sugars, which are easily digested, then stored or used as energy.
Protein
Digestion of proteins begins in the stomach, and then continues into the small intestine. Proteins are first broken down into chains of amino acids called peptides, and then into individual amino acids. Most proteins are broken down and absorbed in the middle part of the small intestine. The absorbed amino acids pass directly into the bloodstream, which carry them, via the liver, to the tissues that use them. Some amino acids act as building blocks of new proteins, while others simply supply energy.
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