The digestion of fat begins in the mouth where the food you chew is mixed with a small amount of lingual lipase that is found in your saliva. Lingual lipase is a digestive enzyme that breaks fatty acids apart from triglycerides.
Once you swallow your food, digestion continues in the stomach. A small amount of lipase is secreted into the stomach, but most fat digestion takes place in the small intestine.
Fat Digestion in the Small Intestine
Your liver produces bile, which is stored in the gall bladder until it's triggered by eating foods that contain fat. Bile is released into the small intestine where it works like a detergent to emulsify the fats into smaller droplets. This makes it easier for pancreatic lipase to get to the triglycerides.
The bile and lipase break fats down into smaller pieces that are absorbed into the blood stream. The bile, which contains cholesterol, is either re-absorbed into the blood or bound by soluble fiber in the intestine and eliminated in the stool. Eating foods with lots of soluble fiber helps keep your cholesterol levels healthy by grabbing more of the cholesterol from the bile and eliminating it from your body.
A healthy digestive system will absorb about 95 percent of the dietary fat that you eat. People with malabsorption disorders like celiac sprue, pancreatic lipase deficiency and bile salt deficiency usually can't absorb fats properly.
Fats and oils contain nine calories per gram. Your body takes the extra fatty acids and stores them as adipose tissue, which is better known as body fat. Adipose tissue can be broken down and turned into glucose when you need more calories -- that's why counting calories is important if you want to lose weight.
Fat in the Diet
The USDA suggests that you get about 30 percent of your calories from fat. For a 2,000 calorie per day diet, that would equal 600 calories from fat. Since fat has nine calories per gram, that would be equal to about 67 grams of fat. You should watch your cholesterol and saturated fat intake as well.
The USDA suggests no more than 300 mg cholesterol each day, less than 10 percent of your daily calories from saturated fat and less than one percent from trans-fats.
A typical Western diet often includes much more than that because fats add texture and flavor. Fats also slow down gastric emptying, so high fat meals are more satisfying. Unfortunately, that means too many calories for a lot of people.
Short Chain Fatty Acids
Remember reading about fiber in the carbohydrate lesson? Your body can't digest fiber. That's good for adding bulk to the stool, but, fiber also has one other important function. The friendly bacteria that live in your colon ferment the fiber and produce short chain fatty acids that are easily absorbed into the walls of the colon, help keep the colon tissue healthy and can reduce inflammation.