Sitting On An Exercise Ball While Pregnant

Fat Metabolism

When triglycerides are consumed from foods, they are broken down in the small intestine through bile emulsification and hydrolyzed predominantly through pancreatic enzymes to yield free fatty acids. Short- and medium-chain fatty acids go through the portal vein and enter into circulation where they bind with a carrier protein such as albumin. Long-chain fatty acids are resynthesized into triglycerides and are packaged into lipoproteins called chylomicrons in the mucosal cells of the small intestine. These chylomicrons slowly enter into circulation via lymphatic vessels. The chylomicron, now in the blood, eventually comes into contact with an enzyme called lipoprotein lipase. This enzyme is found on the walls of capillaries that innervate muscle and fat cells and causes the fatty acids within the triglyceride portion of the chylomicron to be released and is rapidly absorbed by muscle and fat cells. Once inside the cell, the free fatty acids will either be used as a substrate for energy via aerobic metabolism or be repackaged once again and stored as adipose or intramuscular triglycerides. The fact that muscle can store triglycerides is significant, just as they can store carbohydrates. These proximal storage forms allow for accessible energy provision.

Fat’s Role in Exercise

Just as some carbohydrates have healthier properties than others, not all fats are created equally. Avoiding fat altogether is not recommended and a low-fat diet can be a detriment to performance as well as health. However, type of fats included in the diet is of importance. Trans fat should be limited or avoided in the diet as high intakes of these types of fats increase ones risk for heart disease (Ackland et al. 2012; Eckel et al. 2014), and there is no need for trans fat in the diet. Currently, there are efforts being made to ban the use of trans fats in food manufacturing, though the outcome is yet to be seen.

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There is evidence to support that limiting dietary saturated fat intake may decrease one’s risk for heart disease (Eckel et al. 2014), though complete removal of these food sources from the diet is not necessary and recent research has brought into question if saturated fat is as “bad” as once believed. Specific types of saturated fats, such as medium-chain triglycerides (MCTs), which get metabolized differently in the body, may actually offer specific health properties. This has given rise to the increased popularity of coconut and coconut products, of which half the fat content comes from MCTs. At the time there is insufficient evidence to support replacing other fats in the diet with MCT-containing foods, like coconut oil. However, these products continue to gain popularity and, to date, no adverse cardiovascular effects have been reported (Bueno et al. 2015).

Unsaturated fats, including mono- and polyunsaturated fats, are considered more “healthful” because of their association with reduced risk for heart disease. Polyunsaturated fats also include sources of the essential fatty acids, omega-3 and omega-6, that are required for certain metabolic functions. Unsaturated fatty acids should make up the bulk of calories coming from fat.

Practical ways to include unsaturated fatty acids include: using olive oil in cooking and salad dressings, placing avocado on sandwiches and salads, adding nuts to oatmeal, eating nuts as a snacks, and regularly consuming fish. Additionally, essential fats such as omega-3 fatty acids are required for the body’s anti-inflammatory system to function adequately and help the body to appropriately handle inflammation in the body. See “Practical Implications” for a closer look at Omega 3 fatty acids and athletic performance.

Overall, an athlete should not consume a low-fat diet but rather a diet that is “moderate” in fat (about 20 to 35 percent of total kcal intake) and limit their intake of trans fat, and include sources of mono- and polyunsaturated dietary fat with each meal. Remember, fat not only serves as an energy source during exercise, but also has important roles in maintaining overall health and performance.

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