If you’ve read a newspaper in the past 40 years, you’re probably already aware that not all fat is created equal. There are three major categories of fat in the diet: unsaturated fat, saturated fat, and trans fat. Unsaturated fats are considered “good” fats because small amounts of these in the diet can improve blood cholesterol levels and slow hardening of the arteries (atherosclerosis) that contributes to high blood pressure and cardiovascular disease.
Saturated fat is considered “bad” fat because it has the opposite effect: It raises low-density lipoprotein (LDL, or “bad”) cholesterol levels and promotes atherosclerosis.
Trans fat is the new bully on the block. It has been shown not only to raise LDL cholesterol levels but also to lower high-density lipoprotein (HDL, or “good”) cholesterol. Both of these effects increase the risk for heart disease, stroke, and high blood pressure. Because heart disease and stroke are the main causes of death among people with diabetes, it is especially important for those with diabetes to focus a discerning eye on the type and amount of fat in the diet as well as the type and amount of carbohydrate.
What is trans fat?
Trans fat is produced when liquid oils are solidified into margarine or vegetable shortening by a process called partial hydrogenation. The term trans fat is a chemist’s way of describing the straight chain of particles that make up this unhealthy fat molecule. (For an illustration, see “Chemical Structure of Fat.”) Believe it or not, the difference between straight-chained fats and bent-chained fats is the difference between healthy and unhealthy fats. Saturated fat likewise has a straight chain, which is why both saturated and trans fats do similar damage in the arteries and are both categorized as “bad” fats. However, as an oil derivative, trans fat is technically still an unsaturated fat, but because it is now shaped differently, it has vastly different properties than the naturally occurring unsaturated fats found in liquid oils, nuts, seeds, and fish.
Partial hydrogenation of any type of oil will result in trans fat formation. (Full hydrogenation of oil does not result in the creation of trans fat, but the end result should be considered a saturated fat.) Common food sources of trans fat are fast foods (such as French fries, chicken nuggets, and fish fillets), prepared and frozen foods (such as burritos, pizza, pancake mix, and croutons), snack foods (such as crackers, microwave popcorn, chips, and granola bars), and baked goods (such as hamburger buns, doughnuts, cookies, cakes, and pies). (To get an idea of how much trans fat is in standard servings of various foods, check out “Amount of Trans Fat in Typical Servings.”) Using margarine or vegetable shortening will add trans fat to home-cooked foods.
If trans fat is like saturated fat, does it matter which one you eat as long as you do not eat too much of either? It may. At the very least, trans fat is as harmful as saturated fat, but many recent studies have shown that it is even more so. An article published in April 2006 in The New England Journal of Medicine reviewed many studies in which diets containing saturated fat were compared with diets containing an equal amount of trans fat. The people whose diets had the trans fat had higher levels of LDL cholesterol, lower levels of HDL cholesterol, and higher levels of triglycerides (which are lipids, or fats, circulating in the blood). Each of these is a well-known risk factor in the development of cardiovascular disease. Other findings in the trans fat groups included elevated levels of Lp(a) lipoprotein and smaller LDL particles, both of which also translate into a higher risk of heart disease.