Fat Intake in the Healthy Diet
Due to the ever-growing epidemic of obesity, leading to coronary heart
disease in the United States, fat intake has been looked at as one of
the primary causal contributors. However, despite continued efforts to
stem the rising consumption of fats in the American diet, the rates of
obesity in the United States continue to rise. Research now indicates
that the type of fat consumed is more important than the total amount
of fat intake. While trans- and saturated fats increase the risk of coronary
heart disease, unsaturated fats appear to be cardio-protective.
- Trans-Fats: While some appears naturally in foods, most trans-fats are
a result of industrial processing of unsaturated fats, also known as “hydrogenation”.
Consumption of trans-fats is associated with an increase in LDL (“bad
cholesterol”) and a decrease in HDL (“good cholesterol”).
It may also interfere with the body’s metabolism of omega-3 polyunsaturated
fats, which are important in heart health and pregnancy. Overall, these
fats increase the risk of coronary heart disease and should be avoided,
- Saturated Fats: Derived primarily from animal products (e.g., dairy, red
meat), consumption of saturated fats increases total blood cholesterol
levels (including LDL and HDL), leading to an increased risk of coronary
heart disease. Its consumption should be minimized.
- Monounsaturated Fats: Replacing trans-fats with monounsaturated fats may
lower LDL while maintaining HDL levels. Found in vegetables, animal products
and partially hydrogenated (partially processed) fats, monounsaturated
fat consumption is also associated with a decrease in oxidation of LDL
in the blood, thought to be a key step in atherosclerosis (development
of fatty plaques in blood vessels). Of note, while it is thought that
vegetable sources of monounsaturated fats are heart-protective, it is
unknown if the same benefits can be gained from animal sources.
- Polyunsaturated Fats: Abundant in various vegetables, seeds/nuts and fatty
fish, the omega-6 and omega-3 family of fats are essential nutrients for
humans. Both are currently thought of as heart-protective; however, the
evidence for omega-3 fats is much stronger. Of note, some studies replacing
saturated fats with omega-6 fats show a possible increase in heart disease,
and increased omega-6 consumption has been linked to cancers in animal
studies. Further test are needed to fully understand the health effects
of omega-6 fats.
The current US dietary guidelines recommend that for an adult, 20% to 35%
of calories should come from fat. Furthermore, trans-fat consumption should
be kept as low as possible, ideally being replaced by monounsaturated
and polyunsaturated fats.
However, the key to a healthy diet isn’t one with low to no fat,
or even one devoid of “unhealthy” fats. It is important to
remember that there are also many other non-fat components of a diet that
can affect health (e.g., carbohydrates, proteins, antioxidants, folate,
and other vitamins/minerals). Ultimately, a healthy diet is one with all
the essential nutritional components in good balance.
U.S. Department of Agriculture and U.S. Department of Health and Human
Services. Dietary Guidelines for Americans 2010. 7th Edition, Washington,
DC: U.S. Government Printing Office, December 2010.