Last week I wrote about carbohydrates, a major energy source in our diets. This week the topic is fats, including saturated fats, unsaturated (monounsaturated, polyunsaturated and trans) fats, omega-3 fats and cholesterol.
Fats tend to get a bad reputation since they are higher in calories than carbohydrates and protein and have traditionally been associated with obesity and heart disease when eaten in excess. In reality, some dietary fats are detrimental to your health, while others have health benefits. These consequences are partly linked to the effect of the fats on the LDL – “bad” – and HDL – “good” – cholesterol in your blood and partly to other factors, including blood clotting and inflammation.
Traditionally, cholesterol and saturated fats have been linked to heart disease because they raise levels of LDL cholesterol. Cholesterol is only found in animals, whereas saturated fats are in animals and tropical oils such as palm and coconut oil. This is why you may have heard that you should avoid foods that contain these fats, including red meat and eggs.
It turns out that the link between saturated fat, cholesterol and heart disease isn’t what we long believed, so these dietary recommendations are being revisited. It seems that high fat intake along with excessive sugar and refined carbohydrates is particularly problematic, so fats themselves may not be to blame for poor health.
Unsaturated fats are found in plant oils. Polyunsaturated fats tend to lower both LDL and HDL cholesterol. Monounsaturated fats are associated with lower LDL but they do not lower HDL cholesterol – this is better. Oils high in polyunsaturated fats include corn and soybean oil while olive and canola oils are rich in monounsaturated fats.
Trans fats are found mostly in modified oils which are hydrogenated to make them more solid and have a longer shelf life. For example, when corn oil (unsaturated fat) is partially hydrogenated it becomes more trans and is more solid – margarine. Trans fats are used in baked and fried foods and can be identified on food labels (most of the time) or by the words “hydrogenated” or “partially hydrogenated” in the ingredient list. Trans fats have the effect of raising LDL while lowering HDL cholesterol – a bad combination! Fortunately, trans fats are less common now than they were even a few years ago, but staying away from fried foods and checking the labels on prepackaged snacks will help you avoid trans fats.
There are three essential omega-3 fats in the diet: ALA, EPA and DHA. Two of these, EPA and DHA, are primarily found in fish and are associated with reduced risk of heart attack due to their beneficial effects reducing inflammation and blood clotting. Other sources of omega-3 fats include flax seeds, which are high in ALA. The evidence is strongest for beneficial health effects of EPA and DHA, so eating fish or taking fish oil supplements is a common recommendation.
Dietary fat should account for 20–35% of your total calories. The typical American diet is a bit too high in total fat, mostly from unhealthy sources. Your goal should be to make food choices that will shift your intake of fat away from unhealthy sources (trans fats) to healthier sources (monounsaturated and omega-3 fats).
Just as with carbohydrates, you should get your dietary fats from real food (like olive oil or butter), not processed foods (margarine). If you do that, you won’t need to worry so much about the types of fats you eat. And don’t forget that all fat contains calories, so don’t overeat even the healthier fats, especially if you are trying to control your weight!