How to Choose a Vegetable Oil

How to Choose a Vegetable Oil

In the past 15 years olive oil has taken on the status of a health food, especially for those trying to lower their cholesterol and protect their heart. The fact is, corn, sunflower, and other polyunsaturated oils are just as good at lowering cholesterol as olive oil. But there are other health issues besides cholesterol.

Why olive oil became HOT
Olive oil is high in monounsaturated fat (see box below for more on the types of fat), delicious if you like it, and historically important as well. It has been the basic cooking oil around the Mediterranean since the Bronze Age. Four thousand years or so later, in 1958, the Seven Countries Study gave olive oil a boost when it found that men who ate the lowest amounts of saturated fat had the lowest blood cholesterol and the lowest rates of heart disease. Amazingly, though, the very lowest rates were found in Greece, on the isle of Crete, where the diet was high in fat—but the fat came primarily from olive oil. Perhaps more important, the Cretans ate very little meat and lots of grains and vegetables; they also did hard physical work every day. (One often overlooked fact: the Japanese, who ate no olive oil at all, but did avoid saturated fats, were also found to have a very low rate of heart disease.)

Smart marketing played a big role, too. The olive oil industry tirelessly promoted its product, along with the "Mediterranean diet," not only among consumers, but also among nutritional experts.

So which oil is best for lowering cholesterol?
Since 1958 much research has been done on the relationship between dietary fats and blood cholesterol. Most studies found that polyunsaturated fats, such as safflower or soybean oil, lower total blood cholesterol impressively; others tilted toward monounsaturated fats, such as olive or canola oil. The consensus now is that, as far as cholesterol goes, it doesn’t matter which of these you choose. The most important thing is that the oil replace saturated fats in your diet. If your chief concern is blood cholesterol, you have nothing to gain by choosing olive oil or another monounsaturated oil over corn, soybean, or other polyunsaturated oils. None of these oils contain any cholesterol, of course, since only animal products do.

But what about HDL?
It used to be thought, on the basis of a few early studies, that polyunsaturated oils also lower HDL ("good") cholesterol, while monounsaturated oils do not. But since then, most research has found that all these oils, in the amounts commonly consumed, have little or no effect on HDL. If raising or maintaining your HDL is a primary concern, keep in mind that one drawback of going on a low-fat diet for some people is that it lowers HDL levels. That’s one reason to replace the saturated fats found notably in meats, whole milk, and cheese with healthy unsaturated fats such as those in oils (fish and nuts are also good sources of healthy fats). This will lower both total cholesterol and LDL ("bad") cholesterol, and maintain HDL or boost it slightly.

Olive and canola may have other benefits

Monounsaturated fats do have the following potential health advantages:

• Beyond their effect on cholesterol, these fats may reduce other cardiovascular risk factors. For instance, there’s some evidence they reduce the tendency of the blood to clot, which may lower the risk of a heart attack or stroke. And preliminary research suggests that a diet rich in monounsaturates may reduce blood pressure.

• They are less likely to contribute to—and may even reduce—the oxidation of LDL ("bad") cholesterol in the blood. Oxidation contributes to the development of dangerous plaque in the arteries.

• They can help some people with diabetes control their blood sugar, according to the latest guidelines about diabetes. In addition, they are recommended for those with Metabolic Syndrome, which typically features elevated blood sugar.

• Oils high in monounsaturated fat are healthier for cooking, because polyunsaturated oils are more susceptible to oxidation in cooking. Oxidation creates cell-damaging free radicals and other by-products. This is more of a problem, however, when the oil is heated at very high temperatures and for prolonged periods—as in some restaurants. Reheating the oil is especially damaging.

• Canola, walnut, soybean, and especially flaxseed oils supply alpha-linolenic acid, an omega-3 fatty acid related to those in fish. Several studies have found that this polyunsaturated fatty acid can reduce the risk of heart attacks.

Bottom line: Choose olive oil if you like it. Canola oil is nearly as high in monounsaturated fat as olive oil and costs less—plus it has heart-healthy alpha-linolenic acid. (Internet rumors about the health risks of canola are untrue.) Safflower, corn, sunflower, peanut, and many other oils are also good.

But when these oils are used in packaged foods, watch out for the words "partially hydrogenated" before them in the ingredients list. Hydrogenated oils are more saturated and contain trans fat, which is especially bad for your heart.

Last words: Sorting out fats

All vegetable oils are pure fat, and all are combinations of saturated, monounsaturated, and polyunsaturated fatty acids. They are categorized according to the predominant type of fatty acid. Canola oil, for instance, is called monounsaturated, since 61% of its fatty acids are monounsaturated (21% are polyunsaturated, 8% saturated). Safflower and corn oil are called polyunsaturated, since they are respectively 71% and 57% polyunsaturated. Fatty acid molecules vary in length and in degree of saturation (that is, how many hydrogen atoms they carry), both of which help determine whether a fat is solid or liquid (oil) at room temperature.

Saturated fatty acids carry all the hydrogen atoms they can hold. Highly saturated fats come chiefly from animal sources and include butter, whole milk, and meats. Three vegetable oils—coconut, palm, and palm kernel—are also highly saturated. But these tropical oils do not act like other saturated fats in the body, and may not be as unhealthy as once thought.

Unsaturated fatty acids, primarily from plants and fish, do not have all the hydrogen atoms they can carry. If one pair of hydrogen atoms is missing, the fatty acids are called monounsaturated (olive, canola, and peanut oils contain mostly monounsaturated fatty acids). If two pairs or more of hydrogen atoms are missing, these fatty acids are called polyunsaturated (safflower, sunflower, flaxseed, walnut, grapeseed, corn, soybean, and cottonseed oils are primarily polyunsaturated). "High-oleic" sunflower or safflower oil is made from seeds specially bred to contain a higher percentage of monounsaturated fat. Sesame oil contains equal amounts of monounsaturated and polyunsaturated fat.

Kitchen advice
There is no perfect oil for every purpose. For Mediterranean dishes, many cooks prefer olive. For Asian fare, peanut and dark sesame oil are often good choices. For salads, walnut oil adds a light, nutty flavor. For everyday cooking, canola, with its neutral taste, might be best. There are many things to consider when choosing oils, including the flavor: a bland or mild flavor may work better for certain cooking needs than oils with a full flavor, such as olive or peanut oil. In addition, olive or canola oil is usually better for high-temperature frying (see above).

UC Berkeley Wellness Letter 2009