Are all saturated fats bad for you? What about coconut oil? Is it dangerous to heat olive oil? Which is better: polyunsaturated or monounsaturated fat? We asked a few of the country's leading nutrition experts, and here are their answers.

Is it true that you should not heat olive oil?

According to Dr. David L. Katz, a professor at the Yale School of Public Health, "Olive oil is, in general, a very nutritious choice; another is canola oil. Unsaturated oils are less tolerant of heat than saturated oils, however. When unsaturated oils are heated, some trans fat can form. This is the basis for claims that unsaturated oils such as olive oil, which is predominantly monounsaturated, are unsafe to cook with." But the claims are unfounded. "The degradation of oils occurs mostly at the 'smoke point,' literally the temperature above which the oil gives off smoke. This temperature is reached in deep fryers but is rarely reached with home cooking. With home cooking, there will still be some degradation of olive oil, but the effect is minimal. Population studies indicate that use of olive oil is associated with net health benefit — and that certainly includes use in cooking."

Bottom line: Olive oil is safe to cook with, but don't deep-fry in it.

Are all saturated fats unhealthy?

There is clear evidence that not all saturated fatty acids are created equal. "Stearic acid, for instance, appears innocuous; it does not raise serum cholesterol or increase the risk of heart disease. This is one of the reasons why dark chocolate is as heart-healthy as it is," says Katz.

So why has saturated fat been vilified? "Most of the demonization of saturated fat is based on the belief that it always raises cholesterol, an argument that has two huge holes in it," says nutrition specialist Jonny Bowden, author of "The Healthiest Meals on Earth" (Fair Winds Press).

The fact is that saturated fat doesn't always raise cholesterol, though it sometimes does. "We now know that there are many more types of cholesterol than just the commonly understood 'LDL-bad' and 'HDL-good.' LDL alone has at least five different subtypes, and some of them (LDL-A) are absolutely harmless while others (like LDL-B) are not. Saturated fat tends to raise LDL, but it sometimes raises the harmless subtype, not the 'bad' subtype. It also raises HDL, frequently more than it does LDL, leaving an overall better blood lipid profile than before, even though the total cholesterol number may have gone up," Bowden says.

Additionally, "Cholesterol is turning out to be a very poor predictor of cardiovascular disease and death, as we saw in those trials of the cholesterol drug that lowered cholesterol more than any before but did nothing for heart disease, plaque or mortality. If you take the fear of cholesterol-raising out of the equation, what's the problem with saturated fat? Not too much," adds Bowden.

However, that doesn't mean you should start doubling up on the prime ribs. "Some saturated fatty acids are still very much implicated — in particular, palmitic and myristic acid. So red meat is still a concern; choosing meats that are lean with relatively low saturated fat content is the way to go," says Katz.

Pritikin Nutrition Research Director Dr. James J. Kenney is strongly opposed to any levels of saturated fat in the diet. "There are no naturally occurring fats that are high in saturated fats that do not raise LDL-C (low-density lipoprotein cholesterol), because they contain palmitic, myristic and lauric acids — the three saturated fatty acids proven to raise LDL-C and promote atherosclerosis." He goes on to argue that the only difference among the LDLs is that in some people some LDL patterns may be less harmful than in others — however, they are still dangerous.

Bottom line: While no one is suggesting a diet high in saturated fat, limited amounts of whole-food sources such as "eggs, butter, grass-fed meat and the like may not be as bad as we once thought, especially when intake is balanced with plenty of anti-inflammatory omega-3s and phytonutrients from vegetables and fruits," Bowden says.

Coconut oil — can it be healthy with all that saturated fat?

As for coconut oil, the jury is still out.

"There is evidence that the mix of saturated fatty acids in coconut oil may not be as harmful as once believed, but there is evidence to the contrary, too. It is likely that coconut oil will prove to be less harmful/atherogenic than once believed, but very unlikely that it will emerge as competition for olive oil or canola oil as one of the most healthful options. It may, however, make a good alternative to trans fat in commercial foods," says Katz.

However, Kenney believes that the mere suggestion that coconut oil is safe is naive, saying, "Coconut oil is extremely high in the three saturated fatty acids proven to raise LDL-C and promote atherosclerosis."

Bowden is more optimistic. "Coconut oil — provided it's 100 percent organic and extra virgin (like Barlean's Coconut Oil, for example) — is a superfood. It suffered from a bad rap due to two concerns: One, it's high in saturated fat, and two, the early coconut oil sold in the '70s was an inferior product, high in trans fats and highly processed (definitely an unhealthy oil)."

"The fat in coconut oil is largely lauric acid, a particularly healthy fatty acid that has antiviral and antimicrobial properties and is helpful for the immune system. It also contains the fatty acid caprylic acid, which is well known as a 'yeast' fighter," says Bowden.

Bottom line: Probably not as bad as once thought, and certainly worth trying when using oil — but use it sparingly. One tablespoon is still about 120 calories. Just for comparison purposes, olive oil also has 120 calories per tablespoon, but only 1.86 grams of saturated fat, whereas coconut oil has 11.76 grams of saturated fat. Kenney, however, has a different bottom line: "The more coconut oil you eat, the higher your total and LDL-C levels will go, and the more atherosclerosis you will develop. If Americans eat more butter and/or coconut oil, buy stock in the drug companies making cholesterol-lowering statin drugs."

Which is better: polyunsaturated or monounsaturated fat?

Both do good things for the body, but monounsaturated fatty acids might win by a nose in the race for heart health. According to Lona Sandon, a professor of nutrition at the University of Texas Southwestern Medical Center at Dallas, "Monounsaturated fats help lower total and LDL cholesterol levels while increasing the artery-protective HDL cholesterol. Monounsaturated fats may also help lower levels of inflammation in the body. Foods rich in monos include olive oil and tree nuts such as walnuts."

Polyunsaturated fats include the much-talked-about essential fats known as omega-3s and omega-6s. In general, polyunsaturated fats lower total and LDL "bad" cholesterol, but they can also lower heart-healthy HDL cholesterol — which is not good.

"Omega-3s are known for lowering triglycerides, blood fats and decreasing total cholesterol. They are also helpful for lowering inflammation and maintaining a healthy brain. Although omega-6s are essential for your diet, too much may lead to more inflammation.

"Corn, safflower, soybean, sesame and sunflower oils, and nuts or seeds are all good sources of polyunsaturated fats. The omega-3 type is found in greatest amounts in fatty fish like salmon and tuna. Walnuts and ground flaxseed are also sources of omega-3s," says Sandon.

Bottom line: Both are good in moderation.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.