Classification of Dietary Fats

HDL versus LDL (and cholesterol)

Fat in the diet (and body fat as well) is in the form of fatty acids and cholesterol. A certain amount of cholesterol is needed as an important component in the structure of cell walls. But too much cholesterol, which is synthesized in the liver as well as from your diet, can cause fatty deposit in blood vessel walls. Cholesterol is transported to the cells by special molecules called lipoproteins. The two main lipoproteins are LDL and HDL. HDL is better than LDL from the perspective of developing fatty deposits in blood vessel walls - it appears that LDL is the major culprit in allowing deposits to form while HDL may actually be able to transport some cholesterol OUT of the blood vessel walls. What you want is a high HDL/LDL ratio.

This Dr. Mirkin blog from 2020 updates what we know about HDL and explains why a high HDL alone is not a reliable indicator of cardiovascular health. The reason? There are 2 forms of HDL - regular HDL cholesterol and another form called Nascent HDL. NHDL can clear plaque-forming particles from the arteries, and carry them to the liver, a thousand times faster than regular HDL and as such is much more effective in preventing cholesterol build up in artery wall plaque. The current test for HDL cholesterol does not differentiate the two types. Thus a high HDL by itself does not provide the whole picture.

FOUR TYPES OF FAT

• Saturated fat is hard at room temperature, usually comes from animal fats (meat, cheese, dairy products), and is the least desirable from a health perspective. It increases the level of low density cholesterol (LDL, the bad one) and can facilitate the development of clogged arteries, strokes, and heart attacks.

• Monounsaturated fat is in vegetable oils (olive, canola, peanut oils) and can actually have a slight cholesterol lowering effect if your overall fat intake is low (less than 60 grams per day). It is generally felt to be neutral in terms of cholesterol, and does not raise the level of either LDL or of HDL. Its chemical structure keeps it a liquid at room temperature. And as an added benefit there is some evidence that there may be a decreased risk of certain cancers with an increased intake of monounsaturated versus polyunsaturated fats.

• Polyunsaturated fat is also found in plant oils such as soybean, cottonseed, corn, sunflower, and safflower. These fats increase the level of LDL and reduce the level of HDL. Note that not all plant oils are polyunsaturated - coconut, palm, and cocoa butter are highly saturated.

• Trans fat is formed when food companies hydrogenate (add hydrogen molecules to solidify) unsaturated fat. They do this to meet public demand for unsaturated fats while providing a product that is not greasy or oily. Unfortunately, this also makes the fat act like a saturated fat in terms of LDL and HDL. In fact they may be worse than saturated fats as they not only raise the LDL, but also LOWER the level of HDL - a double whammy.

FISH and FAT (omega-3 fatty acids)

There are many studies that have supported the benefits of eating fatty fish - albacore tuna, salmon, and mackerel - at least two to three times a week. And it appears that the omega-3 fatty acids are the heart healthy component. This is based on the observation that eating an equal number of servings per week of fish with a low omega-3 fat levels has no effect on heart attack risk. Vegetarians can find omega-3 fatty acids in ground flax seed (and its oil) as well as in walnuts.

The current recommended daily intake has been set at 0.3 to 0.4 grams. What are the best fish for omega-3s?