Good Fats, Bad Fats: Get with the (blood) flow

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There’s a reason why you don’t pour vats full of fat down your sink; fat clogs up the drain and it shuts down. And that’s exactly what happens to your arteries when you overload them with “bad” fats; namely, saturated fat and trans fat.

These types of fats cause a plaque to form on the walls of your arteries. When your arteries are blocked up with this plaque, oxygen-rich blood can no longer get through the arteries to reach your heart, brain and other organs in your body. And (you guessed it) heart attack and stroke are just around the corner.

So what can you do to reduce the risk of this happening to you? Read on to find out more.

Bad fats, blocked arteries and organ disease

When you eat saturated and trans fats, cholesterol is deposited in the arteries. When you eat too much of these fats, high deposits of fatty substances and cholesterol in the arteries (among other things) cause a plaque to form and the arteries to harden and narrow; artherosclerosis is the medical term that describes this hardening and narrowing of the arteries. (Athero is Greek for paste; sclerosis means hardness). Eventually, the build up of plaque can get large enough to actually restrict blood flow through the artery, or it can rupture and cause a clot to form. This clot then travels to other parts of the body.

A plaque-blocked artery, or a clot in the artery, affects the organ to which the artery is connected. In both cases the organ that is supplied by the artery is starved of blood and oxygen and the organ’s cells may die or suffer severe damage. If the organ is the heart, the blockage or clot can cause a heart attack (coronary thrombosis); if the organ is the brain, the blockage or clot can cause a stroke. If blood supply to the arms or legs is restricted, it can cause difficulty with movement, and, eventually, gangrene.

The good news is that unsaturated fats, or “good” fats, can have the opposite effect by improving blood cholesterol levels, lowering platelet stickiness (platelets are the cells in the blood involved with the process of clotting) and reducing the adhesion of plaque to the artery walls.

Blood cell aerobics

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Saturated fats further restrict blood flow through the arteries because they stiffen red blood cell membranes and increase blood viscosity (thickness). Stiff red blood cells are inflexible and can’t easily navigate their way down the arteries. They can also pile up to form what look like coin stacks, called rouleaux. In narrow blood vessels this makes blood flow and oxygen release even more difficult.

But again, the good news is that unsaturated fats improve blood flow by reducing blood viscosity and increasing the flexibility of red blood cells. Flexible blood cells can turn and twist themselves more easily and thereby squeeze through tiny arteries and capillaries which are often half their diameter.

Good or bad? How to tell the big “fat” difference

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It’s comforting news that some fats are not in the healthy-eating “sin bin”. What’s important now, however, is to make sure we eat the right types of fats – some of them do need to stay permanently off the field – and the right amounts of them. Replacing “bad” fats with “good” fats leads to much healthier cholesterol levels, and when cholesterol levels are low, there is less chance of atherosclerosis. So how do you tell the difference between the two?

It’s not too difficult, actually. Fats that are described as saturated or trans are the most critical ones to limit (limit to 10% of your total calories). Fats described as monounsaturated or polyunsaturated, on the other hand, are ones you should include as a regular part of your diet. Overall, fat calories should make up between 20% to 30% of your daily calorie intake.

Most foods that contain fat will have a mixture of types of fat, but one fat will usually be predominate. The following table shows the four main fat groups and foods containing mostly that type of fat.

Monounsaturated Olives, olive oil, canola oil, peanut oil, cashews, almonds, peanuts and most nuts, avocados
Polyunsaturated Corn, soybean, and safflower oils, fish
Saturated Full cream milk, butter, cheese, ice-cream, red meat, chocolate, coconuts, coconut milk, coconut oil, palm oil
Trans Vegetable shortening, partially-hydrogenated vegetable oil, some fast-foods, some commercial baked goods

You can also check food labels for fat content. Although listing trans fat is not yet required in Australia, listing saturated fat is a requirement. If you read the label, and keep in mind which sorts of foods are also going to be high in trans fat, you should be able to work out fairly easily whether a food is a “goodie” or a “baddie” in terms of fat content. But don’t forget to watch the other nutritional values as well, especially the calories if you are trying to manage your weight. And, as always, keep portion sizes under control, whether they’re full of good fat or not!

Related links :

References :

This article was compiled in consultation with Calorie King experts and in reference to the following sources:

American Heart Organisation, ‘Atherosclerosis,’ www.americanheart.org

Charlotte Grayson, MD, ‘Trans Fat Raises Bad Cholesterol,’ WebMD Medical News, April 2004, www.content.health.msn.com

Gordon M. Wardlaw, Contemporary Nutrition (2003), McGraw-Hill Higher Education, New York, pp 143-159

Calorie King
CalorieKing's mission is to provide the best information, tools and education to Australians to help them conquer their weight.

CalorieKing is the brainchild of Allan Borushek, registered dietitian, co-found here at food.com.au and author of "Allan Borushek's Pocket Calorie & Fat Counter", Australia's best-selling calorie counter for over 30 years.

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