THE PLOT THICKENS OVER FAT.

Byline: Steven Pratt Chicago Tribune

The story of dietary fats is a slippery one that gets more complicated the more research is published. But despite the tangle of information, some rules remain clear.

A decade or so ago things seemed pretty simple: Saturated fats were bad because they raised levels of cholesterol, a primary risk factor for heart disease and stroke. Polyunsaturated fats were good because they didn't.

Dietitians recommended diets high in carbohydrates and low in fat, especially saturated fats.

Then we started learning about low-density lipoprotein (or LDL), the bad cholesterol; and high-density lipoprotein (or HDL), the good cholesterol. And researchers started talking about monounsaturated fatty acids, such as those in olive oil.

Saturated fatty acids, we learned, would raise LDL and HDL. If you substituted polyunsaturated fatty acids, the LDLs went down - but so did the HDLs, though not as much. Monounsaturates, on the other hand, lowered LDLs but slightly boosted HDLs when substituted for saturates.

Then up popped another risk factor: triglycerides, the molecules that transport the fatty acids and vitamins through the blood. High triglyceride levels also increase risk of heart disease and other disorders. Saturated fats elevate triglycerides, as do polyunsaturates, though not as much. Monounsaturates may lower triglycerides slightly.

At the same time, those high-carbohydrate diets recommended earlier started being blamed for raising triglycerides and for contributing to diabetes.

That helped propel the olive oil-rich, Mediterranean diet into vogue.

As intricate as this fat story was, the plot thickened even more.

Food manufacturers scrambling to keep pace with dietary trends began eliminating saturated fats like butter, lard and tropical oils, replacing them with polyunsaturated vegetables oils that had been chemically stiffened and stabilized. But these ``hydrogenated oils'' created new troublesome substances called trans fatty acids.

Research showed that trans fatty acids can raise LDLs and may lower HDLs. Some scientists have asked the government to require them to be labeled as saturated fats.

The truth is that although the terms saturated, polyunsaturated and monounsaturated are convenient, there are dozens of kinds of fats in the diet, each with its own profile.

The latest wave of studies confirms some characteristics of two polyunsaturated fatty acids, the so-called omega 3s, which are abundant in fish. Unlike other polyunsaturates, these ``fish oils'' may help protect against heart disease by keeping the blood from clotting. They also may counteract the inflammation of rheumatoid arthritis and lower cholesterol.

Can we sort through such an information tangle? Is there a take-home message?

``Fats do have some beneficial effects, but how much and in what proportion is still a big hole in our knowledge,'' says Penny Kris-Etherton, professor of nutrition at Pennsylvania State University in University Park. ``It's complex, but there are some basics:

``Universally, scientists agree on the need to lower saturated fat to less than 10 percent of calories. If you do that, you also reduce your total fat and calories. For some people, that diet is perfectly appropriate, especially for those who are overweight.'' You lower your risk of several diseases in addition to heart disease and diabetes, she says.

But some people don't need to lose weight - or don't want to. But if you reduce saturated fat, with what will you replace those calories - carbohydrates or another fat?

Monounsaturates, which are pretty neutral, probably won't decrease your HDL or increase triglycerides.

But omega 3s, which are polyunsaturated fats, also may have some benefits, especially for people with arthritis. And they help keep blood platelets from sticking and clots from forming.

Omega 3s must come from eating fish: They aren't readily available in vegetable oils. You can take fish oil supplements, but only under medical supervision, Kris-Etherton says.

One solution is to eat two fish meals a week in place of meat: That would supply a good measure of omega 3 fatty acids while decreasing saturated fat intake, she says.

If you replace the saturated fat with monounsaturates from olive oil, canola and nuts, be especially cautious of the amount, she says. ``Just because you change from high-fat whole milk to skim doesn't mean you can start sopping up a saucer of olive oil with your bread.'' Olive oil is still a concentrated fat.

Replacing fat calories with carbohydrates has many advantages. Population studies worldwide show that the more fat that people consume, the more overweight they are, she says. Skinnier people consume fewer fat calories.

The real skinny on fats

Even though some fats are more healthful than others, none is all good or bad. Olive oil, for instance, is touted for its high proportion of monounsaturated fat (77 percent), but even lard consists of 47 percent monounsaturated fat. But by reducing your intake of saturated fat, you also achieve the desirable objective of trimming your total fat consumption.

Which fats do what?

Saturated fatty acids

Sources: Tropical oils, animal fats, meats, eggs, dairy products.

Uses: Provide mouthfeel.

Health effects: Raise LDLs, HDLs and triglycerides

Stearic acids

Sources: Red meat, chocolate.

Uses: Enhances flavor of baked goods.

Health effects: Neutral on LDLs and HDLs.

Trans fatty acids

Sources: Hydrogenated vegetable oils, margarine, snack foods, cookies.

Uses: Stiffens margarine, gives body and mouthfeel.

Health effects: Raises LDLs slightly, lowers HDLs slightly.

Monounsaturated fatty acids

Sources: Olive oil, canola oil, avocados, nuts.

Uses: All-purpose cooking oils.

Health effects: Lowers LDLs, neutral on HDLs, may lower triglycerides.

Polyunsaturated fatty acids

Sources: Corn, soy and safflower oils; nuts, seeds.

Uses: All-purpose cooking oils.

Health effects: Lowers HDLs and LDLs, may raise triglycerides.

Omega 3

Sources: fatty fish, fish oil, flax seed.

Health effects: Lowers LDLs, may raise HDLs, retards clotting, relieves inflammation.

CAPTION(S):

Box

Box: The real skinny on fats (See text)