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The Truth About Fats

Millions of Americans grew up believing that carbohydrates — starches and sugars — were the major dietary villains. They viewed potatoes and cakes as fattening, and thought weight loss involved limiting the total number of calories one ate. The centerpiece of restaurant diet plates was a ground beef patty.

But in the last 20 years, nutrition scientists have shown that fat is the primary villain in the American diet. Carbohydrates, including fruits, vegetables, beans, and grains, provide most of the body's energy. Even long-vilified sugar doesn't hurt most people when eaten in moderation.

As far as weight control is concerned, if you limit fat calories, you don't have to worry much about your total caloric intake. "It's not the potato that's fattening," says Ron Goor, Ph.D., co-author (with his wife, Nancy) of The Choose to Lose Diet: A Food Lover's Guide to Permanent Weight Loss. "It's the butter, sour cream, and bacon bits people put on it. The same goes for sugar. Cakes, pies, and ice cream are fattening not because they contain sugar, but because they're loaded with fat. It's people's 'fat tooth,' not their sweet tooth, that gets them into trouble."

Why fat calories are the real villain

How could this be? Simple: All calories are not created equal. One gram of carbohydrate or protein contains only four calories, but one gram of fat contains nine. "Fat calories really sneak up on you," Goor says. "A few handfuls of potato chips have the same number of calories as two medium-sized baked potatoes topped with nonfat yogurt and steamed vegetables."

Carbohydrates have a lot of bulk per calorie. Eating them triggers feelings of fullness, so it's difficult to overeat if you base your diet on them. "If you reduce your fat consumption from the typical 35% to 40% of calories down to the 10% level of my program," says Dean Ornish, M.D., the doctor who pioneered heart disease reversal using a low-fat diet, "you can eat one-third more food without increasing your total number of calories. You feel full and satisfied, but still reduce your risk of heart disease and the other fat-related diseases — and you lose weight."

The body uses fats differently

In addition to their high calorie content, fats are also metabolized differently from carbohydrates. The body uses most carbohydrates quickly, and can only store about one day's worth as glycogen in the liver and in muscle tissue. "If you eat normal amounts," Goor says, "carbohydrates are never stored as fat."

Fats, on the other hand, are not metabolized right away. They are stored as fat in adipose tissue, which has an almost unlimited capacity to bulge with fat. Unlike carbohydrates, fat calories don't cause feelings of fullness, so you keep eating and eating, gaining weight, and increasing your risk of all the fat-related diseases.

Everyone must consume some fats because they are necessary for the synthesis of essential fatty acids. But you only need about 5% of your calories to come from fat to produce all the essential fatty acids your body needs to function optimally.

If a high-fat diet contributes to obesity, does a low-fat diet spur weight loss? In Ornish's program, the average participant lost 22 pounds in one year.

And if a high-fat diet contributes to a host of diseases, does a low-fat diet help prevent them? Here is the conclusion of a report co-sponsored by the American Heart Association, the American Cancer Society, and the Center for Science in the Public Interest, a Washington-based consumer nutrition organization: If Americans cut their fat consumption by about one-third (down to approximately 20% of calories from fat), heart disease and cancer would decline significantly, and the nation's healthcare bill would plummet $17 billion a year. Now that's slimming down.

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