In the name of good health, you switched from butter to margarine, traded three-egg omelets for oat bran pancakes and gave up T-bone steaks altogether.

Then you were told that eating eggs is fine, butter is better than margarine, oat bran's benefits are overblown and red meat is an essential part of a balanced diet.No wonder 21 percent of Americans say contradictory health information is their biggest obstacle to eating right.

What are they to believe? That health is an inexact science, for starters. That research moves slowly and not always forward. And that you can't always believe everything you read.

"Our nation is focused on getting a quick fix, and people seize on any new information that comes out," says Mary Lee Chin, a Denver dietitian. "No one is willing to wait and see how it fits in with what else we know."

Even scientists are confused when they read stories about "amazing research results." So much research is under way that no one can keep up with it all, and unless they read about it in scientific journals - and read the rebuttal that follows in later journals - you're not getting the whole story.

When scientists read other's results, here's what they keep in mind:

- One study does not the truth make. Scientific knowledge is built one piece at a time, the result of many studies over long periods. Experts analyze the findings, throw out odd ones and accept those that point to the same results time and again.

- All studies are not created equal. "It's easy to publish a paper," says Dr. Bradley Hurst, reproductive endocrinologist at the University of Colorado Health Sciences Center, "but whether it's done well is another story. My best advice is to look at everything with some skepticism."

- Different methods result in different findings. If a group of people is observed, for example, scientists can only spot trends and make educated guesses about why they're happening. Laboratory scientists must follow up, designing experiments to test the theories.

"Sometimes they prove the opposite," says Dr. Tim Byers, a nutritional epidemiologist at the University of Colorado's Health Sciences Center.

But while this adds to the body of scientific knowledge, it also exasperates people who read stories about the first theory and take a knee-jerk reaction.

Here's what some experts say, for example, about 10 research findings that seem to contradict earlier advice:

- Is butter better than margarine, or vice versa?

Butter has saturated fat, which is hard on the arteries and can contribute to heart disease, while margarine has unsaturated fat. But later research found margarine also has transfatty acids, which can cause cancer.

Neither is good for your heart, and neither is better for your waistline.

The advantage of margarine: it's softer, so you can spread it thinner than hard butter. Whipped tub spreads are even better.

- Can you protect yourself from cancer by taking beta carotene? That's what scientists thought, but two studies showed an increase in the incidence of lung cancer among smokers who took beta carotene capsules.

It's a classic case of noticing a health benefit and trying to figure out why. People who ate fruits and vegetables filled with carotene had lower cancer rates, but feeding others pure beta carotene didn't duplicate the effects.

"It now seems you need the complex combination of nutrients you can get only in fruits and vegetables," says dietitian Liz Marr, spokeswoman for the American Dietetic Association.

- How thin must you be to be "healthy"?

Very thin, one set of researchers reported in September. But losing more than 10 or 20 pounds can be hazardous, another found.

The answer may lie someplace in between, Byers says. The "very thin" recommendation came from the Harvard Nurses' Study, a long-term look at the health of 115,000 nurses. Those who weighed within 20 pounds of their high-school weight lived longer, and those who kept it very low lived longest.

Although the study is good, that finding isn't, Byers says. It's based on faulty analysis, he wrote in a letter to the journal that published the original results. "There's no evidence that being thin is particularly good," he says, "but there's a lot of evidence that being overweight is bad."

The earlier study found that overweight people who lose a lot of weight don't lengthen their lives and may harm their health. Byers thinks it indicates that focusing on weight isn't the answer - living a healthy lifestyle is.

- Is it safe to eat eggs again?

It never wasn't safe, but to hear the reports from 10 years ago, swallowing eggs was akin to downing rat poison. Researchers warned to stay away from cholesterol and reported that egg yolks had huge amounts of the stuff.

Later studies identified a scarier culprit in heart disease as transfatty acids, not cholesterol. More accurate tests found 213 grams of cholesterol in egg yolks, not 275.

The bottom line: Eggs are a great source of protein and shouldn't be avoided unless your doctor prescribes a low-cholesterol diet.

- Can fish (and fish oil) really protect against heart disease?

The jury's still out, Chin says. Some studies have found people who eat a lot of fish have lower rates of heart disease. Another found that men who load up on fish are just as likely to have heart trouble as those who don't.

Chin's advice: Keep eating fish, not because it's a magic potion but because it's a good source of low-fat protein. Fish oil tablets haven't been proven effective.

- Are beer and wine your friends or your enemies?

It depends on how much you drink. Dozens of studies have found one drink a day (especially red wine) keeps your heart healthy. Dozens more show that too much alcohol can damage the liver, add to your love handles and wreak havoc in your life.

The best advice: If you don't drink, there's no health-related reason to start. If you do drink, relax and enjoy a cocktail. As a side benefit, you'll eat more slowly if you're sipping wine.

Just remember: "Nobody's saying more is better," says James Hill, executive director of the Center for Human Nutrition at CU's Health Sciences Center.

- How hard should you exercise?

Don't sweat it, say the Centers for Disease Control and Prevention and the American College of Sports Medicine. If you walk or garden for 30 minutes a day - even in three bursts of 10 minutes - your risk of heart disease begins to drop.

No strain, no gain, counters Harvard researcher Dr. I-Min Lee. She's spent 26 years studying the same group of men and found those who exercise strenuously add years to their lives.

The trick is reading between the lines. The first set of guidelines was established to help sedentary people get moving, says Jackie Berning, a dietitian and exercise physiologist at the University of Colorado in Colorado Springs. The second looks at which amateur athletes are healthier.

"The evidence is clear that every little bit helps. Five minutes of exercise will help you burn more calories, although it may not do much to improve your fitness level," he says.

Adds Berning: "The thing to remember is that, with exercise, anything is good. If you do 30 minutes of moderate exercise every day, it won't make you svelte, but you'll be healthier."

And yes, if you do more than 30 minutes or boost the intensity, you will get bigger gains.

- Should you load up on carbohydrates and cut back protein, or load up on protein and cut the carbs?

Dietitians and scientists alike have urged people to cut back on fats and proteins and boost their carbohydrate intake. That's because the body prefers to burn carbohydrates while it stores fats.

Now authors are promoting a high-protein diet, saying too many carbohydrates can make you fat.

It's all a question of balance, Chin says. Trying to live on bagels and chips is as silly as eating nothing but pineapples and cabbage. The best diets are less than 30 percent fat, 15 percent protein and 55 percent complex carbohydrates.

- Can estrogen increase women's risk of breast cancer?

Half the studies say yes, half say no. Until more research is done, it's anyone's guess.

"If there is an increased risk, it doesn't seem to be dramatic," Hurst says. Scientists agree that estrogen therapy lowers women's risk of heart disease after menopause. They also agree that estrogen, taken alone, contributes to increased uterine cancer. Those risks go away when progesterone is added.

Why do breast cancer studies differ? "Even when the studies are done well, there's a chance the women who are taking hormones are treated differently," Hurst says. "Most doctors are vigilant about breast exams with women who are on hormones, and other women may not be screened as closely."

- Is red meat a no-no, or should it be part of your diet?

When cholesterol and saturated fat were targeted a decade ago, red meat fell out of favor. Now experts say that, without red meat, you can't get the iron, zinc, B vitamins and trace minerals you need.

As vegetarians have known for years, it's possible to get vitamins and trace minerals from fish and grain, but it takes effort. However, red meat has come back into favor for other reasons, too.

In response to early reports, the cattle industry is now producing leaner beef, and is advertising it as one ingredient in a healthy meal. "You don't see anyone holding up a hunk of beef anymore," Chin says. "They show it as part of a stir-fry dish instead."