a way to stoke the inner furnace with energy needed during the day. Today it seems like every bite must be scrutinized for saturated fat, cholesterol, sodium, fiber and complex carbohydrates.

The adage "you are what you eat," coined by the late nutrition guru Adele Davis, has been replaced with a litany of warnings. Trim fat. Stay lean. Go for the skim. The words roll off the tongue with a religious fervor once reserved for saving souls, not for reducing the risk of early bodily demise from heart disease and cancer.

But what does it all mean? Should one worry about consuming everything from caffeine to fat? Must old-time favorite foods be scorned forever in order to gain healthful redemption and, presumably, longer life?

In a word, no.

Most of the dietary changes recommended today do not switch the concerned consumer to food martyrdom, but rather back to the way Americans ate at the turn of the 20th century. That means more potatoes (sans butter, of course). Less meat. More oatmeal. Fewer whole-milk products, but more low-fat dairy foods. More vegetables. More beans. More fruit. More rice. More bread. Less junk food -- particularly the 40 gallons of sugar-sweetened soda pop consumed by the average American in 1983.

For everyone except die-hard health food fanatics, all the debate boils down to this: Cut fat and increase the amount of starchy foods. These two fairly simple changes in eating habits lead to a host of healthful rewards.

"The most important, the number one thing, is to eat less fat," says Michael Jacobson, director of the Center for Science in the Public Interest, a nonprofit, Washington-based consumer group. "That means fat of all types, but especially saturated fat because of the risk of heart disease and cancer."

High-fat diets -- and the American diet ranks among the fattiest in the world -- are associated with increased levels of cancer of the breast, colon, uterus and prostate. And since high dietary fat increases blood levels of cholesterol, these diets are also linked to an increased risk of heart attacks, stroke and other cardiovascular diseases.

The average American consumes 40 of every 100 calories from pure fat. As a result, some "35 percent of all cancer deaths may be related to the way we eat," the National Cancer Institute reports in a new pamphlet for consumers. NCI is joining the National Academy of Sciences, the National Heart Lung and Blood Institute and the American Heart Association in recommending that Americans reduce total fat intake to 30 percent or less of daily calories. For a 2,000-calorie daily diet, that works out to about 600 calories a day of fat -- still higher than many countries, but a level that health experts believe can be achieved comfortably by most Americans.

"Thirty percent fat is a reasonable interim guideline," says Dr. William DeWys of the National Cancer Institute. "If too drastic a change were suggested, people would get frustrated and abandon the effort. To go below 30 percent takes discipline and hard work."

Trim the fat and, automatically, calories are trimmed. One gram of fat contains nine calories -- more than twice the calories contained in either a gram of protein or a gram of carbohydrates. People who cut down on fat usually lose weight, and that helps with another chronic American health problem -- the on-going battle of the bulge.

The National Health and Nutrition Examination Survey, conducted from 1976 to 1980, disclosed that about 33 million adults are overweight in the United States. Of these, some 12 million are severely overweight.

"Obesity per se is a risk factor generally recognized for at least half a dozen diseases," explains Walter Mertz, director of the Department of Agriculture's Human Nutrition Unit. Among those diseases are high blood pressure, heart disease, diabetes, gout and cancer. "Independent of the fat in the diet , there seems to be some association with obesity and cancer," says Dr. Peter Greenwald, director of cancer prevention and control division at the National Cancer Institute. "The main ones are cancer of the endometrium uterus , the gall bladder and possibly the breast. If you want to be surest, you probably keep trim."

But forget fanatical dieting and major sacrifices. Super skinny is not being advocated. These are moderate guidelines, based on scientific research, and they recommend desirable weights for each person based on sex, age and body type.

"I would really get across the concept of maintaining desirable body weight, and by that, I mean staying within the range of the 1959 Metropolitan [Life Insurance Co.] weight tables," recommends Dr. Artemis Simopoulos, director of the National Institutes of Health Nutrition Coordinating Committee. The 1959 tables suggest lighter body weights than the revised tables published in 1983.

After cutting back on fat, both in the diet and on the body, the next step is to increase the amount of starchy foods. For most people, this switch will come naturally. Foods high in fat offer high energy, and paring fat from the diet can increase hunger. People hungry after cutting down on fat tend to reach for carbohydrates, and that includes a range of foods from fruits and vegetables to bread and rice.

"When you cut fat, automatically you're going to increase carbohydrates eaten ," Simopoulos says. "Whether you increase complex carbohydrates is a choice. Some people like it and some people don't."

Carbohydrates come in two varieties. Simple carbohydrates are sugars. Sucrose. Glucose. Fructose. All have chemical structures that enable them to be absorbed easily by the intestinal tract. Complex carbohydrates also contain simple sugars, but they're linked together to form large chemical units. It takes a little longer for the body to break these complex carbohydrates down into simple sugars.

Whole grain foods contain complex carbohydrates, as do potatoes, pasta, rice and beans. "People have the misconception that those foods are fattening," Jacobson says. "But these types of foods tend to be rather filling, and provided you don't slather butter and sour cream all over them, they will not promote obesity."

The other benefit is that complex carbohydrates are also rich sources of vitamins, minerals and fiber. Thus one simple diet change -- cutting down on fat -- starts a cascade of healthful changes that helps control weight, while adding vitamins, minerals and fiber to the diet.

Studies show that a diet rich in fiber can offer protection against cancer and perhaps help lower blood cholesterol levels as well. There's also some evidence that fiber may help control diabetes.

Today, the average American consumes about 10 to 20 grams of fiber a day -- about half of what the National Cancer Institute recommends in a new pamphlet for consumers.

"Populations that consume diets containing twice this amount have a lower rate of cancers of the colon and rectum," the pamphlet says. "So the National Cancer Institute recommends that you eat foods which provide 25 to 35 grams of fiber a day. Larger individuals would be at the upper end of the range; smaller individuals at the lower end."

Why fiber protects against some diseases still isn't known, although there are some important clues. One theory suggests that fiber speeds up the transit time of food through the intestine, which may minimize the effects of cancer-causing agents called carcinogens.

Fiber derived from some vegetables may offer protection because they contain high levels of beta-carotene, a vitamin A precursor. Fruits containing vitamin C seem to inhibit the formation of "nitrosamines, carcinogens that may be involved in a number of different cancers in the digestive system," says NCI's DeWys.

Then there are the cruciferous vegetables, which contain indoles and isothiocyanates. Studies in mice show that these substances help prevent the formation of intestinal tumors. Among the cruciferous vegetables are broccoli, cauliflower, brussels sprouts and cabbage. Experts recommend eating these vegetables at least three times a week.

As for taking supplements of the vitamins, minerals and fiber found in fruits, vegetables and other complex carbohydrates, there's no evidence yet that this will be as protective as eating the real thing.

"If the diet is over 1,500 calories a day and consists of a variety of foods, you don't need supplements for any vitamins or minerals," says Simopoulos.

"The best source of vitamins are in the foods that you buy in the grocery store," adds DeWys. "You get some other protective effects as well that you wouldn't get if you just ate purified vitamin tablets ."

The same advice goes for adding fiber to the diet. "Fiber supplements, unless they're prescribed by your physician, aren't the answer," advises the NCI pamphlet for consumers. "All studies to date show the protective effects are associated with fiber-rich foods. You can add more fiber to your diet if you eat foods like potatoes, apples, pears and peaches with their skins on." (The NCI pamphlet, soon to be published, will be available by calling 636-5700.)

What about all the other foods and food additives that have made headlines in the past decade? Caffeine, nitrites, saccharin, salt and sugar. Here's how they fit into the streamlined dietary picture:

* Caffeine. "There's no clear evidence that it causes any problem," says DeWys. A highly publicized study published a few years ago suggested that cancer of the pancreas might be related to coffee. But one of the faults of that study, DeWys says, was the control group, which turned out to be hospitalized ulcer patients -- people who for medical reasons often don't drink coffee. A closer look at the research, he says, "clarified things to the conclusion that coffee was not associated with cancer of the pancreas."

Other evidence suggests that caffeine may be harmful to some people with high blood pressure. "The caffeine story is a very muddy one," says USDA's Mertz.

"The evidence in my opinion is not strong enough to make sweeping regulations . . . Every nutrient -- and there is not one single exception -- reaches a danger point when you have too much."

* Food additives, though sometimes potentially harmful, "are a much smaller problem than the basic nutritional value of food," says CSPI's Jacobson.

"Probably the worst aspect of additives is that they have made possible the tremendous proliferation of processed foods that are high in sugar and salt and low in dietary fiber."

As for nitrates, NCI's Greenwald suggests limiting their level in the diet. Nitrites are preservatives found in many processed meats, including hot dogs and bacon, and evidence suggests they can be converted into cancer-causing chemicals in the body. He points out, however, that "limiting the level" of nitrates is "not at the level of concern of limiting dietary fat or increasing vegetables."

Smoked, cured and salted foods made in the United States, says NCI's DeWys, are also less worrisome than they once were -- nitrite levels have been cut, for example -- largely because of food industry processing changes.

* Saccharin. Says NCI's Greenwald: "I think that the weight of the evidence is sort of like the additives. There really has not been any real harm demonstrated. I would put this as more of a question."

* Salt. "There is controversy about whether excessive salt intake is a risk factor for everybody," says the USDA's Mertz. "There's pretty much agreement that it is not. The real controversial question is if salt is a significant risk factor for a significant portion of the population. There is absolutely no agreement on that."

The danger is that many people may not know they have high blood pressure. "Here one would say that the use of salt within reasonable limits is probably all right for most people." But the 38 million Americans with high blood pressure "should be careful" about salt consumption.

* Sugar. One teaspoon of sugar contains 16 calories, making this sweetener a high-calorie food. For that reason, sugar is another one of those foods that need to be limited for weight control. It's also a major contributor to tooth decay -- a problem that costs billions of dollars each year.

Eating large amounts of sugar, explains CSPI nutritionist Bonnie Liebman, "dilutes other nutrients in the diet" by displacing calories that could better be consumed from foods containing vitamins, minerals and protein. Sugar appears in various guises in processed foods including as corn syrup, honey, fructose, dextrose and sucrose.

"People need to find out what is best for them," says NIH's Simopoulos. "People have to make changes in a way that's not painful for them. You don't have to suffer. In fact, anything that increases stress we know is detrimental to health."

Perhaps the best way to sum up this new approach to diet is a story that Simopoulos tells about Hippocrates, the father of medicine. Several thousand years ago, Hippocrates advised his patients not to eat figs. The high sugar content, he said, would decay teeth.But an ingenious person helped solve the problem by stuffing each fig with an almond or a walnut. The nuts "automatically cleared the mouth of the figs. They weren't as sticky anymore," she explains.

"The point is you don't always have to give things up. You have to learn how to modify so that you can have your figs and eat them too."