Are Americans really changing what they eat? And if so, is it making a difference in the nutritional status of the nation?

The answer is a qualified yes, based on new results of a nationwide food survey by the U.S. Department of Agriculture.

Yes, Americans are changing what they are eating. Yes, they are getting the message about eating more fiber, more starches, more fish and poultry and less red meat. Yes, they are cutting back on fat and cholesterol. And yes, these changes are making inroads on the nutritional status of the nation -- but not always for the better.

The survey found, for example, that women who ate the least amounts of fat and cholesterol in their diets, also consumed the lowest amounts of the key nutrients calcium, iron and zinc.

"This . . . cautions us that guidance on how to reduce dietary fat must also emphasize getting needed nutrients," said Dr. Susan Welsh, director of the Nutrition Education Division at USDA's Human Nutrition Information Service. "It makes us wonder about guidance that suggests that meat, with its highly available iron and zinc is an undesirable food."

Results of the USDA survey, which was conducted in 1985, were presented on October 1 at a food safety and nutrition conference, sponsored by the USDA and the Food and Drug Administration.

The study found that while significant deficiencies in the American diet are rare, women and children are still not getting adequate amounts of folacin, iron, zinc, vitamin B-6, magnesium and calcium. Diets that skimp on these vital nutrients increase the risk of some long-term nutritional problems, ranging from anemia to osteoporosis.

"More than 80 percent of women did not achieve RDA {Recommended Daily Allowance} levels for these nutrients," Welsh said. Over a period of four days, more than half the women were getting less than 70 percent of the RDA for these key nutrients.

Like their mothers, most of the children studied, especially those 1 to 3 years old, fell short on daily consumption of iron, zinc and calcium. Slightly older children, those 4 and 5, also were not receiving enough vitamin B-6, magnesium or folacin to meet U.S. RDA requirements, the survey found.

At the same time, it's clear that Americans are changing their eating habits in the name of good nutrition. An FDA telephone survey of 4,000 randomly selected consumers conducted in 1986 found that 61 percent of participants reported eating differently because of health concerns.

The USDA survey also found that between 1977 and 1985: Women consumed more skim and low-fat milk. They ate fewer eggs, more mixtures of food containing meat, poultry or fish and more grain products, such as pasta, bread and crackers, and less meat. Children ages 1 to 5 also showed some of the same dietary shifts as their mothers. They, too, drank more skim and lowfat milk. They ate more grain products and less meat and eggs. But unlike their mothers, they ate 30 percent more vegetables and fruits in 1985 than in 1977. They also drank far less carbonated soft drinks, even though their mothers drank more. Despite making these dietary changes, most women were not successful at meeting the new recommendations for fat. About 37 percent of calories in women's diets still came from fat -- a figure well above the 30 percent of calories recommended by the American Heart Association and other groups.

What's more, the higher a woman's income, the higher her fat intake, the USDA survey found. High income women consume more fat not by eating more meat or by drinking whole milk than low income women but rather by eating more cheese, cream desserts, salad dressings and table fats, such as butter or margarine. Confusion about nutritional facts may also explain why many consumers have failed to achieve desired dietary goals. In reporting on the FDA survey, Dr. James T. Heimbach, head of the agency's research and education staff at the Center for Food Safety and Applied Nutrition, noted that the study revealed three key misunderstandings about cholesterol and saturated fat.

Almost half of those surveyed mistakenly believed that a food labeled "cholesterol-free" was also low in saturated fat. In fact, many cholesterol-free foods contain large amounts of saturated fat, which also raises blood cholesterol levels. Examples include fried foods -- for instance, french fries -- baked goods, including some crackers, and vegetable oils and shortenings, including margarine.

Most consumers were also confused about the meaning of hydrogenated oil or fat. When a fat or oil is hydrogenated, it becomes more saturated. For example, nutrition-minded consumers may choose to use corn oil because it contains largely polyunsaturated fat -- the type that helps lower blood cholesterol levels. But often food manufacturers process corn oil by adding hydrogen atoms -- hydrogenating it -- a process that at room temperature turns the liquid corn oil into more of a solid.

Because hydrogenated fats are saturated fats, they raise blood levels of cholesterol. That means some cholesterol-lowering effects of polyunsaturated fat in corn oil are canceled by the hydrogenating process. In the FDA survey, more than 60 percent of consumers reported that they didn't know what hydrogenated fat or oil was and almost 30 percent of participants thought a hydrogenated oil or fat was less saturated than it had been before. Misunderstandings also surfaced regarding which foods contain cholesterol. Almost half of those surveyed mistakenly thought that all products with fat or oil also contained cholesterol, and 16 percent said they didn't know which foods had cholesterol.

Only about one third of the respondents knew that it is animal products alone -- meat, poultry, eggs, dairy foods and fish -- which contain cholesterol. How foods appeal to a particular consumer can also make a difference in the amount of nutrients that are consumed. In one study, according to Dr. Walter Mertz, director of the USDA's Human Nutrition Research Center in Beltsville, people from Thailand were fed a diet of Swedish food, which was much more bland than their usual fare, and people from Sweden ate Thai foods, which were far spicier than the usual Swedish dishes. Researchers found that the Thai subjects absorbed much less iron when they ate Swedish food than when they ate spicy Thai food, even though the iron content was identical. Similarly, the Swedish subjects absorbed much less iron from the Thai food. In both cases, the lowered iron absorption had nothing to do with eating less food.

The findings suggest, Mertz said, "that if you don't like the flavor or taste of a particular food, that you don't get as much of the benefit from the food."

Exactly why taste should account for such a striking effect on absorption of a key nutrient like iron is not known, Mertz said. But such a result points to the importance of personal preference in looking at the whole nutrition picture.

With so much consumer confusion and the rapid pace of new nutritional knowledge, the best bet for consumers, said Mertz, is to follow common sense and eat a variety of foods.