The No. 1 nutritional bad guy of the early 1990s still will be fat as people worry about how much they consume and how it affects their health.
The surgeon general, with the support of almost every mainstream health organization, has branded dietary fat as the most problematic nutrient. Not only is it the prime contributor to heart disease and obesity, and a longstanding national health obsession, but also current research indicates that fat may figure prominently in colon, breast and prostate cancer as well as high blood pressure.
Researchers long have known that a diet high in fats can elevate blood cholesterol levels in many individuals, beginning with young children; but fat nutrition is not that simple. Saturated fats-those found in abundance in animal products such as milk, cheese, butter and meats as well as in tropical fats such as palm kernel and coconut oil-tend to be the nastiest contributors to raising levels of low-density lipoproteins (LDLs) in the blood, or what some call bad cholesterol.
Compared to saturated fats, the polyunsaturated fats-those found in soy, corn, safflower, sunflower and walnut oils-tend to lower LDLs. But they also lower high-density lipoproteins (HDLs), the ``good`` cholesterol.
Lest you believe that solves everything, consider that some research indicates that the polyunsaturates also may contribute to the development of cancer-prone cells in the stomach and elsewhere in the digestive system.
Monounsaturated fats-found in high amounts in olive, canola and peanut oils-tend to lower LDLs without effecting HDLs and thus have a somewhat positive effect on blood cholesterol. But remember, they still are fats, with all the other attendant consequences.
Other types of fats, introduced by technology, are processed vegetable oils that contain chemically altered fatty acids to adapt them for modern food products. These are made by adding hydrogen atoms to molecules of unsaturated fatty acids (a process known as hydrogenation) to make the molecules more saturated and thus more viscous and stable for use in products such as margarine, shortenings, baked goods and peanut butter.
These hydrogenated oils are called trans-fatty acids and constitute about 2 to 4 percent of our fat intake. Though still sparse, research is showing that trans-fatty acids can raise LDLs while having little or no effect on HDLs, although not to the extent of the saturates.
Because they contribute strongly to flavor and texture, fats turn up in much of our food, especially processed foods. Many current labels list the fat, and proposed regulations by the Food and Drug Administration will require almost all foods to put fat content on the label.
The National Research Council, a government-appointed agency that sets the recommended dietary requirements, states that fats should be limited to less than 30 percent of total calories.
There is a growing trend among heart and cancer researchers, however, to recommend stricter limits. Many now believe that holding fat to less than 20 percent of calories might be a better goal for good preventive nutrition.
For a person whose daily calorie intake is 2,200, about that of a typical woman 19 to 50 years old, a 20 percent fat diet is about 48 grams of fat daily.
To calculate fat limitations for your diet, determine your daily calorie intake, multiple by 30 or 20 percent, then divide by 9, the number of calories per gram in fat. The result will be the number of grams of fat you should consume in a day.
Carbohydrates and sugar
If fats are America`s nutritional culprits, carbohydrates are the good guys, especially those complex carbohydrates found in grains, legumes, fruits and vegetables. Though relatively low in calories, they are the preferred source of energy for the body and convey fiber, vitamins and other nutrients through the system.
Carbohydrates do not increase cholesterol, contribute to cancers or cause obesity (unless used to great excess). Most nutritionists recommend that at least 50 to 55 percent of calories come from carbohydrates, about 10 percent more than the 45 to 47 percent most Americans now consume.
One of the primary simple carbohydrates that has been abused by some consumers and vilified unjustly by others is sugar.
Unlike many of the complex carbohydrates, sugars contain few other nutrients and thus sometimes are considered ``empty`` calories. For people who require few calories, sugar may not be a good source because its calories can replace necessary nutritients from other foods. But for people whose energy requirements are large, sugar can help fulfill them.
In the past sugar has been blamed for obesity, but nutritionists now know that sugar provides no more calories than pasta, potatoes, bread or broccoli. Some studies show that obese people actually eat less sugar than those whose weight is normal or below normal.
However, sugars frequently are accompanied by high-calorie fats in foods such as ice cream, chocolate and pound cake, so the idea of avoiding