By Melissa Tennen, HealthAtoZ writer
First of two parts.
The nation's recipe for healthy eating may need additional ingredients, say researchers from the Harvard School of Public Health in this two-part article on healthy eating and dieting.
The Harvard group serves up an alternative to the traditional Food Guide Pyramid and its companion Dietary Guidelines for Americans, developed by the U.S. Department of Agriculture (USDA). When people in the Harvard study followed new guidelines designed by the researchers, the risk for cardiovascular diseases was significantly lower than for people following the federal model.
"We wanted to improve the guidelines, and make more specific guidelines," says Marjorie McCullough, D.Sc., R.D., lead researcher of the study and an epidemiology researcher at the American Cancer Society.
Men whose diets followed the guidelines for Harvard's Alternative Healthy Eating Index (AHEI) lowered their overall risk of major chronic disease such as heart attacks, stroke and cancer by 20 percent. Women decreased their overall risk by 11 percent. For cardiovascular disease, men whose diets most closely followed the AHEI guidelines lowered their risks by 39 percent and women by as much as 28 percent.
The USDA pyramid includes six to 11 servings of bread, cereal, rice and pasta; two to four servings of fruit; three to five servings of vegetables; two to three servings of milk, yogurt and cheese; and two to three servings of meat, poultry, fish, dry beans, eggs and nuts. At the top of the pyramid are fats, oils and sweets, which should be used sparingly.
"The pyramid definitely needs some rebuilding," McCullough says.
The "Fat" Facts
The Harvard guidelines make a distinction between red and white meats. Americans tend to eat too much red meat, which is a high-calorie, high-fat food, instead of leaner proteins such as chicken, turkey and fish.
Also, the USDA pyramid doesn't address healthy fats that can be found in vegetable oils such as olive and canola and nuts. Healthy fats can raise good cholesterol in the blood stream when they replace less healthy choices.
The government's guidelines also do not consider hidden trans fatty acids, which are created by partially hydrogenated vegetable oil and can be in everything from cookies to crackers. Trans fats often show up on nutrition labels as "partially hydrogenated vegetable oil". Scientists are researching the links between trans fats and health.
The AHEI takes trans fats into consideration when accessing overall eating habits and health risks. The Journal of the American Dietetic Association found that Americans should eat only 5 grams of trans fat a day, or 3 percent of total daily calories.
Fat plays an important role in health, so some is necessary, but all fats have more calories than protein or carbohydrates. Too much of certain kinds can lead to high cholesterol, a risk factor for heart disease. It also may increase cancer risk.
But not all fats are created equal. Fats and oils are made up of basic units called fatty acids. Saturated fat acids are found mostly in animal sources such as meat and poultry, whole or reduced-fat milk, and butter. Some vegetable oils such as coconut, palm kernel oil and palm oil are saturated.
Healthy fats such as polyunsaturated fatty acids are found mainly in vegetable oils such as safflower, sunflower, corn, flaxseed and canola oils, as well as seafood. These are vital for cell structure and for making hormones.
Cholesterol
Blood (serum) cholesterol and dietary cholesterol are two different types of cholesterol. Dietary cholesterol is found in food of animal origin such as egg yolks, organ meats and full-fat dairy products such as whole milk. Blood cholesterol is a waxy substance, which occurs naturally in the body. It is used to make estrogen, testosterone and bile, all necessary for digestion.
But if the level of cholesterol in the blood is too high, cholesterol and other fats can stick to artery walls. Because blood cholesterol is waxy and cannot dissolve in water, it is carried through the blood in packages called lipoproteins. HDL (the "good" cholesterol) gathers up excess cholesterol in the blood and carries it to the liver, which then excretes it. HDL also may help remove some cholesterol from artery walls. Too much LDL (the "bad" cholesterol) can increase the risk of heart disease as it builds up on artery walls. The type of fats and oils we eat helps control LDL levels.
The "Carb" Truth
The USDA food pyramid does not differentiate between the types of carbohydrates found in breads and pastas. Some are healthier than others, McCullough says. Foods with whole grains are better for cardiovascular health than refined carbohydrates found in overly processed breads, for example.
The quantity of "carbs" Americans consume also is a problem, McCullough says. Americans tend to eat too much of nutrient-void French fries and white bread, leading to high blood sugar and an increased risk for conditions such as type 2 diabetes. Fruits, vegetables and whole grains are good carbohydrates necessary for energy without dangerously raising blood sugar.
This article was reviewed and updated June 2007.
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