Coronary artery disease prevention has not been convincingly linked to any specific anti-dietary cholesterol regimen. A healthy balanced diet, with plenty of whole grains, fruits and vegetables, is analyzed, and is better than adding any dietary supplements or dropping any specific foods.
A great deal of attention has been given in the past three decades to fat and cholesterol in our diets. These nutrients have been linked in numerous studies to heart disease through mechanisms usually involving blood levels of the potent risk factor, low density lipoprotein (LDL) cholesterol concentrations. The overall importance of saturated fat as a cholesterol-raising nutrient is clear. Controversy continues, however, concerning the importance of dietary cholesterol.
In addition, questions about specific types of fat have been raised and must be addressed. In particular: Are margarines containing trans-fatty acids worse than butter? Should omega-3 fatty-acids supplements be recommended to lower blood cholesterol? Uncertainty about other nutrients and vitamins exists as well. Is the type of protein consumed important in controlling blood cholesterol? Are vitamins, including vitamin C, beta-carotene, vitamin E, folic acid, vitamins [B.sub.12] and [B.sub.6], flavonoids, and carotenoids protective against heart diseases? What about organic compounds in plants classified as phytochemicals? These may act like estrogen, the main female hormone, which is being prescribed increasingly. And how strong are the studies implicating iron and homocysteine in the development of coronary disease?
Research findings from various studies presented to the American public by the media have left them wondering about the adequacy of the current recommendations and confused about what is left to eat! What nutrients are most important? What can vitamins really do beyond treating vitamin deficiencies? What should an average person do about managing his or her diet to prevent coronary heart disease? In this article we will summarize the information that has become available recently, and provide you with guidelines.
Dietary fat and fatty acids
The link between dietary saturated fat and heart disease is clear. The National Cholesterol Education Program recommends that American people lower their fat intake from the current level of 34 percent of total calories to less than 30 percent of total calories and reduce saturated fat in the diet. Indeed, people who have heart disease may benefit significantly by lowering their fat even further. Dr. Dean Ornish showed that when diets with less than 10 percent of calories were consumed, regression of coronary arteriosclerosis occurred.
Bottom Line: Lower your fat intake as much as you can and still keep your diet varied as well as tasty. However, reaching and maintaining a healthy body weight is important, and calories from nonfat foods do count!
Recent studies showing only “modest” increases in blood cholesterol with the daily feeding of eggs to young healthy men and women have raised the question” Can I eat one egg daily instead of sticking to the American Heart Association’s recommendation of no more than four per week?”
Bottom Line: Although those studies showed only a modest (yet significant) rise in blood cholesterol with the daily consumption of eggs, the effect of dietary cholesterol on blood cholesterol can vary from person to person: some individuals are more sensitive to dietary cholesterol than others, and there is no simple test to identify them. In addition, for most Americans even the small blood-cholesterol-raising effects of dietary cholesterol can contribute to higher overall risk of coronary heart disease. So stick to the recommendation of no more than four eggs a week for now.
Trans-fatty acids are partially hydrogenated fats found in margarine and shortenings, in baked products made with partially hydrogenated fats and (in small amounts) in meats and dairy products. They have been shown to raise LDL cholesterol. Trans-fatty acids may also increase the risk of heart disease by raising Lp(a), a form of LDL that may interfere with the normal breakdown of blood clots. Trans-fatty acids behave like saturated fats although, on the food label, they are included with the unsaturated fats. Trans-fatty acids in the American diet range between 2 and 8 percent of calories consumed.
Bottom Line: Lower your total fat intake and saturated fat intake. Use small amounts of unsaturated liquid oil, e.g., olive oil, canola or corn oil, if needed in cooking and baking, in place of butter, margarine or shortening. If you need a spread for your bread, use jam or jelly or the low-fat or nonfat margarine. Select low-fat or nonfat dairy and baked products.
Omega-3 fatty acids
Omega-3 fatty acids are polyunsaturated fats from plant (linolenic acid) and marine sources (eicosapentaenoic, docosaheaenoic fatty acids) found in fish oil capsules and in salmon, bluefish, mackerel and (in smaller amounts) in other seafood. Eating fish rich in omega-3 fatty acids can cause significant reductions in serum triglycerides (blood fat) in individuals who start out with very high blood levels (>500 mg/d). In addition, omega-3 fatty acids may slow the process of blood clotting. These fatty acids are not, however, helpful in lowering blood cholesterol levels.
Bottom Line: Include fish within the allowance of 5 oz.-6 oz. per day of lean meat or poultry without skin. Do not take fish oil capsules unless prescribed by your doctor. Concentrated levels of omega-3 fatty acids in fish oil capsules can have bad effects when taken with certain drugs like coumadin or in patients with diabetes.
There have been a number of studies in which soy protein has been shown to lower serum cholesterol levels in hypercholesterolemic individuals when compared to protein from dairy products (casein) or beef protein. Soy has isoflavones called daidzein and genistein (plant estrogens) that may play a role in cholesterol metabolism or it may be the amino acid pattern of the protein itself. The protein quality of soybean is close to that of animal proteins. Some Asian populations include soybean daily as tofu, soy milk and tempeh. These foods have been consumed safely for centuries. All soybean products, including soy protein isolate, do, not have the same amounts of isoflavones. Tofu is the best source. Soybean products do contain fat-4 ounces of tofu has 5 grams of fat (which is mainly unsaturated) and 9.4 grams of protein.
Bottom Line: Soybeans can be included in the meal plan in place of animal products and could be a very useful adjunct to the low-saturated-fat, low-cholesterol diet.
It has been suggested that large doses of antioxidant vitamins can retard the “oxidation” of LDL cholesterol. Oxidized LDL is more damaging to the arterial wall. In animal studies it has been shown that supplementing the diet with antioxidants inhibits the progression of arteriosclerosis. The nutrients studied in these experiments have been ascorbic acid (vitamin C), alpha-toco-pherol (vitamin E) and beta-carotene.
The animal studies are supported by studies comprising populations in different countries where high levels of blood vitamin C, vitamin E and vitamin A (a product of beta-carotene) are associated with lower rates of heart disease. However, there have been no clinical trials in humans that have used these vitamins to prevent or retard arteriosclerosis.
Bottom Line. More data is needed before antioxidant vitamin supplements are recommended to the general public. Individuals can, however, consult their physicians on antioxidant use.
Food sources of antioxidant vitamins
- wheat germ
- whole-grain bread and cereals
- green leafy vegetables
- citrus fruits and juices
- dark green leafy vegetables
- sweet potatoes
- winter squash
Fruits and vegetables are powerhouses of phytochemicals which may help in the prevention of chronic degenerative diseases like heart disease, hypertension and diabetes. Each food is loaded with several phytochemicals. For instance, carrots have more than 500 carotenoids; beta-carotene is one of them. In order to get the full potential benefits of these substances, it has been suggested that we eat several servings of vegetables and fruits dairy.
The phytochemicals may be a natural way to increase estrogen levels (or estrogen-like activity). A large body of data suggests that estrogen replacement prevents heart disease and death in postmenopausal women. Estrogen treatment can lower LDL and raise HDL cholesterol levels. Clinical trials are under way to test directly if estrogen can protect postmenopausal women. It should be used only under the supervision of a physician.
Bottom Line: We should all eat several servings of fruits and vegetables each day.
Niacin, or nicotinic acid, is a member of the B vitamin family. The recommended dietary allowance for this vitamin is 15 mg/day, while the doses used to lower LDL cholesterol and raise HDL cholesterol range from 1,000 to 4,000 mg(day. At these very high doses, there is the potential for serious adverse effects: this is particularly so with the slow-release niacin preparations that do not cause flushing and itching, but are more likely to adversely affect the liver.
Bottom Line: Niacin, when used to lower LDL and raise HDL cholesterol, should only be taken under a physician’s supervision.
High iron stores have been associated with heart attacks in a study done in Finland. However, only a small proportion of the population–those with high serum ferritin and high serum LDL–had higher risk of heart disease. Furthermore, separate studies of U.S. physicians and of Icelandic men and women showed no association between serum level of ferritin or iron and the risk for heart attacks.
Bottom Line: The data presently available for a link between iron and heart disease are inconsistent, and do not justify changes in food fortification policy or dietary recommendations.
Elevated levels of hombcysteine (a nonessential amino acid) has been found to be an independent risk factor for heart attack and stroke. High homocysteine levels may reflect reduced availability of folic acid, vitamin [B.sub.6] or vitamin [B.sub.12] Adequacy of these vitamins in the diet, particularly folic acid, may normalize plasma homocysteine levels.
Bottom Line: Building your meals with grains, beans, vegetables and fruits will help increase your folic acid intake. You should however, check with your doctor to make sure you do not have vitamin [B.sub.12] deficiency. Too much folic acid (from foods or supplements) can mask vitamin [B.sub.12] deficiency. Supplementation with vitamin [B.sub.6] for long periods can also cause neurological problems. Aim to get more than 400 micrograms of folate in the diet from food sources and discuss measurement of your homocysteine level with your doctor.
Folic acid in Foods
Food (1 cup) Folic acid
cooked/ ready-to-eat (mcg)
Total cereal 466
Product 19 cereal 400
Lima beans 273
Red kidney beans 229
Split peas 127
Orange juice (diluted
from concentrate) 109
Artichoke (1 medium) 53
SOURCE: USDA AGRICULTURE HANDBOOK NO. 8
There is no argument concerning the need to reduce dietary saturated fat, achieve a healthy body weight, exercise regularly and avoid cigarettes when you undertake a program to lower your risk for developing coronary artery disease. In addition, a diet rich in fruits, vegetables and whole grains will contain many vitamins and other micro-nutrients that may add further protection against arteriosclerosis. The use of supplements to increase consumption of these vitamins and micro-nutrients is not recommended at this time. Finally: Before you accept any recommendation, you should know:
- that any one study you read about is not the last word on how you should eat.
- that removing or adding one food or supplement to the diet does not guarantee that you will then be eating a healthful diet. A healthful diet is about the foods you can eat and not about the ones you are told to avoid.
- that nutritional science is evolutionary and not revolutionary. A story about nutrition gets media attention because it is unusual and because it proposes a new theory. The new information should remain theory until it is tested further and confirmed.
- how the study upon which a new recommendation is based was conducted. A randomized clinical trial is the best design for clinical research. Data from studies on animals, or from observational studies, are not the final prescription.
Dr. Ginsberg is the director of the Irving Center for Clinical Research and the Irving Professor of Medicine, College of Physicians and Surgeons at Columbia University.
Ms. Karmally is the director of Nutrition, Irving Center for Clinical Research, Columbia-Presbyterian Medical Center, N.Y.C., spokesperson for the American Directors Association and on the board of directors for the N. Y. Affiliate of the American Heart Association.