Other research indicates that eating fish reduces triglycerides and lipoprotein (a).
Eating fish also appears to protect the nervous system and may reduce risks for other disorders, including rheumatoid arthritis, asthma, ulcerative colitis, and some types of cancers.
At this time, most studies indicate that eating moderate amounts (one or two servings weekly) of fish offers the most benefits. Some studies found that very high amounts (five or six servings weekly) can be harmful. This risk may be due to the presence of mercury in many kinds of fish (salmon is one exception).
Soy. Soy is an excellent food. It is rich in both soluble and insoluble fiber, omega-3 fatty acids, and provides all essential proteins. Soybeans also contain natural estrogens called isoflavones, which have positive effects on lipid levels. A number of studies have indicated that subjects that consume about 40 grams of soy protein each day reduce LDL by 13%, triglycerides by 11%, and increase HDL by 2%. Four ounces of tofu equals about eight to 13 grams of soy, and a soy burger contains about 18 grams. Powdered soy protein that contains at least 60 mg of isoflavones may provide similar benefits. Tablets of individual isoflavones found in soy, however, do not appear to offer any advantages. (Note: soy sauce contains only a trace amount of soy and is very high in sodium.) Of possible concern, a high intake of soy during pregnancy may have some adverse effect on the fetus, although only animal studies have suggested this. More research is important.
Meat. For heart protection, one 1999 study suggested that it didn't matter if you chose fish, poultry, beef, or pork as long as the meat was lean. (Saturated fat in meat is the primary danger to the heart.) The fat content of meat varies depending on the type and cut. It is best to eat skinless chicken or turkey; the leanest cuts of pork (loin and tenderloin), veal, and beef are nearly comparable to chicken in calories and fat and their effect on LDL and HDL levels. It should be noted, however, that even chicken and lean meat do not improve cholesterol levels, and, in terms of cardiac health, fish is a more desirable choice.
Fats and Oils
General Recommendations for Fat Intake. About two-thirds of cholesterol in the body does not come from cholesterol in food but is manufactured by the liver, its production stimulated by saturated fat (mostly found in animal products). The dietary key to managing cholesterol, then, lies in understanding fats and oils. When it comes to studying the effects of fat on the body, however, the problem is compounded by its complex nature. All fats and oils found in foods are made up of chains of molecules composed of carbon and glycerol called fatty acids and which are bound by hydrogen atoms. There are three major chains:
Monounsaturated fatty acids. One pair of carbon atoms is missing hydrogen bonds. Found in plant products.
Polyunsaturated fatty acids. Two or more pairs of carbon atoms are missing hydrogen bonds. Found in plant products.
Saturated fatty acids. All carbon atoms have the maximum hydrogen bonds. Found in animal products.
The oils and fats that people and animals eat are nearly always mixtures of all three fatty acids, but one type usually predominates. In addition, there are three chemical subgroups of polyunsaturated fatty acids called essential fatty acids: they are omega-3 and omega-6, and polyunsaturated fatty acids and omega-9 monounsaturated fatty acids.
To complicate matters, there are also trans-fatty acids. Most of these are not natural fats but are manufactured by adding hydrogen atoms, a process known as hydrogenation, to polyunsaturated fatty acids. These subgroups are being heavily researched for their specific effects on health.
All fats, both good ones and bad, add the same calories. In order to calculate daily fat intake, multiply the number of fat grams eaten by 9 (one fat gram is equal to 9 calories, whether it's saturated or unsaturated) and divide by the number of total daily calories desired. One teaspoon of oil, butter, or other fats equals about five grams of fat.
Although there is much controversy on the overall effects of fat on health, virtually all experts strongly advise limiting intake of saturated fats and trans-fatty acids (found in commercial baked goods and fast foods). Other fatty acids, however, appear to offer benefits.
Harmful Fats. Reducing consumption of saturated fats and trans-fatty acids is the first essential step in managing cholesterol levels through diet.
Saturated Fats. Saturated fats are found predominantly in animal products, including meat and dairy products. They are strongly associated with higher cholesterol levels. (The so-called tropical oils, palm, coconut, and cocoa butter, are also high in saturated fats. Evidence is lacking, however, about their effects on the heart. The countries with the highest palm-oil intake, Costa Rica and Malaysia, also have much lower heart disease rates and cholesterol levels than Western nations.)
Trans-fatty Acids. Most trans-fatty acids are also dangerous for the heart and may pose a risk for certain cancers. They are created during a process aimed at stabilizing polyunsaturated oils to prevent them from becoming rancid and to keep them solid at room temperature. Some experts believe that these partially hydrogenated fats are even worse than saturated fats because they both increase LDL and reduce HDL cholesterol levels and may have harmful effects on the linings of the arteries. One study of 80,000 nurses reported that women whose total fat consumption was 46% of total caloric intake had no greater risk in general for a heart attack than did those for whom fat represented 30% of calories consumed. Women whose diets were high in trans-fatty acids, however, had a 53% increased risk for heart attack compared to those who consumed the least of those fats. Hydrogenated fats are used in stick margarine and in many fast foods and baked goods, including most commercially-produced white breads. (Liquid margarine is not hydrogenated and is recommended, as is margarine labeled "trans-fatty acid free.") The FDA has now required that food labels include information on trans-fatty acids.
Beneficial Fats and Oils. It should be noted that some fat is essential for health, and fat is essential for healthy development in children. Public attention has mainly focused on the possible benefits or hazards of monounsaturated (MUFA) and polyunsaturated (PUFA) fats. Polyunsaturated fats are found in safflower, sunflower, corn, cottonseed oils, and fish, while monounsaturated fats are mostly present in olive, canola, and peanut oils and in most nuts. Studies, however, do not all agree on their effects. For example, early studies indicate that monounsaturated fats help to maintain healthy HDL levels while polyunsaturated fats reduce them. In general, evidence is not clear on the effects of either MUFA or PUFA on blood glucose and insulin. Some studies have found no effect. In one study, however, sunflower oil, a PUFA, was associated with deterioration in glucose control as well as higher cholesterol levels. Researchers are most interested in the smaller fatty-acid building blocks contained in these oils called essential fatty acids, which may have more specific effects on lipids: three important fatty acids are omega-3, omega-6, and omega-9. Food oils often contain a combination of these building blocks, which may account for the mixed results observed in people consuming them.
Omega-3 fatty acids: They are further categorized as alpha-linolenic acid (sources include canola oil, soybeans, flaxseed, olive oil, and many nuts and seeds) and docosahexaenoic and eicosapentaenoic acids (sources are oily fish and breast milk).
Alpha-linolenic Acid. Studies have indicated that vegetable oils containing alpha-linolenic acids are heart protective. Extra virgin olive oil has been associated with lower blood pressure. A 2000 study further reported olive oil (as opposed to sunflower oil) may have specific benefits for people with diabetes type 2. Many studies have singled out nuts, which contain omega-3 fatty acids, fiber, and other important substances as being particularly beneficial for the heart by lowering LDL and total cholesterol without increasing triglycerides.
Docosahexaenoic and Eicosapentaenoic Acids. Fish oils, which contain docosahexaenoic and eicosapentaenoic acids, do not have much effect on cholesterol but they may benefit the lining of blood vessel (the endothelium) and therefore improve blood flow. In one animal study, fish oil improved insulin sensitivity. [See also Protein, above.]
Omega-6 polyunsaturated fatty acids: They are further categorized as linoleic acid (sources are flaxseed, corn, safflower, soybean, and canola oil) or arachidonic acids. PUFA oils containing linoleic constitute most of the oils consumed in the U.S. Some studies have found greater protection against heart disease from omega-6-oils than omega-3, but omega-6 is also associated with increased production of compounds called eicosanoids, which enhance tumor growth in animals.
Omega-9 fatty acids: (Source is olive oil).
Studies indicate that, in a healthy balance, all of these fatty acids are essential to life. For example, both omega-3 and omega-9 fatty acids contain chemicals that block the harmful eicosanoids found in omega-6 fatty acids. Research suggests, however, that our current Western diet contains an unhealthy ratio (10 to 1) of omega-6 to omega-3 fatty acids. The bottom line, then, is to try to obtain a better balance of fatty acids without consuming too many calories.
Fat Substitutes. Fat substitutes added to commercial foods or used in baking deliver some of the desirable qualities of fat, but do not add as many calories. They include the following:
Some replacers, such as the cellulose gel Avicel, Carrageenan (made from seaweed), guar gum, and gum arabic, have been used for decades in many commercial foods.
Plant substances known as sterols have long been known to reduce cholesterol by impairing its absorption in the intestinal tract. A sterol called sitostanol, also called stanol, is now being used in margarines (Benecol, Take Control). Benecol is derived from pine bark and Take Control from soybeans; both are effective. Studies on stanol margarines are reporting that either two servings a day as part of a low-fat diet can lower LDL and total cholesterol. Of concern is the possibility that stanol may block absorption of important fat-soluble nutrients, including vitamins A, E, and D and carotenoids (compounds, such as beta carotene, that convert to vitamin A). One study suggested that it had no effect on the vitamins but did impair absorption of beta carotene. In people already on a low-fat diet, the addition of this margarine may not produce much additional benefit.
Olestra (Olean) passes through the body without leaving behind any calories from fat. (It should be noted, however, that foods containing olestra still have calories from carbohydrates and proteins.) A 2000 study reported healthful changes in cholesterol levels in people who had been eating olestra for a year. Early reports of cramps and diarrhea after eating food containing olestra have not proven to be significant. Of greater concern is the fact that even small amounts of olestra deplete the body of certain vitamins and nutrients that are important for protection against serious diseases, including cancer. The FDA requires that the missing vitamins be added back to olestra products, but not other nutrients.
Under investigation are fat substitutes derived from beta-glucan, the soluble fiber found in oats and barley (e.g., Nu-Trim). They may have health benefits beyond reducing calories and replacing hydrogenated or saturated fats.
People should try to limit even reduced-fat foods and fat substitutes in their diets. Although one might believe that eating reduced-fat or fat substitute products means consuming fewer calories, this is often not the case. Many commercial, lowered-fat products have extra calories from sugar and other carbohydrates. A study has found that people who consume foods that contain fat substitutes do not learn to dislike fatty foods, while people who learn to cook using foods naturally lacking or low in fat eventually lose their taste for high fat diets.
Some Examples of Healthy Foods
Dietary Cholesterol
The story on cholesterol found in the diet is not entirely straightforward. Cholesterol is found only in animal tissues, with high amounts occurring in meat, dairy products, egg yolks, and shellfish. The American Heart Association recommends no more than 300 mg of cholesterol per day. One study estimated, however, that reducing dietary cholesterol intake by 100 mg/day would only produce a 1% decrease in cholesterol levels. Of note, however, are studies indicating that although dietary cholesterol itself does not appear to increase the risk for heart disease in most individuals, people with diabetes, especially type 2, may be an exception. Until more research is done, they should consider avoiding eating eggs or other high-cholesterol foods (such as shrimp) more often than once a week.
Vitamins
Antioxidant Properties. Currently, the most important benefit claimed for vitamins A, C, E, and many of the carotenoids and phytochemicals is their role as antioxidants, which are scavengers of particles known as oxygen-free radicals (also sometimes called oxidants). These chemically active particles are by-products of many of the body's normal chemical processes. Their numbers are increased by environmental assaults, such as smoking, chemicals, toxins, and stress. In higher levels, oxidants can be very harmful:
They can damage cell membranes and interact with genetic material, possibly contributing to the development of a number of disorders including diabetes, cancer, heart disease, cataracts, and even the aging process itself.
Oxygen-free radicals can also enhance the dangerous properties of low-density lipoprotein (LDL) cholesterol, a major player in the development of atherosclerosis.
Antioxidant vitamins (A, C, and E), carotenoids, and many phytochemicals can neutralize free radicals and may reduce or even prevent some of their damage. Unfortunately, although it is clear that vitamins are required to prevent deficiency diseases, the possible benefits of higher-dose supplements are still unproven in most cases. To date, there is no strong evidence that antioxidant supplements offer any real protection. In some cases, high doses may be harmful. [See Special Warning on High-Dose Antioxidant Supplements, below.]
Vitamin E. Vitamin E may prevent blood clots and the formation of fatty plaques and cell proliferation on the walls of the arteries. Long-term studies of people who took vitamin E supplements, however, are mixed. Many have found little or no benefits. One major 2000 study, for example, reported that patients who took a natural vitamin E at 400 IU for four to six years did not gain any protection against cardiovascular disease. Of interest, however, is a very small 2000 study reporting that when people with type 2 diabetes took high doses (1,200 IU) of vitamin E, they had less evidence of inflammation in blood vessels, an indicator for a higher risk of heart disease and stroke. Other studies have found similar results for people with type 1 diabetes after long term vitamin E supplementation as well as beneficial effects on cholesterol levels. Some experts, in fact, recommend life-long vitamin E supplements specifically for people with type 1 diabetes. Different vitamin E compounds, such as gamma tocopherol or tocotrienol may have benefits that the standard synthetic supplement (dl alpha tocopherol) does not. Studies are fairly consistent in indicating that eating foods rich in natural vitamin E may be protective.
Vitamin C. Vitamin C appears to maintain blood vessel flexibility and to improve circulation in the arteries of smokers. Generally such findings have occurred in the laboratory. There is no evidence, however, that supplements of vitamin C offer any actual protection against heart disease. And there is some evidence that high doses may even speed up existing damaging processes in the arteries.
B Vitamins. Several important studies have demonstrated a link between deficiencies in the B vitamins folic acid (folate), B6, and B12 and elevated blood levels of an amino acid homocysteine, a risk factor for atherosclerosis and possibly for higher mortality rates in people with type 2 diabetes. Folic acid is particularly potent in reducing homocysteine levels. (Eating green vegetables and legumes, enriched cereals and grains, and orange juice, which are rich in folate, can also reduce them.) It is not clear yet, that reducing homocysteine levels will actually protect against heart disease. Major studies are under way and early results of small studies are promising. Another important B vitamin is niacin (Vitamin B3), which has special benefits for patients with unhealthy cholesterol levels. There has been some concern that high levels may actually have adverse effects on glucose control. One 2000 study, however, found that niacin improves cholesterol and triglyceride levels with no significant effect on glucose levels.
Special Warning on High-Dose Antioxidant Supplements
Some studies are now suggesting that excessive use of antioxidant supplements may interfere with other nutrients or convert into pro-oxidants and become harmful. Of particular concern are studies that have found an increase in lung cancer and overall mortality rate among smokers who took beta carotene supplements. A 2000 study further reported a higher risk for cancer in male smokers who took multivitamins plus A, C, or E. In determining reasons for this disturbing effect, one animal study suggested that beta carotene increased enzymes in the lungs that actually promote cancerous changes. And, even more worrisome, in people with existing cancer, high doses of antioxidant vitamins, such as vitamin C or beta carotene, may actually protect cancer cells (just as they do healthy cells). Some evidence also exists that high doses of vitamin C may speed up atherosclerosis.
Minerals
Magnesium. Magnesium deficiency may have some role in insulin resistance and high blood pressure. One study reported that low magnesium levels as measured in blood tests were associated with a higher risk for type 2 diabetes in whites but not in African Americans. Dietary intake of magnesium, however, did not appear to play any role in increasing or reducing risk for either population group. It is more likely that diabetes may cause magnesium loss. No supplements are recommended at this time for patients with adequate levels of magnesium. For people taking diuretics for high blood pressure, extra potassium may be needed, but in other cases, including certain kidney problems, an overload of potassium may occur, so no regular supplements are recommended without consulting a physician.
Chromium. Some studies have reported an association between deficiencies in the mineral chromium and a higher risk for type 2 diabetes. Studies on fat rats that were given chromium reported improvement in insulin sensitivity and glucose metabolism. Studies on human type 2 patients, however, reported few benefits and some adverse side effects.
Many type 2 diabetics are also deficient in zinc; more studies are needed to establish the benefits or risks of taking supplements. Zinc has some toxic side effects, and some studies have associated high zinc intake with prostate cancer.
Salt and Sodium
Salt can raise blood pressure, and people with diabetes should limit salt intake, particularly if they have hypertension, are overweight, or both. Overweight people who have a high sodium intake may be at increased risk for death from heart disease. High salt diets in people who are sensitive to its effects may harm the kidney and brain, even independently of high blood pressure. Restricting salt also enhances the benefits of nearly all standard antihypertensive drugs by reducing potassium loss, and may help protect against kidney disease in patients who are also taking calcium-blocker drugs.
Although it is not clear whether restricting sodium adds any benefits for most people whose diets are rich in fruits, vegetables, and low-fat dairy products and who are not salt-sensitive, it is always wise to aim for a maximum of 2,000 mg sodium intake. Simply eliminating table and cooking salt can be beneficial. Salt alternatives, such as Cardia, containing mixtures of potassium, sodium, and magnesium are now available but are costly. It should be noted, however, that about 75% of the salt in the typical American diet comes from processed or commercial foods, so the benefits of table-salt substitutes are likely to be very modest. Some sodium is essential to protect the heart, but most experts agree that the amount is significantly less than that found in the average American diet.
Caffeine and Alcohol
Alcohol. Studies in 1999 and 2000 have suggested that light to moderate alcohol intake (one or two glasses a day) may have specific benefits for people with type 2 diabetes. In one it was associated with a reduced risk for death from heart disease, and in the other it protected against type 2 diabetes itself. Wine particularly appears to have health benefits. In one study, drinking red wine at meals even reduced blood glucose levels in some cases. (Alcohol itself had no effect on blood glucose or insulin.) In those taking insulin or sulfonylureas, however, alcohol may cause a hypoglycemic reaction, of which the drinker may not be aware. Pregnant women or those at risk for alcohol abuse should not drink alcohol.
Caffeinated Beverages
Tea. Tea may have a very positive effect on the heart. Although it contains caffeine, it also is rich in flavonoids and other substances that offer protection against damaging forms of LDL. Green tea is often cited for its health benefits but black tea may also be beneficial. In one study, higher intake of black tea, particularly by women, was associated with a reduced risk for severe coronary artery disease. Tea also contains folic acid, which reduces homocysteine levels, a possible factor in coronary artery disease.
Coffee. Regular intake of coffee has a harmful effect on blood pressure in people with existing hypertension. (Caffeine causes a temporary increase in blood pressure in everyone, which is thought to be harmless in people with normal blood pressure.) Unfiltered coffee (Turkish coffee, Scandinavian boiled or French pressed coffee, and espresso) contains an alcohol called cafestol, which may raise cholesterol levels. Filtered coffee does not contain this residue. Of some concern is a study that reports high levels of homocysteine in people who drink many cups of coffee per day (decaf does not raise these levels). Homocysteine is a possible factor in coronary artery disease. On the other hand, coffee, like red wine, contains phenol, which helps prevent oxidation of LDL cholesterol. A 1999 study reported an effect of caffeine on the brain that has implications for diabetes: it reduces blood flow in the brain even in the presence of sufficient glucose. People with diabetes who drink even two or three cups of coffee may actually believe they are hypoglycemic when their blood glucose levels are normal. One study suggested that this effect may actually help increase awareness of hypoglycemia in some people who have difficulty recognizing its symptoms
