Of all the dietary factors related to chronic diseases prevalent in developed countries, high intakes of certain fats are by far the most significant. A person who chooses a diet too high in saturated fats or trans fats invites the risk of cardiovascular dis-ease (CVD), and heart disease is the number-one killer of adults in the United States and Canada.
As for cancer, evidence is less compelling than for heart disease, but it does suggest that a diet high in certain kinds of fat is associated with a greater-than-average risk of developing some types of cancer. Conversely, some research suggests that omega-3 fatty acids from fish may protect against some cancers.
Obesity carries serious risks to health. A diet high in energy-rich fatty foods makes it easy for people to exceed their energy needs and encourages unneeded weight gain. An increasing waistline, in turn, often increases blood triglycerides, which can indicate an increased risk of heart disease and other chronic diseases.
The health risks of obesity focus on weight management. The links between diet and disease are the focus of much research. Some points about fats and heart health are presented here because they underlie dietary recommendations concerning fats.
Cholesterol travels in the blood within lipoproteins. Two of the lipoproteins, LDL, and HDL, play major roles with regard to heart health and are the focus of most recommendations made for reducing the risk of heart disease.
A high blood LDL cholesterol concentration is a predictor of the likelihood of suffering a fatal heart attack or stroke, and the higher the LDL, the earlier the episode is expected to occur. A low blood concentration of HDL cholesterol also signifies a higher disease risk.
Most people realize that elevated blood cholesterol is an important risk factor for heart disease. Most people may not realize, though, that cholesterol in food is not the main influential factor in raising blood cholesterol.
Saturated Fats and Blood Cholesterol
The main dietary factors associated with elevated blood LDL cholesterol are high saturated fat and high trans fat intakes. High LDL cholesterol levels increase the risk of heart disease because high LDL concentrations promote the uptake of cholesterol in the blood vessel walls.
Solid fats are foods or ingredients in foods (such as shortening in cakes or pies) that provide abundant saturated fat, trans fat, and/or cholesterol and many calories. The current American diet delivers excessive amounts of solid fats—representing an average of almost one-fifth of the day’s total calories.
The easiest way to lower saturated fat, then, is to limit solid fats in the diet. Grain-based desserts, pizza, cheese, and processed and fatty meats are major providers of solid fats. Solid fats from animal sources contribute a great deal of the saturated fat in most people’s diets. Some vegetable fats (coconut oil, palm kernel oil, and palm oil) and hydrogenated fats such as shortening or stick margarine provide smaller amounts of saturated fats.
It is important to note that replacing dietary saturated fats with added sugars and refined starches is often counterproductive.16 The best diet for health not only replaces saturated fats with polyunsaturated and monounsaturated oils, but also is adequate, balanced, calorie-controlled, and based on mostly nutrient-dense whole foods.
Trans-Fatty Acids and Blood Cholesterol
Consuming commercially derived trans fat poses a risk to the health of the heart and arteries by raising LDL and lowering HDL cholesterol, and by producing inflammation. Commercially derived trans fats are found in the partially hydrogenated oils used in some margarines, snack foods, and prepared desserts. The risk to heart health from trans fats is similar to or slightly greater than that from saturated fat, so the Dietary Guidelines for Americans suggest that people keep trans fat intake as low as possible.
Limiting the intake of trans fats can improve blood cholesterol and lower the risk of heart disease. To that end, many restaurants and food manufacturers have taken steps to eliminate or greatly reduce trans fats in foods.
For example, margarine makers have reformulated their products to contain much less trans fat. Soft or liquid varieties are made from unhydrogenated oils, which are mostly unsaturated and so are less likely to elevate blood cholesterol than the saturated fats of butter. Some margarines contain olive oil, omega-3 fatty acids, or plant sterols (mentioned earlier), making these products preferable to butter and other margarines for the heart. The words hydrogenated vegetable oil or shortening in an ingredients list indicate trans-fatty acids in the product.
In the past, most commercially fried foods, from doughnuts to chicken, delivered a sizeable amount of trans fats to consumers. Today, newly formulated commercial oils and fats perform the same tasks as the previously used hydrogenated fats but with fewer trans-fatty acids.
Some manufacturers, however, merely substitute saturated fats—which pose well-established risks to heart health—for trans fats. When reformulating their products, food companies must consider not only the fat composition, but also the taste, texture, cost, and availability of materials. No health benefits can be expected when saturated fats replace trans fats in the diet.
Dietary Cholesterol and Blood Cholesterol
Although its effect is not as strong as that of saturated fat or trans fat, dietary cholesterol may contribute to elevated blood cholesterol in some people. Less clear is its role in heart disease. The Dietary Guidelines recommend limiting dietary cholesterol to less than 300 milligrams per day for healthy people (less than 200 milligrams for some people with or at high risk of heart disease).
On average, women take in about 240 milligrams a day and men take in about 350 milligrams. Foods providing the greatest share of cholesterol to the U.S. diet are eggs and egg dishes, chicken and chicken dishes, beef and beef dishes, and all types of beef burgers. In healthy people, evidence suggests no association between consuming one egg per day and an increased risk of heart disease. For individuals with or at high risk of heart disease, however, consuming one egg per day may worsen or accelerate the progression of heart disease. The cholesterol content of one egg is about 210 milligrams.
Monounsaturated Fatty Acids and Blood Cholesterol
Replacing saturated and trans fats with monounsaturated fat such as olive oil may be an effective dietary strategy to prevent heart disease. The lower rates of heart disease among people in the Mediterranean region of the world are often attributed to their liberal use of olive oil, a rich source of monounsaturated fatty acids. Olive oil also delivers valuable phytochemicals that help to protect against heart disease.
Polyunsaturated Fatty Acids, Blood Cholesterol, and Heart Disease Risk Polyunsaturated fatty acids (PUFA) of the omega-3 families are potent protectors against heart disease. The omega-3 fatty acids EPA and DHA, which are found mainly in fatty fish, exert their beneficial effects by influencing the function of both the heart and blood vessels. Specifically, EPA and DHA protect heart health by:
- Lowering blood triglycerides.
- Preventing blood clots.
- Protecting against irregular heartbeats.
- Lowering blood pressure.
- Defending against inflammation.
The primary member of the omega-3 family, linolenic acid, may benefit heart health as well, but evidence for this effect is much less certain than for EPA and DHA.
The Dietary Guidelines recommend choosing 8 to 12 ounces of a variety of seafood each week, or about one of every five ounces of protein foods, to provide an average of 250 milligrams of EPA and DHA per day along with the beneficial array of other nutrients that seafood provides.
Greater heart health benefits can be expected when fish is grilled, baked, or broiled, partly because the varieties prepared this way often contain more EPA and DHA than species used for fried fish in fast-food restaurants and frozen products.
Additionally, benefits are attained by avoiding commercial frying fats, which may be laden with trans fat and saturated fat. Further benefits arise when fish replaces high-fat meats or other foods rich in saturated fats in several meals each week. Some species of fish and shellfish, however, may contain significant levels of mercury or other environmental contaminants.
Most healthy people can safely consume most species of ocean fish several times a week, but for some, the risks are greater. Women who may become pregnant, pregnant and lactating women, and children are more sensitive to contaminants than others, but even they can benefit from consuming safer fish varieties within recommended limits.
For everyone, consuming a variety of different types of fish to minimize exposure to any single toxin that may accumulate in a favored species is a good idea. The fish most heavily contaminated with mercury are: king mackerel, shark, swordfish, and tilefish (also called golden bass or golden snapper). Those lower in mercury are: catfish, pollock, salmon, sardines, and canned light tuna. Canned albacore (“white”) tuna generally contains more mercury than light tuna. Consumers should check local advisories to determine the safety of freshwater fish caught by family and friends.
Fish, not fish oil supplements, is the preferred source of omega-3 fatty acids. High intakes of omega-3 polyunsaturated fatty acids may increase bleeding time, interfere with wound healing, raise LDL cholesterol, and suppress immune function. Evidence is mixed for people with heart disease—several studies show hopeful results, while others reveal no benefits from supplements.
Because supplements pose risks, such as excessive bleeding, those taking daily fish oil supplements need medical supervision. The benefits and risks from EPA and DHA illustrate an important concept in nutrition: too much of a nutrient is often as harmful as too little.
High intakes of saturated or trans fats contribute to heart disease, obesity, and other health problems.
High blood cholesterol, specifically, poses a risk of heart disease, and high intakes of saturated fat and trans fat contribute the most to high blood cholesterol. Cholesterol in foods presents less of a risk.
Polyunsaturated fatty acids of the omega-6 and omega-3 families protect against heart disease.
When monounsaturated fat such as olive oil replaces saturated and trans fats in the diet, the risk of heart disease may be lessened.
Though some fat in the diet is necessary, health authorities recommend a diet moderate in total fat and low in saturated fat, trans fat, and cholesterol.