"Eat a low-fat, low-cholesterol diet" has been the mantra for healthful eating for decades. Touted as a way to lose weight and prevent or control heart disease and other chronic conditions, millions of people have followed (or, more likely, have tried to follow) this advice. Detailed research—shows that the total amount of
fat in the diet isn't really linked with weight or disease. What really matters is the type of fat in the diet. Bad fats, meaning trans and saturated fats, increase the risk for certain diseases. Good fats, meaning monounsaturated and polyunsaturated fats, do just the opposite. They are good for the heart and most other parts of the body.
What about cholesterol in food? For most people, the mix of fats in the diet influences cholesterol in the bloodstream far more than cholesterol in food does. Almost all foods contain some fat. Even quintessential fat-free foods like carrots and lettuce contain small amounts of this nutrient. That's a testament to how important fats are for life. Fat provides a terrific source of energy as well as a great depot for storing it. It
is an important part of cell membranes, helping govern what gets into cells and what comes out. The body uses cholesterol as the starting point to make estrogen, testosterone, vitamin D, and other vital
compounds. Fats are also biologically active molecules that can influence how muscles respond to insulin's "open up for sugar" signal; different types of fats can also fire up or cool down inflammation. Fat and cholesterol can't dissolve in water or blood. The body gets around this basic chemistry problem by packaging fat and cholesterol into tiny, protein-covered particles called lipoproteins. Although
lipoproteins can carry quite a bit of fat, they mix easily with blood and flow with it. Some of these particles are big and fluffy, others small and dense. The most important ones are low-density lipoproteins (LDL), high-density lipoproteins (HDL), and triglycerides.
What can I do to lower my total cholesterol and LDL?
A. Several strategies can help you lower the amounts of total and harmful LDL cholesterol in your bloodstream, and thus your risk of heart disease.
• Low-density lipoproteins (LDL) carry cholesterol from the liver to the rest of the body. Cells latch onto these particles and extract fat and cholesterol from them. When there is too much LDL cholesterol in
the blood, these particles can form deposits in the walls of the coronary arteries and other arteries throughout the body. Such deposits, called plaque, can narrow arteries and limit blood flow. When plaque breaks apart, it can cause a heart attack or stroke. Because of this, LDL cholesterol is often referred to as bad, or
harmful, cholesterol.
• High-density lipoproteins (HDL) scavenge cholesterol from the bloodstream, from LDL, and from artery walls and ferry it back to the liver for disposal. Think of HDL as the garbage trucks of the
bloodstream. HDL cholesterol is often referred to as good, or protective, cholesterol.
• Triglycerides make up most of the fat that you eat and that travels through the bloodstream. As the body's main vehicle for transporting fats to cells, triglycerides are important for good health. But as is
the case for so many things, an excess of triglycerides can be unhealthy. In general, the lower your LDL and the higher your HDL, the better your chances of preventing heart disease and other chronic conditions.
Diet and Cholesterol: How Fat and Cholesterol in Food Affect Blood Levels
The types of fat in the diet determine to a large extent the amount of total and LDL cholesterol in the bloodstream. Cholesterol in food matters, too, but not nearly as much. Good Fats: Unsaturated Fats
Unsaturated fats are called good fats because they can improve blood cholesterol levels, ease inflammation, stabilize heart rhythms, and play a number of other beneficial roles. Unsaturated fats are predominantly found in foods from plants, such as vegetable oils, nuts, and seeds. They are liquids at room temperature.
There are two types of unsaturated fats:
• Monounsaturated fats are found in high concentrations in canola, peanut, and olive oils; avocados; nuts such as almonds, hazelnuts, and pecans; and seeds such as pumpkin and sesame seeds.
• Polyunsaturated fats are found in high concentrations in sunflower, corn, soybean, and flaxseed oils, and also in foods such as walnuts, flax seeds, and fish. Omega-3 fats, which are fast becoming the
darling of the supplement industry, are an important type of polyunsaturated fat. The body can't make these, so they must come from food. An excellent way to get omega-3 fats is by eating fish two or three times a week. Good plant sources of omega-3 fats include chia seeds (sold as Salvia), flax seeds, walnuts, and oils such as flaxseed, canola, and soybean.
Researchers conducted an analysis of 60 trials that examined the effects of carbohydrates and various fats on blood lipid levels. In trials in which polyunsaturated and monounsaturated fats were eaten in place of carbohydrates, these good fats decreased levels of harmful LDL and increased protective HDL. More recently, a randomized trial known as the Optimal Macronutrient Intake Trial for Heart Health
(OmniHeart) showed that replacing a carbohydrate-rich diet with one rich in unsaturated fat, predominantly monounsaturated fats, lowers blood pressure, improves lipid levels, and reduces the estimated
cardiovascular risk.
Most people don't get enough of these healthful unsaturated fats each day. No strict guidelines have been published regarding their intake. Prudent targets are 10 to 25 percent of calories from monounsaturated
fats and 8 to 10 percent of calories from polyunsaturated fats. Since no one eats by percentage of daily calories, a good rule of thumb is to choose unsaturated fats over saturated whenever possible.
Bad Fats: Saturated Fats
Our bodies can make all the saturated fat we need, so we don't need to eat any of it. That's why saturated fat can be in the bad category—because we don't need to eat any of it, and it has undesirable effects in cardiovascular disease. Saturated fats come mainly from meat, seafood, poultry with skin, and whole-milk dairy products (cheese, milk, and ice cream). A few plant foods are also high in saturated fats, including coconut (debatable, because our doctor says it is not harmful) and coconut oil, palm oil, and palm
kernel oil. Saturated fats boost total cholesterol by elevating harmful LDL. Like all dietary fat, saturated fat also raises the protective HDL. Unsaturated fat is much preferable since it lowers the bad cholesterol and raises the good.
As a general rule, it's a good idea to keep your intake of saturated fats as low as possible. Saturated fats are part of many foods, including vegetable oils that are mainly unsaturated fats, so we can't eliminate them from our diets. Seven percent of total calories or lower is a good target. Red meat and dairy fats are the main sources of saturated fat in our diets, so keeping these low is the primary way to reduce intake of saturated fat.
Very Bad Fats: Trans Fats
Trans fatty acids, more commonly called trans fats, are made by heating liquid vegetable oils in the presence of hydrogen gas, a process called hydrogenation. Partially hydrogenating vegetable oils makes them more stable and less likely to spoil. It also converts the oil into a solid, which makes transportation easier. Partially
hydrogenated oils can also withstand repeated heating without breaking down, making them ideal for frying fast foods. (Fully hydrogenating a vegetable oil creates a fat that acts like a saturated fat.) It's no
wonder that partially hydrogenated oils have been a mainstay in restaurants and the food industry.
The Bottom Line: Recommendations for Fat Intake Although the different types of fat have a varied—and admittedly confusing—effect on health and disease, the basic message is simple: Out with the bad, in with the good. As you limit the amount of trans and saturated fats in your diet, there is no good evidence that
replacing saturated fat with carbohydrates will protect you against heart disease, while there is solid proof that replacing saturated fat with unsaturated fats will help.
• Try to eliminate trans fats from partially hydrogenated oils. Check food labels for trans fats; avoid fried fast foods.
• Limit your intake of saturated fats by cutting back on red meat and full-fat dairy foods. Try replacing red meat with beans, nuts, poultry, and fish whenever possible, and switching from whole milk and
other full-fat dairy foods to lower fat versions.
• In place of butter, use liquid vegetable oils rich in polyunsaturated and monounsaturated fats in cooking and at the table.
• Eat one or more good sources of omega-3 fats every day—fish, walnuts, canola or soybean oil, ground flax seeds or flaxseed oil.
