The Role of Dietary Fats and Cholesterol in Heart Health
The Role of Dietary Fats and Cholesterol in Heart Health
It's time to demystify dietary fats and explain their impact on risk factors for heart disease and other health problems. You'll learn about the various types of fat--as well as some basics about cholesterol, HDL, LDL and triglycerides--then find out how the Atkins can be a powerful agent in preventing heart disease.
Some Basic Facts About Fat
You will learn about:
- The role of the various types of fat in a healthy diet
- What cholesterol is and how it's measured
- The medical profession's changing view of the role that diet--especially fats--plays in risk factors leading to heart disease
- How the Atkins goes against conventional notions about fats in the diet
Good Fats vs. Bad Fats
Natural fats include saturated, monounsaturated and polyunsaturated fats. All are "good" fats, meaning that they have positive health benefits, unlike heavily processed, potentially deadly manufactured trans fats. First let's explore the three good fats.
Monounsaturated fats are found in all nuts, including almonds, pecans, cashews and peanuts, as well as in avocados and olive and canola oil. They are widely acknowledged as beneficial. Some groundbreaking studies, such as Ancel Keys' Seven Countries Studies, indicate that monounsaturated fat found in olive oil can reduce risks for heart disease, stroke and some kinds of cancer. Harvard's long-running Nurses' Health Study showed a correlation between high consumption of nuts--a good source of monounsaturated fats--and low incidence of heart disease.
These fats are found in fish, sunflower seeds, soybeans, and flaxseeds as well as in cottonseed, corn and safflower oils. Like monounsaturated fats, these fats have many health benefits. Among other things, polyunsaturated fats provide essential fatty acids for healthy skin and the development of cells in the body.
All unprocessed foods containing fats contain a mixture of the three good fats. For example, the fat in steak is 51 percent monounsaturated, 45 percent saturated and 4 percent polyunsaturated. A healthy diet includes a balance of the different types of natural fats. This balance can be achieved by consuming predominantly whole foods.
Numerous studies show that saturated fats play many beneficial roles in our bodies, including enhancing the immune system, protecting the liver, forming cell membranes and helping build healthy bones. However, the health effects of saturated fats are in dispute. Saturated fats have been demonized as unhealthy and linked to high rates of heart disease. But in reality, there is no conclusive scientific evidence that saturated fats are unhealthy. Moreover, the link between saturated fat and heart disease is not as strong as many people believe.
Why, then, does saturated fat have such a bad reputation? Part of the reason lies in the fact that all research conducted on saturated fat and its impact on disease examines saturated fats in the context of high-carb diets. Unless saturated fat is isolated from the rest of the diet, such studies can be seriously flawed. In fact, in the context of a low-carb diet, saturated fats have been shown, in several studies, to reverse cardiovascular risk factors. Practically speaking, most people can enjoy saturated fats in the form of cream, butter and meat without health concerns--as long they are correctly following a controlled-carb dietary program.
Bad Fats = Manufactured Trans Fats
Also known as hydrogenated or partially hydrogenated vegetable oil, manufactured trans fat is a heavily processed vegetable oil that is extremely bad for you. (All hydrogenated and partially hydrogenated oils are trans fats, but the two terms are not synonymous. Natural trans fats are found in dairy products and certain other foods.) Vegetable shortening and most margarines contain trans fats. Trans fats begin as natural, polyunsaturated fats that are then exposed to chemical processes that change the molecular structure by artificially saturating the fat with hydrogen in the manufacturing process. So manufactured trans fats are synthetic saturated fats.
Partially hydrogenated vegetable oil is one of the top ingredients in most packaged foods: cookies, snack chips, pretzels, most peanut butter and shortening. Many fast food chains fry their foods in partially hydrogenated oils.
Why is manufactured trans fat so bad? Take a look:
- It accumulates in your body and clogs arteries. A study published in The Lancet in 1994 showed that almost 75% of the fat found clogging arteries is unsaturated and comes from artificially hydrogenated vegetable oils, not animal fats.
- It raises LDL (bad) cholesterol levels and lowers HDL (good) cholesterol levels.
- It raises levels of triglycerides, another form of lipid, which increase the risk of heart disease.
- It's linked to risk factors for Type-2 diabetes and other serious health problems, including breast cancer and asthma.
Cutting out manufactured trans fats is one of the best things people can do for their health. But as we've shown, not all fats are bad. And by now, Americans should already know that eating low-fat doesn't necessarily mean you slim down--or improve your health. The popularity of the low-fat, high-carb diet recommended by the USDA corresponds to a meteoric rise in American obesity and Type-2 diabetes rates, as we'll see in the next section.
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Changing Views of the Role of Dietary Fat and Cholesterol
The popularity of the low-fat, high-carb diet recommended by the USDA corresponds to a meteoric rise in American obesity rates. Before we take a look at some research results in this area, let's take a little time to review some terminology.
Blood Chemistry 101: HDLs, LDLs and Triglycerides
Cholesterol is a waxy, fat-like compound manufactured by your body. It is not actually a fat, but like fat, cholesterol is critical for health; it contributes to normal cell function. Cholesterol only becomes a problem when levels of so-called "bad" cholesterol (LDL) become elevated--a condition that has been linked to increased risk for heart disease.
First, it's important to understand the difference between dietary cholesterol and serum cholesterol.
- Dietary cholesterol is found primarily in animal foods such as meat, eggs and dairy products, as well as shellfish. In the body, dietary cholesterol serves as a structural component of cell membranes and contributes to other functions. Until recently, dietary cholesterol had a bad rap for giving people high serum (blood) cholesterol levels. This viewpoint is now changing as researchers reveal that the liver contributes much more cholesterol to the body's total count than diet does. In addition, only a small amount of cholesterol ingested is actually absorbed.
- Serum cholesterol is a soft, waxy substance present in all parts of the body, including the nervous system, skin, muscle, liver, intestines and heart. It is made by the body and obtained from fatty substances in the diet. Cholesterol is manufactured in the liver for normal body functions, including the production of hormones, bile and vitamin D. It is transported in the blood for use by all parts of the body.
Serum cholesterol is what people are talking about when they talk about cholesterol levels. A lipid profile is a blood analysis that measures HDL (so-called "good" cholesterol), LDL (so-called "bad" cholesterol), triglycerides and total cholesterol. Here's a more detailed rundown of what these terms mean.
- LDL (low-density lipoprotein): LDL is a carrier molecule that transports cholesterol and triglycerides in the blood from the liver to the body's cells. A high level of LDL is associated with a high risk of heart attack because it indicates there is too much artery-clogging cholesterol in the blood. Although long considered the "bad" cholesterol, recent research indicates that some sub-fractions of LDL actually protect the heart.
- HDL (high-density lipoprotein): Considered the "good" cholesterol, HDL is actually a carrier molecule that transports cholesterol in the blood. HDL is responsible for returning cholesterol and triglycerides (fats) from the cells and the vessels to the liver. A high HDL blood level is associated with a lowered risk of heart attack.
- Triglyceride: The chief form of fat in the diet and the major storage form of fat in the body. Serum levels of triglycerides indicate how much fat is moving through the body, potentially clogging arteries. A level below 150 milligrams per deciliter (mg/dL) is considered healthy. Dr. Atkins, however, recommended the optimum level of triglycerides as less than 100mg/dL.
In general, LDL moves cholesterol toward the heart, where excessive amounts can raise the risk for heart disease. On the other hand, HDL typically moves cholesterol away from the heart and toward the liver, where excess cholesterol is flushed out of the system--thus the characterizations as "bad" and "good."
Dismantling the Diet-Heart Hypothesis
The role that diet--especially fats--plays in heart disease has been a subject of medical study and opinion for over a hundred years. Since the 1970s, the premise that a low-fat, high-carbohydrate diet will lower cholesterol has been heavily promoted. A recent article by Sylvan Lee Weinberg, MD, MACC in The Journal of the American College of Cardiologists points not just to the changing medical opinion and health evidence in favor of controlling carbs, but also to the negative health consequences of the low-fat high-carbohydrate diet:
"The low-fat high-carbohydrate diet, promulgated by the National Cholesterol Education Program, the National Institutes of Health, the American Heart Association...and the Department of Agriculture food pyramid...may well have played an unintended role in the current epidemics of obesity, lipid abnormalities, type II diabetes and metabolic syndromes. This diet can no longer be defended by appeal to the authority of prestigious medical organizations or by rejecting a growing medical literature that the much-maligned low-carbohydrate high-protein diet may have a salutary effect on the epidemics in question."
-- from the abstract of "The Diet-Health Hypothesis: A Critique" by Sylvan Lee Weinberg, MD, MACC in The Journal of the American College of Cardiologists, Vol, 33, pp. 731-33, 2004.
Over the years, doctors and the media have tended to associate high fat content with high serum cholesterol levels--without differentiating among the various types of fats. Also, many dietary studies measuring the effects of dietary fat on lipids use protocols that contain considerable amounts of dietary carbohydrates. The problem with that is, as we've learned, consuming carbohydrates affect what the body does with dietary fat--whether it stores it or burns it as an energy source. Failure to take that into account has resulted in erroneous conclusions about the health effects of dietary fats.
Modern studies show that the worst diet of all consists of a combination of high carbs and high fat --especially diets high in trans fat. A diet high in carbohydrates can result in elevated levels of triglycerides and bad cholesterol, which can lead to heart attacks, strokes, diabetes and other serious problems. Very low-fat diets are associated with a rise in triglycerides and a decrease in "good" carbohydrates--a potentially deadly combination.
On the other hand, the controlled-carb, high-fat Atkins eating plan forbids manufactured trans fats--and in the presence of moderate amounts of carbohydrates, makes sure that primarily fats are burned for energy. One good indicator of heart health is a combination of high HDL cholesterol and low triglycerides. People on the ANA typically see their HDL levels climb and their triglyceride levels drop. For example, a recent study at Durham Veterans Affairs Medical Center found that mildly obese volunteers who ate a controlled-carbohydrate, high-fat, high-protein diet showed significant average decreases in total cholesterol and triglyceride levels and increases in HDL.
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Atkins vs. Low-Fat Methodology: What the Studies Show
Fat and cholesterol do interact, but not necessarily in an unhealthy way. A high-fat diet alone does not raise bad cholesterol levels. Combined with excessive carbohydrates and too many calories, too much fat is dangerous--especially in the form of manufactured trans fats. But a growing body of research shows that in the absence of lots of carbohydrates, high-fat diets may be perfectly healthy. This is supported by numerous peer-reviewed studies.
For example, the 1998 Willi, Oexmann, Wright study of extremely obese teenagers summarized: "Researchers ultimately concluded that the low-calorie ketogenic (low-carb) diet is a safe and effective weight loss regimen for morbidly obese adolescents and that the weight loss with this approach is rapid, consistent and almost exclusively from body fat stores."
In 2003, major studies demonstrated that that Atkins actually works better than many low-calorie, low-fat diets:
- Short-term studies found that low-carb dieters lost more than those on other programs--including the American Heart Association plan--without higher cholesterol or blood pressure levels. A study presented at an American Association for the Study of Obesity meeting in fall 2003 noted that people who ate an extra 300 calories a day on a very low-carb diet lost the same amount during 12 weeks as those on a standard low-fat diet. Over the course of the study, the low-carb group ate 25,000 more calories--which should have added up to about seven additional pounds, but didn't.
- A report in the New England Journal of Medicine found people following Atkins lost twice as much weight as those on standard low-fat diets. Plus, the Atkins group generally had better levels of "good" cholesterol and triglycerides, or fats in the blood, than those following the low-fat programs. There was no difference in levels of "bad" cholesterol or blood pressure. The report cited two studies: A six-month study by the U.S. Veterans Affairs Department and a year-long study led by Gary D. Foster, who runs the weight-loss program at the University of Pennsylvania School of Medicine. After six months, the Atkins group had lost an average of 15 pounds, while those on low-calorie, low-fat diets lost an average of seven pounds. After a year, Atkins followers kept off an average of 9.5 pounds, the others about 5.5 pounds, and Atkins participants had no ill health effects.
The link between dietary fat, cholesterol and heart health is important, since many people don't realize they have heart disease until it's too late. Certain kinds of fat can have a role in a healthy diet, and it's time to question the low-fat, high-carb hypothesis of the past. Numerous studies show that a low-carb diet like Atkins may be effective in helping to combat heart disease.