Sunday, June 14, 2009

Health & nutrition tip

Good Fats, Bad Fats
Exposing the myths—and truths—about saturated fat.
By Rachel Johnson, Ph.D., M.P.H., R.D.,

When it comes to breaking science, I try to keep an open mind. But when I read statements like "It's become clear that natural saturated fats are good for you" (in a major food magazine last year), I blink. In the professional groups I'm involved with—including the American Heart Association—the idea that saturated fats increase the risk of heart disease is an unquestioned, fundamental principle.

Saturated fats—found mainly in fatty meats, butter, cheese and whole milk—are "saturated" with hydrogen atoms, which gives them a rigid structure and makes them solid at room temperature. (Unsaturated fats—those in nuts, olives, fish and vegetable oils—are fluid at room temperature.) Most experts agree that saturated fats raise levels of LDL ("bad") cholesterol in the blood. That's damaging to the heart and arteries, we believe, since excessive LDL accumulates in artery walls and can trigger inflammation, eventually leading to a heart attack or stroke. That would seem to be the end of the story—or is it? I decided to evaluate some common assumptions.

Myth: "All saturated fats are bad."

It's easy just to lump all saturated fats into one "heart-threatening" group, but the reality is that there are many different kinds of saturated fats in foods. Some research suggests that certain types are more harmful than others. For example, a handful of studies show that while coconut oil, rich in lauric acid, raises blood levels of LDL ("bad") cholesterol, it also raises HDL ("good") cholesterol slightly. Stearic acid, a type of saturated fat that makes up about half the fat in dark chocolate and accounts for 15 percent of the fat in beef, doesn't raise LDL at all. Experts consider stearic acid "neutral" when it comes to cardiovascular risk: it doesn't help, but it doesn't hurt either.

On the flip side, some saturated fats appear more likely than others to cause the buildup of fatty plaque in arteries. Palmitic acid, which is the main fat in palm oil and another saturated fat present in beef, is one such fat. But the fact that beef contains both "bad" palmitic acid and "neutral" stearic acid underscores the point that foods rich in saturated fats contain a mixture of different types.

And, of course, despite a widespread trend to eliminate trans fats from our food supply, many packaged snacks still contain these man-made fats that act like saturated fats. And trans fats, or "partially hydrogenated" fats, are the unhealthiest of all: they increase ("bad") LDL and decrease ("good") HDL.

Bottom line: Saturated fats are not all created equal. Foods contain a variety of saturated fats, and a "neutral" one won’t negate the impact of a "bad" one. To minimize intake of "bad" saturated fats, choose lean sources of protein and low-fat or nonfat dairy products. Read labels on packaged foods, such as cookies, crackers and microwave popcorn, to avoid palm and coconut oils and trans fats. (While coconut oil may be marginally better than palm, you're still better off avoiding both.)

Myth: "Saturated fats are the worst offenders in our diets."

As more research uncovers the role diet plays in cardiovascular disease, it's becoming obvious that fats aren't the only villains in the picture. Increasingly, scientists are recognizing that you should also watch out for some carbohydrates—specifically, sugars and refined grains. "I believe that a diet containing moderate amounts of saturated fat is okay, and possibly better, than a low-saturated-fat diet that is rich in sugars and refined carbohydrates," says Ronald Krauss, M.D., director of atherosclerosis research at Children's Hospital Oakland Research Institute and a past chair of the American Heart Association's Nutrition Committee. "Although saturated fats raise ["bad"] LDL cholesterol, sugars decrease ["good"] HDL cholesterol and raise triglycerides [another harmful fat in the blood]," he explains. Those findings are confirmed by studies conducted at Harvard in more than 80,000 women.

Bottom line: Refined carbohydrates, such as white bread and sugary sweets, may be just as bad for your heart and arteries as cream and butter—one more reason to limit them.

Myth: "A low-carb diet is always bad for your heart."

When most people hear "low-carb diet," they usually think of an eating plan that virtually eliminates carbohydrates and allows unlimited amounts of high-protein, high-saturated-fat foods, such as bacon. But today's low-carb diets have evolved from those popular in the 1970s. Plans like South Beach and even Atkins do not promote marbled steaks and other saturated-fat-laden foods; instead, they emphasize eating fewer refined carbohydrates, such as white bread. A low-carb diet that emphasizes lean proteins, such as fish and beans, and vegetables, as well as "good" carbohydrates (e.g., brown rice), can actually look pretty good to a cardiologist. In fact, last summer an Israeli study published in the New England Journal of Medicine reported that people following a low-carb (Atkins) diet lost more weight and ended up with bigger improvements in blood-cholesterol numbers than those who followed a reduced-calorie, low-fat diet.

In this study, subjects were told to select vegetarian sources of fat and protein, which means it was likely that they were eating more unsaturated fats than saturated ones. In some ways they were following the current guidelines of the American Heart Association, which no longer advocates strictly limiting total fat but rather advises people to replace saturated fats with healthier unsaturated ones (e.g., olive oil for butter).

Bottom line: A "low-carb" diet based on lean sources of protein, vegetables, unsaturated fats and a judicious amount of whole grains is heart-healthy.

So what now?

I doubt we'll ever have all the facts about saturated fat. But I'm not going to start eating a half-pound of bacon for breakfast anytime soon. We know that when it comes to heart health, unsaturated fats, such as those in oils, salmon, nuts, and avocados, are better choices than the saturated fats in fatty meats and butter. I'll also continue to choose whole grains over refined carbohydrates as much as I can, and exercise most days of the week. That incorporates most of the heart-healthy thinking I need.