When Good Carbs Turn Bad
By Lawrence Lindner, Special to The Washington Post|
washingtonpost.com (Tuesday, June 19, 2001; Page HE11) — It sounds like a plug for the Atkins program: A high-carbohydrate diet may be bad for you.
It's true though it goes against the advice of virtually every health-promoting organization in the country. But it's not because carbohydrates make you fat. They don't. Only excess calories can make you fat, and it doesn't matter whether they come from carbohydrates, fat or protein. It's because too many carbohydrates can make some people more prone to develop heart disease.
The evidence has accumulated to the point that even the latest guidelines on preventing heart disease, released last month by the National Heart, Lung, and Blood Institute (NHLBI), mention that high-carbohydrate diets could present problems for certain people at increased risk for heart attacks and other cardiovascular problems.
In those individuals, eating the majority of calories as carbohydrates can:
Raise undesirable blood fats known as triglycerides.
Keep down blood levels of "good" HDL-cholesterol.
Increase the risk for high blood pressure, an independent risk factor for heart disease.
Render "bad" LDL-cholesterol more harmful by making the LDL
particles smaller and
Make the blood more likely to form clots.
This cluster of problems commonly goes by the name of Syndrome X, a term coined in 1988 by Stanford University physician and endocrinology researcher Gerald Reaven. Syndrome X (which NHLBI refers to as Metabolic Syndrome) occurs in people who are hyperinsulinemic, meaning they secrete too much of the hormone insulin. Reaven estimates that one in four American adults up to 50 million people are afflicted, many of them without knowing it.
Normally, a biologically appropriate level of insulin gets secreted when carbohydrates are eaten. Once carbohydrates are broken down to blood sugar, or glucose, it's insulin's job to get the sugar out of the blood and into all the organs and other tissues, where it's used as body fuel. But in someone with Syndrome X, insulin levels spike too high in response to carbohydrates, and that causes the cascade of side effects that raises the risk for heart disease.
(Another end result that can occur in someone who secretes too much insulin is diabetes. In fact, some researchers consider Syndrome X a pre-diabetic condition, even though the majority of people who have the condition don't go on to develop diabetes.)
The Syndrome X solution? The first lines of approach are to lose excess weight and step up physical activity. Reaven says so, and so does the NHLBI. Extra body fat, especially around the abdomen, and inactivity account for half the effects of hyperinsulinemia in this country, Reaven notes.
The good news: A loss of just 10 to 15 percent of body weight is often enough to blunt Syndrome X's effects by bringing insulin levels in line. Losing weight makes the body more insulin-sensitive less insulin is required to move sugar from the bloodstream and into the various tissues.
For physical activity to make a difference, "you have to be really more active," Reaven says, "jogging or walking rapidly, not strolling. You have to work up a sweat three to four times a week for at least 30 minutes. And you have to keep it up. You can't stop, because you lose the benefits very quickly."
Unfortunately, even if you're lean and physically fit, you can still be hyperinsulinemic and have all the problems associated with Syndrome X. That's when it might pay to consider eating fewer carbohydrates to lower the amount of insulin that has to be secreted.
What to replace the carbohydrates with? Fat. Not the saturated fat found in burgers, ice cream and doughnuts. That's no good for the heart, either, because it raises "bad" LDL-cholesterol. The fat should be mono-unsaturated and polyunsaturated, which means foods such as nuts, olive oil, canola oil, avocados, oily fish (like mackerel and salmon) and tofu. It works, as clinical studies have shown.
Consider findings published in 1997 from a study conducted on a small group of women who appeared to be hyperinsulinemic. For three weeks, Reaven put them on a conventional heart-healthy diet that contained 60 percent of calories as carbohydrate and 25 percent as fat. For another three weeks, they ate a diet with the same number of total calories that contained only 40 percent of calories as carbohydrates and 45 percent as fat. (Protein remained constant at 15 percent of total calories.) To up the fat and lower the carbohydrates, Reaven made such changes as giving the women a tablespoon of peanut butter at breakfast rather than bread and half a tablespoon more salad dressing at dinner with a little less potato.
The upshot: On the lower-carb, higher-fat diet, the women lowered their triglycerides by an average of 60 points, from 174 to 114 (the closer to 100, the better). They also maintained better HDL-cholesterol levels.
Of course, many heart disease specialists are loath to tell people to eat more fat, even if it's "good" fat. That's because it's all too easy to go overboard on calories when you add fat to the diet. After all, an ounce of carbohydrate or protein has only 113 calories, whereas an ounce of fat has 255.
Robert Eckel, immediate past chairman of the American Heart Association's nutrition committee and an endocrinologist at the University of Colorado Health Sciences Center in Denver, is one of those critical of making a broad-based recommendation to eat more fat.
"If you put people on a metabolic ward" and carefully control the number of calories they eat while you change carbohydrate and fat proportions, he says, you can see an effect. But in an outpatient setting, things don't always work so smoothly. "I'm not saying there isn't room for that kind of modification," he comments, but in only "a handful of patients over 20 years have I had to raise fat content [and lower carbohydrate content]. Mostly, it's lose weight and get more physical activity."But Reaven argues that more than a handful would benefit from making the shift. He offers this story: "This guy at a meeting approached me, this nice, tall, slim guy. A physician. His HDL was about 35 [when it should have been closer to 50 to 60], his triglycerides were up to 230. He kept trying to fix it" by cutting back on fats and adding carbohydrates, but every time he did that, his triglycerides went up further.
No wonder, says Reaven, who notes that "this fetish for a low-fat diet"
is not helping everyone. Making matters worse still, he notes, is that a lot
of reduced-fat foods contain more carbohydrates than regular versions of the
same products. That's because the fat that's removed is replaced with carbohydrate
in the form of sugar to add bulk, texture and flavor.
What to do? First, you need to get some numbers from your doctor: your triglyceride level, your HDL level, your blood sugar level (all three require an overnight fast) and your blood pressure. If the numbers are out of whack (see box at right) and your body weight is healthy and you exercise vigorously several times a week, consider, upon consulting with your physician, cutting back a little on carbohydrate-rich foods (especially sugary ones and starches made from refined instead of whole wheat) and adding a bit in the way of things like nuts, seeds, fatty fish and olive oil. If you can keep your weight stable while making the changes, you might find the numbers have improved by your next doctor's visit.
Eating Right columnist Lawrence Lindner is executive editor of the Tufts University
Health & Nutrition Letter.|
|© 2001 The Washington Post Company