Low carbohydrate diets are all the rage, though their medical benefits are unclear. One of the stated health benefits of a low carbohydrate diet is that it lowers blood cholesterol. The results of the study reported here counter this potential benefit. The study found that although a low carbohydrate diet resulted in lower cholesterol levels, it lowered both the good (HDL) and bad (LDL) cholesterol. Since it is the relative amounts of HDL and LDL cholesterol (the ratio) that is important in determining the risk for vascular disease, the decrease in cholesterol caused by a low carbohydrate diet should have no effect on vascular disease. The justification for low carbohydrate diets will have to be found somewhere other than with cholesterol.
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Carb-Linked Dip in 'Good' Cholesterol OK, Study Finds
By E.J. Mundell
FRIDAY, May 7 (HealthDayNews) -- In the pre-Atkins era, high-carbohydrate, low-fat diets were all the rage, and they remain the American Heart Association's ideal regimen for cardiovascular health. However, proponents of low-carb, high-fat diets have pointed out that high consumption of carbohydrates can lower blood levels of high-density lipoprotein (HDL) -- the "good" cholesterol -- over time.
Now a new study suggests that carbohydrate-based dips in HDL pose no real threat to health, because blood levels of low-density lipoprotein (LDL), the "bad" cholesterol, tend to fall in equal proportion at the same time.
"If that ratio doesn't change when HDL goes down, then there's no real reason for concern," said Dr. Alice H. Lichtenstein, director of the cardiovascular nutrition laboratory at Tufts University and a spokeswoman for the American Heart Association (AHA).
Through the 1990s, food products with labels proclaiming them "nonfat" or "low-fat" were ubiquitous in American supermarkets, as consumers sought to trim waistlines and improve cardiovascular health by avoiding fat in favor of carbs.
At the same time, studies began show that these types of diets could produce a decline in blood levels of HDL, a form of cholesterol that actually helps arteries stay healthy.
The issue caused "a fair amount of concern" for dietary experts, Lichtenstein said.
The latest research, presented Friday at the AHA's annual conference on Arteriosclerosis, Thrombosis, and Vascular Biology in San Francisco, may allay those concerns.
A research team led by Sophie Desroches, a doctoral student in nutrition at Laval University in Quebec City, Canada, had 65 adult men consume the AHA's recommended diet for six weeks. The AHA regimen advises that people consume 58 percent of their total daily calories from carbohydrates, 26 percent from fat (less than 7 percent from saturated fat), and 16 percent from protein.
According to the researchers, blood levels of HDL cholesterol fell by an average of 10 percent in men placed on this diet over the six-week study period. However, levels of LDL fell in equal proportion, so that the all-important ratio of good-to-bad cholesterol remained stable.
In a statement, Desroches said the findings suggest that carbohydrate-linked reductions in HDL "should not raise concerns about cardiovascular health."
Lichtenstein agreed. "When you institute any kind of dietary modification, you want to make sure you don't decrease HDL without also decreasing LDL," she explained. "You want to make sure that that ratio doesn't go up."
She said advocates of the dietary craze of the moment, the Atkins diet, have long pointed to lowered HDL levels as a reason to abandon carbohydrates. But Lichtenstein said high-calorie intakes -- not carbs -- are most responsible for extreme dips in HDL, whatever the diet.
In the 1990s, "there was a proliferation of low-fat and nonfat products," she pointed out, "so many people started gorging on low-fat ice cream, cookies, and chips in the mistaken notion that they wouldn't gain weight."
Waistlines expanded, she added, and "when your body weight increases, that does have an adverse effect on blood lipids."
"That's when people said, 'Aha! See? This high-carbohydrate diet causes weight gain; it's really bad for you,'" she said.
What's needed, she believes, is a change in attitude among the American public towards eating in general.
Whether it's a high-carb or low-carb diet, "there's this feeling that 'Oh, if I choose this side or that side, I can eat what I want and still lose weight,'" she said. "The bottom line is that that never turns out to be the case."
Experts at the AHA continue to reject the Atkins regimen because of its reliance on artery-clogging fats. As to Atkins' effects on HDL cholesterol, Lichtenstein says there's not enough long-term data to show an effect one way or another.
"We really don't know," she said.
When it comes to the AHA's recommended diet -- which emphasizes carbohydrates sourced from whole grains, vegetables and fruits -- "everyone is simply recommending moderation," Lichtenstein said. "In all diets, it's all about calories -- that's the bottom line."
SOURCES: Alice H. Lichtenstein, M.D., director, cardiovascular nutrition laboratory, Tufts University, Boston, and spokeswoman, American Heart Association; May 7, 2004, presentation, American Heart Association's annual conference on Arteriosclerosis, Thrombosis and Vascular Biology, San Francisco
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