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HDL drop on low-fat, high-carb diet not worrisome.

SAN FRANCISCO -- A declining plasma concentration of high-density lipoprotein cholesterol induced by a low-fat, high-carbohydrate diet may well be a cardiovascular-risk red herring, according to a Canadian researcher.

Although conventional wisdom suggests that higher HDL-cholesterol levels bolster cardiovascular health, the observed HDL drop from the diet may just reflect a reduction in the circulation's need for HDL activity, reported Sophie Desroches, a doctoral candidate in nutrition at Laval University in Quebec City.

In other words, the apparent downside (lower HDL) may be merely the normal metabolic response to the diet's positive upside (lower LDL cholesterol). She said the diet led to lower production and breakdown of a key LDL protein, apolipoprotein A-I (apo A-I), compared with a diet high in monounsaturated fatty acids (MUFA).

The lower HDL level "may reflect an attenuated requirement for reverse cholesterol transport in a metabolic environment in which LDL cholesterol is reduced," she said in a prepared statement accompanying a poster presentation at a conference on arteriosclerosis, thrombosis, and vascular biology sponsored by the American Heart Association. Ms. Desroches and her colleagues concluded that reduced HDL induced by a low-fat, high-carb diet "should not raise concerns about cardiovascular health."

Ms. Desroche was reporting the results of a 6-week study of 65 men (mean age, 37.5 years) who were randomized to a diet low in fat and high in carbohydrates or a diet high in MUFA. The low-fat, high-carb diet was similar to the plan recommended by the AHA and the National Cholesterol Education Program. The high-MUFA diet resembled a Mediterranean-style diet. The men had a mean body mass index of 29.2, she said at the meeting, also sponsored by the National Heart, Lung, and Blood Institute.

Men in both groups were allowed to eat as much as they wanted. Their fasting lipid levels were measured at baseline and after 6-7 weeks. Both eating plans resulted in significant decreases in LDL levels and ratios of total cholesterol to HDL. Yet HDL levels fell 10% among men in the low-fat/high-carb group and declined 3% among men in the MUFA group.

Detailed apo A-I analyses of 18 men showed that decreased HDL among those eating the low-fat, high-carb diet was due almost entirely to decreased production and fractional catabolic rates of apo A-I. These apo A-I kinetic changes did not occur in men eating the high-MUFA diet.

"Our results indicate that variations in HDL composition and metabolism induced by ad libitum feeding of a low-fat, high-carbohydrate diet may not be considered as pro-atherogenic and detrimental in terms of cardiovascular risk," she reported. "It may simply reflect adaptive changes to a metabolic state in which LDL cholesterol is reduced."

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Title Annotation:Cardiovascular Medicine; High-density lipoprotein
Author:Finn, Robert
Publication:Family Practice News
Geographic Code:1USA
Date:Nov 1, 2004
Words:443
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