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Low fat, not low carb, for heart health
Summarized by Susan Aldridge, PhD, medical journalist
March 10, 2008

Summary
A comparison of low fat and low carbohydrate diets shows that while both produce weight loss, they differ in their impact upon the arteries. Low fat improves arterial functioning, which will aid heart health, while low carbohydrate has the opposite effect.

Introduction
Obesity is now well known as an independent risk factor for heart disease, which is one reason why 45 percent of women and 30 percent of men in America are trying to lose weight. Many diets produce weight loss but not much is known about effects their individual food contents have on other aspects of health. The American Heart Association advocates a diet with a low fat content, where 30 percent of calories come from fat. Another popular diet is the Atkins approach, where the emphasis is upon restricting carbohydrate to just 20 grams a day, although fat intake can be as high as 50 percent of calories or more. Researchers at the Medical College of Wisconsin, Milwaukee, have compared how the two diets impact upon the function of the endothelium, which is the inner lining of the arteries. The endothelium is important because it releases nitric oxide, a gas that has anti-inflammatory and anti-thrombotic (blood clotting) properties. It is known that endothelium-dependent flow-mediated dilation (FMD)1 is a good indicator of heart health and this is what the researchers measured in their diet comparison study.

What was done
A group of 20 obese, but otherwise healthy, participants was assigned to either a low fat or low carbohydrate diet for six weeks. Brachial artery2 FMD, was measured with ultrasound, along with blood pressure, cholesterol profile and weight loss.

What was found
Participants in both groups had similar, and significant, losses of weights after six weeks on their diet. They also showed a decrease in blood pressure and the low carbohydrate group a decrease in triglycerides. At six weeks, brachial artery FMD had increased in the low fat group, but had decreased in the low carbohydrate group. A decrease in this measure is known to risk factor for cardiovascular disease and a prognostic measure for future heart attack or stroke.

What this means
There are many different mechanisms by which the low fat or low carbohydrate dietary approach could differently impact on heart health. Loss of fat mass through a low fat diet could decrease inflammation in the body which could improve endothelial function. The high fat content of a typical Atkins diet could have the opposite effect, for previous research has shown that a single high fat meal can impact endothelial function for six hours or more3. The researchers conclude that the traditional low fat diet could be a more effective way of improving heart health than the Atkins approach, although this was a small study deserving of repetition on a larger scale.

Source

Benefit of Low-Fat Over Low-Carbohydrate Diet on Endothelial Health in Obesity SA. Phillips, JW. Jurva , et al, Hypertension, 2008, vol. 51, pp. 376--382

Footnotes

1. Endothelium dependent flow-mediated dilation (FMD)is a measure of endothelial function; increased FMD is an early indicator of cardiovascular disease , -, -

2. The brachial artery is the artery in the arm , ,

3. Impaired flow-mediated vasoactivity during post-prandial phase in young healthy men S. Marchesi, G. Lupattelli, et al, Atherosclerosis, 2000, vol. 153, pp. 397—402

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