High Fat Diet to Slow Coronary Disease? Can It Be True?

Summarized by Robert W. Griffith, MD
December 22, 2004

We've been hearing for years that saturated fats raise LDL-cholesterol levels - the 'bad' cholesterol - and are responsible for atherosclerosis leading to coronary heart disease, while, on the other hand, consuming unsaturated fats have an almost protective effect. Now there's a study that points in the opposite direction.¹ This has been critiqued in an editorial in the American Journal of Clinical Nutrition, which is summarized here.

The new study

The Estrogen Replacement Study (ERA) enrolled postmenopausal women with coronary heart disease (CHD) to examine the effect of hormone replacement therapy on the development of their coronary atherosclerosis. This meant they had coronary angiography² done at baseline and at the end of the study, to assess the degree of coronary artery atherosclerosis. Among other investigations, they had their dietary intake of different foods assessed by food-frequency questionnaires.

Of 309 women entering the study, 255 had angiography done just over 3 years later. They had an average of 25% saturated fat in their diets, which is on the low side. By dividing the women into 4 equally-sized groups, or quartiles, based on their saturated fat intake, the investigators were able to show that a higher saturated fat intake was associated with less progression of CHD, according to quantitative angiography. On the other hand, increased carbohydrate intake was associated with increased progression of atherosclerosis.

This effect was found even after statistical adjustments were made for the other variables in the study - differences in age, educational level, diabetes, smoking, use of lipid-lowering drugs, hormone replacement therapy, and so on.

What's special about these new results?

All the women in the ERA study had CHD, 70% had high blood pressure, 23% had diabetes, and their BMIs averaged 29.5 (i.e. verging on the obese). Their lipid levels were raised, and all these findings were suggestive that a number of them had the metabolic syndrome. And, of course, two thirds of them were taking sex hormones.

The authors of the editorial comment on the result of the study. Other studies show that the effects of a low-fat, high carbohydrate diet vary in people with 'simple' elevation of LDL-cholesterol and those with what's called 'combined hyperlipidemia', in which the triglycerides are around 200 mg/dL, the HDL is 40-50 mg/dL, and the LDL is 135-140 mg/dL. In simple hypercholesterolemia, a fat intake below 25% and carbohydrate intake of over 60% of calories produces a sustained increase in triglycerides and a decrease in HDL. In contrast, a low-fat intake and high carbohydrate intake in people with combined hyperlipidemia causes no worsening of triglyceride and HDL levels; on the other hand, a raised fat intake (above 40%) with reduced carbohydrate (below 45%) produces lower triglyceride levels. The women in the ERA study had combined hyperlipidemia, so a higher fat intake could have lowered their triglycerides and raised their HDL, leading to the lessened atherosclerosis that was found.

Triglycerides and HDL levels are better predictors of CHD in women than in men, and the ERA study was confined to women. On the other hand, the LDL-cholesterol level is a better predictor of CHD in men. A similar gender difference is found with the risk of diabetes; the development of insulin resistance and obesity is linked with combined hyperlipidemia to a greater degree in women than in men.

In obese, insulin-resistant persons, it's been shown that the effect of a high saturated fat diet is about one third that of its effect in lean, insulin-sensitive people. (It's thought that a high blood cholesterol lessens cholesterol absorption from the intestine.) So the women in the ERA study were less "at risk" from their relatively high-fat diet than the rest of us.

What this means to you

The authors of this editorial address the paradox that a high-fat, high-saturated fat diet is linked to a slowing of progression of coronary atherosclerosis in women with the metabolic syndrome, while high-fat intake in men with high LDL levels is linked to accelerated coronary disease. The advice to limit dietary fat is therefore perhaps a little too simple - it obviously depends on your metabolic status at the time.

The study results, taken together with those from earlier studies, show that we should all be more aware of our metabolic status, before we rush into an Atkins or a low-fat diet. Find out if you could have the metabolic syndrome (see first link below). Know (or find out) your full lipid profile; it's not enough to know your total and LDL-cholesterol, you should know your HDL-cholesterol and triglyceride levels too. This information should enable you to work with a good dietician to establish the healthiest eating pattern to suit your profile.

If all that seems too complicated, just limit your total calories, eat plenty of fish, green vegetables, fruit and nuts, and take plenty of exercise (with your doctor's permission, of course).

Source

• Saturated fat prevents coronary artery disease? An American paradox. RH. Knopp, BM. Retzlaff, Editorial. Am J Clin Nutr, 2004, vol. 80, pp. 1102--1103

Footnotes
1. Dietary fats, carbohydrate, and progression of coronary atherosclerosis in postmenopausal women. D. Mozaffarian, EB. Rimm, DM. Herrington, Am J Clin Nutr, 2004, vol. 80, pp. 1175--1184
2. Coronary angiography is a procedure in which a contrast material that can be seen using an x-ray is injected into one of the arteries of the heart. This allows the physician to view the flow of blood through the heart tissue.

Related Links
Tool: Do You Have the Metabolic Syndrome (Syndrome X)?
Even Newer Cholesterol Guidelines
Moderate-Fat Diets for Weight Loss?

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