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When Studies Mislead: The Skinny on Low Fat Diets

When I read the front page headline in the February 7 edition of the New York Times, LOW-FAT DIET DOES NOT CUT HEALTH RISKS, my 35 years as a cardiologist-researcher told me something was probably amiss. The article that followed seemed to faithfully report the conclusions of an 8 year, $4.15 million study of nearly 49,000 postmenopausal women from the Women’s Health Initiative (WHI) Trial. But after carefully reviewing the original reports in the Journal of the American Medical Association, I discovered the problem. Fundamental flaws in the research invalidated the dangerously misleading headline.

The government sponsored study followed women, ages 50 to 79, to determine whether a group assigned to a low-fat diet lowered their risk of breast and colon cancer, heart attacks and strokes when compared to those allowed to eat whatever they pleased. The researchers found no difference for any of the diseases between the two groups.

Authorities hailed the report. Newspaper quotes read: “revolutionary,” “the Rolls-Royce of studies,” “overturning three decades of wisdom,” “largely closes the book on a highly publicized chapter of dietary history.” Does it? If the women who ate whatever they pleased did as well as those struggling to cut fat intake, doesn’t that mean that we are finally and forever free to pursue a diet of bacon cheeseburgers, and chocolate cheesecake? Unfortunately, the answer is no. The reason? The problems with the WHI study make it impossible to draw valid conclusions.

The women assigned to the low-fat group were instructed to reduce their total fat to 20% of total energy intake. They fell far short of that goal, decreasing the fat to 29%. Additionally, the comparison group (after receiving a copy of the Dietary Guidelines for America, and other health-related materials) also decreased their dietary fat to approximately 35%.

Given the minor dietary differences between the two groups, the resulting minor differences in their “bad” (LDL) cholesterol levels was predictable. In the “low-fat” group, average LDL-cholesterol fell from 133 to 123 mg/Dl, while the “eat anything” group also fell, from 134 to 127! Both levels are well within the recently revised Federal guidelines that recommend LDL-cholesterol be kept below 130 in individuals without additional cardiovascular risk factors.

In addition to the low “bad” cholesterol levels, both groups had high amounts of “good” (HDL) cholesterol, ranging from 58 to 60 mg/Dl. Normal “good” cholesterol levels are 30 to 60, and those in the higher ranges are at a significantly lower risk for cardiovascular disease. Thus, both groups had highly desirable cholesterol profiles.

It should come as no surprise that the “eat anything group” had a 30% lower incidence of developing cardiovascular diseases than the researcher-statisticians originally anticipated. The higher prediction of disease occurrence was the main reason why the study was designed to be only eight years in duration.

How does this study apply to men? According to the Los Angeles Times, “it probably applied to men as well because the disease mechanisms are the same.” Even if the study was valid, that conclusion would not be, because the assumption about similar disease mechanisms omits a crucial fact. Since men typically have much lower “good” (HDL) cholesterol levels than women, decreasing their “bad” (LDL) cholesterol is considerably more important.

Confused? Don’t be. A solid body of evidence supports the notion that lifestyle changes do decrease the risk of cardiovascular disease. Last year, the American Journal of Epidemiology published a large report-with a 20 year follow-up–from the Nurses’ Health Study of dietary fat intake and risk of coronary heart disease. It showed clearly favorable results. In January of this year, a report in The Lancet analyzed the effect of fruit and vegetable consumption in eight studies that included a total of 257,551 men and women with a 13 year average follow-up period. The investigators concluded: “Our results provide strong support for the recommendations to consume more than five servings of fruit and vegetables per day, which is likely to cause a major reduction in strokes.”

Since the WHI study was undertaken, a revolution has taken place in our understanding of specific types of dietary fat. Intakes of specific fats are related far more strongly to heart disease risk than total fat. Collectively, these analyses demonstrate that a diet lower in saturated fat (fatty meats and butter) and trans fat (processed foods, and stick margarines), and higher in monounsaturated (olive, canola and peanut oils) and polyunsaturated fat (safflower, sesame and corn oils), as well as amounts of fruit and vegetables not approached in the WHI Trial, help prevent heart disease. In fact, a trend was observed toward reduction of cardiovascular disease risk in the quartile of women who ate the lowest amounts of saturated and trans fat, and highest monounsaturated and polyunsaturated varieties. If the study had been carried out longer, this observation might well have become statistically significant.

The WHI investigators noted this, stating that “Trends toward greater reductions in CHD (Coronary Heart Disease) risk was observed in those with lower intakes of saturated fat or trans fat or higher intakes of vegetables/fruits.” They concluded by suggesting that “more focused diet and lifestyle interventions may be needed to improve risk factors and reduce CVD (cardiovascular) risks.”

So, what to do? My advice may surprise you. The primary goal of healthy eating is to reach and maintain a normal body weight in order to lower the risks of diabetes, high blood pressure or the metabolic syndrome (the combination of diabetes, hypertension and a particularly malignant form of high LDL-cholesterol). This is best achieved, not by “going on a diet,” but by learning to develop sensible eating habits. Heart-healthy eating is easier and more satisfying than one might think. There is no need to deprive yourself of an occasional steak or delectable dessert, while nibbling miserably on raw carrots for the rest of your days. Healthy eating is a long-term commitment. It is about choosing nutritious foods that are satisfying by making sensible substitutes, modifying favorite recipes, adopting an experimental attitude, and discovering over time what works best for you.

To round out a heart-healthy lifestyle, become physically active. Exercise is the great health facilitator because it increases HDL (“good”) cholesterol, lowers blood pressure, helps prevent diabetes, and improves heart function. In addition, physical activity is a natural antidepressant, and a great way to rediscover the wonders of your body. Research has shown that you can reap major health benefits with a minimum amount of effort and time. Begin by taking brisk walks for 30 minutes or more, several times a week. Decrease sodium intake if you have a tendency towards high blood pressure, and of course, avoid tobacco exposure.

Despite the findings from the WHI Trial, it is vital for women, and men, to understand that simple lifestyle changes do provide invaluable health benefits. They also provide a wonderful bonus. In addition to being healthier, you will look and feel healthier too!

Richard Helfant, MD, was Chair of Cardiology at Cedars-Sinai Medical Center and was Professor of Medicine at UCLA and UC Irvine. His book, Courageous Confrontations, is about how the mind-body relationship can combat heart disease.