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!

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