No Miracle Diets for Heart Disease or Cancer

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No Miracle Diets for Heart Disease or Cancer

Three major studies of 50,000 women show how hard it is to prove that

eating healthfully makes a difference

By CHRISTINE GORMAN

Starting a low-fat diet in mid-life does not, by itself, decrease a

woman's risk of heart disease or stroke or dramatically reduce her

risk of breast or colorectal cancer, according to three studies

published today of almost 50,000 healthy, post-menopausal women. But

don't break out the ice cream just yet. Once you get into the nitty

gritty of the study, the investigators stress, the findings still

support the general idea that you need to pay attention to how much

fat — and particularly what kinds of fat — you eat.

Still, the results of these studies, which were sponsored by the

National Heart, Lung and Blood Institute and published in the Journal

of the American Medical Association, cannot be ignored, or easily

dismissed. This is by far the largest, most scientifically rigorous

attempt ever to test a low-fat diet — defined as 20% or less of total

calories coming from fat. Researchers randomly divided the

participants into two groups, worked hard to get one group to cut its

fat intake and then compared the results for each of them for the next

several years.

Through focus groups and sessions with nutritionists, the so-called

intervention group was given a lot of help and information on how to

cut the amount of fat in their diet. As a group they weren't able to

get all the way down to 20% fat intake, but they did manage to reduce

it to 24% in the first year, though it slid back up to 29% by the

sixth year. The other, so-called control group received printed

material on dietary guidelines but no other help on healthy eating.

The fat content of their diets was 35% after one year and crept up to

37% after six years — and they gained a little weight to boot. (The

intervention group lost weight or stayed the same.)

All told, the women in the two groups showed no overall difference in

the number of heart attacks or strokes they suffered over the eight

years of the study. Part of the reason may be that the level of LDL or

" bad " cholesterol dropped in the intervention group by a tiny 2.4% —

too small a reduction for the study to be able to detect a difference

in outcome.

It's also possible that if you want to prevent cardiovascular disease,

it's not enough to focus just on the total number of fat in the diet;

you also have to look at the types of fat — particularly saturated and

trans fats — as well as exercise and physical activity levels. Why

didn't the study focus more intently on these variables? Researchers

were not as aware of how important they were back in the late 1980s,

when they were designing the trial.

Women in the low-fat group suffered 9% fewer breast cancers than those

in the control group. Although that difference was not statistically

significant, it is very suggestive. Given how long it takes for most

tumors to grow, it may simply be that the study has not lasted long

enough to show a significant effect. In addition, there was a clear

benefit for one sub-group of women — those who began the study with

the highest total fat consumption and who were able to make and

maintain the greatest reduction in the number of fat calories in their

diet. This group benefited from a 15%-to-20% drop in the incidence of

breast cancer.

Women in the low-fat group did not see a significant drop in their

rates of colorectal cancer, but here again, it may mean that the study

simply hasn't lasted long enough. The low-fat group did have 9% fewer

polyps and other precancerous lesions in their lower gastrointestinal

tract — and that is a statistically significant finding. Given how

long it takes colorectal cancer to develop, it's reasonable to be

heartened by those results.

Why is a 9% difference significant in the colorectal cancer group but

not in the breast cancer group? Welcome to the wild and complex world

of statistics. After looking at the variation in the data with various

mathematical tools, research statisticians determined that they

couldn't rule out the possibility that the 9% difference in breast

cancer results was due to chance alone. (It could be chance; it could

also be due to the low-fat diet.) On the other hand, after applying

those same mathematical tools to the data in the colorectal cancer

study, they determined that the 9% difference in the number of polyps

was unlikely to be due to chance alone.

So, in many ways these studies raised more questions than they

answered. (They're on solid ground there, considering they were

conducted as part of the Women's Health Initiative, which famously

concluded in 2002 that long-term hormone replacement therapy does not

protect women's hearts after menopause. There are plenty of doctors,

and quite a few patients, who are still trying to figure what that

actually means.) Strictly speaking, the results do no apply to men,

who tend to get heart disease earlier than women do and for whom a

low-fat diet might be particularly beneficial. But this study has set

the gold standard for diet studies in the future. Fortunately, there

are enough research funds to continue following the WHI participants

for another five years. Here's hoping that is long enough to get more

answers that are statistically significant — and potentially life saving.

http://www.time.com/time/health/printout/0,8816,1157412,00.html