HEALTH SENSE - Food fight
By Judy Foreman, [Boston] Globe Staff, 7/31/2001
In the swampy world of nutrition books, clarity and credibility are as scarce as tofu and sprouts at
Dunkin' Donuts.
But clarity and credibility are precisely the reasons you should toss out your old diet books, forget
the government's famous but flawed food pyramid, and get your hands on a new book, ''Eat, Drink
and Be Healthy,'' by Walter Willett, a nutritionist based at Harvard University.
His book is powerful not only for its independence from both doctrinaire nutritionists and New Age
nonsense, but for its no-holds-barred attack on the nutrition advice doled out by the US
Department of Agriculture in posters and brochures that reach millions of schoolchildren each year.
Among other things, the USDA food pyramid utterly fails to make clear that there are both good
(unsaturated) and bad (saturated and trans) fats, as well as good (whole grain) and bad (refined)
carbohydrates.
The Agriculture Department, citing longstanding policy, declined to comment on Willett's criticisms.
Willett, whose lean figure is visible proof that he follows his own advice, is one of the nation's
leading nutrition researchers and chairman of the nutrition department at the Harvard School of
Public Health.
Unlike most nutrition books out there, his is based on mountains of data from huge epidemiological
studies. And his willingness to simply say that the federal pyramid is wrong is welcome news to
nutrition researchers in a country where so much of the debate about diets is based on
special-interest advertising (''Beef: It's what's for dinner'') or celebrity endorsements of fad
weight-loss plans.
Perhaps this is the summer of science in the nutrition debate. Tufts University nutritionist Miriam
Nelson, virtually a one-woman health advice industry, also has written a diet book, ''Strong Women
Eat Well,'' that finds Americans get lousy nutrition advice from many quarters.
For instance, Americans who load up on refined carbohydrates, including supposedly healthful
low-fat cookies, which are actually high in calories, have been getting steadily fatter, often without
violating USDA guidelines, noted Nelson, an associate professor at the university's School of
Nutrition Science and Policy. Half of all adults Americans are now overweight, studies show, and
more than 20 percent are obese, twice as many as in 1960; diabetes also has risen nearly 40
percent in the last 20 years.
Yet, you could look at the USDA pyramid and conclude all sorts of bad nutritional habits are fine -
for instance, that it's OK to eat three servings a day of red meat. It's not: Red meat is loaded with
artery-clogging saturated fat.
You could also figure, looking at the food pyramid, that it's OK to eat six to 11 helpings a day of
Wonder Bread. Wrong again: White breads are made from refined carbohydrates, which lower
good HDL cholesterol and can lead to weight gain.
The reason the pyramid gives such erroneous messages, Willett said, is that it was cooked up
primarily by the Agriculture Department and was ''yanked this way and that by competing powerful
interests,'' which include the formidable meat, dairy and sugar industries.
The pyramid, in Willett's view, ''was built on shaky scientific ground back in 1992'' and has been
steadily eroded by new data ever since.
But, when one looks, as Willett does, not at industry's claims but at data from big research
projects, the picture becomes far more nuanced, and presumably, accurate. Willett uses large
studies such as the Nurses' Health Study of 122,000 women; the Physicians' Health Study of
22,000 male doctors; the Health Professionals' Follow-up Study of 52,000 male doctors, dentists
and veterinarians; the Iowa Women's Health Study of 42,000 women; and numerous others.
Among other things, the emerging data show it's time to re-think how we classify carbohydrates.
The old way was to label them ''simple'' or ''complex,'' depending on the number of sugar molecules
linked together.
A better distinction, Willett said, is between whole grains (good carbohydrates) and refined (bad).
The good category includes brown rice, oats, whole-wheat pasta and beans, and you should base
your diet on these. The bad ones are regular pasta, white bread, white rice, some cereals and
commercially baked cookies and the like made with refined flour.
Why are pasta and the other refined carbohydrates such no-nos? Because they are essentially
simple sugar. The minute you swallow these starches, your digestive system transforms them into
glucose and pumps it into the bloodstream almost as fast as if you had eaten jelly beans. The result
is a spike of insulin, the hormone that escorts sugar into cells. Once glucose enters cells, your
blood-sugar levels plummet, your brain interprets that as a hunger signal and you want to eat again.
Worse yet, this sugar-insulin roller coaster can lead to diabetes and heart disease.
In fact, Willett said, it is now clear that the bad carbohydrates - the refined ones that the body
rapidly metabolizes - are more likely to cause heart disease, probably by lowering good cholesterol
and raising triglycerides (three fatty acids linked together), than some good kinds of oil, like the
unsaturated fats in walnuts.
Dr. Gerald Reaven, professor of medicine at Stanford University School of Medicine, agreed.
People trying to reduce cholesterol ''would do better by eating less carbohydrate and substituting
good fats'' such as those in nuts, he said.
Just as the USDA food pyramid lumps all carbohydrates together at the bottom of the pyramid, it
lumps all fats and oils together at the top of the pyramid, with a ''use sparingly'' label. That's partly
right: Bad fats should be used sparingly. These are the saturated fats (from whole milk or red meat)
and the trans fats (trans-fatty acids) found in vegetable shortenings and some margarines. Saturated
fats contribute to clogged arteries, resulting in heart attacks and strokes, and trans-fats are even
worse, Willett said.
In fact, trans-fats are so worrisome that Nelson recommends sometimes eating butter despite its
high saturated fat content because many margarines contain trans-fats.
But just as important as avoiding the bad fats is increasing the good fats in your diet, Willett said.
The good fats are the monounsaturated and polyunsaturated types found in olive, canola or peanut
oil, nuts, other plant products and fish. These fats can lower the bad kind of cholesterol without
lowering the good.
Willett also has weighed in in favor of moderate alcohol consumption. Although more than one
drink of alcohol a day can raise the risk of breast cancer, for instance, he noted that this risk can be
offset by the B vitamins, particularly folate, that are standard in most multivitamins.
And what about the current darling of health-food industry advertising, soy? It does help lower
cholesterol, Willett noted, but it doesn't reduce hot flashes in menopausal women much. And in high
doses (three to four glasses of soy milk a day or supplements), it may actually drive proliferation of
breast-cancer cells, not retard it.
Unlike many nutritionists who often stick to an ''eat-your-vegetables-or-else'' line, Willett also
advocates a multivitamin a day, on top of loads of fruits and vegetables.
As for potatoes, both Willett and Nelson take a dim view. Nelson said it's OK to eat a small one
occasionally. Willett said that because the starch in a potato turns to sugar soon after digestion, it
shouldn't even be dignified by the term vegetable.
Willett also attacks those annoying milk mustache ads, noting that, despite what the USDA says,
there are more reasons not to drink milk in large amounts than there are to drink it - among them
the high calories and saturated fat in whole milk. Nelson takes a somewhat softer line, arguing the
milk campaign is ''not ridiculous'' for children and young adults who may not get enough protein
otherwise.
The bottom line? Eat more good fats and fewer bad ones. Eat more good carbohydrates and fewer
bad. Substitute a small handful of walnuts for a midafternoon cookie. Get more of your protein from
beans and nuts, fish, poultry and eggs, and less from red meat. Drink alcohol, but not to excess,
and pop a multivitamin while you're at it.
Most important, get or keep your weight low and stable. Health risks may begin to accrue at a
shockingly low body mass index of 22, suggesting that a 6-foot man weighing 165 pounds could
have a weight problem. (To calculate your body mass index, or BMI, divide your weight in pounds
by your height in inches; divide that number by your height in inches and multiply that number by
703.)
The benefits to eating right are huge - a lower risk of heart attack, stroke, high blood pressure, high
cholesterol, diabetes and certain cancers, including those of the uterus, colon and kidney and, for
women past menopause, of the breast.
On balance, that seems well worth trading your morning bagel for a nice big bowl of kashi.
Judy Foreman's column appears every other week in Health-Science. Her past columns are
available on Boston.com and myhealthsense.com. Her e-mail address is foreman@globe.com. |
