Are low-fat diets really a big fat lie? Are carbs guilty? EN weighs in.
The author's premise was that the recommendation to eat a diet low in fat--long lauded by government and health organizations--has in fact triggered the U.S. obesity epidemic. He goes on to say that Americans' love affair with carbohydrates--especially low-fat, high-carb foods--is to blame. But is it really? It may not be as clear cut as fat or carbohydrate being the lone villain. It may be that we have met the enemy and it is us and how much--more than what--we eat.
Has the Low-Fat Mantra Failed Us? Taubes' article gave the distinct impression that nutrition researchers have ditched the low-fat idea and are jumping on the low-carb bandwagon en masse. Yet, EN has spoken with several prominent experts in the obesity field, and they take issue with Taubes' dubious interpretation of the scientific evidence and provocative conclusions.
In the much-debated New York Times article, Taubes' commented that Americans are eating less fat but are still gaining weight.
"That's misleading," says Barbara Rolls, Ph.D., professor of nutrition at Penn State University. "Yes, the percentage of calories we get from fat has decreased, but only because the number of calories we ate increased," she points out. "In terms of actual grams, fat intake has stayed pretty consistent."
Why Not Replace Carbs with Fat? There are a couple of very valid reasons why weight-watchers should still be mindful of their fat intakes.
First, "Studies show that when people have access to high-fat foods, they are more likely to overeat," says James O. Hill, Ph.D., director of the Clinical Nutrition Research Unit at the University of Colorado Health Sciences Center and co-director of the National Weight Control Registry. "People don't overeat on apples; they overeat on high-fat foods."
Second, there is no question that fat contributes more than twice the calories per gram than either protein or carbohydrate. Moreover, your body easily converts the extra calories from dietary fat into body fat. (Though if you overeat fat, carbs or protein, you'll put on pounds.)
So, how much fat is okay? The government now says that a moderately high fat-diet, up to 35% of calories, might be okay if you choose the right fats (see story, page 3). That includes fat from fish, olive and canola oils, nuts, seeds, avocadoes and whole grains.
Good Carbs vs Bad Carbs. If fat was the enemy of the '90s, carbohydrates appear to hold that dubious distinction today--though just as unfairly as when fat was the fabled foe. That notion has been fueled by books such as Dr. Atkins' New Diet Revolution (M. Evans & Co., 2002) and The Zone (Harper-Collins, 1995), which promote low-carb eating as the panacea for being overweight.
"Low-carbohydrate diets do produce weight loss, but so do low-fat diets," says Hill. "In fact, virtually any diet--the Cabbage Soup Diet, the Grapefruit Diet, you name it--produces weight loss, because calories are kept low," he explains. Everyone loves a villain, but painting all carbs with the same brush is naive.
"There's a big difference between fiber-rich carbohydrate foods and refined carb foods," says Glenn Gaesser, Ph.D., professor of exercise physiology at the University of Virginia. "A wealth of data shows that people who eat high-fiber diets have improved [blood sugar and blood cholesterol levels]."
Moreover, carbohydrate foods rich in fiber, like whole-grain breads and cereals, vegetables, fruits and legumes, are converted into blood sugar more slowly, thus stimulating insulin less. Plus they help control hunger by making you feel full on fewer calories.
The Insulin Connection. But Atkins Diet proponents and The New York Times' Taubes have a valid point when they note that carbohydrates stimulate insulin secretion to help convert carbs into blood sugar. Not a problem ordinarily. But when carbohydrates are consumed in excess of what's needed for "fuel," the body converts the excess into fat for storage. And insulin triggers this process. That's why eating too many carbs--and likely too many calories--can indeed make you fat.
While there isn't enough evidence to place all blame for our expanding waistlines on increased consumption of foods high in refined carbohydrates, their proliferation in the American diet is a valid concern. (See EN next month for a look at the glycemic index.)
Gaesser points to a recent six-month study of 39 overweight people from England that looked at the effect of replacing 25% of daily fat intake with either refined or high-fiber carbohydrate foods. Although told not to consciously lose weight, participants eating a low-fat, high-fiber diet lost an average of nine pounds anyway and saw their cholesterol profiles improve. Those eating a low-fat, refined carb diet did not gain weight, but neither did they lose weight spontaneously and they showed no changes in blood cholesterol levels.
It's Boring, But Calories Do Count. When it comes to shedding pounds, how much you eat is the single most important factor in determining weight-loss success. Research shows that a diet low in fat, low in carbs or high in fiber can influence weight gain, but these factors pale in comparison to the number of calories you take in--regardless of their source. Yet their source can be important if it influences how much you eat. Penn State's Rolls warns of such danger.
Based on her extensive research on the effect of portion size on food intake, she cautions, "If you give people bigger portions of palatable foods, they tend to eat more." That's what has happened at fast-food and even sit-down restaurants as serving sizes have ballooned. (See page 5 for the "best" fast food.)
It's Time to Get Moving. In the argument over fat vs carbs, we can't forget we're not just eating too many calories, but moving too little. Together, that's a recipe for obesity. All the experts we spoke with agree that exercise is a critical ingredient in the recipe for leanness.
"Our lack of exercise is at least equivalent to diet in terms of explaining [the current spate of] obesity," says Gaesser. Our convenience-laden world--from remote controls to e-mail to elevators--makes it much easier not to move. It takes extra thought and effort to be more active.
EN's Bottom Line. "There is no need to reinvent nutrition in order to manage weight," says Rolls. The best advice is as basic and boring as it's always been, says every one of our experts:
* Increase activity.
* Watch portion sizes.
* Eat a diet moderate in fat.
To that, EN adds more specific advice:
* Concentrate on whole grains to help cut back on refined carbs.
* Fill up on fruits and vegetables.
* Eat lean sources of protein (legumes, fish) to help cut back on fatty meats.
* Favor foods high in monounsaturated fats (e.g., olive and canola oils, nuts and seeds) over those high in saturated or trans fats (e.g., fatty cuts of meat, full-fat dairy, butter, French fries, cookies, crackers).
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|Date:||Oct 1, 2002|
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