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Is your diet up-to-date?
New recommendations have changed the standard advice.
Over the past decades numerous popular diet books--such as Dr. Atkins' New Diet Revolution, Sugar Busters!, and The Zone--have challenged the conventional wisdom that fat is bad and carbohydrates are good. Mainstream nutritionists generally dismissed the authors as crackpots.
Then last September the Institute of Medicine (IOM), which helps the government set dietary guidelines, offered some scientific support for those views. The IOM's latest dietary report lowered the amount of carbs that one needs to consume and increased the allowable amount of total fat (and protein). A study presented soon afterward at the annual American Heart Association (AHA) meeting took that tendency one step further, suggesting that the Atkins diet--a very high-fat, low-carb regimen--may actually help you lose more weight and be better for your heart than the standard low-fat weight-loss diet.
That's not the only recent dietary surprise that has people staring at their plates in confusion. For example:
Such conflicting or disturbing news may tempt people to abandon all dietary advice and just eat what tastes good. Some recent evidence may even back that idea: A study found that enjoying food boosts its nutritional value, by increasing the body's absorption of its nutrients.
This report aims to put all that provocative nutrition news into context, and tell when it really warrants dietary changes and when it doesn't.
Should I eat fewer carbs and more fat?
That depends on your current diet and health status. At first glance, the new IOM report seems to be abandoning traditional principles and simply giving in to what Americans crave, at least regarding fat. The guidelines raise the maximum amount of fat you're allowed to consume from the traditional 30 percent of dietary calories to 35 percent. And they reduce the minimum amount of carbohydrates--from fruits, vegetables, grains, and sugars--that you need to consume from 50 percent to 45 percent. For someone who consumes 2,000 calories a day, the new limits would allow no more than 700 calories from fat (supplied by, say, three tablespoons of oil, a cheeseburger, and a glass of 2 percent milk), and they'd require at least 900 calories from carbohydrates (provided by six slices of whole-wheat bread, a baked potato, two cups of milk, and five typical servings of produce.)
But those new, more flexible standards come with a crucial proviso: Eating more fat and fewer carbs can be healthful only if you're eating the right types of each. The report refused to set an acceptable upper limit for the intake of "bad", cholesterol-raising fats--saturated fat, mainly from animal foods, and trans fat, mainly from hard margarine and certain fast or packaged foods. Instead, it urged Americans to avoid those artery-clogging fats as much as possible. But it permitted people to consume plenty of unsaturated fat, from vegetable oils such as olive, peanut, and canola, as well as from fatty fish and nuts. Such fat does not increase cholesterol levels and may even offer some coronary protection, in part by inhibiting blood clots that can trigger a heart attack or stroke.
As for carbohydrates, the report lowered the minimum intake for two reasons: You don't need more than 45 percent of calories from carbs if you're eating mostly fruits, vegetables, and whole grains; and most people eat too much of the wrong carbs, from nutritionally weak processed or sugary foods such as white bread and cookies.
All that doesn't mean, of course, that you have to consume more fat or fewer carbs, merely that it's possible to eat a healthy diet at those levels. "The main message now isn't that fat is bad, but that not all fats--and carbs--are created equal, so choose carefully," says nutrition researcher Walter Willett, M.D., at Harvard University. Willett and other experts expect that the report may serve as a basis for a new dietary pyramid that places wholesome fats and carbs at or near the base, and moves their unhealthful counterparts to the top, as in the healthful diets typically consumed in Mediterranean and Asian countries.
In the recent unpublished study of the Atkins diet (which was funded by the Atkins Foundation), after six months, his high-fat, low-carb diet didn't elevate the "bad" LDL cholesterol, probably because the fat--especially that derived from nutritional supplements--was mainly unsaturated. And it lowered triglycerides, a type of artery-clogging fat, while slightly raising the "good" HDL cholesterol, probably for the reasons described below. Consuming more fat and fewer carbs may be especially beneficial in people with an increasingly common condition called insulin resistance, and it amy help individuals lose weight, too (see below.)
Insulin resistance. One-quarter of Americans have a metabolic disorder in which the body resists insulin's action: the transfer of glucose, or simple sugar, from the blood into the muscle and fat cells. Too much sugar, white flour, or other refined grains--which the body converts quickly into glucose--stimulates the pancreas to try to control blood sugar by secreting more and more insulin. The excess insulin increases coronary risk, in part by raising blood pressure, reducing the HDL level, and elevating the triglyceride level. Replacing some carbohydrates with unsaturated fat can attenuate those changes; so can eating fruits, vegetables, and whole grains rather than refined grains and sugars, since the fiber in those healthful foods slows the conversion of their carbs into sugar.
Excess weight. Consuming wholesome carbohydrates and reasonable amounts of healthful fat may encourage weight loss (which helps reduce insulin resistance). The blood-sugar gyrations caused by refined grains and sugars may make certain people feel extra hungry, according to some research. And fat can make a weight-loss diet more palatable, thereby enhancing long-term compliance with a healthful diet. A recent clinical trial found that dieters getting about 30 percent of calories from fat stuck with the regimen longer--and lost more weight--than those whose diet supplied as many total calories but less fat.
The Atkins dieters in the recent study lost more weight--an average of 11 pounds more--than the low-fat group, for several likely reasons. They, too, stuck with the diet longer. The limitation on high-carb foods, which comprise the majority of dietary choices, tends automatically to limit caloric intake. And the diet was high not only in fat, but also in protein. (see next section)
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