Panel
Urges Hour of Exercise a Day
By JANE
E. BRODY
 mericans
need to exercise more — at least an hour a day, twice as much as
previously recommended — to maintain their health and a normal body
weight, according to new guidelines issued yesterday by the
Institute of Medicine, the medical division of the National
Academies.
In a thousand-page report, a team of 21 experts suggested for the
first time a range of recommended amounts for what are called
macronutrients — proteins, fats and carbohydrates — and also
included advice on how much dietary fiber and exercise people should
strive for to maintain good health. Previous reports over the last
60 years have dealt only with recommended levels of vitamins and
minerals.
The panel's recommendations give wide leeway in choosing an
acceptable diet. The report said that to meet daily needs for energy
and nutrients while minimizing the risk of developing chronic ills
like heart disease and diabetes, adults should get 45 percent to 65
percent of their daily calories from carbohydrates. It recommended a
maximum of 25 percent of calories from added sugars, 20 percent to
35 percent of calories from fats, and 10 percent to 35 percent of
calories from protein. In addition, the panel recommended that adult
men 50 and under consume 38 grams of fiber a day and adult women 21
grams a day.
The new guidelines, called the Dietary Reference Intakes, are
intended for use by professional nutritionists in private practice,
hospitals and schools, as well as by individuals.
The panel said it was especially concerned about the rapidly
rising number of people who are overweight or obese. The
recommendations are meant to help people achieve and maintain a
normal body weight, said Dr. Joanne Lupton, chairwoman of the panel
and professor of nutrition at Texas A&M University.
Dr. Lupton emphasized that calculations of a person's caloric
needs must take into account activity levels. The panel advised that
adults and children spend at least one hour a day doing moderately
intense physical activities, like brisk walking, swimming or
cycling.
The previous recommendation for the minimum amount of physical
activity, established in 1996 in a report from the United States
surgeon general, was at least 30 minutes of moderate activity on
most days.
Dr. Lupton said the increased amount of exercise recommended was
based on biochemical measurements of how much exercise healthy
people engage in each day, instead of on reports from the people
themselves, which can result in inaccurate estimate. She said the
group was surprised to find out how much exercise healthy people
actually did.
Dr. Marion Nestle, chairwoman of the department of nutrition and
food studies at New York University, called the exercise
recommendation "amazing but impractical," given that 60 percent of
the population is now totally sedentary.
"I hardly know anyone — and I know a lot of health-conscious
people — who exercises an hour a day," Dr.
Nestle said. "This
creates a lot of tension between what's ideal and what's possible.
We know half an hour a day confers substantial benefits. Wouldn't it
have been better to say some exercise is better than none, and more
is better than some?"
Dr. Nestle said she was also concerned about the panel's
recommendation that as much as 25 percent of calories could come
from added sugars, the caloric sweeteners added to manufactured
foods and beverages like soda, candy, fruit drinks, cakes, cookies,
ice cream and other sweets. The 25 percent limit would allow a
person who consumes 2,000 calories a day to drink three and a third
12-ounce sodas each day, if soda was that person's only source of
added sugars.
"This is a huge amount of added sugars in a country where soft
drinks, a major source of sugars in the American diet, are
increasingly a factor in the rise in overweight," Dr. Nestle said,
adding that most earlier recommendations called for no more than 10
percent of calories from added sugars."
Dr. Lupton explained that in arriving at an upper limit for added
sugars, the panel reviewed all studies examining the effects of
various levels of sugar intake on the amount of micronutrients —
vitamins and minerals — a person was likely to consume each day.
"The data suggested that at 25 percent or more of calories from
added sugars, there was a significant decline in intake of certain
important micronutrients, especially vitamin A and calcium," she
said. When excess sugar is consumed, there is less room for more
wholesome foods, she said.
The Center for Science in the Public Interest, a Washington-based
nutrition advocacy group, yesterday recommended an upper limit of 8
percent of calories from added sugars, or 40 grams a day for a
person consuming a 2000 calorie diet.
With regard to dietary fats, the panel's recommendation of 20 to
35 percent of calories was very flexible, lower at the low end than
most recommendations and somewhat higher at the upper end than
recommendations from groups like the American Heart Association, the
American Cancer Society and the National Institutes of Health, which
suggest no more than 30 percent of calories from fat.
Studies show that when people eat very low levels of fat combined
with very high levels of carbohydrates, concentrations of
high-density lipoprotein — or so-called good cholesterol — decrease
and triglyceride levels rise, increasing the risk of heart disease,
the panel wrote.
"Conversely," it noted, "high-fat diets can lead to obesity and
its complications if caloric intake is increased as well, which is
often the case. Moreover, high-fat diets are usually accompanied by
increased intakes of saturated fatty acids, which can raise plasma
LDL cholesterol concentrations and further heighten risk for
coronary heart disease. We believe these ranges will help people
make healthy and more realistic choices based on their own food
preferences."
In discussing the different kinds of fats in common diets,
however, the panel advised that consumption of saturated fat, which
can raise the levels of artery-damaging cholesterol in the blood and
increase the risk of heart disease, should be kept "as low as
possible." Saturated fats are most often found in meats, baked goods
and full-fat dairy products (hard cheese, butter, cream cheese,
cream, whole milk, whole-milk yogurt and ice cream).
The panel also said there was no safe level for so-called trans
fats, which occur naturally in meats but are most prominent in foods
prepared with partially hydrogenated vegetable oils. Trans fats are
often found in cookies, crackers, fast foods and some dairy
products. They confer no known health benefit and are known to raise
the level of harmful cholesterol in the blood. The panel refrained,
however, from suggesting a ban on trans fats, saying that such a
move would be impractical and make it difficult to consume a
nutritionally adequate diet.
Dr. Nestle questioned the panel's reasoning and suggested that it
should at least have advocated a ban on trans fats in processed and
prepared foods.
As for carbohydrates, there is again a wide range of recommended
intakes — 45 to 65 percent of calories — to allow for dietary
flexibility. This range recognizes that both the high-carbohydrate,
low-fat diet of many Asian peoples and the higher-fat diet of
Mediterranean peoples, most of whose fat comes from olive oil, are
both associated with good health.
But while not emphasizing a need to favor unrefined carbohydrates
that are rich in natural fiber, the panel advised consuming an
amount of dietary fiber significantly greater than most Americans
now do. The report particularly noted the value of soluble fiber,
like pectin (the substance in many fruits that makes jelly gel) and
the fiber in oats and rice bran, which can help reduce cholesterol
levels and slow down digestion, which in turn increases satiety and
reduces the risk of overeating.
The report does not change existing recommendations for protein
intake — between 10 and 35 percent of calories, though for the first
time it establishes age-based requirements for all nine of the
essential amino acids found in dietary protein. While noting that
evidence is conflicting for the health effects of a diet higher in
protein, the report cautioned against consuming levels significantly
greater than those normally found in foods.
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