Old Advice to Extend Life by Cutting Back Calories
Applies to Fat Mice Not Normal Seniors
Study in Journal of Nutrition suggests it may
not be a good idea for normal sized senior citizens
Jan. 23, 2009 Researchers
have been telling senior citizens for years that the fountain of youth
is found in restricting calorie consumption. Now, a new study funded by
the National Institute on Aging says that old advice is good for fat
laboratory mice but not normal size people.
If you are a mouse on the
chubby side, then eating less may help you live longer.
For lean mice and possibly
for lean humans, the authors of a new study predict the anti-aging
strategy known as caloric restriction may be a pointless, frustrating
and even dangerous exercise.
Death rates for 8 of the 10 leading causes of death
in U.S. all dropped significantly in 2006; Alzheimers passed diabetes
becoming the sixth leading cause of death
"Today there are a lot of very
healthy people who look like skeletons because they bought into this,"
said Raj Sohal, professor at the University of Southern California's
School of Pharmacy.
He and Michael Forster, of the
University of North Texas Health Science Center, compared the life span
and caloric intake of two genetically engineered strains of mice.
The "fat" strain, known as
C57BL/6, roughly doubles in weight over its adult life. That strain
benefited from caloric restriction, Sohal said.
The "lean" strain, DBA/2, does
not become obese. Caloric restriction did not extend the life of these
mice, confirming previous work by Forster and Sohal.
The results appeared online
Jan. 13 in advance of print publication in the Journal of Nutrition.
"Our study questions the
paradigm that caloric restriction is universally beneficial," Sohal
said. "Contrary to what is widely believed, caloric restriction does not
extend (the) life span of all strains of mice."
By measuring the animals'
metabolic rate, Sohal and his colleagues came to a deceptively simple
conclusion: Caloric restriction is only useful when, as in the case of
the obese mice, an animal eats more than it can burn off.
"Your energy expenditure and
your energy intake should be in balance," Sohal said. "It's as simple as
that. And how do you know that? By gain or loss of weight.
"The whole thing is very
commonsensical."
For humans of normal weight,
Sohal strongly cautions against caloric restriction. In a 2003 study, he
and Forster found that caloric restriction begun in older mice both in
DBA and leaner C57 individuals actually shortened life span.
However, Sohal said that obese
individuals are probably better off cutting calories than increasing
their exercise to make up for overeating. Overly vigorous exercise can
lead to injuries and long-term wear and tear.
In other words, it is better
to skip the double cheeseburger than to turn up the treadmill after
binging at Carl's Jr.
Sohal's study is not the first
to question the allegedly universal benefits of caloric restriction. A
study by Ross et al. published in Nature in 1976 ("Dietary practices and
growth responses as predictors of longevity") found that caloric
restriction works best in mice that gain weight rapidly in early
adulthood, Sohal said.
Studies of caloric restriction
in wild types of mouse strains have shown minimal life span extension,
he added.
Next, the researchers want to
understand why the obese mice have a lower metabolic rate that promotes
weight gain.
Background Information
The other members of the
research team were Melissa Ferguson and Barbara Sohal of the USC School
of Pharmacy.
Funding for the study came
from the National Institute on Aging, part of the National Institutes of
Health.
Keep up with the latest news for senior citizens, baby
boomers
Jan. 23, 2009 Researchers
have been telling senior citizens for years that the fountain of youth
is found in restricting calorie consumption. Now, a new study funded by
the National Institute on Aging says that old advice is good for fat
laboratory mice but not normal size people.