Contact: Carl Marziali
University of Southern California
Eating less may not extend life
Caloric restriction only benefits obese mice: The Journal of Nutrition
If you are a mouse on the chubby side, then eating less may help you live longer.
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.
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.
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."
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
"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."
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.
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.
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.
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.
Read the study at http://jn.nutrition.org/cgi/content/abstract/jn.108.100313v1