When It Comes To Living Longer, It�s Better To Go Hungry Than Go Running

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Mouse Study: When It Comes To Living Longer, It & #65533;s Better To Go Hungry

Than Go Running

BETHESDA, Md. (May 14, 2008) & #65533; A study investigating aging in mice has

found that hormonal changes that occur when mice eat significantly

less may help explain an already established phenomenon: a low calorie

diet can extend the lifespan of rodents, a benefit that even regular

exercise does not achieve.

& #65533;We know that being lean rather than obese is protective from many

diseases, but key rodent studies tell us that being lean from eating

less, as opposed to exercising more, has greater benefit for living

longer. This study was designed to understand better why that is, & #65533;

said M. Huffman, the study & #65533;s lead author.

The study applies only to rodents, which are different in some key

ways from humans, cautions Huffman. However, at least two studies

which examined people who engage in high-volume exercise versus people

who restricted their calorie intake, had a similar outcome: caloric

restriction has physiological benefits that exercise alone does not.

Researchers expect that clues to the physiology of longevity in mice

will eventually be applied to people, Huffman said.

The study, & #65533;Effect of exercise and calorie restriction on biomarkers

of aging in mice, & #65533; appears in the May issue of the American Journal of

Physiology published by The American Physiological Society (APS;

www.The-APS.org). The study was carried out by Huffman, R.

Moellering, E. Grizzle, Cecil R. Stockard, S.

and Tim R. Nagy, all of the University of Alabama-Birmingham (UAB) and

funded by the UAB Center for Aging. Dr. Huffman is now at the Albert

Einstein College of Medicine in New York.

The study built upon previous studies that showed:

*

Rats that exercise regularly will, on average, live longer

compared to a group that eats the same amount but does not exercise.

This is because exercise prevents some diseases, which allows more

individual animals to live out their expected life span.

*

However, when comparing the rats in these two groups that eat

the same amount, the longest-lived animals in the exercise group don & #65533;t

live any longer than the longest-lived rats in the non-exercise group.

Taken together, these findings indicate that exercise can prevent an

early death from disease in some rats, but does not extend the maximal

lifespan of any of the rats.

*

When comparing rats that exercise to those that don & #65533;t exercise

but eat much less, the longest-lived rats are from the group that ate

less.

Two theories

Taken together, these findings indicate that caloric restriction

protects against disease better than exercise does, and has the added

benefit of extending the life span of some rats. Physiologists have

been trying to unravel the reasons for this, and two major theories

have emerged.

One theory is that exercise places stress on the body, which can

result in damage to the tissues and DNA. Another theory is that

caloric restriction leads to physiological changes which benefit the body.

Huffman and his colleagues designed a study to examine the roles of

exercise and caloric restriction, singly and combined. They controlled

for factors such as weight and the amount of energy expended versus

the calories consumed.

They found:

*

Mice allowed to eat as much as they wanted had higher insulin

levels, regardless of whether they exercised. That is, how much the

mice ate determined their insulin level, while exercise did not have

much effect. High insulin levels are associated with a risk of diabetes.

*

The animals that ate as much as they wanted and did not exercise

had the highest levels of insulin-like growth factor (IGF-1), which

plays a key role in regulating cell growth and cell death. The animals

on caloric restriction had the lowest levels of IGF-1. Exercise also

seemed to play an important role in regulating IGF-1 levels.

*

There were some elevated levels of heat shock proteins, a

measure of oxidative stress and possible tissue damage among the

exercising mice. But total protein carbonyls, another stress measure,

were not significantly different.

*

Both exercise and caloric restriction moderated the level of

8-hydroxyguanosine (8-OHdG), a marker of DNA damage. Among the animals

that ate all they wanted, those that did not exercise had the highest

levels of 8-OHdG and those that exercised had much lower levels. The

researchers concluded that DNA damage increases with age and is

accelerated by obesity but could be slowed by caloric restriction

and/or exercise. The researchers noted, however, that the results may

differ if they had used older mice or subjected them to greater

caloric restriction than the mild (9% fewer calories) or moderate

(18%) restriction this study employed.

Overall, these findings indicate that the physiological stress of

exercise did not produce enough damage to tissues or DNA to explain

why exercise does not lengthen life span. Instead the study suggests

that caloric restriction creates beneficial changes in the body & #65533;s

hormone levels which exercise does not. The researchers concluded that

these metabolic changes play a role in extending life.

A handful of studies comparing calorie restricted people to people who

are avid exercisers, found similar hormonal benefits among those

eating less. However, calorie restriction studies are difficult to

carry out in people because participants often complain of feeling

hungry, lethargic, and cold.

Huffman also emphasized that the benefits of exercise may be greater

for humans than for mice because people are more prone to develop

cardiovascular diseases, and exercise is particularly good at warding

off those diseases. Mice tend to die of kidney disease and cancer,

Huffman said.

& #65533;I wouldn & #65533;t say this study has direct implications for people

right

now, & #65533; Huffman said. & #65533;But it shows what physiological changes

caloric

restriction and exercise produce. We can continue to build upon these

findings until we can get a better understanding of how this works in

people. & #65533;

--End--

http://www.the-aps.org/press/journal/08/21.htm