related to humans) have had intriguing
results. In a study conducted at NIA, monkeys
affect how long you live?
fed a calorie-restricted diet had a notably
decreased and/or delayed onset of age-related
Your body needs food to survive. However, the
diseases, compared to the control group of
very process of extracting energy from food—
“normal” eaters. In a University of Wisconsin
metabolizing food—creates stress on your body. study supported by NIA, calorie-restricted Overeating creates even more stress on the
rhesus monkeys had three times fewer age-
body. That’s part of the reason why it can lead to related diseases compared to the control a shorter lifespan and serious health problems
group. The Wisconsin study also found that
common among older people, including cardio- rhesus monkeys on a restricted diet had fewer vascular disease and type 2 diabetes.
age-related deaths compared to their normal
Calorie restriction, an approach primarily
fed controls. In 2007, when the findings from
(but not exclusively) used in a research set-
the study conducted at NIA were published,
ting, is more tightly controlled than normal
it was too early to determine whether calo-
healthy eating or dieting. It is commonly
rie restriction had any effects on lifespan.
defined by at least a 30 percent decrease in
Research in primates continues.
BIOLOGY OF AGING: RESEARCH TODAY FOR A HEALTHIER TOMORROW 27
Despite its apparent widespread acceptance, Given that ample studies have demon-calorie restriction does not increase lifespan
strated mostly positive effects of calorie
in all animals. In studies of non-laboratory
restriction in many organisms, today’s
(wild) mice, researchers found that on aver-
scientific studies focus on finding the mecha-
age, calorie restriction did not have any effect nisms and pathways by which calorie restric-on lifespan. Some of the calorie-restricted
tion works. Researchers are also studying
mice actually lived shorter than average lives.
compounds that might act the same way
This may be due to differences in the genetics
in the body, mimicking the benefits of
of the wild mice. A 2010 NIA-funded study
calorie restriction.
provides further evidence that genetics may
A wide range of possible mechanisms for
play a role in whether or not calorie restric-
calorie restriction are being investigated.
tion will have a positive effect on longevity.
Some scientists are exploring the possibility
Looking at 42 closely related strains of labora- that metabolizing fewer calories results in less tory mice, researchers found that only about a oxidative damage to the cells. Other scientists third of the strains on a calorie-restricted diet are looking at how the relative scarcity of had an increase in longevity. One-third of the
nutrients caused by calorie restriction might
strains of mice on a calorie-restricted diet had induce heat shock proteins and other defense a shortened lifespan, and the other third had
mechanisms that allow the body to better
no significant difference in lifespan com-
withstand other stresses and health problems.
pared to mice on a normal diet.
Some researchers wonder if the effects of calo-
While animal studies are ongoing, researchers rie restriction are controlled by the brain and are also exploring calorie restriction in humans nervous system. In one NIA-conducted study, to test its safety and practicality, as well as to
calorie restriction increased the production
see if it will have positive effects on health.
of brain-derived neurotrophic factor, or
Participants in a 2002 pilot of the Compre-
BDNF, a protein that protects the brain from
hensive Assessment of Long-term Effects of
dysfunction and degeneration, and supports
Reducing Intake of Energy (CALERIE) study
increased regulation of blood sugar and heart
had, after 1 year, lowered their fasting glucose,
function in animal models. Still other studies
total cholesterol, core body temperature, body indicate calorie restriction may influence weight, and fat. At the cellular level, they had
hormonal balance, cell senescence, or gene
better functioning mitochondria and reduced expression. It is likely that calorie restriction DNA damage. However, in terms of practi-works through a combination of these mecha-
cality, scientists observed that adapting and
nisms, and others yet to be identified.
adhering to the regimen could be difficult.
There is an intriguing overlap between
A longer-term trial is underway.
the pathways that control normal aging and
28