One of the most durable theories of aging is the free radical theory. This theory postulates that damage from free radicals (unstable molecules), generated mainly from metabolizing food into energy, ultimately damages vital body molecules (tissue, DNA, etc.). This damage accumulates with time until, like an old car, we fall apart. In support of this theory, one of the most important findings in free-radical research has been that eating fewer calories increases life span (Sohal RS, et al. Science 1996;273:59-63; Heilbronn LK, et al. Am J Clin Nutr 2003;78:361-9). The initial evidence that this may work in humans has been indirect and based on observation of the low caloric intake of the Okinawans and their long life expectancy (Willcox DC, et al. Biogerontology 2006). More direct evidence suggests that Okinawans following the traditional ways have low blood levels of free radicals. The elders had significantly lower levels of lipid peroxide-compelling evidence that they suffer less free-radical-induced damage. This may indicate healthier lifestyles but may also be due to gene variants that result in lower blood levels of free radicals. This is currently under investigation.
Okinawan centenarians have been lean throughout their extraordinarily
long lives, with an average body mass index (BMI) that ranged from 18 to
22 (lean is less than 23). The Okinawans have traditionally kept eating
a low-calorie, low glycemic load diet, practicing calorie control in a
cultural habit known as hara hachi bu (only eating until they are 80%
full), and keeping physically active the natural way. Particular
exercise interventions are under study for their role in healthy aging.