The search for the fabled Fountain of Youth symbolizes the desire to remain young that has been a sought-after goal throughout history. It has been thought to be truly unattainable. Little did we know that the mythical waters of youth have resided within us all along. The human body is an amazing, resilient machine, shown to survive and thrive no matter what the external forces may be. Our evolutionary road has been a long, sometimes harsh one and yet we've adapted and flourished. How?
Researchers postulate that when our ancestors struggled through extended periods without food, the body's remarkable survival instinct would kick in and somehow slow down their aging. This allowed our species to live through difficult times—responding to hardships and challenges by becoming stronger and more resilient. The common thread appears to have been food, or rather, lack of food. The fact that consuming fewer calories somehow slowed the aging process has inspired scientific research for many decades. Most recently, science has begun to shine a light on what is happening on the genetic level.
Since the 1930s, when Dr. Clive McKay's breakthrough studies showed that calorie restriction greatly extended the lives of mice, scientists have been trying to discover how calorie restriction works. Thousands of studies have documented the broad range of health and longevity benefits of calorie restriction, but most theories on how it slows aging focus on only one of CR's many effects.
For example, identified effects of calorie restriction include:
- More effective disposal and renewal of cells
- Preservation of irreplaceable cells
- Reduced rate of growth
- More efficient energy production, including increased formation of mitochondria, the cells' energy generators
- Enhanced DNA stability
- Reduction of age-related decline of the immune system
Each is a positive health benefit and may contribute to longevity. However, a theory has emerged—hormesis—that explains these positive effects (and many others) of calorie restriction as the body's natural response to the low-level biological stress produced by reduced food intake.
Just think about weight lifters who want to build their biceps. They determine a workout schedule with weights heavy enough to stress their arm muscles but not so heavy that they produce injury. The bodybuilders challenge the biceps with a form of hormesis, purposely pushing the muscle just beyond the standard, day-to-day activity to strengthen it. So we manage our amount of hormesis.
Now compare overeating to limiting calories intelligently: When you eat more calories or food energy than you need, your body often must cope with the added fuel by secreting insulin to process the high glucose levels circulating in your bloodstream. Some of the excess is stored for future use. But much of it is simply not needed, so it can end up being stored as fat tissue or deposited as plaque in your arteries. With so much food intake, your body does not need to use it efficiently, so your cells may run amok. Their job of reproducing themselves can be disrupted, sometimes resulting in unregulated cell reproduction that, in turn, can become cancerous cell growth. Your pancreas—the digestive organ that produces insulin—works overtime and becomes less able to do its job, and your heart beats more stressfully just to circulate blood to the extra tissue.
Calorie Restriction—A Beneficial Challenge
In contrast, when you limit your intake of calories intelligently, you challenge your body with a beneficial stress, or hormesis. With fewer calories available for energy production, your body shifts away from storing fat to actually using fat as well as protein for energy. Soon your cells produce energy more efficiently and your stamina increases. Meanwhile, cell reproduction slows—giving the body time to protect against mutations and preserving cells that may be irreplaceable. As your body continues to adapt, you get stronger—becoming more resistant to disease and the deterioration caused by aging.
Your longevity system
The incredible fact that humans have a survival system that can be switched on by the hormesis of calorie restriction came to light through a progression of discoveries at the lab of Dr. Leonard Guarente, at the Massachusetts Institute of Technology (MIT), in the late nineties. Research in 1999 produced the discovery of a gene—SIR2—that is activated by calorie restriction and promotes longevity. (SIR stands for Silencing Information Regulator, that is, a gene that regulates the deactivation or "silencing" of other cell signaling. Just as you send an e-mail message, your cells send information internally by electrical or chemical signals.)
Initially, many scientists considered the SIR2 "discovery" debatable. Later, work in labs around the globe corroborated that the SIR2 gene is conserved in many species, including human beings. So far, seven genes, a family called "sirtuins," have been discovered in humans and labeled SIRT1 through SIRT7 (Note: the T stands for 2 of SIR2, reducing the confusion of two numerals next to each other).
Of the seven sirtuin genes, SIRT1 is the most studied in mammals. It has been found that SIRT1 is activated by the stress of calorie restriction and that it silences a number of natural age accelerating triggers in humans, such as activation of growth-related hormones and increased inflammation. Sister genes SIRT3 and SIRT4 preserve cell life by facilitating energy production when calories are limited.
Our species might not have survived without the sirtuin family of genes to coordinate our hormesis response by shutting down the body's aging system when food is unavailable. We can use this capability directly by reducing the caloric intake into our bodies to trigger this survival mode, inhibiting our own aging systems.
Growth—a mixed blessing
The miraculous process of growth helps you develop from a child to an adult. But it may also kill you. Just because you've reached physical maturity doesn't mean your body then shifts into idle. While SIRT1 may slow the rate of growth in some tissues, other growth regulators fuel the growing process throughout life and some may even accelerate it—contributing to the development of cancer and other age-related diseases.