Fries are a big no-no if you've adopted calorie restriction.

Tooga/Digital Vision/Getty Images

Life Extension Methods

Though elixirs of eternal youth have long been peddled by hucksters, scientists have come such a long way in understanding how the human body ages that they see it as completely possible that an anti-aging pill is in our foreseeable future. By taking such a pill, humans would not only live longer lives, they would live healthier lives.

What might this anti-aging pill do in our bodies? That depends who you ask, and how that person views the aging process. According to the free radical theory of aging, our bodies age because damage done by free radicals, or molecules with an unpaired electron. Free radicals are created as byproducts of essential tasks, including respiration and metabolism. As we get older, though, our bodies lose the ability to control these molecules, which go on to wreak havoc in other cells. Antioxidants fight free radicals to some extent, but finding a better way to slow production or the progress of free radicals in the body could slow or end the aging process.

Rather than protecting cells from free radicals, some say it's more important to protect cells from themselves. As cells age, they divide, but this causes a tip of a chromosome, known as a telomere, to shrink a little bit. When the telomere is gone, then it can no longer protect the rest of the cell, and the cell dies. Telomerase, an enzyme that repairs telomeres, could be the key to longevity, if scientists could determine how to boost its production.

Calorie restriction, a diet that involves consuming 30 percent fewer calories, has been shown to dramatically increase the life span of organisms and animals in the laboratory. However, such a diet has proven near-impossible for humans to adopt, so scientists are working at determining exactly why this diet might slow aging so they can find a substance that mimics the effect. One theory is that calorie restriction activates a gene, known as SIRT1 in humans, that suppresses dangerous genes that can cause malfunction in the body. SIRT1 might also be activated by resveratrol, an ingredient in red wine, though humans would have to consume several hundred bottles a day to see any effect.

If anti-aging can be tied to a mere gene or two, then genetic tinkering or engineering could be possible. Some people already pay $20,000 a year for regular injections of human growth hormone, which is believed to keep the human body in a youthful state that includes little body fat and increased lean muscles.

Though scientists have these various theories, further study is required for all of them. However, studying life extension methods in humans is extremely tricky, given that an experiment to see if a human could live to 120 years would take, well, 120 years. But scientists are hoping that once they find the true trigger of aging, they'll find a way to stop the activation of that trigger. Then, they're hoping to replicate that process in pill form. A tall order, no doubt, but let's say they manage to pull this off. What would the world be like if no one aged?