Track 16

Unit 11

Biology

The fountain of youth

Pages 106 and 107

Listen for main ideas and listen for details

Okay, today I’d like to look at some theories of aging. Many theories of aging have been suggested but most of them fall into just two categories: program theories and damage theories.

Program theories say that our bodies are programmed to live for a limited amount of time, that information about our lifespan is encoded in our DNA. Damage theories however, believe the damage to ourselves is responsible for aging. Some early damage theories were based on the idea that the human body is mechanical like a car. So, it naturally breaks down over time. Now, that is true to some extent but unlike cars, our body has the capacity to heal and repair itself.

So, let’s look at these two theories about aging and along with that, considers some approaches to life extension. Okay, let’s first look at a program theory, the Hayflick Limit theory. This theory was proposed in the 1960s by two biologists who discovered that some cells divide about 50 times, then suddenly stop dividing. These were like long muscle and heart cells, for example.

In other words, after about 50 generations of cell division, which takes place over many years, the DNA just stops functioning. One interpretation of this is that a cellular clock is at work, that your time alive is genetically predestined. Now, this sounds like bad news, right? But there is some good news here and here it is: the rate of cell division is directly affected by the amount of waste products in the cell, okay?

So, if we reduce the amount of waste, then the cells will divide more slowly. This means we can slow the hands of the clock and live longer. So how do we reduce cellular waste? Well, some scientists think they found an effective way to do this: eat less, about 30% less. It’s called calorie restriction or CR. You cut out foods high in calories and low in nutrition, like those desserts we all love and replace them with foods that are high in nutrition and low in calories, like fresh vegetables, for example.

Currently, CR is the only known way to consistently increase lifespan. It’s actually been shown to work well in dogs and monkeys. Also, CR doesn’t just slow cell division, it lowers metabolic rate. Now, this is potentially important because in mammals, lower metabolic rates are associated with longer lifespans. So, listen carefully, the benefits of CR are twofold, right? One, slower cell division and two, slower metabolism. Both of these can offer life extension.

However, let’s think about the implications of a CR diet, for a moment. Like what economic impact would have on the 1 million-plus restaurants in the US. After all, they generate $500 billion annually. Or, what about the people who earn a living on their physical strength? Could they function effectively on a CR diet?

Okay, a second theory of aging and this is the damage theory states that our cells accumulate free radical damage with the passage of time. Now what are free radicals? They’re molecules in our body that have an extra electron. In normal molecules, electrons are paired, so that their electrical energies are balanced. But free radicals have an extra negative charge and this causes them to attach to other molecules and cause an imbalance.

They’re caused by environmental factors that concern oxygen intake, air pollution and cigarette smoke, for example. And not only do they damage a cell’s membrane and DNA, but they also make it more difficult for cells to repair the damage. This in turn causes aging to accelerate. So, is there any good news here? Is there any way to reduce the number of free radicals? Yes and the key is oxygen. We know that animals with lower metabolic rates, metabolize less oxygen. And less metabolized oxygen means a lower production of free radicals, which means less cell damage, makes sense? So note that this is the second benefit of a lower metabolic rate.

So, scientists have learned in the last few decades, a lot about why we age, but what can we do about it? Well, on one side, we have what might be called high tech approaches. For example, the use of stem cells to act as a repair system for part of the body. Another approach is Xenotransplantations which uses animal tissues and organs to treat human beings. But both these approaches are controversial.

On the other side, we have the natural approach which is the approach I personally subscribe to. It’s based on three common sense ideas. First, eat a high nutrition, low calorie diet that means lots of fruits and vegetables. Second, don’t overeat or as I mentioned before, reduce your intake of calories by about 30%. Third, supplement good eating with moderate exercise. Basically the high-tech approach becomes unnecessary if we just apply this more natural approach.