Everyday we are killing ourselves without even being aware of it. We are damaging our bodies as if we are standing in front of an x-ray machine. That is how much oxidative stress that our bodies accumulate on a daily basis if we do nothing about it.

Oxidative stress comes from several places, UV irradiation from the sun, toxins (such as cigarette smoke and pollution) and our very own metabolism. When we use fuel for energy (primarily carbohydrates) free radicals are produced. Free radicals, biproducts of metabolism, are molecules that are missing an electron and are therefore highly reactive. They are created in our mitochondria (the cell organelle which transforms our food into an energy source used by cells, kind of like the power plant of a cell) and damage first the mitochondrial membrane and then the mitochondrial DNA making the mitochondria less efficient at energy production and more likely to produce free radicals. Some of the free radicals escape the mitochondria and travel to other areas of the cell doing damage to cellular proteins, membranes and maybe worst of all DNA. When the cells DNA is damaged then there is a greater likelihood that cancer will result. Cancer cells are normal cells with damaged DNA.

So free radical damage can result in a myriad of problems for the cells and the tissues that are made up of the cells. If the cells are in the arterial walls then aging cells due to free radical damage causes hardening of the arteries and plaque formation. IF the cells are damaged in the skin you get less collagen production and more wrinkles. If the damaged cells are in the brain you have a higher likelihood of dementia including Alzheimer's disease.

The short answer is any time we burn fuel we produce toxins and create oxidative free radicals. The free radicals damage cells causing aging and other types of disfunction including cancer.

So, what can we do about it? Well our bodies have evolved several mechanisms to combat oxidative stress otherwise we would be cancer balls in short order (probably before we were grown). One solution that our body has is to produce antioxidants that neutralize free radicals. However our bodies antioxidant system is easily overwhelmed and so we have evolved a second mechanism to prevent too much free radical damage. This second mechanism is called eating antioxidants from plants which produce gobs of them. Plants produce free radicals to protect themselves from the sun and other environmental sources of free radical damage. When we eat fresh raw plant foods we get the antioxidants from the plants and use them to reduce our own oxidative stress load.