CHAPTER 15

Prevention and Lifestyle: Weight and Exercise

PART 1 Cancer Is a Preventable Disease

Cancer is, for the most part, a preventable disease. Only 5-10% of all cancer cases are caused by genetic defects. The remaining 90-95% are brought about by environmental and lifestyle factors: overweight, lack of exercise, poor diet, smoking, overuse of alcohol, and overexposure to UV and other forms of radiation. Of all cancer-related deaths, it’s thought that 25–30% are due to tobacco, 30–35% are linked to diet, about 15–20% are due to infections.

That’s good news, because most lifestyle and environmental factors can be changed or modified. There are even vaccines that can provide protection against certain forms of cancer.

PART 2 Cancer and the Inflammatory Response

Why is lifestyle, including diet, weight, and exercise, so important? The answer may lie in the body’s inflammatory response.

Inflammation is a normal part of your body’s immune system response to injury. The problem is that sometimes inflammation becomes long term, or chronic. When that happens, levels of many potent inflammatory chemicals go up. These substances include cytokines (including TNF, IL-1, and IL-6), enzymes (such as COX-2, and 5-LOX) and adhesion molecules. All of these various chemicals have been linked to the development of cancerous tumors. In fact, chronic inflammation is known to precede tumor growth in most types of cancer. READ MORE

Most of the known risk factors for cancer, including obesity, smoking, alcohol, infectious agents, and carcinogens in food and in the environment, have been shown to cause chronic inflammation in the body. The longer the inflammation continues, the greater the risk of cancer. LESS

PART 3 Cancer and Overweight

There’s a clear link between obesity and cancer. It’s thought that, in the US, excess weight or obesity cause 14% of cancer deaths in men and 20% of cancer deaths in women. Obesity is linked to cancers of the colon, breast, endometrium (uterine lining), esophagus, kidneys, and more.

Why is obesity linked to cancer? The answer seems to be inflammation. Obesity creates a state of chronic, low-level inflammation throughout the body. That’s because fat cells are highly metabolically active and secrete numerous potent hormones and cytokines, signaling cells of the immune system, into the bloodstream. The more overweight someone is, the higher the level of cytokines, and the greater the chance that precancerous cells will become cancerous. READ MORE

One cytokine implicated in cancer is a growth factor called IGF-1, which is similar to insulin and inhibits cell suicide. It’s possible that IGF-1 promotes the growth of tumors. Other cytokines produced by fat cells, such as leptin and tumor necrosis factor, activate nuclear factor -kB (NF-kB), a protein complex that controls the transcription of DNA. Hyperglycemia, a comorbidity of obesity, also activates NF-kB. There is considerable evidence that NF-?B is a major player in the development of cancer.

So it’s important to maintain a healthy weight to help prevent cancer, and for many other reasons as well. When you keep your weight down to a normal level, you can also prevent the many comorbidities of obesity, including diabetes, high blood pressure, cardiovascular disease, fatty liver disease, and osteoarthritis. LESS

PART 4 Exercise Protects Against Cancer

Exercise has a proven protective effect against cancer. Regular physical activity lowers levels of IGF-1 and other cytokines in the bloodstream, and it does this even if the person who exercises remains overweight. The lower levels of these cancer promoters are one possible explanation for the protective effect of regular exercise. READ MORE

Exercising regularly reduces a woman’s chances of getting breast cancer, possibly because doing so lowers blood levels of insulin and estrogen. Risk of colon cancer, too, is greatly reduced when you exercise, probably because being active decreases the amount of time it takes food to pass through the intestines. That means the colon is in contact with potential carcinogens for a shorter period of time.

Leading a sedentary (physically inactive) life makes it more likely that you’ll develop cancer of the pancreas, endometrium (uterine lining), or lung, as well as melanoma. One study found that sedentary men have a 56% and women a 72% higher incidence of melanoma than people who exercise 5-7 days per week. LESS

PART 5 How Much to Exercise

You should try to be physically active for 30 minutes or more on most days of the week. Remember, being physically active doesn’t necessarily mean going to the gym or running on a treadmill. Anything that gets your heart beating faster and your breathing rate up counts as exercise—whether it’s going for a brisk walk, walking up and down stairs, or raking leaves. You can break your exercise up into smaller periods, too—for instance, you might take three 10-minute exercise breaks a day.