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How exercise can help you ward off cancer

Editor's note: This is the first in a two-part series. See part two:Exercise for cancer survivors.

If all you had to do to lower your cancer risk was a brisk walk, would you take 30 minutes out of your day?

According to one cancer researcher, physical activity can curb your obesity risk, which in turn can reduce your odds of a life-threatening cancer.

About 35.7 percent of U.S. adults are obese, according to the Centers for Disease Control and Prevention. Obesity has been linked to increased risk of chronic diseases including heart disease, stroke and Type 2 diabetes.

In addition, the National Cancer Institute reports that obesity raises risk for cancers of the esophagus, pancreas, colon, breast (after menopause), endometrium (lining of the uterus), kidney, thyroid and gallbladder, with recent studies reporting increased rates of obesity-related cancers among Americans.

There are several reasons why obesity is such a major risk factor for cancer. Dr. Karen Basen-Engquist, director of MD Anderson's Center for Energy Balance in Cancer Prevention and Survivorship in Houston, Texas, told that obesity can cause metabolic dysfunction, or disrupt how your body uses the energy from the foods that you eat. Obesity is also known to increase inflammation by interrupting the process of cytokines, which are small molecules that help cells send signals to each other.

In addition, obesity can affect sex hormones. In the case of estrogen-receptor-positive breast cancer, having more fat tissue may increase the amount of estrogen, which in turn can fuel the growth of these tumors, she added.

The CDC recommends that adults get a minimum of 150 minutes of moderate-intensity workouts or 75 minutes of vigorous-intensity exercise each week, in addition to strength-training exercises. Basen-Engquist said studies show that a good benchmark to aim for is 30 to 60 minutes a day -- and all you might have to do is walk.

"When we're talking about moderate-intensity exercise, we're talking about doing exercise kind of at the level of a brisk walk," Basen-Engquist explained. "So, your heart rate goes up, you're breathing a little bit faster, but you're not doing an all-out run."

One simple way to tell if you're exercising hard enough is that you should be able to talk to the person next to you during moderate-intensity exercise, but you won't be able to sing, Basen-Engquist said. If you are exercising vigorously, you'll be able to chat, but it will probably be two or three words at a time.

Also, you don't have to work out all at once. Studies show breaking up your workouts into manageable time chunks still may provide health benefits.

"It's important to know even if you do (exercise) in 10 minute bouts throughout the day you can still benefit from that," she said.

Studies show that time may pay off: Women who worked out 10 hours or more a week reduced their breast cancer risk by 30 percent according to a 2012 study in Cancer.

What may be most important is you don't stay sedentary all day. A July 2012 study showed that sitting less than three hours a day may add up to two years to your life. Long periods of sitting has been tied to increased risk of weight gain, diabetes, heart disease and certain forms of cancer including colorectal, ovarian and endometrial, Basen-Engquist said.

"We've been finding out that independent of that time you spend exercising, there's also are negative effects of the time we spent sitting," she said.

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