Interviewer: Diet and exercise can help reduce cancer risk. Talk about that next on The Scope.
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Interviewer: Cancer can be caused by many different factors, but some of them like diet and exercise is actually something a lot of us can control. Dr. John Sweetenham is a medical oncologist from Huntsman Cancer Institute. And how much of cancer risk is related to diet?
Dr. Sweetenham: Well, overall in the U.S., the current estimates are that about 20% to 30% of all cancers are related in some way to either excess body weight, to poor nutrition, or to inactivity and lack of exercise.
Interviewer: So to round up, maybe around a third. That's pretty substantial. Give me an idea of how that fits in context with maybe some of the other risk factors that are out there like genetics or smoking or stuff like that.
Dr. Sweetenham: Sure. I mean, if you look overall at risk factors for kind of cancers globally, we know for example, that tobacco and smoking is a very significant cause for lung cancers. And we can kind of rest the blame for certain types of cancer on certain types of lifestyle changes and behaviors.
For excess weight and for inactivity, it seems like it affects a whole breadth of different types of cancers. So there are many cancers which are more common in folks who are maybe overweight and folks who are inactive and who have deficiencies of whatever type in the diet or excesses of diet in the diet like high fat and so on.
Interviewer: Yeah. I'd like to delve into some of those details here. But before we kind of get into the how's and why's of some of those details, let's just lay out what a good diet and exercise plan for cancer prevention would look like, and then we'll go from there.
Dr. Sweetenham: Sure. So we don't know the absolute details of that, but some general rules are to eat plant based foods as much as you can, plenty of vegetables, beans, any other plant-based foods, they're helpful in that regard. They seem to reduce cancer risk. And stay away particularly from cured and processed meats and red meats. They seem to be particularly risky. And then finally, the other components of the diet that's well known about is high fat foods. So it's difficult to eliminate those from diet, but if you can reduce the amount of high fat food that you have, that can be a big help.
Interviewer: So this might be a bit of a technicality, but is it plant-based foods are good just because they're not the bad foods? Or are there actually some positive health benefits to those?
Dr. Sweetenham: Yeah. That's a great question. There are very definite health benefits from those. For example, the fiber content of your diet, we know that that can reduce your risk of certain cancers like colon cancer. So it isn't just about not eating bad foods, there are positive benefits from a lot of vegetables and fruits and so on.
Interviewer: Yeah. So the bad foods, what's going on there? How are they causing damage?
Dr. Sweetenham: So we don't really know in detail. We know for sure that if you are for example, overweight, that can affect the way that your body reacts to levels of insulin, and that is thought to be one reason why some folks develop cancer as a result of the way the body handles insulin.
Some of the hormone levels are affected by excess weight. Estrogen levels are thought to be affected by how heavy somebody is, and that may be responsible for certain types of cancer such as breast cancer. But exactly why it is that excess weight causes cancer is still something that a lot of people are researching.
Interviewer: Yeah. So we have pretty good research to show that the diet that you laid out, plant-based diet, avoiding a lot of red meats and processed foods, we just don't know the why's kind of that.
Dr. Sweetenham: Absolutely, yeah. The evidence for that is very good. The cause is still a little unclear.
Interviewer: Got you. So what about a lack of activity? We started out by talking about food and exercise. So you're talking about how people that have excess body fat could be at more risk of cancer. Is the activity just about keeping a lean physique so that doesn't happen, or are there actually benefits to activity?
Dr. Sweetenham: There are clear benefits to activity, and we see that at several levels. Partly in cancer prevention it seems to reduce the risk. But also there's increasing information around how someone who already has cancer, how they may respond to their treatments and what their likely outcome is going to be, if they're able to exercise during the treatment after the diagnosis. So now, some really interesting evidence that exercising during and after your treatment can reduce your risk of a cancer coming back.
Interviewer: Yeah. So is it generally thought that it's chemical reasons? Again, for the exercise and for the food it's the chemical changes that are going on in the body that might be affecting the cell division?
Dr. Sweetenham: Yes, it probably is. Again, a number of large research programs addressing that and we have some big research programs at Huntsman Cancer Institute which are specifically looking at why that is and how it is that exercise can reduce your cancer risk, and improve your cancer outcome if you do develop the condition.
Interviewer: Yeah. Here's what I think I know. I want you to tell me if this is right, and then fit it into the context of this conversation. So cancer is an uncontrolled division of cells which is caused by genetic mutation. So every time your cell divides there's a chance of a genetic mutation happening. Some are . . . it doesn't matter, some could be bad, some could be good.
Dr. Sweetenham: Correct.
Interviewer: Over time, you get enough of these genetic mutations, then the cancer or the cell loses its ability to control its division speed.
Dr. Sweetenham: Yeah. The brakes come off.
Interviewer: Okay, the brakes come off, and that's when you start to get cancer.
Dr. Sweetenham: Exactly.
Interviewer: So eating red meats, we don't know why that's causing that genetic breakdown.
Dr. Sweetenham: There are clues. It may be that there are substances within the red meats, or within the processed meats that actually kind of accelerate that mutation, that genetic change within the cells. But again, we don't know in great detail why that is.
Interviewer: Got it. Are some people more susceptible to one trigger than others? Meaning, for one person it might be the foods they eat or don't eat, but for them smoking isn't quite as much of a risk. I guess what I'm trying to ask here, is there a cumulative protection in all of it? Like the more right things I do, the better chance I'm going to have of not developing cancer.
Dr. Sweetenham: At the moment, all the evidence would suggest that's the case. Yeah. The more healthy behaviors that you're able to follow, the lower your risk of cancer. So that as you eliminate one of these risk factors from your life, your risk of cancer goes down in proportion. So if you stop smoking, you reduce your risk of certain types of cancer. If you lose weight, you're reducing your risk of additional types of cancer. So absolutely. It all adds up.
Interviewer: Yeah. And all 30% of it you can control.
Dr. Sweetenham: Absolutely.
Interviewer: With just diet and nutrition.
Dr. Sweetenham: That seems to be the case. Yeah. Absolutely.
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