Cancer is that terrifying disease we spend our lives hoping not to get. Although billions of dollars in research have increased our understanding of what it is and how to best treat it, we still don’t have all the answers, and cancer continues to be a major threat to public health. 

In The Cancer Code, author Dr. Jason Fung gives us a history lesson of how the war on cancer began, taking us through the successes and failures of cancer research that have helped scientists redefine their understanding of this disease. Fung is a physician and a researcher and the cofounder of The Fasting Method, a program that has helped many patients lose weight and reverse their type-2 diabetes through intermittent fasting. 

For decades, attacking cancer meant going after its strengths, namely its ability to grow and acquire mutations. But it took the work of a physicist to understand that the seed of cancer lives in every one of our cells, and that it is our environment that allows it to flourish. 

The great news is that the incidence for most cancers is decreasing, and obesity-related cancers, which are on the rise, are preventable through lifestyle changes. “For the most part, dietary prevention of cancer boils down to one key strategy: avoiding diseases of hyperinsulinemia, including obesity and type 2 diabetes,” says Fung in his book. We spoke with him about how cancers come about and spread and how getting your weight under control with intermittent fasting can be an effective prevention strategy. 

This interview has been edited for brevity and clarity.

Your book reminded me of a 1973 essay titled ‘Nothing in biology makes sense except in the light of evolution.’ Does that apply to cancer as well?  

We thought that cancer was a collection of random mutations, but it turns out they’re not random at all. Evolution is guiding the mutations that you see in cancer. And that’s the big change in thinking. What is guiding this evolution is the interaction between the organism and its environment. [If you take two patients with breast cancer, the tumors] may look identical under the microscope, but when you look at the genetics, they may have a hundred different mutations that are different between the two. 

What’s important is not the mutations themselves, but what is guiding them. For example, you have flying squirrels in America and in Australia. They look very similar and they both fly, but if you look at the genetics of the two of them, they’re completely different. Their [environment] selected for the mutations that [produced] a flying squirrel. It’s the same thing with cancer. Getting down into the actual mutations themselves means you get bogged down so much in the details that you miss the reason they’re evolving. We went so far into the genetics of cancer that we couldn’t understand what was causing these different mutations. What is guiding them is the interaction between the organism and its environment. So, therefore, what we need to do is focus much more on the environment, which includes things like obesity and diet.

Can evolution also explain metastasis, or the spread of a tumor from its initial site to a secondary site?

The process of metastasis is very mysterious because in order for, say, a breast cancer cell to live in the liver, it needs to completely change what it’s doing. It actually needs a whole lot of changes to its genetic makeup to even survive [outside of the breast]. What happens is that the breast cancer is continually shedding off cells that get killed in the blood. But the issue is that this is the process of evolution. So you have cells which can mutate and undergo selection pressure. And by chance, one of these cells survives in the blood just a little bit longer than normal,  and it might be able to get back to the original site of the breast cancer. It can survive there because it’s where it came from. But now this cell, which is a little bit more survivable, sheds back into the bloodstream. So every time it gets better at surviving in the blood. And every time it comes back to the original tumor site. So it’s a continual process of evolution towards a more survivable state. And by being able to circulate through the blood, it can go to other sites, like the liver, where most will die because they don’t know how to survive there. But ,again, just by chance, one is able to survive there and that’s what allows it to go.

You talk about the overdiagnosing of cancers, such as breast and prostate cancers, and how that’s a problem because we are treating patients that likely don’t need it. How can you as a patient protect yourself from that?

For screening [to be successful] you have to reduce late stage cancer, not simply find more early stage cancer. Cervical cancer with pap smears and colon cancer screening with colonoscopy were extremely successful in reducing the burden of those types of cancer.  The problem with mammograms [in the case of breast cancer], is that you increase the number of early cancers you find, but you don’t decrease the number of late cancers. So you’re not actually preventing any problems. What you’re doing is finding a bunch of early cancers that you may not necessarily need to treat, but then by treating them, you may actually cause more problems because you’re doing chemotherapy and surgery, which have side effects. [As a patient,] the best thing is just to follow the standard guidelines. People sometimes say, well, if I should screen with a mammogram at age 50, maybe I should do it at 35. But you could be doing yourself harm by screening yourself at age 35.

What lifestyle changes can we apply to prevent cancer and specifically how can we use intermittent fasting as a prevention strategy?

Both type two diabetes and obesity increase your risk of certain types of cancer. There are about 13 cancers that are listed by the World Health Organization as obesity-related. Those are the cancers that are increasing in the world, which is important because we can do something about it. If you are overweight, you can try to reach a normal weight. If you have type two diabetes, you can try to reverse that type two diabetes and hopefully reduce your future risk of cancer. Lifestyle measures, including intermittent fasting, can help you maintain a normal weight. There are some studies that looked at periods of fasting in breast cancer. And those who fast regularly for 13 hours overnight have a lower risk of cancer. I think that the most important thing is to maintain a normal weight and  hopefully reverse type two diabetes. Do whatever works for you. 

Are fasting and fasting-mimicking diets a useful strategy in cancer treatment?

The standard way you can use fasting and fasting-mimicking diets is in addition to the standard treatments. [Intermittent fasting] seems to lower the incidence of side effects of chemotherapy, which allows you to tolerate the treatment better and get a full-dose treatment, which may improve your prognosis. 

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