Most of us don't really understand cancer: What it is, where it comes from, and how to, if not fully prevent it, or at least lower our odds of ever being told we have it. Dr. Jason Fung has written a comprehensive book, The Cancer Code, that looks at cancer in its entirety, from the earliest science surrounding the discovery and treatments of cancer, up to current-day medical research on the latest treatments, approaches, and potential preventative measures to take against this devastating disease. On every page, he debunks what we thought we knew as "fact," including the new understanding that cancer is within us and part of us. Whether it ever shows up and causes us trouble is another story.

Spoiler alert: Cancer is not something that happens to us, due to our genetic code or toxic load, or other factors. It's a constantly playing symphony of cellular growth and suppression that is continually taking place in our bodies. It's always there, as cells grow, multiply and die, rarely expressed loudly enough to be heard. Whether cancer gets out of control, causing tumors of "liquid" cancers of the blood, is largely due to factors that allow our bodies to control cancer and cart it safely off for disposal, or allow it to gain a foothold and grow, and eventually metastasize and find footholds in new regions of the body.

We can lower our cancer risk through lifestyle choices

Whether we "get cancer" is in large part (but not always) a result of factors that are due to cellular changes that get "turned on" or "turned off" by behavior that is within our own control, namely: Not smoking, eating a healthy whole-food diet, and practicing stress coping mechanisms, including getting enough sleep, according to Dr. Fung.

"Thirty years ago people thought that getting cancer was the result of one of these unlucky genetic lotteries and that once you got it there was nothing you can do about it," Dr. Fung says. But there is an interplay between the pro-cancer and anti-cancer events in the body. Some things are going to make it better and some things are going to make it worse."

There are of course rare cancers, childhood cancers, and genetically triggered cancers that are unlucky events, he concedes, and those are not "made worse" by diet and behavior. But those are such rare events that to understand cancer, it makes more sense to look at the vast majority of cases, which happen by the hundreds of thousands, not the handful, each year.

Since the 1970s, when President Nixon declared a "War on Cancer," cancer rates have shot up despite the billions of dollars spent on research and treatment breakthroughs that have helped elongate survival rates. By now, scientists had predicted we would have found a cure for cancer. But even billions of dollars later, cancer is still with us, and other than a drop in lung cancer rates, due to smoking cessation trends, cancer has been on the march, with rates rising, especially among those cancers that are related to obesity and type 2 diabetes, creating a clear link between diet and cancer risk.

Why are cancer rates still so high, despite our medical advancements?

The Western or American diet, heavy in meat, saturated fat, added sugar, processed ingredients, and packaged food, and lacking in nutrients, fiber and adequate intake of whole foods such as vegetables, fruit, whole grains, and nuts and seeds is one cancer culprit, Fung says. A Harvard study found that people who follow a plant-based diet have lower rates of cancer as well heart disease.

"When you look at the data of people in Africa back before they started eating a European diet, they rarely got cancer. And then when these populations started to westernize they started to get cancer. It's the same for Japanese women, who never got cancer in Japan, but when they moved to America and began eating an American diet, started to get cancer." Some people add stress as a factor that bumps up the cancer rate since stress suppresses the immune system. The point is, Dr. Fung says. when it comes to risk, "there are lifestyle behaviors that play a role. There are lifestyle factors that impact whether we get cancer."

The immune system matters when it comes to cancer, more than genetics

There are pro-cancer and anti-cancer events in the body and the immune system is orchestrating what happens when a cell dies and needs to be carted away, or grows too rapidly and needs to be neutralized. "Anything that strengthens our immune systems is an anti-cancer factor since our immune system is our first line of defense against runaway cells," Dr. Fung explains.

So anything that inflames our bodies, hampers our immunity, and contributes to the over-zealous growth of cells can contribute to the growth of cancer. "That includes diet, and specifically processed foods, and simply too much food, in the form of eating larger portions and more food more frequently throughout the day."

If you take an immune-suppressing drug that could wipe out your anti-cancer defenses. That's why transplant patients have such a high risk of cancer. Your immune system is affected by stress, sleep, and overall health.

For those who read this and think that genetics causes cancer, Dr. Fung says it is one part of the picture since while genetics can make someone predisposed to cancer, it does not necessarily lead to cancer, and only five percent of cancers are attributable to genetics.

Cancer has grown in the US by 84 percent from 1969 until 2014 and only took a minor dip in the intervening years due to smoking cessation trends. Once lung cancer retreated, the statistics on cancer started to look better, but other than smoking, which accounts for 35 percent of attributable risk for cancer, the second largest risk factor is obesity.

People who have type 2 diabetes and are overweight have twice the risk of cancer than those without type 2 diabetes or obesity. Dr. Fung believes that the connection is simple: Insulin is a growth hormone. It's one of several nutrient sensors that, when we eat, urge the cells to grow.

The nutrition cancer connection: Obesity and type 2 diabetes are risk factors

Dr. Fung points out that tobacco has been the biggest single contributor to cancer in our lifetime, accounting for 35 percent of the attributable risk, but right on its heels is our American diet, full of processed food and too much fat, sugar, and meat, which accounts for 30 percent of total attributable cancer risk.

As the use of tobacco has dropped, the cancer rate for lung cancer has fallen, but this leaves a disturbing new reality exposed: Those with the highest risk for cancer used to be smokers but as their numbers decline, it is clear that people who are overweight or obese, with a BMI of 30 or over, have twice the rate of some cancers than those who maintain a healthy weight. Obesity is linked to a higher risk of getting 13 types of cancer, the CDC tells us, and Dr. Fung points out that this is not coincidental, scientifically speaking.

Here's how to eat to lower your risk of cancer, according to a doctor

People with type 2 diabetes have twice as high a risk of developing certain cancers as those without type 2 diabetes, Dr. Fung, explains. He trained in internal medicine at the University of Toronto and then practiced nephrology—the study of kidney diseases such as diabetes and cancer–and his observations are backed up by scientific explanations as to why this link between diet and cancer may be happening. The simple explanation is that insulin and other nutrient sensors in the body such as mTOR, which reacts to protein, tell your cells to grow. So when you eat more than you need, your cells are instructed to grow more than is healthy.

When we eat more food in greater portions, or more often than our cells require to be fueled and energized for healthy activity, it prompts an unhealthy level of cell growth, and ultimately this shows up as a tumor or other type of cancer (blood cancers are not tumors but fluid, so to call cancer tumor is simplistic, he explains). Fung acknowledges that beyond our diet, there are other factors contributing to our risk of cancer, such as toxins and carcinogens as well as genetics. But genetics accounts for only about five percent of all cancers, while the other 95 percent of cancers are triggered by environmental or behavioral factors.

Here's how to lower your risk of cancer, from a doctor

Dr. Fung: Nutrition and cancer are related. This is because of nutrients sensors, and how the body reacts to the food we eat. Researchers spend more time looking at cancer growth and not enough time looking at how to prevent it through behaviors we do every day, like our diet.

To change your risk, change your lifestyle

In the past 30 years, we have found that diet plays a massive role in the occurrence of cancer, almost as much as smoking,

"The role of diet and nutrients in cancer risk came up in research in the mid-2000s and as a result of this huge study. When the first dietary recommendations were launched in the 1970s, one of the things we thought caused cancer was vitamin deficiencies," according to Dr.Fung. "So we gave daily vitamins to people, especially kids and it didn't work."

Sleep and stress relief are both helpful in bolstering your immune system. But understanding the role of nutrition and cancer is important, and rather than focusing on taking multivitamins, I would advise that Americans change their diet instead.

Genetics vs. diet and maintaining a healthy weight

People who follow a traditional American diet can increase their cancer risk by eating processed foods, too much food, or eating all the time, Dr. Fung says. While cancer is a disease that is affected by genetics, it is not just about genetics. "Clearly, more than just genetics is at play here," he says. "There is a mutation in a gene and for some women and men, that causes cancer, but that simplistic understanding of cancer is really prevalent. People want more screening, total body MRI. there is a reason these don't work.

But lots of people can get cancer and they don't have the genetic mutation. So it's about diet and lifestyle or events and genetics together. In Japan, one-third of cancers are not caused by diet. But when Japanese women move to the United States, their cancer risk goes way up. So the role of genetics versus lifestyle is hard to study because it manifests over a lifetime. There is a tendency to say, about cancer: It's genetic.

"Clearly, that plays a huge role. But you can't do anything about your genes, at this point. So you want to focus on what you can change, and what has been shown to have an impact on lowering your risk. So what is that? Diet.

Other than lung cancer, the rate of cancer rose almost in tandem with the rate of obesity in the past 40 years, Dr. Fung writes. "Obesity rose from the '70s and '80s and in the '90s, and so did incidents of cancer. We found a big correlation between obesity and cancer."

The World  Health Organization defines 14 types of cancer as obesity-related cancer, he notes. "Breast is one of the big ones and so is colorectal cancer. There is a big change in hormones when you gain weight, and that is what is driving the link between obesity and cancer."

"Intentional weight loss can reduce the risk of cancer death by 40 to 50 percent," he writes in The Cancer Code. In Europe and North America, 20 percent of incident cancer cases are attributable to obesity, so maintaining a healthy weight is one way to lower your risk at any age.

The role of insulin, nutrient sensors, and cancer growth

Lots of factors drive up your risk for cancer, Dr. Fung writes, including high insulin levels, and high nutrient sensors, such as mTOR which responds when we eat protein, and AMPK, a pathway that helps us metabolize all macronutrients. "If you have a high insulin level and high nutrient receptors, then that is going to promote the growth of cancer cells" explains Dr. Fung. "High insulin diet promotes cancer. And if you have cancer then eating to prevent cancer could be enough to tip the balance in your body, and help put cancer back into remission.

Type of diet plays a big role, he says, and people have looked at plant-based diets and found those who eat less meat, dairy, and saturated fat have lower cancer rates: "When you look at vegetarian diets, as opposed to meat-centric diets, cancer risk tends to be a lot lower."

The 3 Ways to Eat to Lower Cancer Risk

1. Eat Less food, especially processed food.

Most food that we buy is packaged (in plastic bags, cardboard boxes, or cans, and made with loads of added sugar, and preserved with chemicals to give it a long shelf life). Process foods disrupt your hormones and send signals to your cells to grow, Dr. Fung explains. Instead, eat whole foods that grow directly out of the ground, and eat less overall.

"The processing of foods is probably the number one thing that is bad for us. It's not a question of meat versus vegetables. If you're vegan you can still be eating processed foods. Donuts can be vegan. It's the ultra-processing of the foods that is the problem. You need to eat natural foods." Dr. Fung says. It's not just how much you eat but how processed your food is."

2. Don't eat all the time. Eat less often to allow your cells to function better.

If you are eating all the time, several snacks and meals throughout the day, then you are constantly signaling the body to grow and grow and grow. And unless you're a kid, you don't want that, Dr. Fung explains. "When you eat macronutrients, especially carbs, that signals insulin, and when you eat protein, that activates another nutrient sensor called mTOR (Mechanistic Target of Rapamycin) which is essential for protein synthesis. A third nutrient sense called AMPK responds to all three macronutrients, carbs, protein, and fat, and works long term. In each case, when you keep feeding your body, 10 times a day, and telling the body to grow, grow and grow! then some of that would become cancerous growth," he says.

It makes sense that our cancer rates have climbed as our eating habits have changed, Dr. Fung posits. "In the 1970s, people were eating three times a day, and in the 2000s, people are eating six times a day. Breakfast, snack, lunch, snack, dinner, snack. We don't go more than two hours without eating, most days. There are snacks between halves in soccer games!" Dr. Fung advocates intermittent fasting as a way of lowering your risk of cancer.

3. Eat natural foods that are minimally processed and nutrient-dense.

It turns out that eating a diet high in vegetables, fruit, whole grains, nuts, seeds, and legumes (in other words natural unprocessed foods) will help shift the gut microbiome, and ultimately the fiber and nutrients in these types of foods will help to limit insulin and mTOR from driving cell growth. You will have plenty of fuel and ready energy, but without the excess that can spark problems. These whole foods (you've heard to eat the color of the rainbow for added phytochemicals and antioxidants) help boost immunity and keep your immune cells running on high alert, ready to take down any suspicious activity they find in the body.

The body cells coordinate growth and nutrient availability. When no nutrients are around, your cells don't want to grow because if they tried, they would die. But when you have an abundance of nutrient sensors and too much growth, then cancer forms, and if your immune system is suppressed or busy, then that is the link to cancer. So when you eat, excessively– especially carbs and protein–and mTOR surges and your cells are going to grow excessively and you are going to grow disease.

They found a pathway in the 1960s and it turns out to be an important pathway for cancer. It's called the AMPK pathway and now they have developed drugs that disrupt these pathways but you can't completely wipe them out or your cells would get no energy. They would die.

By giving people insulin who have type 2 diabetes it may raise cancer risk

People with type 1 diabetes, sometimes called childhood diabetes because it's genetic, take insulin.  Type 2 diabetes is caused when you produce too much insulin, over time your cells become insensitive to it, which is insulin resistance. As you gain weight, diabetes gets worse and your insulin system essentially stops working properly.

"The way we have treated diabetes is the opposite of what we want to do, which is to get the insulin level low and under control through diet and weight loss," writes Dr. Fung. Instead, we give patients insulin. More insulin will bring blood sugar down which helps your blood sugar level get better but you are treating it as what is called "symptomatic disease."

So as he explains it: While it looks like you're helping to alleviate the symptoms, but actually things are not better. if you give insulin, then blood sugar will get better, but the more insulin you take, the worse it is for you and the higher your cancer risk. The blood sugar will come down but you have not done anything to help cure the disease.

The most important way to treat diabetes is to change the way you eat: Less processed food, less often, and less food. It's the same way to eat to lower your risk of cancer. And the type of food you eat is whole foods: Vegetables, legumes, fruit, nuts, seeds, and whole grains.

One of the things that are part of this idea is only eating when you're hungry and leaving time between meals, says Dr. Fung. People eat all the time but there is a lot that goes into it. If you eat simple carbs, then you are hungry shortly thereafter. "The types of foods you eat create different levels of satiety," so choose foods that are high in nutrients and fiber." If you are having a hungry day, he explains, it could be stress or hormones, or lack of sleep. So prioritize sleep and stress management. Clearly, other issues go along with what drives hunger.

Bottom Line: To lower the risk of cancer, eat less processed foods, eat less often and when you do eat, choose foods that are whole foods full of healthy fiber and nutrients. "You need to figure out how and when to eat so that you let your body function at its most healthy and not get the constant bombardment of nutrient sensors telling it to grow. The key is if you are not hungry then you don't need to eat. But if you are hungry then eat really good food."