By Dr. Mercola
Obesity is a frequently overlooked factor that can contribute to an increased cancer risk, yet less than 10 percent of Americans are aware of this link.1 According to the National Cancer Institute,2 an estimated 84,000 annual cancer cases are linked to obesity.
Obesity may also affect the efficacy of cancer treatments. With rising obesity rates among young children in particular, it's becoming really important to understand this link.
Childhood obesity has nearly tripled since 1980, and one in five kids is now overweight by age six; 17 percent of children and adolescents are now obese.3 Unfortunately, childhood obesity has become so prevalent that many parents fail to recognize that their children are in fact overweight.4
Research5 has confirmed this perceptual shift, concluding that overweight/obese children are now nearly 25 percent less likely to be perceived as overweight compared to the previous decade.
While body acceptance is a good thing, it can also be dangerous if potent risk factors for lethal disease are simply ignored as "normal" in the process.
As noted in a recent position statement on obesity and cancer by the American Society of Clinical Oncology6 (ASCO), obesity is "quickly overtaking tobacco as the leading preventable cause of cancer." To address this overlooked cause of cancer, ASCO has established a "multipronged initiative," which includes:
- Education to raise awareness about the evidence linking obesity and cancer
- Tools and resources to help oncology providers address obesity with their patients
- Advocating for policy and systems change to address societal factors contributing to obesity and improve access to weight management services for patients with cancer
Processed Food Drives Obesity and Cancer Epidemics
The obesity epidemic is directly related to excessive sugar consumption (virtually every single processed food is now loaded with hidden sugar and fructose, including baby food and foods thought of as "health foods"), and this is also a major driving factor for the cancer epidemic.
The link between a high-sugar diet, obesity, and cancer can be summarized in two words: insulin resistance. Both obesity and cancer result when your body loses its ability to burn fat as fuel.
Sugar also causes chronic inflammation, which also raises the risk of cancer. And, as noted in the featured CNN article:7
"Fat tissue also produces hormones called adipokines, which can stimulate or inhibit cell growth8... If these hormones are out of balance, the body may not be able to properly fight cell damage."
One of the most effective ways to reverse insulin resistance is intermittent fasting, along with making some basic changes to your diet, which revolves around restricting your sugar and fructose intake, and replacing carbs with healthy fats.
Studies Showing Obesity-Cancer Link
A number of studies have linked obesity to an increased risk for about a dozen different cancers, including cancer of the colon, esophagus, kidney, breast, and pancreas, as well as a heightened risk of dying from the disease:
- A 16-year long study9 published in 2003 that included more than 900,000 Americans found that obese participants were more likely to be diagnosed and die from cancer, compared to those of normal weight
According to the authors, obesity "could account for 14 percent of all deaths from cancer in men and 20 percent of those in women"
- A recent report published in the journal Cancer Research10 projects cancer incidence and death from cancer in the US will continue to rise over the next decade and a half, in large part due to rising obesity rates
- A recent study11 involving 80,000 breast cancer patients found that pre-menopausal women with a body mass index (BMI) over 30 had a 21.5 percent chance of death whereas women with average BMI had a 16.6 percent chance of dying from the disease
A recent study published in the peer-reviewed journal JAMA Internal Medicine12 found that most adults (just over 71 percent) get 10 percent or more of their daily calories from added sugar. Approximately 10 percent of American adults get 25 percent or more of their daily calories from added sugar!
On average, Americans consume about 350 calories a day from added sugar, which equates to about 22 teaspoons, and this is a sure-fire recipe for chronic poor health...
In the JAMA study just mentioned, those who consumed 21 percent or more of their daily calories in the form of sugar were twice as likely to die from heart disease compared to those who got seven percent or less or their daily calories from added sugar. The risk was nearly tripled among those who consumed 25 percent or more of their daily calories from added sugar.
But cancer is also fed by excess sugar, so while cancer risk was not assessed here, there's little doubt that your cancer risk will rise right along with your risk for heart disease...
Your Body Has Limited Ability to Process Sugar
The main problem with sugar, and processed fructose in particular, is the fact that your liver has a very limited capacity to metabolize it. According to Dr. Robert Lustig, you can safely use about six teaspoons of added sugar per day unless you are vigorously exercising. But the average American consumes 22 teaspoons of added sugar a day.
All that excess sugar is metabolized into body fat, and leads to all of the chronic metabolic diseases we struggle with, including cancer.
Four grams of sugar is equivalent to about one teaspoon, and I strongly recommend limiting your daily fructose intake to 25 grams or less from all sources, including natural ones like fruit. That equates to just over six teaspoons of sugar a day.
If you're among the 80 percent majority who have insulin or leptin resistance (overweight, diabetic, high blood pressure, or taking a statin drug), you'd be wise to restrict your total fructose consumption to as little as 15 grams per day, until you've normalized your insulin and leptin levels.
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While lack of exercise certainly plays a role in rising obesity rates13 among both children and adults, it's important to understand that you cannot exercise your way out of a poor diet.
The food industry has responsibility here that it has, so far, failed to accept. It spends more than $1.8 billion marketing junk food to kids each year,14 while paying lip service to concerns about obesity by now and then promoting exercise.
These processed junk foods are also loaded with hormone-mimicking chemicals that further contribute to cancer and other health problems. In short, the current generation of children raised on a processed food diet has a much higher risk of devastating health problems than their parents, thanks to the processed food industry.
The risks are significant. In girls, obesity exposes them to higher estrogen levels because estrogen is both produced and stored in fat tissue. Girls carrying excess body fat therefore have more estrogen and leptin, which can lead to insulin resistance and the development of more fat tissue, which produces even more estrogen—it's a vicious cycle that can result in premature puberty, and raises the risk of estrogen-sensitive cancers such as breast cancer later on in life.
Understanding the Sugar-Cancer Connection
Cancer cells need glucose to thrive, and if you have insulin resistance, it doesn't matter if that glucose comes from added sugar, fructose, or grains. In order to starve the cancer cells, or prevent them from forming in the first place, you have to eliminate its primary food source, i.e. the sugars, which include all non-vegetable carbohydrates.
In 1934, Otto Warburg received a Nobel Prize for his research on cancer cell physiology, which clearly demonstrated cancer cells require more sugar to thrive. Unfortunately, many oncologists still have not fully grasped the importance of this knowledge, nor do they apply it when devising a cancer treatment plan. Not everyone is clueless, however. Lewis Cantley, director of the Cancer Center at Beth Israel Deaconess Medical Center at Harvard Medical School, has noted that as much as 80 percent of all cancers are "driven by either mutations or environmental factors that work to enhance or mimic the effect of insulin on the incipient tumor cells"15
Even in terms of treatment, cancer has been shown to respond to diet alone. A ketogenic diet, which is high in healthy fat and very low in sugar, especially for those who are insulin resistant, has been shown to reverse cancer in many cases, and research shows a lot of promise in this area. It can be very useful in addressing the underling insulin resistance. Once the insulin resistance resolves, a ketogenic diet is typically not required. Recent research16 has further added to the knowledge pool, showing that not only does sugar feed existing cancer; it also appears to initiate cancer growth. As reported by GreenMedInfo.com,17 this study:
"'...provide[s] evidence that increased glycolytic activation itself can be an oncogenic event...' That is to say, the activation of sugar-based metabolism in a cell – driven by both the presence of increased quantities of glucose and the increase glucose receptors on the cell membrane surface (i.e. 'overexpression of a glucose transporter') – drives cancer initiation. Moreover, the study found that 'Conversely, forced reduction of glucose uptake by breast cancer cells led to phenotypic reversion.' In other words, interfering with sugar availability and uptake to the cell causes the cancer cell to REVERSE towards its pre-cancer structure-function (phenotype).
To Address Insulin Resistance, You Must Cut Sugar Consumption
If you're overweight, step number one is to reduce your overall sugar and grain consumption. I recommend keeping your total sugar/fructose intake below 25 grams a day, or as little as 15 grams a day if you have any health problems related to insulin and leptin resistance, such as high blood pressure, diabetes, or heart disease, until your insulin/leptin sensitivity has been restored. One of the easiest ways to dramatically cut down on your sugar and fructose consumption is by switching to a diet of whole, unprocessed foods, as most of the added sugar in your diet comes from processed fare. Ideally, aim to:
- Avoid processed sugar/fructose, grains, and processed foods
- Eat a healthful diet of whole foods, ideally organic, and replace the grain carbs with:
- Large amounts of vegetables
- Low-to-moderate amount of high-quality protein (think organically raised, pastured animals)
- As much high-quality healthful fat as you want (saturated and monounsaturated from animal and tropical oil sources). Most people actually need upwards of 50-85 percent fats in their diet for optimal health—a far cry from the 10 percent currently recommended.
Other ways to cut down on your sugar consumption include:
- Cutting back on the amount of sugar you personally add to your food and drink
- Using Stevia or Luo Han instead of sugar and/or artificial sweeteners. You can learn more about the best and worst of sugar substitutes in my previous article, "Sugar Substitutes—What's Safe and What's Not"
- Using fresh fruit in lieu of canned fruit or sugar for meals or recipes calling for a bit of sweetness
- Using spices instead of sugar to add flavor to your meal
Intermittent Fasting—One of the Most Effective Ways to Reverse Insulin/Leptin Resistance
Once you've addressed your basic food choices, you can further boost your fat loss efforts by incorporating the principles of intermittent fasting. Exercising in a fasted state will bring it up yet another notch. A simple way to get started with intermittent fasting is to simply omit breakfast, making lunch the first meal of your day. I usually recommend this kind of eating schedule, but if you want to eat breakfast and skip dinner instead, that's okay too. The key is to limit your eating to a specific, narrow window of time each day (about 6-8 hours), rather than eating every two to three hours, all throughout the day.
Intermittent fasting is by far the most effective way I know of to shed unwanted fat, eliminate sugar cravings, and normalize your insulin/leptin sensitivity. Intermittent fasting helps reset your body to use fat as its primary fuel, and mounting evidence confirms that when your body becomes adapted to burning FAT instead of sugar as its primary fuel, you dramatically reduce your risk of chronic disease. Another mechanism that makes intermittent fasting so effective for weight loss is the fact that it provokes the secretion of HGH18—a fat-burning hormone that has many well-recognized "anti-aging" health and fitness benefits.
Daily intermittent fasting tends to have the highest compliance rate, and mounting evidence suggests intermittent fasting can provide many if not most of the same benefits as longer, more rigorous fasts. Again, when you fast daily, you restrict your eating to a specific window of time, such as an eight hour window or less. You do this every day until your insulin/leptin resistance improves (which means your weight, blood pressure, cholesterol ratios, or diabetes normalizes). After that, you just need to do it as often as you need to maintain your healthy state.
If you want to reduce, and in many cases virtually eliminate your risk of cancer and other chronic diseases, I suggest you get serious about restricting your sugar/fructose consumption to 25 grams per day—or less if you're already struggling with insulin-related health issues—and give intermittent fasting a try.
Again, you don't need to continue intermittent fasting for the rest of your life (unless you really want to). I believe that most who are insulin/leptin resistant would benefit from doing it continuously until the resistance resolves. However, once your weight is ideal, and you have no high blood pressure, abnormal cholesterol ratios, or diabetes, then you can resume eating more frequent meals until or unless the insulin/leptin resistance returns.
Remember, exercise will not compensate for a diet too high in sugar, and such a diet will destroy many of the benefits of exercise too boot. So you really need to address what and when you eat if you want to shed excess weight and lower your risk for cancer and other chronic disease. There's no magic bullet, but a healthy lifestyle may be as close as you'll ever get to one.