Elevated Blood Sugar Sets the Stage for Cancer Growth


Story at-a-glance

  • Obesity can promote cancer via a number of different mechanisms, including mitochondrial dysfunction, overeating, excess sugar in your diet, chronic inflammation and overproduction of certain proteins and hormones
  • Study: Cancer patients diagnosed with type 2 diabetes were 23 percent more likely to have received a cancer diagnosis during the decade preceding their diabetes diagnosis compared to non-diabetics
  • Previous research has shown that those with prediabetes have a 15 percent higher risk of cancer, especially cancers of the liver, stomach, pancreas, breast and endometrium


This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.

By Dr. Mercola

The fact that sugar and obesity are linked to an increased risk of cancer is now becoming well-recognized. Obesity has also been linked to an increased risk of death from all causes.

According to research published in 2013, nearly 1 in 5 U.S. deaths is associated with obesity.1 More recently, researchers published findings from a meta analysis of 239 studies covering four continents, saying excess body weight is responsible for 1 in 5 of all premature deaths in the U.S. and 1 in 7 in Europe.2,3,4

On average, carrying excess weight may reduce your life expectancy by about one year, while being moderately obese may result in a three-year reduction in lifespan. Those of normal weight had the longest life expectancy and the lowest risk of dying before the age of 70.

Considering facts such as these, it's no surprise that the financial burden of excessive sugar consumption is also great.

According to the Credit Suisse Research Institute's 2013 study5 "Sugar: Consumption at a Crossroads," as much as 40 percent of U.S. healthcare expenditures are for diseases directly related to the overconsumption of sugar, and this includes obesity, diabetes and cancer.

So, sugary processed foods may be cheap on the front end, but they exact a hefty price tag down the line.

Diet Can Influence Your Cancer Risk in More Ways Than One

Your diet plays a crucial role when it comes to obesity and related health problems such as elevated blood sugar, insulin resistance and cancer. Research suggests obesity can promote cancer via a number of different mechanisms.

One of the key mechanisms by which sugar promotes cancer and other chronic disease is by causing mitochondrial dysfunction. Sugar is not an ideal fuel for your body as it burns "dirty," creating far more reactive oxygen species (ROS) than fat does when it's metabolized.

As a result, excessive amounts of free radicals are generated when you eat excessive sugar, which in turn causes mitochondrial and nuclear DNA damage, along with cell membrane and protein impairment.

So, contrary to conventional teaching, nuclear genetic defects do not cause cancer. Rather, mitochondrial damage happens first, and this then triggers nuclear genetic mutations.

Research6 has shown that chronic overeating in general has a similar effect, as it places stress on the endoplasmic reticulum (ER), the membranous network found inside the mitochondria of your cells.

When the ER receives more nutrients than it can process, it signals the cell to dampen the sensitivity of the insulin receptors on the surface of the cell.

Thus continuously eating more than your body really needs promotes insulin resistance by the mere fact that your cells are stressed by the additional work placed on them by the excess nutrients. Insulin resistance in turn is at the heart of most chronic disease, including cancer.

Sugar Is a Key Contributor to Cancer

Most people who overeat also tend to eat many sugar-laden foods, which promotes elevated blood sugar levels and insulin resistance. So overeating sugary foods equates to a double-whammy in terms of cancer risk, compared to overeating whole, unprocessed fare.

In fact, recent research has identified sugar as the top contributor to the worldwide cancer surge. According to a report7 on the global cancer burden, published in 2014, obesity is responsible for an estimated 500,000 cancer cases worldwide each year.

The reason for this is because cancer cells are primarily fueled by the burning of sugar anaerobically. Without sugar, most cancer cells simply lack the metabolic flexibility to survive.

Normal, healthy cells have the metabolic flexibility to adapt from using glucose to using ketone bodies from dietary fats. Most cancer cells lack this ability so when you reduce net carbs (total carbs minus fiber), you effectively starve the cancer. This is why nutritional ketosis appears to be so effective against cancer.

According to recent research from the University of Texas MD Anderson Cancer Center, refined sugar not only significantly increases your risk of breast cancer; it also raises your risk of tumors spreading to other organs.8

It was primarily the refined fructose in high-fructose corn syrup (HFCS) found in most processed foods and beverages that was responsible for the breast tumors and the metastasis.

The Role of Genetics, Proteins and Hormones

While genetic defects are not a primary cause of cancer, genes can still play a role. Scientists have discovered that a number of genes known to promote cancer by influencing cell division — including a gene called AKT — also regulate cells' consumption of nutrients.

So certain genes actually appear to play a role in cancer cells' overconsumption of sugar. Whereas healthy cells have a feedback mechanism that makes it conserve resources when there's a lack of food, cancer cells do not have this mechanism and feed continuously.

Recent research has also found that overweight women who lost weight reduced their risk of cancer by lowering their levels of certain proteins linked to cancer development.9

These proteins (VEGF, PAI-1 and PEDF) promote angiogenesis, a process your body uses to build blood vessels that tumors need to thrive. The greater the women's weight loss, the greater their reduction in these proteins.

Previous research suggests losing weight can reduce your risk of breast, colon and prostate cancer by as much as 20 percent, and this effect is thought to be due to reductions in these proteins and other inflammatory compounds stored in fat cells.10

Obesity also triggers overproduction of certain hormones, such as estrogen, which is associated with an increased risk for breast cancer.

Links Between Diabetes and Cancer Are Getting Stronger

Overall, insulin resistance is one of the key contributors to a heightened cancer risk, and many studies have confirmed that type 2 diabetics are at greater risk.

One recent study, which included more than 1 million adult cancer patients, found that those diagnosed with type 2 diabetes were 23 percent more likely to have received a cancer diagnosis during the decade preceding their diabetes diagnosis compared to non-diabetics.11,12

Recent research has also noted that a growing number of obese Americans have poor blood sugar control, which in turn promotes rising rates of type 2 diabetes and associated health conditions. To combat this trend, the researchers urge overweight people to consider "serious weight loss efforts." As reported by WebMD:13

"Between 1988 and 2014, rates of diabetes rose from 11 percent to 19 percent, which was due to increases in blood sugar, the researchers said.

The investigators found that the rate of obese adults without the three key risk factors for heart disease — diabetes, high cholesterol and high blood pressure — held steady at just 15 percent.

But the rate of obese adults with all three risk factors rose 37 percent — to nearly [1] in [4] ... Risk for all three factors increased progressively from age 40 on ...

'We have two choices: letting this population get sick and provide monies for treatment of complications and disability; or intervene early and prevent diabetes by encouraging weight loss, leading to a healthier and more productive life,' [Dr. Joel] Zonszein, [director of the Clinical Diabetes Center at Montefiore Medical Center] said."

Prediabetes Also Raises Your Cancer Risk

Both of these findings tend to strengthen previous research showing that even prediabetes is a risk factor for cancer. More than 1 in 3 Americans aged 20 and older has prediabetes,14 a condition in which your glucose (blood sugar) levels are higher than normal but not yet high enough to be diagnosed as full-blown diabetes.

Of those with prediabetes, 15 percent to 30 percent will develop type 2 diabetes within five years.

A meta-analysis15 published in 2014, which included data from nearly 900,000 people, found that those with prediabetes have a 15 percent higher risk of cancer, especially cancers of the liver, stomach, pancreas, breast and endometrium. Other research has shown that people with the highest insulin levels at the time of a cancer diagnosis have significantly increased risks of cancer recurrence, as well as a greater risk of being diagnosed with a particularly aggressive form of cancer.16

From my perspective these findings aren't the least surprising and precisely what you would predict if you understand the mechanism of most cancers, which are essentially being fueled by a metabolism that is driven by sugar (glucose), generating loads of unnecessary and damaging free radicals, as opposed to clean burning, high-quality fats that generate far less ROS.

Ketogenic Diet May Be Key to Cancer Recovery

Nutritional ketosis is part of the answer here. In this type of diet, you replace net carbs (total carbs minus fiber) with moderate amounts of high-quality protein and high amounts of beneficial fat. Since cancer cells need glucose to thrive, and carbohydrates devoid of fiber turn into glucose in your body, cutting out net carbs quite literally starves the cancer cells. Additionally, low protein intake tends to minimize the mTOR pathway, which also helps restrict cell proliferation.

The video above features Thomas Seyfried, Ph.D., who discusses how, as a metabolic disorder involving the dysregulation of respiration, malignant cancer (in this case brain cancer) can be managed by altering your metabolic environment.

That said, this kind of diet (low in net carbs, moderate in high-quality protein and high in healthy fats) will also help normalize your weight and boost your general health for the simple reason that it helps you convert from carb burning mode to fat burning, which helps optimize your mitochondrial function.

How Fasting May Benefit Cancer Patients

Fasting is another strategy that helps reverse obesity and optimize mitochondrial function, and it too can offer hope in the fight against cancer. In fact, one research group is reportedly looking into the possibility of getting intermittent fasting approved by the U.S. Food and Drug Administration (FDA) as an adjunct therapy for cancer patients.17,18,19

Valter Longo, Ph.D., has published a number of studies on fasting and its impact on cancer. His most recent research, published in the journal Cancer Cell,20 found that fasting during chemotherapy boosts cancer-killing T cell activity, thereby improving the effectiveness of the chemotherapy. As reported by Science Daily:21

"[R]odents that received caloric restriction mimetics alone or chemotherapy combined with a fasting-mimicking diet had smaller tumor masses over time than those that received only chemotherapy ...

Mice with breast or skin cancers were given a low-sugar, low-protein, high-fat, low-calorie diet and were observed for [six] weeks while receiving doxorubicin, cyclophosphamide or no chemotherapeutic drugs. All of the mice receiving the diet-drug combination saw their tumors shrink to half the volume of the tumors in mice that received chemotherapy alone."

According to Longo:22 "The biggest factor exposing cancer cells to the T cells is the effect on the enzyme heme oxygenase-1, which is normally at high levels in cancer cells. Fasting reduces oxygenase levels and gives rise to a number of changes that included the increase of tumor-killing cytotoxic T cells."

What to Eat for Optimal Health and Cancer Prevention

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From my perspective, ignoring diet as a cancer prevention tool is foolhardy at best. I'm convinced most cancers are preventable through proper nutrition. Avoiding toxic exposures (such as pesticides) is another important factor, and this is one reason why I recommend eating organic foods, especially grass-fed or pastured meats and animal products, whenever possible.

Make no mistake about it, the FIRST thing you want to do if you want to avoid or treat cancer if you have insulin or leptin resistance is to cut out all forms of sugar/fructose and grain carbs from your diet. This step will optimize the signaling pathways that otherwise might contribute to malignant transformation.

Remember, the foundational aspect that must be addressed is the metabolic mitochondrial defect discussed earlier, and this involves radically reducing the net (non-fiber) carbohydrates in your diet and replacing them with high-quality fats. Moderating your consumption of protein, and being mindful of the quality of the protein, is also important, as excessive protein can also trigger cancer growth. To learn more about this, please see my previous article, "The Very Real Risks of Consuming Too Much Protein".

So, in summary, for optimal health you need sufficient amounts of carbohydrates, fats and protein. However, there are healthy carbs and unhealthy ones. Ditto for fat and protein. From my review of the molecular biology required to optimize mitochondrial function, it may be wise to aim for a diet with the following nutrient ratios:

Healthy fats, 75 to 85 percent of your total calories. Beneficial monosaturated and saturated fats include olives and olive oil, coconuts and coconut oil, butter made from raw grass-fed organic milk, raw nuts such as macadamia and pecans, seeds like black sesame, black cumin, pumpkin and hemp seeds, avocados, grass-fed meats, lard and tallow, ghee (clarified butter), raw cacao butter, organic pastured egg yolks, animal-based omega-3 fats and small fatty fish like sardines and anchovies.

Harmful fats that contribute to disease are primarily trans fats and highly refined polyunsaturated omega-6 vegetable oils (PUFAs). Remember, glucose is an inherently "dirty" fuel as it generates far more ROS than fat burning does. But to burn fat, your cells must be healthy and normal. Cancer cells lack the metabolic flexibility to burn fat and this why a diet high in healthy fats appears to be such an effective anti-cancer strategy.

When you switch from burning glucose as your primary fuel to burning fat for fuel, cancer cells must struggle to stay alive, as most of their mitochondria are dysfunctional and can't use oxygen to burn fuel. At the same time, healthy cells are given an ideal and preferred fuel, which lowers oxidative damage and optimizes mitochondrial function. The sum effect is that healthy cells begin to thrive while cancer cells are "starved" to death.

Carbohydrates, 8 to 15 percent of your daily calories. Aim for twice as many fiber carbs as non-fiber (net) carbs. This means if your total carbs is 10 percent of your daily calories, at least half of that should be fiber. Fiber has a number of other health benefits, including weight management and a lower risk for certain cancers.23

I personally believe that most would benefit from reducing net carbs (not just fructose) to less than 100 grams (g) per day, and keeping your total fructose intake to a maximum of 25 g per day from all sources. If you are insulin resistant, you'd do well to make your upper fructose limit 15 g per day.

Cancer patients would likely be best served by even stricter limits. By reducing the amount of net carbs you eat, you will accomplish four things that will result in lowered inflammation and reduced stimulation of cancer growth. You will:

Lower your serum glucose level

Reduce your mTOR level

Reduce your insulin level

Lower insulin growth factor-1 (IGF-1, a potent hormone that acts on your pituitary gland to induce metabolic and endocrine effects, including cell growth and replication. Elevated IGF-1 levels are associated with breast and other cancers).

I typically keep my net carbs around 50 to 60 g per day While this may sound awfully complicated, the easiest way to dramatically cut down on your sugar and fructose consumption is to switch to real foods, as the vast majority of added sugar and fructose you end up with comes from processed fare.

Excellent sources of high-fiber carbs that you can eat plenty of include chia seeds, berries, raw nuts, cauliflower, root vegetables and tubers such as onions and sweet potatoes, green beans, peas, broccoli, Brussels sprouts and psyllium seed husk.

Protein, 7 to 10 percent of your total calories. Quality is important, so look for high-quality grass-fed or pastured meats and animal products. As a general rule, I recommend limiting your protein to 0.5 g of protein per pound of lean body mass, which for most people amounts to 40 to 70 g of protein a day.

(To estimate your protein requirements, first determine your lean body mass. Subtract your percent body fat from 100. For example, if you have 20 percent body fat, then you have 80 percent lean body mass. Just multiply that percentage by your current weight to get your lean body mass in pounds or kilos.)

Again, the reason for limiting protein is because excessive amounts have a stimulating effect on the mTOR pathway, which plays an important role in many diseases, including cancer. When you reduce protein to what your body needs for cell repair and maintenance, mTOR remains inhibited, which helps minimize your chances of cancer growth.


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