Does Sugar Feed Cancer – Dietitian Doc Explains

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Have you been avoiding sugar because you’re worried that it can make your cancer grow faster?

But does sugar feed cancer? And if so, should you avoid sugar?

What exactly should you avoid? Does it mean you should avoid all types of sugars?

And who should avoid them?

There’s no need to feel confused any longer. Keep reading and we’ll set the record straight once and for all.

We’ll dispel common cancer myths in regards to sugar, and explain what sugar does to cancer risk and what you as a cancer patient should do.

The Sugar vs Cancer Controversy

The question does sugar feed cancer is somewhat controversial and it can be a touchy subject.

There’s a lot of misinformation in the popular press and it’s one of the most common questions that cancer nutritionists get.

It’s also tied to a lot of emotion and anxiety for survivors and patients undergoing cancer treatment.

But basically, the concern does sugar feed cancer is based on a bit of a myth. Let’s see if the Mayo Clinic agrees.

There is a myth circulating that sugar feeds cancer. Sugar does not cause cancer. However, it may be indirectly involved in the development of cancer.

Mayo Clinic

Yup, they do. Let’s dissect this further and see what it’s all about.

Where Did the Idea Originate?

The idea does sugar feed cancer originated with a diagnostic technique where sugar uptake in cancer cells is used to detect cancer.

This, although useful in cancer screening and follow-up, has little to do with the energy utilization in cancer cells.

Somehow it snowballed into the current sugar and cancer controversy.

So, What’s the Story?

Before we dive in to does sugar feed cancer, let’s set a few things straight.

Firstly, sugar is a carbohydrate, or carb, and they come in many forms.

Secondly, sugar and cancer links pertain to concentrated forms of sugar, not all carbs.

Thirdly, a diet low in complex carbs void of fiber, vitamins, and antioxidants can actually increase your risk of cancer.

And, lastly, even though all cells use sugar for energy, most also use proteins and fats.

So do cancer cells.

What is Sugar?

Table sugar, or sucrose, which is the chemical name, consists of two molecules bound together, with equal parts glucose and fructose.

Thus, table sugar is what’s called a simple carbohydrate.

But how do plants make sugar?

Well, plants make sugar from water, sunlight, and carbon dioxide using chlorophyll in their leaves. This is called photosynthesis.

And sugar beets or sugarcane are especially good at this and have the most sugar of all plants.

Thus, they’re often grown for sugar harvesting.

Sugar beets are grown in a large swath of the northern US, while sugarcane is grown in Texas, Florida, and Louisiana.

Once they’re harvested, they’re processed into different forms of sugar.

Some of the more commonly used sugars in food are cane sugar, maltose, dextrose, invert sugar, molasses, and caramel.

Do Complex Carbs Also Turn into Sugar?

Yes, complex carbs also turn into sugar when they’re metabolized.

Complex carbs have anywhere from a few up to many thousands of single units of glucose, fructose, or galactose, linked together in a chain.

Thus, they’re called complex carbs.

And when they’re broken down, glucose is the end product.

Examples of complex carbs include starch, glycogen, and fiber.

And they’re present in foods like fruits, vegetables, whole grains, beans, and sweet potatoes. 

Starch is glucose stored in plants, while glycogen is glucose stored in human muscle and liver.

Fiber is a remnant of carbs in plants that give structure to their cell walls.

Although fiber isn’t digestible by humans, it’s very important for intestinal health and function.

And fiber, vitamins, minerals, antioxidants, and phytochemicals from complex carbs can help reduce the risk of cancer.

How Much Sugar Should You Eat?

Since the Daily Value (DV) for sugar hasn’t been established, food labels won’t tell you how much total sugar you should have in a day. 

However, Dietary Guidelines for Americans recommend limiting calories from added sugar to less than 10% of total calories per day.

Thus, on a 2,000-calorie diet, you should limit your intake of added sugar to 50 grams per day, or about 12 teaspoons (tsp).

The American Heart Association, on the other hand, go even further They suggest limiting added sugar to less than 6% of total calories.

This translates to 30 grams per day or just over 7 tsp for a person eating 2,000 calories per day.

GuidelineTotal SugarsAdded Sugar, % of Total CaloriesGrams per DayTeaspoons per Day
Dietary Guidelines for AmericansN/A<105012
American Heart AssociationN/A<6307
US Guidelines for intake of added sugar, based 2,000 calorie diet.

You can also check the food label to see how much sugar is added to food.

Pro-Tip: Look for foods that have <10% added sugar.

Graphic showing a food label and all its parts pointing out total and added sugar.
Design: Heselholt Group, LLC/Canva.

However, the problem is that the average American eats way more than 10% of their total calories as sugar.

Based on the National Health and Nutrition Examination Survey (NHANES) data from 2017-2018, the average intake for adults >20 years was 17 tsp of added sugar per day!

That’s 42% more than the Dietary Guidelines for Americans and 143% more than the American Heart Association recommends.

The average American eats 143% more sugar than the American Heart Association recommends.

To put this into perspective:

  • 1 can of soda can have as much as 11 tsp sugar
  • 1 cup of yogurt 7 tsp
  • 1 breakfast bar 3.5 tsp
  • 1 cup of bran cereal 5 tsp
  • 1 cup of a juice product 7 tsp

Is High Fructose Corn Syrup Safe to Use?

High-fructose corn syrup (HFCS) is a man-made sweetener that’s commonly used in a lot of foods.

It’s a cheap, shelf-stable product made from corn that’s usually genetically modified.

HFCS can easily be added during food processing and can be found in:

  • Breakfast Cereals and Bars
  • Baked Goods
  • Candy
  • Condiments and Salad Dressings
  • Fast Food Items
  • Packaged Frozen Desserts
  • Peanut Butter
  • Pre-packaged Meals and Pizza
  • Canned Fruit and Vegetables.
  • Sweetened Yogurts

HFCS provides more fructose than a natural diet but has no nutrients.

Just like with table sugar, a high intake of fructose may lead to obesity and high blood sugars, which indirectly may increase the risk for cancer.

It can also be pro-inflammatory and stress the liver. 

To help lower the risks of chronic disease and cancer, it’s best to limit the intake of HFCS.

Pro-Tip: Check the ingredients list for the words high-fructose corn syrup or corn syrup to know if it’s present in food.

Sugar Is a Primary Source of Energy

Sugar is a simple carb and a form of energy for our bodies, but as mentioned above, carbs also come in more complex forms.

All types of carbs are broken down to sugar, or glucose, which is used for energy by our cells.

The mitochondria in our cells use carbs to fuel everyday functions like breathing, thinking, absorbing food, and fighting diseases.

Think of the mitochondria as small furnaces where carbs are burned to produce energy for the body to use.

What’s more, although other fuels can be used under certain conditions, most cells prefer to use carbs.

This is simply because that’s what the machinery primarily was designed to use.

Is Glucose Essential for Cells?

Certain cells, like brain cells, are especially picky with their fuel of choice.

Because the brain controls so many vital functions of the body, its supply of any compound is tightly controlled.

Thus, in brain cells, you can’t easily replace glucose as an energy source with fats or proteins.

If demand outweighs supply, it can be supplemented temporarily by using lactate from carbs and ketones from fat.

But it still won’t meet the high energy demand of the brain.

Glucose is an essential source of energy for the brain.

National Institutes of Health

What Do Cancer Cells Feed On?

The National Cancer Institute defines cancer cells as abnormal cells that are constantly dividing and growing.

And those cells need a lot of energy.

However, all cells, including cancer cells prefer carbs for energy. Cancer cells just aren’t as picky as the brain cells we just talked about.

If cancer cells are in a pinch, they can use both proteins and fats for energy to keep division going.

Thus, restricting carbs will affect brain function more than cancer growth.

Cancer and Sugar – Is There a Link?

Yes, there is most likely a link.

But does sugar feed cancer? No, not directly, although indirectly it can create an environment where cancer thrives.

But let’s be clear, it’s not the case that eating sugar causes cancer or that drinking sugar-sweetened beverages cause cancer.

Cause and effect hasn’t been proven.

It’s more of an indirect relationship.

That is, if you consume large amounts of concentrated sugars in foods or drinks, you may be at higher risk of cancer.

With that, you’re more likely to experience weight gain, develop high blood sugar levels, and be exposed to oxidative stress and inflammation.  

These metabolic changes are what indirectly may promote tumor initiation and growth. They essentially make cancer thrive.

Researchers suggest that these mechanisms increase the risk of pancreatic cancer, breast cancer, and colorectal cancer.

Furthermore, sugar provides a lot of fructose and fructose can be difficult to metabolize for the liver.

Although recent cancer research on mice suggests that the gut may be protecting the liver.

That is, fructose may be processed in the gut first before it’s handled by the liver so the liver has to handle less.

Either way, fructose in large amounts can stress the liver and lead to fatty liver and inflammation.

And anytime there’s inflammation present, it increases the risk for chronic disease and cancer.

Although, more clinical trials are needed to ascertain some of these relationships.

Sugar and Breast Cancer

Although drinking sugar-sweetened beverages (SSBs) seem to be linked to breast cancer, it’s not a clear relationship.

But here’s what the studies say, and basically it increases the risk.

JournalsOutcomes of Drinking Sugar Sweetened Drinks (SSBs)
Journal of Nutrition (2021)Lean women were at slightly higher risk of developing breast cancer
Cancer (2021) Breast cancer survivors had a higher risk of dying when drinking 1-3 or more SSBs/week
Cancer Epidemiology, Biomarkers & Prevention (2021)Survivors who had >5 SSBs/week were at a higher risk of dying
European Journal of Nutrition (2021)Higher total sugar intake, including from fruit juice, was associated with poorer prognosis among survivors

So, What Should Cancer Patients Do?

Does sugar feed cancer? Well, as we’ve seen, the relationship is indirect. But there are some things you can do to lower your risk of cancer.

If you’re a cancer survivor or want to prevent cancer, it’s probably best to limit the intake of concentrated sugars in food and drinks.

You can do this by:

  • Checking food labels for added sugars, aim for <10%
  • Choosing foods low in high fructose corn syrup, cane sugar, maltose, dextrose, invert sugar, molasses, and caramel
  • Limiting sugar-sweetening drinks, fruit juices, and sodas
  • Limiting baked goods, sweets, and candy
  • Choosing complex carbs such as whole grains and starchy vegetables instead of simple carbs

It’s also important to stay at a healthy weight, exercise, eat healthy, and limit fast food, red and processed meats, and alcohol.

Graphic showing cancer prevention recommendations.
Cancer Prevention. Design Heselholt Group LLC/Canva.

These guidelines are based on decades of research and it’s a good idea to implement as many of them as possible.

Final Thoughts

Sugar is a form of carb our body uses for energy and most healthy cells and cancer cells prefer to use carbs for energy.

But cancer cells can also use proteins and fats for energy.

But does sugar feed cancer? No, not directly, although indirectly it can create an environment where cancer thrives.

And that happens because a high intake of sugar may make you gain weight, develop high blood sugar levels, and expose you to oxidative stress and inflammation. 

These metabolic changes may promote tumor initiation and growth.

And this may lead to an increased risk of pancreatic cancer, breast cancer, and colorectal cancer.

So, to be on the safe side, it’s best to limit the intake of concentrated sugars in food and drinks.

And it’s also important to stay at a healthy body weight, exercise, eat healthy, and limit fast food, red and processed meats, and alcohol.


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This general information regarding does sugar feed cancer is for educational purposes. It’s not individualized medical or nutritional advice.

It’s especially important for people who are trying to prevent cancer or are a survivor. During cancer care and treatment, it’s always best to follow guidance from your cancer treatment center.

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