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Sugar isn’t inherently cancer-causing; no evidence that removing sugar from diet cures cancer

Posted on:  2023-05-05

Key takeaway

Cancer is the result of mutations that lead to uncontrolled cell growth and proliferation. The International Agency for Research on Cancer recognizes obesity as a cause of at least 13 different cancers. Obesity, defined as excessive fat accumulation that poses a health risk, is generally caused by eating more calories than one expends. People who consume a high-fat, high-sugar diet are thus prone to becoming obese, which could increase their risk of developing cancer.

Reviewed content


Sugar causes cancer; eliminating sugar from the diet can cure cancer

Source: YouTube, The School of Greatness, Barbara O'Neill, Mark Hyman, 2023-03-23

Verdict detail

Incorrect: Eating too much sugar can lead to obesity, and obesity is a cause of certain cancers. However, sugar in itself isn’t carcinogenic (cancer-causing). It’s an important fuel source for healthy cells. Removing sugar from one’s diet won’t cure cancer and could even be harmful to cancer patients.

Full Claim

Sugar causes cancer; eliminating sugar from the diet can cure cancer


A popular belief about cancer is that sugar feeds cancer cells, thereby aggravating the disease, and that removing sugar from the diet will prevent or even cure cancer. Some go as far as to label sugar as the cause of cancer, like physician Mark Hyman, who made this claim during an interview with sportsman Lewis Howes on Howes’ podcast “The School of Greatness”.

The interview dates back to February 2020, but a clip of that interview was uploaded by Howes to TikTok in March 2023, accruing more than 260,000 views. Hyman is a proponent of “functional medicine”, a practice that promotes scientifically unproven therapies, including “detoxification” and chiropractic.

Others, like naturopath Barbara O’Neill, have gone a step further, claiming that eliminating sugar from one’s diet will help cure cancer.

However, these claims oversimplify the relationship of sugar to cancer development so far as to be misleading. And the claim that removing sugar from one’s diet can cure cancer is unsubstantiated by scientific evidence and can even be harmful, as we will explain below.

Sugar provides an important source of energy and is part of many healthy foods

Sugar comes in various forms, but the simplest form is glucose, which is the fuel used by cells to power chemical reactions that keep us alive. Sugar has its place in a healthy diet, as it is naturally present in various healthy foods, such as fruit, vegetables, and grains.

The basis for the claim that starving cancer cells of glucose will cure cancer likely rests in the unusual energy requirements of cancer cells. Cancer cells proliferate in an uncontrolled manner as a result of mutations. Sometime in the 1920s, scientist Otto Warburg discovered that cancer cells generally consumed much more glucose than normal cells[1].

Thus on an intuitive level, it may seem like removing sugar from one’s diet would naturally starve cancer cells and keep them from growing.

However, this fails to account for the fact that healthy cells also require glucose to function properly and maintain health. Indeed, when our cells are deprived of glucose, which can happen in type I and type II diabetes for example, it results in a serious illness known as diabetic ketoacidosis. And currently, there isn’t a way to deliver sugar only to healthy cells but deny it to cancer cells.

Furthermore, if glucose is lacking, the body will simply switch to converting protein and fat into glucose, a process called gluconeogenesis that is carried out in the liver. Therefore, simply eliminating sugar from one’s diet wouldn’t cut off the body’s access to glucose, explained Craig Thompson, an expert in cancer metabolism and the president of Memorial Sloan-Kettering Cancer Center.

The switch to gluconeogenesis isn’t without repercussions either. The MD Anderson Cancer Center warned that the breakdown of the body’s protein stores for glucose can lead to muscle loss and malnutrition, which creates its own set of problems.

More importantly, there’s no scientific evidence showing that a diet excluding sugar reduces a person’s risk of developing cancer. On the contrary, cancer patients could benefit from additional nutrition. Thompson stated that cancer patients undergoing treatment could benefit from additional calories and nutrients to recover.

The non-profit organization Cancer Research UK highlighted the fact that certain cancer treatments lead to weight loss or place the body under a lot of stress. Therefore, “poor nutrition from restrictive diets could also hamper recovery, or even be life-threatening,” it concluded.

Excessive sugar consumption is an important contributor to obesity; obesity increases one’s risk of cancer

That said, this doesn’t mean that our intake of sugar has absolutely no relationship with our risk of cancer—only that the relationship is more indirect than Hyman and O’Neill’s claims let on.

While sugar can be part of a healthy diet, processed food like baked goods and soft drinks contain large amounts of refined sugar, which is obtained by purifying sugar from natural sources. Unlike natural sources of sugar, refined sugar doesn’t normally come with sufficient amounts of nutrients like vitamins, minerals, and fiber.

Thus a diet that is high in processed foods is also very likely to carry a high sugar content, making it easy to consume more calories than one needs. Indeed, the American Heart Association found that, on average, American adults consume 17 teaspoons of added sugar a day, which is about two to three times greater than men and women should consume, respectively. And excessive calorie consumption can lead to obesity.

Obesity, defined as excessive fat accumulation that poses a health risk, is recognized by the International Agency for Research on Cancer as a cause of at least 13 different types of cancer (see Figure 1 for examples). It could also contribute to poorer cancer survival. Obesity is generally the result of consuming more calories than one expends, therefore consuming a lot of high-fat, high-sugar foods is one of the main contributing factors to obesity. The other contributing factor is a lack of physical activity.

Figure 1 – Increased cancer risks from obesity. Source: The International Agency for Research on Cancer.

Research on how obesity causes cancer is still ongoing, but scientists have discovered various ways in which excessive fat can increase cancer risk.

It’s common knowledge that fat acts as an energy storage unit in the body, but that’s not all it does. Scientists have found that fat cells also release chemical signals that influence inflammation, growth, and proliferation, as Cancer Research UK explained in this article. Thus excessive fat accumulation could push cells into becoming cancerous.

Figure 2 – Various pathways through which excessive fat can contribute to cancer development. Source: Cancer Research UK.

Thompson highlighted the role of fat in regulating inflammation:

“Inflammation is a natural response to infection or injury. But inflammation also makes it more likely that you’ll damage the DNA of cells that survive, and this increases the chances that a cell might turn cancerous. More and more we’ve come to understand that cancer grows out of areas of regeneration and repair, places where there’s likely to be inflammation.”


In summary, a person’s diet can influence their risk of developing cancer, which is the result of mutations that lead to uncontrolled growth and proliferation. Fat in the body produces chemical signals, and excessive fat accumulation can trigger a cascade of reactions leading to cancerous transformation. However, the claim that sugar causes cancer is false—sugar in itself isn’t carcinogenic (cancer-causing), and removing sugar from one’s diet won’t cure cancer and could even put cancer patients at risk.


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