Does sugar feed cancer? What the evidence says about common cancer myths

Wrong ideas about cancer are not harmless. They cause needless worry, and they can steer people away from good prevention and treatment decisions [s1]. Several of the most durable myths sound plausible, which is exactly why they persist. Here is what the evidence actually says.

Does eating sugar make cancer worse?

No. This is the myth that reaches almost every patient. It is true that cancer cells consume more sugar, or glucose, than normal cells — but no studies have shown that eating sugar makes cancer worse, or that cutting sugar makes a cancer shrink or disappear [s1]. The real link runs one step removed: a high-sugar diet may contribute to excess weight gain, and there is consistent evidence that higher amounts of body fat are associated with an increased risk of several cancers, including cancers of the endometrium, oesophagus, upper stomach, liver and kidney [s1][s3]. Body fat, not the sugar molecule itself, is the part supported by evidence.

Do phones and power lines cause cancer?

Cancer is caused by genetic mutations, and mobile phones emit a type of low-frequency energy that does not damage genes; by the best studies completed so far, they do not cause cancer [s1]. The electromagnetic energy from power lines is likewise a low-frequency form of radiation that does not damage genes [s1]. The caveat worth stating honestly: in 2011 the International Agency for Research on Cancer classified mobile phone use as "possibly carcinogenic to humans," a category that reflects limited and inconclusive evidence rather than a demonstrated hazard [s2].

Can surgery or a biopsy spread cancer?

The chance that surgery or a tumour biopsy causes cancer to spread through the body is extremely low [s1]. Surgeons follow standard procedures specifically to prevent it — for example, using different instruments when tissue must be removed from more than one area [s1]. The fear that "letting air get to it" makes a cancer spread is also unfounded [s1].

Does a positive attitude affect whether you get or survive cancer?

There is no convincing scientific evidence linking a person's attitude to their risk of developing or dying from cancer [s1]. It is normal to feel sad, angry or hopeful at different times. A positive outlook may help someone stay socially connected and active, which can help with coping — but it is not a treatment, and no one should feel their mindset caused their illness [s1].

If cancer runs in my family, will I get it? If it doesn't, am I safe?

Both extremes are wrong. Only about 5 to 10 percent of cancers are caused by harmful mutations inherited from a parent; the remaining 90 to 95 percent arise from mutations that accumulate over a lifetime through ageing and exposures such as tobacco smoke and radiation [s1]. So a strong family history does not make cancer inevitable, and an empty family history does not confer safety: based on recent data, about 39 percent of men and women will be diagnosed with cancer at some point in their lives [s1].

Do antiperspirants or herbal cures matter?

The best studies so far have found no evidence linking the chemicals in antiperspirants and deodorants to breast cancer [s1]. And no herbal product has been shown to be effective at treating cancer; some can be actively harmful during chemotherapy or radiation by interfering with how those treatments work [s1].

What this means for a reader

Dismantling myths is not the same as dismissing cancer. The disease is common, but survival has improved markedly — five-year survival for breast, prostate and thyroid cancers is now 90 percent or better, and about 69 percent across all cancers combined [s1]. The productive response is to spend worry where the evidence points: not on sugar, phones or deodorant, but on the modifiable risks that genuinely matter, such as tobacco and excess body fat [s1][s3], and on getting real symptoms checked rather than talking yourself out of them. A myth that stops someone acting on a warning sign is the one that does harm.

Sources

• [s1] Common Cancer Myths and Misconceptions, National Cancer Institute, 2024-07-24
• [s2] Cell Phones and Cancer Risk, National Cancer Institute, 2024-04-04
• [s3] Obesity and Cancer, National Cancer Institute, 2025-01-28