Cancer Myth in the News: Sugar Feeds Cancer Claims

The claim, in one line

The claim is that sugar feeds cancer, so cutting sugar starves it. It travels well because it starts from something true and ends somewhere false.

Here is the true part. Cancer cells do consume more sugar, or glucose, than normal cells. That difference is real enough that medicine uses it. A PET scan works by injecting a small amount of radioactive glucose and photographing where the body takes it up, because cancer cells often take up more.

Here is the false part. The National Cancer Institute states that no studies have shown that eating sugar makes cancer worse, or that stopping sugar makes a cancer shrink or disappear.

Why the leap does not hold

Every cell in your body runs on glucose, including brain cells, muscle cells, and immune cells. The body keeps blood glucose in a narrow range using insulin and other hormones. It does not let that level drop because a person skipped dessert. A tumor does not get its own supply line that you can cut from the kitchen.

Cutting all sugar during cancer treatment can cause real problems in the other direction. Weight loss during treatment is a known risk, not a goal.

The real link runs through body weight

There is a genuine connection between diet and cancer, and it is worth stating precisely, because it is stronger than the myth it replaces.

NCI notes that a high-sugar diet may contribute to weight gain, and that obesity is linked to higher risk of several cancers. Compared with people at a healthy weight, people with overweight or obesity are at greater risk for at least 13 types of cancer.

The size of the effect varies by cancer type. NCI describes increases ranging from about 10 percent to a doubling of risk.

The mechanisms are known in outline:

• Fat tissue makes extra estrogen, which is linked to higher risk of breast, endometrial, and ovarian cancers.
• Obesity often raises blood insulin and insulin-like growth factor 1. High levels are linked to colorectal, thyroid, breast, prostate, ovarian, and endometrial cancers.
• Insulin resistance comes before type 2 diabetes, which is itself a known cancer risk factor.
• Chronic inflammation promotes tumor growth.
• Fat cells release hormones called adipokines. Leptin rises with body fat and can push cells to divide abnormally.

So sugar is not irrelevant. It just acts through weight and metabolism over years, not through feeding a tumor this week. Our page on obesity and cancer risk covers the full list, and diet and cancer risk covers the rest of the food question.

The cancer where this link is clearest

Endometrial cancer, which forms in the lining of the uterus, shows the pattern most sharply. NCI lists obesity and metabolic syndrome as risk factors for it. Taking tamoxifen for breast cancer, or taking estrogen without progesterone, also raises risk.

This is the cancer to know the warning sign for, because it usually announces itself early.

When to get checked

There is no routine screening test for endometrial cancer in average-risk women. Symptoms do the work instead. NCI names unusual vaginal bleeding and pelvic pain as the signs.

Call a clinician for:

• Any vaginal bleeding after menopause, even one spot, even once
• Bleeding between periods, or periods that become much heavier or longer
• Vaginal discharge that is watery or blood-tinged, without a clear cause
• Pelvic pain or pressure that does not settle
• A mass you can feel in the pelvis

Bleeding after menopause is the one to act on fastest. It is not always cancer, but it always earns an examination.

What the workup looks like

A Pap test does not find this cancer, because it starts inside the uterus. Tissue has to be sampled directly. NCI lists three ways:

• Endometrial biopsy. A thin flexible tube passes through the cervix and gently scrapes a small tissue sample.
• Dilatation and curettage, or D&C. The cervix is widened and a spoon-shaped curette removes tissue.
• Hysteroscopy. A thin lighted tube looks inside the uterus and can take samples.

A pathologist reads the tissue. Staging usually follows surgery, because a hysterectomy, the operation that removes the uterus, is normally part of treatment. Tissue from around the uterus is checked for spread.

Treatment and the survival picture

NCI lists five standard treatments for endometrial cancer: surgery, radiation therapy, chemotherapy, hormone therapy, and targeted therapy. Which ones apply depends on stage, grade, and tumor features.

The SEER figures below describe a large group of women. They do not describe any one woman's future.

Five-year relative survival for uterine cancer is 80.9 percent for cases from 2016 to 2022. When the cancer is still confined to the uterus it is 94.9 percent. Once it reaches nearby lymph nodes it is 70.1 percent. Once it has spread to distant sites it is 19.9 percent. About 67 percent are found at that first stage, and the median age at diagnosis is 64.

That gap between 94.9 and 19.9 is what the bleeding symptom is protecting. It is a better use of attention than counting grams of sugar.

Sources

• NCI, Common Cancer Myths and Misconceptions — https://www.cancer.gov/about-cancer/causes-prevention/risk/myths
• NCI, Obesity and Cancer — https://www.cancer.gov/about-cancer/causes-prevention/risk/obesity/obesity-fact-sheet
• NCI Dictionary of Cancer Terms, PET scan — https://webapis.cancer.gov/glossary/v1/Terms/Cancer.gov/Patient/en/pet-scan
• NCI PDQ, Endometrial Cancer Treatment (Patient Version) — https://www.cancer.gov/types/uterine/patient/endometrial-treatment-pdq
• SEER Cancer Stat Facts, Uterine Cancer — https://seer.cancer.gov/statfacts/html/corp.html