If you’ve heard that you must cut out sugar to keep cancer from growing — or that sugar “feeds” tumors — here is the direct answer: eating sugar has not been shown to make cancer grow faster, spread, or come back, and removing sugar has not been shown to make a tumor shrink or disappear. The National Cancer Institute states it plainly: no studies have shown that eating sugar will make your cancer worse, or that stopping sugar will make it shrink. [NCI, 2024]
Does sugar feed cancer? The short answer
Cancer cells do use a lot of glucose, which is the sugar your cells run on. That single fact is where the myth comes from — but using glucose inside a cell is not the same thing as dietary sugar fueling a tumor. The link that actually matters for most people is indirect: regularly taking in a lot of added sugar can add calories and contribute to weight gain, and carrying excess body fat is tied to a higher risk of several cancers. That is a reason to watch sugary drinks and sweets, not a reason to fear an apple or to blame yourself for a diagnosis.
Why the “sugar feeds cancer” idea sounds convincing
Every cell in your body, healthy or cancerous, uses glucose for energy. Many cancer cells take up glucose quickly and burn it in a fast, inefficient way even when oxygen is available — a pattern researchers named the Warburg effect after the scientist who described it nearly a century ago. [AICR]
It is an honest observation about how some tumor cells behave, measured in laboratories. It is not a measurement of what happens in your body after you eat a cookie. Stretching a cell-biology pattern into dietary advice is where the reasoning breaks down.
Why cancer cells using more glucose doesn’t mean sugar feeds tumors
Your blood glucose stays within a fairly narrow range whether that glucose comes from candy, bread, fruit, or is built by your liver from protein and fat. You cannot selectively lower the glucose reaching a tumor by skipping dessert; if you eat less sugar, your body simply makes its own to keep blood levels steady. As Memorial Sloan Kettering oncologist Santosha Vardhana puts it, cancer “will eat anything in your body: protein, fat, even dead cancer cells,” and if you try to starve it of one fuel, it uses another. [MSK, 2025]
This also explains a common source of confusion: the PET scan. A widely used cancer scan relies on a radioactive form of glucose called FDG. Because many tumors take up glucose rapidly, they “light up” on the image, which helps doctors find and track cancer. But that brightness reflects how cancer cells behave — it is not proof that the sugar in your diet made the tumor grow. Inflammation and infection can light up on the same scan, which is why a bright spot is not automatically cancer. [StatPearls / NCBI]
Three questions people are really asking
“Does sugar feed cancer?” usually stands in for one of three different questions. Pulling them apart makes the evidence much clearer.
Does eating sugar make an existing cancer grow or spread?
Current evidence does not show that it does. There is no good human study showing that eating sugar speeds up an existing cancer, or that cutting it out slows one down. [NCI, 2024] This is the point worry tends to fix on, and it is the point the research most clearly does not support.
Does a high-sugar diet raise the risk of developing cancer?
Here there is a real link, but it is mostly indirect. The American Cancer Society notes that added sugar is not thought to directly increase cancer risk; the concern is that too much of it can lead to excess body weight. [ACS] Carrying excess body fat, in turn, is one of the better-established dietary risk factors in cancer prevention. A major evidence review from the World Cancer Research Fund and AICR found convincing evidence that greater body fatness raises the risk of cancers of the esophagus, pancreas, liver, colon and rectum, postmenopausal breast, endometrium, and kidney, with probable links to several more. [WCRF/AICR, 2018]
Sugar-sweetened drinks matter most in this pathway, because they add calories quickly without making you feel full. The takeaway is about calories and weight over time — not sugar acting as a direct carcinogen, and not a verdict that a person’s diet caused their cancer.
You may also run into claims that sugar drives cancer by spiking insulin or inflammation. There is a thread of biology here: carrying excess body fat is associated with chronic, low-grade inflammation, which the American Cancer Society links to a higher risk of some cancers. [ACS] But whether dietary sugar itself raises cancer risk through insulin or inflammation, separate from its effect on weight, is not settled in humans. It is an active research question, not a proven pathway — so it is worth understanding, but not worth treating as a reason to fear every gram of sugar.
Should a person with cancer cut out sugar?
For most people, cutting out sugar is not a proven way to fight an existing cancer, and during treatment it can do more harm than good. More on that below — but the short version is that eating enough usually matters more than eating no sugar.
“Sugar” isn’t one thing
A lot of the confusion comes from using one word for very different things. Glucose is the simple sugar circulating in your blood. Sucrose is table sugar. Added sugars are the sugars and syrups put into sodas, candy, and baked goods during processing or at the table. Total carbohydrate is a much broader category that also includes starches and fiber. And the naturally occurring sugars in whole fruit and plain dairy arrive packaged with fiber, water, protein, and nutrients.
That difference is not a technicality. Whole fruit, whole grains, and beans are tied to lower — not higher — cancer risk, and they are central to the eating pattern cancer-prevention guidelines actually recommend. [ACS Guideline] Cutting them out to “avoid sugar” removes some of the foods most associated with protection. You can read more about those foods in our guide to the foods most consistently linked to lower cancer risk. The target worth limiting is added sugars and sugary drinks — not carbohydrates as a whole.
Current US guidance points the same way. The 2025–2030 Dietary Guidelines for Americans state that no amount of added sugars is needed as part of a healthy diet and advise avoiding sugar-sweetened beverages such as sodas, fruit drinks, and energy drinks. [Dietary Guidelines, 2025–2030] Our overview of a cancer-preventing dietary pattern walks through how to put that into practice.
At a glance: common claims, what the evidence shows, and what to do.
| The claim | What the evidence shows | Practical takeaway |
| Sugar directly feeds cancer, so eating it grows tumors | Cancer cells use glucose, but no study shows that eating sugar makes an existing cancer grow [NCI, 2024] | You don’t need to eliminate sugar to slow an existing cancer. |
| Cutting out all sugar “starves” cancer | The body keeps blood glucose steady from many foods, and tumors switch fuels [MSK, 2025] | A “no-sugar” diet is not a proven cancer treatment. |
| A high-added-sugar diet raises cancer risk | Mainly indirect: added sugar and sugary drinks add calories and can promote weight gain; excess body fat is convincingly tied to many cancers [WCRF/AICR, 2018] | Limit added sugars and sugary drinks — for weight and overall health. |
| Fruit feeds cancer | Whole fruit is linked to lower, not higher, cancer risk and comes with fiber and nutrients [ACS] | Keep eating whole fruit. |
| A ketogenic diet treats cancer | Human evidence is preliminary; studied only as a possible add-on, not a replacement [Frontiers, 2025] | Don’t use keto in place of cancer treatment; ask your team first. |
Can a ketogenic or very-low-carb diet “starve” cancer?
The appeal is easy to follow: cut carbohydrates sharply, lower blood glucose and insulin, and deprive the tumor. In practice, the body defends its blood glucose and tumors adapt to other fuels, so the “starving” idea does not hold up as simply as it sounds.
The human research is still early. A 2025 review of ketogenic and fasting-style diets in gastrointestinal cancers described the evidence as preliminary, limited by small studies, differing protocols, and few randomized trials, and framed these diets as a possible addition to standard treatment rather than a substitute for it. [Frontiers in Oncology, 2025] For now, a ketogenic diet is best understood as investigational for cancer — not an established treatment, and not a reason to delay or skip surgery, chemotherapy, radiation, or other care. Very-low-carb diets are also hard to sustain and can deepen unintended weight loss during treatment, so it is worth talking with your oncology team before trying one.
If you’re in cancer treatment, eating enough comes first
For many people going through treatment, the bigger nutrition risk is not eating too much sugar — it is not eating enough. Malnutrition has been reported in 30% to 85% of people with cancer, and unintended weight loss and loss of muscle are linked to more side effects, lower tolerance of treatment, and worse outcomes. [NCI Nutrition in Cancer Care, 2024]
Cutting out food groups when appetite, taste changes, or nausea already make eating hard can make it even tougher to get the calories and protein your body needs to recover. If you are losing weight without trying, finding it hard to eat, or thinking about a restrictive diet, that is a conversation to have with your oncology team or an oncology-focused registered dietitian nutritionist, who can tailor a plan to your treatment and your symptoms. Guidance during active treatment is individual — this is not the time for a one-size-fits-all rule.
What to do instead
The practical move is not a sugar-free diet but a better overall pattern. Build meals around vegetables, fruits, whole grains, beans, and other minimally processed foods; go easy on sugar-sweetened drinks, processed meat, and ultra-processed snacks; and aim to keep a weight that is healthy for you, with regular physical activity. [ACS Guideline]
A few small changes tend to matter more than any single rule:
- Swap sugary drinks for water, unsweetened coffee or tea, or plain milk — this is where cutting added sugar pays off most.
- Keep whole fruit on the menu; it is not the problem the myth makes it out to be.
- Choose whole grains and beans over refined, heavily sweetened options when you can.
- If you have cancer or are in treatment, let your care team guide changes rather than starting a restrictive diet on your own.
For the bigger picture on lowering risk, our cancer prevention resources pull together diet, weight, activity, and screening in one place.
| Health Disclaimer: This article is for general education and is not a substitute for professional medical advice, diagnosis, or treatment. It does not replace the guidance of your oncology care team. Do not start, stop, or change any treatment, medication, or diet — including a ketogenic, fasting, or sugar-free diet — based on this article. If you have cancer, are in treatment, are losing weight without trying, or are considering a major dietary change, talk with your physician or an oncology-focused registered dietitian nutritionist first. If you have a medical emergency, call 911 or go to the nearest emergency room. |
Frequently Asked Questions
Does sugar make cancer grow faster?
No study has shown that eating sugar makes an existing cancer grow faster or spread. Cancer cells use glucose, but so do healthy cells, and your blood glucose stays steady regardless of whether you eat sweets. [NCI, 2024]
Can cutting out sugar shrink a tumor?
There is no evidence that removing sugar from your diet shrinks or eliminates a tumor. If you eat less sugar, your body makes its own glucose to keep blood levels steady, so the tumor is not “starved.” [NCI, 2024]
Does fruit feed cancer?
No. Whole fruit contains natural sugar, but it also delivers fiber, water, and protective nutrients, and it is linked to lower rather than higher cancer risk. Cancer-prevention guidelines encourage fruit, not the reverse. [ACS Guideline]
Should cancer patients avoid carbohydrates?
Not as a general rule. Cutting out carbohydrate-rich foods can make it harder to get enough calories and protein during treatment, when unintended weight loss and malnutrition are real risks. Ask your oncology team or an oncology dietitian before making major changes. [NCI, 2024]
Can a ketogenic diet starve cancer?
The human evidence is preliminary. Ketogenic diets have been studied mainly as a possible add-on to standard treatment, not a replacement, and they are not an established cancer therapy. Don’t use keto in place of oncology care, and talk with your team first. [Frontiers, 2025]
Is honey, maple syrup, or coconut sugar different?
Not in a way that matters here. Honey, maple syrup, agave, and coconut sugar are still added sugars; your body handles them much like table sugar. They are not a special cancer risk and not a cancer-fighting swap — the sensible goal is simply to keep added sugars modest.
References
- National Cancer Institute. “Common Cancer Myths and Misconceptions” (“Will eating sugar make my cancer worse?”). Updated July 24, 2024. View source
- American Cancer Society. “Sugar, Processed Foods, and Cancer Risk.” cancer.org. View source
- American Cancer Society. “ACS Guideline for Diet and Physical Activity for Cancer Prevention.” cancer.org. View source
- American Institute for Cancer Research. “The Sugar and Cancer Connection.” 2016, updated 2020. View source
- MD Anderson Cancer Center. Levy E (Senior Research Dietitian). “Does sugar cause cancer?” April 16, 2025. View source
- Memorial Sloan Kettering Cancer Center. “No Sugar, No Cancer? A Look at the Evidence” (Vardhana S, MD, PhD). April 10, 2025. View source
- World Cancer Research Fund / American Institute for Cancer Research. “Body Fatness and Weight Gain and the Risk of Cancer” (Continuous Update Project). 2018. View source
- National Cancer Institute. “Nutrition in Cancer Care (PDQ®) – Health Professional Version.” Updated September 20, 2024. View source
- Currie GM, et al. “PET Scanning.” StatPearls. NCBI Bookshelf (NBK559089). Current edition. View source
- Colombo E, et al. “Impact of ketogenic and fast-mimicking diet in gastrointestinal cancer treatment.” Frontiers in Oncology. 2025. View source
- U.S. Department of Health and Human Services and U.S. Department of Agriculture. “Dietary Guidelines for Americans, 2025–2030.” Released January 2026. View source
