Starving cancer or starving the body? The hidden risk behind extreme no-sugar cancer diets

Cancer advice travels fast, especially when it promises control in a frightening situation. One of the most repeated claims today is that “sugar feeds cancer,” and that cutting sugar completely can starve tumours. Families remove rice, fruits, bread, or even all carbohydrates from a patient’s diet hoping it will slow the disease.At first, the logic appears simple. Cancer cells use glucose. So if glucose disappears, cancer should weaken too. But the human body is not that straightforward. Doctors now warn that aggressive food restriction during cancer treatment can sometimes hurt the patient more than the disease itself.Dr Mandeep Singh Malhotra, Director, Surgical Oncology & Robotic Surgery at CK Birla Hospital, New Delhi, says this belief is a “dangerous half-truth.” The science behind it exists, but the conclusion many people draw from it is misleading. Cancer nutrition, experts say, is not about starving the body. It is about helping the body survive treatment, protect immunity, and maintain strength.Everyday household items that collect the most bacteriaThe idea that sugar and cancer are connected did not come out of nowhere. In 1924, German scientist Otto Warburg discovered that cancer cells consume glucose at unusually high rates, even when oxygen is available. This became known as the Warburg Effect.Modern cancer scans still rely on this principle. PET-CT scans use a radioactive form of glucose because tumours absorb it faster than surrounding tissue. That is why cancerous areas often “light up” during imaging.Government-backed research from the US National Cancer Institute also discusses how cancer cells alter the way they use glucose and energy.But here is the detail many social media posts leave out: cancer cells are not the only cells that need glucose.The brain depends heavily on it. So do red blood cells, the immune system, muscles, and the heart. When carbohydrates disappear completely from the diet, the body does not simply stop making glucose. Instead, it enters survival mode. When the body does not receive enough carbohydrates, it begins producing glucose on its own through a process called gluconeogenesis. To do this, it breaks down muscle and protein reserves.That means the tumour may still receive fuel, but the patient loses strength.This becomes especially dangerous because cancer itself already pushes the body toward muscle loss. Tumours release inflammatory substances that reduce appetite and accelerate tissue breakdown. Doctors call this condition cancer cachexia.According to the US National Library of Medicine, cachexia is linked to severe weight loss, fatigue, and declining muscle mass in cancer patients, particularly in advanced disease.The consequences are serious. Weak patients often struggle to tolerate chemotherapy, surgery, radiation, or immunotherapy. White blood cell counts may fall. Recovery becomes slower. In some cases, treatment cycles must be delayed altogether.The painful irony is that in trying to “starve” the cancer, some patients unknowingly weaken the very body that needs to fight it.Doctors are not saying unlimited sugar is harmless. Refined sugar and ultra-processed foods are still unhealthy, especially during illness. The real goal is balance, not elimination.Foods that cause sudden spikes in blood sugar, soft drinks, candies, pastries, refined flour products, and heavily processed snacks, offer little nutritional value. These foods can worsen inflammation, energy crashes, and poor metabolic health.Instead, experts recommend foods that release energy slowly. These include:This approach is often called a low-glycaemic diet. It helps maintain steadier blood sugar levels while keeping the body nourished.Cancer care specialists repeatedly emphasise one point: treatment works better in a body that is adequately nourished. Fasting has become another popular topic in cancer discussions. Some early animal studies suggest intermittent fasting may influence how cancer cells respond to treatment. Researchers are still exploring whether short fasting periods could reduce side effects or improve treatment response in certain settings.However, there is not enough strong human evidence yet to recommend fasting as a standard cancer therapy.For patients already losing weight, prolonged fasting can worsen weakness, delay healing, and reduce immunity. That is why oncologists strongly advise against experimenting with extreme diets without medical supervision.In the end, cancer nutrition is less about punishment and more about preservation. The body needs strength to endure treatment, rebuild tissue, and support immunity. Food is not the enemy. Poor nutrition is.Medical experts consultedThis article includes expert inputs shared with TOI Health by:Dr Mandeep Singh Malhotra, Director, Surgical Oncology & Robotic Surgery, CK Birla Hospital, New Delhi | Chief Mentor, Art of Healing Cancer | Molecular Oncologist (RGCC, Greece).Inputs were used to explain how the belief that “sugar feeds cancer” can sometimes do more harm than good, and why blindly cutting carbohydrates without medical guidance may weaken the patient instead of helping fight the disease.