There is a growing belief that “sugar feeds cancer.” Because of this, many patients and their families conclude that eliminating sugar and carbohydrates entirely can starve cancer cells and help defeat
the disease.
Dr Mandeep Singh Malhotra, Director, Surgical Oncology & Robotic Surgery, CK Birla Hospital, New Delhi | Chief Mentor, Art of Healing Cancer | Molecular Oncologist (RGCC, Greece), feels this is a dangerous half-truth. While the underlying science is not entirely wrong, the conclusion many people draw from it is and it may end up harming patients rather than helping them.
The Science Behind the Claim
In 1924, German biochemist Otto Warburg observed that cancer cells consume significantly more glucose than normal cells, even in the presence of adequate oxygen. This phenomenon, now known as the Warburg Effect, has been validated in numerous subsequent studies. It is also the principle that makes PET-CT scans possible, cancer cells absorb a radioactive glucose analogue far more aggressively than normal tissue, causing tumours to “light up” on scans.
However, Dr Malhotra explains that an important distinction is often lost in public discourse: the fact that cancer cells consume more glucose does not mean cancer can be starved simply by removing sugar from the diet.
Why ‘Starving Cancer’ Can Backfire
Glucose is not optional fuel for the human body. The brain, heart, red blood cells, and immune system all depend on it for basic functioning. When a person completely stops consuming carbohydrates, the body does not simply run out of glucose. Instead, it begins manufacturing glucose on its own by breaking down muscle and protein through a process called gluconeogenesis.
“The cancer cells still receive their fuel,” says Dr Malhotra. “The patient, meanwhile, grows weaker by the day.”
To make matters worse, cancer itself actively works against the body’s nutritional reserves. Tumours release pro-inflammatory cytokines and other mediators that suppress appetite and accelerate muscle breakdown. This is not merely a side effect, it is a hallmark of advanced cancer. The resulting condition, known as cancer cachexia, causes rapid loss of body weight and muscle mass, often regardless of how much the patient eats. Studies estimate that cachexia contributes directly to nearly one-third of all cancer-related deaths.
Dr Malhotra warns that when patients who are already vulnerable to cachexia voluntarily restrict carbohydrates and calories, the consequences can be devastating. Protein levels and white blood cell counts can fall sharply, leaving the body unable to tolerate chemotherapy, surgery, or radiation. Even newer treatments like immunotherapy, which rely on a functioning immune system, may become less effective in a malnourished body.
“In some cases, doctors are forced to delay or discontinue treatment cycles altogether,” he explains.
The irony, he says, is deeply concerning. In trying to starve cancer, patients may weaken their own bodies so severely that they are unable to continue the very treatments that could help save them.
What Should Cancer Patients Actually Eat?
Dr Malhotra emphasises that the answer is not unrestricted sugar consumption, but intelligent and balanced nutrition that supports the body while avoiding unnecessary blood sugar spikes.
The key principle is to avoid foods that cause sudden surges in blood glucose. Refined sugar, sweets, sugary beverages, maida (refined flour), and highly processed foods provide what are essentially empty calories. These foods contribute little to healthy body function while creating conditions cancer cells can exploit more easily.
Instead, nutrition should focus on low-glycaemic-index foods such as whole grains, pulses, vegetables, healthy fats, and adequate protein. A low-glycaemic diet helps maintain stable blood sugar levels, enough for normal cells and the immune system to function properly without creating repeated glucose spikes.
A Word on Fasting
Some animal studies have suggested possible benefits of intermittent fasting during cancer treatment, and researchers continue to study this area closely. However, Dr Mandeep Singh Malhotra points out that there is still insufficient evidence in humans to recommend fasting as a routine part of cancer care.
For patients who are already losing weight or struggling with nutritional deficiencies, prolonged fasting may do more harm than good. “Fasting during cancer treatment should never be undertaken without medical supervision,” he advises.
According to Dr Malhotra, the goal of cancer nutrition is not to starve the patient in an attempt to fight the disease. The priority should instead be to keep the body nourished, resilient, and strong enough to tolerate treatment and maintain immune function.
Muscle mass, he explains, is closely linked to immunity, making proper nutrition an essential part of cancer care itself.
“What is needed is a reduction in refined sugar and high-glycaemic-index foods, not a declaration of war against every carbohydrate,” says Dr Malhotra. “Avoid junk food and processed sugar, but continue eating balanced meals with sufficient protein and calories. Keep the body stable and strong, not weak.”
After all, one cannot win the battle against disease by weakening the body.
