Does sugar feed cancer? Sugar, in the form of glucose, is used by all cells as the body’s primary source of fuel. It is like the gas/petrol in a car. It powers our movements, thoughts, and more or less everything that we do. If sugar is so vital, how can it feed cancer?

The majority of carbohydrates in our diet contain glucose. Glucose is easily absorbed in the body, and once absorbed into the blood stream, it is either used immediately to make energy – especially in brain cells – or it is converted into glycogen and stored. 

A door with a lock and key

For glucose to get from the blood into the cells, it needs the help of insulin. Insulin, a hormone produced in the pancreas, moves glucose into the cells of your body for fuel, or into the liver to be stored as glycogen. To understand how insulin and glucose work together, it can be helpful  to think of a door with a lock and key. The lock/key hole represent the insulin receptors on the membrane of cells, and the key to the door of the cell is insulin. Take a look at the diagram above. 

When blood glucose levels rise after eating, the pancreas secretes insulin. The insulin binds (attaches) to the insulin receptors on the surface of cells (i.e., the key fits into the specific lock) and the door opens into the cell. This allows glucose to enter the cell and be utilized as fuel. When the glucose has entered cells, the blood glucose level drops. At the same time, the pancreas stops secreting insulin and the ‘doors’ into the cell are ‘locked’ again.

When we eat a diet with minimal refined sugars, exercise regularly, and have sufficient vitamins and minerals, we can properly maintain our blood sugar levels.  

The lock gets stuck

However, if our diet is high in sugars and refined carbohydrates, or we aren’t sleeping well, aren’t exercising, are skipping meals, and are under stress, our blood glucose levels can become elevated. The body deals with this situation by increasing its production of insulin. The extra insulin transports the glucose into cells for storage and energy. However, over time, cells can lose their ability to take in more glucose and become insulin resistant.

This means that, essentially, the insulin stops working as the key to the cell; it is as if there is chewing gum in the lock (insulin receptors) and the key (insulin) won’t work, preventing glucose getting into the cells. Both insulin and glucose are left to circulate in the blood stream, and an unhealthy cycle begins… As the cells become deprived of glucose, they develop a strong need for it, but because the insulin has stopped working to open the cell, the glucose is unable to get into the cells to provide fuel. To try and resolve the situation, the pancreas pumps out more insulin – which still doesn’t work. This is called insulin resistance. This process also happens to some extent as we age because our cells become less responsive to insulin.

Insulin resistance and cancer

It is this insulin resistance that can be seen to feed cancer – not the sugar per se. Most cancer cells have a huge requirement for glucose because they have an inefficient metabolism. They also require rapid growth, and have higher energy needs for survival. Because of this, there are many, many more insulin receptors on cancer cell membranes than on other cell membranes.  Even if some of these receptors become resistant to insulin, there will always be some that are functional because there are so many of them.

This means that when healthy cells become insulin resistant, insulin can still bind to the cancer cells and deliver glucose (fuel) into the cancer cell. Consider the scenario where an insulin resistant cancer patient has excess glucose as a result of their diet. Glucose in the blood is unable to get into the normal cell, due to the insulin resistance. As described above, blood glucose levels rise and more insulin is produced – and this is just what the cancer cells want. They still have active insulin receptors – so the insulin binds to the receptors on the cancer cells. This opens the door to let the glucose in, and provide fuel for the cancer cell.

Other consequences of insulin resistance

To make matters worse, when insulin binds to its receptors, other pathways are activated. One such pathway is Insulin-like growth factor-1 (IGF-1). These growth factors send messages to the cancer cell to grow and divide. Some cancers rely almost exclusively on IGF-1 and insulin to stimulate their growth.

Excess insulin also increases production of Arachidonic acid (AA), which is the building block for inflammatory mediators in the body. AA has been shown to also increase production of IL-6 (interleukin-6) which is another inflammatory chemical. Thus chronic excess insulin leads to chronic, sustained inflammation.

Because insulin resistance can be such a strong driver of cancer, it is really important to reverse it. This is one of the reasons we recommend eliminating dietary refined sugar and simple carbohydrates from your diet. Removing these insulin triggers will lower blood insulin and IGF-1 levels. Regular exercise also helps with this.

What about fruit?

Fruit is also high in sugar, but we don’t need to remove fruit from our diet in order to improve insulin resistance. This is because fruit also contains vitamins, minerals,  fiber, and phytonutrients which are important antioxidants and anti-inflammatory molecules. Also, active compounds in fruits can enhance the activity of DNA repair and tumor suppressor genes. This “package” of nutrients slows the release of the sugar and leads to less damaging effects than refined carbohydrates. It is still a good idea to focus on lower sugar fruits however, such as berries, because eating too many high sugar fruits, might increase our desire for more and more increasingly sweet foods. 


It is important to break the cycle of constant insulin secretion to reduce the risk of many chronic illnesses, including cancer. It is possible. Review our previous posts on whether to measure and how to measure blood glucose levels and also the post about the study on sugar and cancer. Figuring out what causes high blood glucose levels for you is a great place to start. We’ll talk more about other strategies next week.

So, as we’ve seen – yes,  sugar is important – but it is really insulin resistance that is at the heart of the matter. Measuring our blood insulin levels would be a lot more useful than just glucose levels. Indeed, some researchers and doctors say that insulin is what we should focus on, not blood glucose levels. But until there are accessible blood insulin tests, our best approach is to track our blood glucose levels. 

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