Breast cancer as a young woman and mother.

Sugar and breast cancer.

The link between sugar and breast cancer.

Does sugar cause breast cancer? Should you stop eating sugar if you have or had breast cancer? This is one of the biggest question marks hanging over patients and survivors of the disease. 

The general advice at the moment is that there is no proven link between sugar and breast cancer. However, the research is mixed and ongoing. In recent years a number of important population studies conducted worldwide have shown a worrying correlation between high sugar consumption and breast cancer. This includes the risk of getting it in the first place, and of disease related death. 

This is something we as patients and survivors simply don’t have the luxury of ignoring. So let’s take a closer look.

What is sugar?

To clarify, when we are looking at the link between sugar and breast cancer we are talking about refined sugar such as that found in biscuits, cakes, cereals, soft drinks, ready made meals etc. Refined means that the sugar has been processed from its natural form so that it is more easily packaged and added to foods and beverages. 

Does sugar feed breast cancer?

When I was diagnosed with triple negative breast cancer, the one piece of advice my oncologist gave me was to cut right back on sugar whilst having treatment. He is pretty old school, and mentioned nothing else about diet or exercise, so it surprised me. I assumed that sugar must feed cancer cells, thus helping them grow.

While this is true to an extent, the full story is a more complicated. 

You see, ALL of our human cells need sugar to survive. Cancer cells do however use about 200 X the amount of glucose as normal cells. (This is why radioactive glucose is injected before pet scans, in case you were wondering about that!) So of course, if you are eating a lot of refined sugar, you are essentially offering the cancer an “all you can eat glucose buffet” which will help it grow. 

BUT even if we cut sugar out of our diets completely they will still find another energy source. Our body will convert other nutrients, such as carbohydrates, down into glucose in order to feed our cells. In order to starve cancer cells we would have to starve ourselves in the process. 

So the statement that sugar feeds cancer is glossing over the fact that there are other more significant factors involved.

Insulin and breast cancer. 

Excess sugar in the blood can affect insulin levels. The pancreas’s job is to release insulin to carry glucose (sugar) from our blood into our cells. The more sugar in the blood, the more insulin is released.                      

Victoria Seewaldt MD, studies cancer prevention at a cancer research centre in LA. She has found that insulin helps stimulate a number of biological changes in the body that are known to cause breast cancer. 

A quote from her research study states that “insulin is a potent hormone that activates many pathways that drive aggressive breast cancer biology.” For this reason she advises her patients to reduce sugar and carbohydrate consumption, much as my own oncologist did.

A different study states that “the association between insulin and cancer is based on the strong anabolic effect of hyperinsulinemia that leads to proliferative tissue abnormalities, stimulation of DNA synthesis and cell proliferation.” 

Simplified, high levels of insulin caused by too much sugar (as seen in type 2 diabetes mellitus) affect us on a cellular level that can cause cancer. 

Obesity and breast cancer. 

Too much sugar in a persons diet also contributes to obesity. It has been proven time and again that increased body mass index (BMI) or obesity, is a big risk factor for 13 types of cancer, including breast. 

The American cancer society states that women with more fat tissue have a higher chance of getting breast cancer. First there is the correlation between obesity and type 2 diabetes mellitus, which takes us back to the previous point about insulin. As well as that, fat cells produce the hormone estrogen, which makes hormone receptor positive cancers grow.

Of course it is more complex than this. The location of the excess fat is a factor. If it is around the belly it is a higher risk factor for breast cancer than if it is around the hips and thighs. Also the risk appears to be more prevalent in women that gained weight as an adult, specifically after menopause. And it is unclear whether or not losing weight then reduces the risk. More research is needed to properly explore the topic.

Recent data also suggests that obesity causes inflammation within the breast and elsewhere in the body. This contributes to the development, progression and metastasis of breast cancer. 


Although there are still some questions to be answered, the research is indisputable. There IS a link between risk of breast cancer and sugar intake. I was disappointed too, but it is not as simple as I first thought. 

It is not the sugar itself that increases our risk of breast cancer and recurrence. All of our cells need glucose (sugar) to live off, not just cancer cells. So the solution is not to cut it out completely.

The danger comes when our consumption of sugar is excessive to the point of causing health problems such as type 2 diabetes mellitus and obesity. These factors can wreak havoc in our bodies and create the perfect environment for breast cancer to grow. 

The solution.

The solution is simple, a healthy well balanced diet. The American Institute for cancer research has highlighted that breast cancer survivors who eat a diet high in vegetables and low in fruit juice and carbohydrates (i.e. sugar) have a lower risk of dying after treatment has ended. 

This article from breast cancer UK explains in more detail the ideal diet to reduce your risk of breast cancer by contributing to your overall health.

If you are already overweight, exercise will reduce your risk of recurrence two fold. By reducing your cancer risk in and of itself, and by reducing your BMI.  

As always, moderation is key. So enjoy that slice of cake, and the occasional biscuit, but don’t over do it. 

I hope that this has helped clarify the situation as it stands between breast cancer and sugar. Researching it has definitely answered a lot of my own questions.

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