"But sugar feeds cancer cells!"
I've lost count of the amount of times I've seen this. It's based on research that has since been totally discredited but, like the anti vaxxers and their discredited sources, it just keeps getting used.
No. Glucose feeds cells. ALL cells. That means that sugars, starches and fats, all of which are broken down by the gut into glucose, feed the cells. Yes, that includes cancer cells, but increasing or decreasing the intake of refined sugar has been shown to have no effect on the growth of existing cancer cells.
It has also been shown that being on a ketogenic diet (less than 20 grams carbohydrate per day) can be harmful to people going through chemotherapy or radiation as at these times the body needs more energy and the ketogenic diet, with its reliance on fat as an energy source, can result in unintentional weight loss, autoimmune problems and lethargy.
Sugar is not the enemy. Too much sugar, yes, that is bad for you, whether you have cancer or not. A high intake of simple carbs such as refined sugar messes with insulin levels, causing the well-known sugar rush followed by the sugar crash. Excess carb intake can also lead to obesity which does have a corresponding increase in risk of cancer, although the researchers have yet to find out the exact correlation - if indeed there is one correlation and not many contributing factors.
As for the Paleo claims that we have not had simple carbs until recently in our evolutionary history, there is clear evidence of this in prehistory, and in the remaining paleo tribes today, in the form of tree saps, honey, use of sugar cane and similar plants, even the collection of sugar ants in native America. It may not have been so prevalent, but it has always been there.
So, does sugar feed cancer? Yes, in as much as it feeds all cells, no in that it makes no differentiation between cancerous and normal cells. Is sugar poison? No. Arsenic is a poison, cyanide is a poison, hemlock and deadly nightshade are poisons. Sugar is a simple carbohydrate that like any food should be taken in moderation. That is all.
https://www.oncologynutrition.org/erfc/healthy-nutrition-now/sugar-and-cancer/
http://www.mayoclinic.org/diseases-conditions/cancer/in-depth/cancer-causes/art-20044714?pg=2
http://www.cancercenter.com/discussions/blog/does-sugar-feed-cancer/
