Cancer controversy: Fruit and Fructose

‘’What about fruit?’’, people ask, ‘’Isn’t fruit good for you?’’. In some moderation, with a healthy metabolism and short term locally in season fruits perhaps! On keto, a small number of blackberries with some yoghurt, might be an appropriate morning snack. See, there are a number of things you must know about fruit.
It contains fructose. It is what makes fruit so sweet tasting and attractive. However, fructose is no ordinary sugar. Fructolysis (fructose metabolism), only occurs in the liver, where it follows an almost identical process as does alcohol.^{(6.38, 6.39)}
The effect of fructose metabolism in the liver is that much gets converted into fats and fatty acid metabolism is paused. This is the reason why eating fructose – either from fruit, fruit juices or fructose added to other foods – is a significant contributor implicated in non-alcoholic fatty liver disease! To put it simply, consuming fructose is almost as bad as consuming alcohol.^{(eg 6.38, 6.39, 6.41, 6.42)}
However, another effect of fructolysis is that it stimulates the liver in creating more glucose (gluconeogenesis) and fat (de novo lipogenesis) from available building blocks and metabolic precursors.^{(6.41, 6.42)} While fructose consumption (like alcohol) stimulates the creation of triglycerides (ie fatty lipids), it impedes fatty acid metabolism.^(6.38) The increase in plasma glucose levels and the breaks being put on fatty acid metabolism puts an immediate halt on your nutritional ketosis!
Consuming fructose therefore contributes to increased levels of insulin and is implicated in insulin resistance and metabolic disease – both very closely linked as causal or significant contributing factors to cancer!^{(eg 6.38, 6.39, 5.1, 5.3)} As far as colorectal cancer is concerned, it comes therefore as no real surprise that fructose consumption stimulates cancer growth and metastasis.^{(eg 6.44, 6.45, 6.48, 6.49)}
Studies have shown that fructose promotes the production of new blood vessels (angiogenesis), which is highly prolific in tumours, as cancer cells need constant feeding of nutrients. It does this by upregulating vascular endothelial growth factors and cell function (VEGF). This is a tough target and many KRAS/colorectal cancers are insensitive to attempts to block this pathway.^{(6.44, 6.48)}
Fructose metabolism has also been shown to drive the metabolic reprogramming of colon cancer liver metastasis.(6.45) Perhaps just as important is that not only does fructose promote cancer proliferation, but it drives chemo-resistance. It therefore causes a significant reduction in your treatment efficacy, rescuing the tumour cells and helping cancer survive.^(6.49)

So, do I think fruit juice fasting or having a heavy fruit based diet is wise for those with cancer? No! Besides, there is not anything in fruit you actually need and cannot get from better more nutritious sources. If you have cancer, are diabetic, overweight, somewhat insulin resistant, any blood sugar sensitivity, have cardiovascular disease or simply wish to maintain a state of nutritional ketosis, you should avoid fructose and therefore fruit!

* ^{reference details can be found in the book}