The view that sugar causes cancer is prevalent in the popular press and on the internet.
A number of doctors and naturopaths hold this view. Since starches are digested as simple sugars then it is recommended that starches should also be avoided.
As a result, a low-carbohydrate diet is endorsed. Some ketogenic diets recommend high levels of vegetables which are high in nutrients but low in the amount of energy that is provided. The absence of starch from these diets results in a calorie restricted diet which is possibly ketogenic. If a diet is restricted in carbohydrates, it will be high in fat and protein.
Ketosis occurs when fat in the body is utilised to obtain energy in the absence of glucose. Glucose is obtained from the digestion of carbohydrates. Ketosis results in the production of ketones which includes acetone. Blood acidity rises with an increase in ketones.
Serious complications with a ketogenic diet have been reported, even when performed under medical supervision.  These issues relate to the high levels of protein and include headaches, nausea, lack of appetite, acidosis and hypoproteinemia. High levels of fat – any fat – has a negative impact on the endothelial cells of blood vessels and reduces the ability of the cells to produce nitric oxide.
Otto Warburg was awarded the Nobel Prize in Physiology or Medicine 1931 and nominated for the second time in 1944. He suggested that cancer growth was caused by “the replacement of the respiration of oxygen in normal body cells by a fermentation of sugar.” 
This talk appears to be one of the sources of the hypothesis that limiting carbohydrates is beneficial in treating cancers. Cancer cells do uptake glucose at a higher rate than normal cells but this does not imply that reducing carbohydrates is beneficial. Ketogenic diets cause acidosis which Warburg implicated as being conducive to cancer. Warburg was very particular in what he ate and advocated an organic, vegan diet – not a ketogenic diet.
Epidemiological studies comparing diet and rates of cancers have failed to show a link between carbohydrate intake and the rate of common IGF-1 related cancers such as breast, prostate, colon and rectal cancers.
Ken Carroll of University of Western Ontario (Canada) studied that components of the diet and the incidence of cancers in more than 30 countries.   These studies showed a strong correlation with the prevalence of a number of cancers (breast, prostate, intestinal, leukeamia, rectal and pancreatic cancers), and the amount of fat in the diet. High levels of fat are frequently associated with high level of animal sourced foods.
Similarly, the China-Cornell-Oxford Project studied 65 counties in China. This showed a positive correlation between the amount of animal source foods and the levels of breast, prostate, colon and rectal cancers. The consumption of animal source foods and prevalence of these cancers is much less than in the USA.
Consumption of carbohydrates was negatively associated with the incidence of the above cancers.
A distinction must be made between added sugars consumed in isolation and carbohydrates that are consumed as part of a whole-food diet. Adding table sugar (sucrose) which is obtained from sugar cane and sugar beets to our diets is not beneficial to our health. High fructose corn syrup is another added sugar commonly found in processed food that has detrimental health benefits.
Cancer cells consume more glucose than normal cells but this does not imply that removing all sugars and carbohydrates from your diet will benefit cancer outcomes.
A study  published in 2012 investigated the effects of different types of sugars in the diet and their effect on cancer. This study investigated the association of total sugars, sucrose, fructose, added sugars, added sucrose and added fructose in the diet with the risk of 24 malignancies.
435,674 participants aged 50-71 years were followed for 7 years. These sugars were not associated with an increased risk of colorectal, breast, prostate, pancreatic or endometrial cancers or with other IGF-1 related cancers. Insulin-like growth factor-1 (IGF-1) is a hormone that promotes the growth of tissues including cancer cells.
All sugars studied were inversely associated with risk of ovarian cancer – the more sugar consumed then the risk of ovarian cancer was reduced.
There was an increased risk with some relatively rare cancers such as esophageal adenocarcinoma, pleural cancer and small intestinal cancers which the researchers suggested the “possibility of chance results”.
- Ballaban-Gil, K. et al. (1998) Complications of the Ketogenic Diet. Epilepsia. 39 (7), 744–748.
- Warburg, O. (1966) Prime Cause and Prevention of Cancer.
- Carroll, K. K. (1975) Experimental Evidence of Dietary Factors and Hormone-dependent Cancers Experimental Evidence of Dietary Factors and Hormone-dependent. Cancer Research. 353374–3383.
- Carroll, K. et al. (1986) Fat and Cancer. Cancer. 581818–1825.
- Tasevska, N. et al. (2012) Sugars in diet and risk of cancer in the NIH-AARP Diet and Health Study. International Journal of Cancer. 130 (1), 159–169.