Body fat has been shown to directly cause cancer via a protein released by fat
A new Michigan State University study now offers new details showing that a certain protein released from fat in the body can cause a non-cancerous cell to turn into a cancerous one.
This indicates a direct casual relationship between body fat and cancer risk. This would seem to indicate that keeping body fat percentages in a low to normal range is important for lowering the risk of cancer. The way to keep body fat percentage within a normal range is to first track body fat percentage by the body weight scale, and to measure calories using a nutritional scale. The combination of using a body weight and nutritional scale can provide the feedback loop necessary to help a person determine their total caloric needs to meet their body fat percentage goals taking into account their activity level.
As stated in a previous post there is also a device which can be purchased (indirect calorimetry) such as the Breezing device to determine with gold standard medical precision the metabolic rate of the user. This information would allow anyone with any level of experience to know precisely how many calories they need to keep their body fat in the low normal range statistically.
The result of this study seems to indicate that BMI is medically useless. BMI doesn't determine or explain body composition which is the ratio of muscle, fat, bone, water. A body weight scale should always reveal body composition and not just weight, as weight and BMI are medically useless as there isn't any direct casual relationship that I know of between BMI or weight and cancer, or any disease. There is a direct casual relationship between having a high body fat percentage and cancer risk though. Fat around the belly or fat between the organs known as visceral fat is also known to be a risk factor for metabolic syndrome and may contribute to the development of diabetes.
Low normal body fat in my opinion for a male is 15% or less while for a female it's 20% or less, but this level has not been established by evidence based methods so the exact number representing low normal isn't certain other than to be on the low end of the normal for the typical US citizen. Note: It is not normal to find a direct casual relationship in a study like this so when we can see there is a direct casual relationship then we can actually do something about it.
References
Michigan State University. (2017, August 24). This is how belly fat could increase your cancer risk. ScienceDaily. Retrieved August 25, 2017 from www.sciencedaily.com/releases/2017/08/170824101756.htm
D Chakraborty, V Benham, B Bullard, T Kearney, H C Hsia, D Gibbon, E Y Demireva, S Y Lunt, J J Bernard. Fibroblast growth factor receptor is a mechanistic link between visceral adiposity and cancer. Oncogene, 2017; DOI: 10.1038/onc.2017.278