Monday, November 12, 2007

Scientists should not believe in the stork

white storks
High insulin, high body fat and high cancer risk are sometimes found together but this link may be of a similar type as in storks and babies.

Trying to "prove" that body fat causes cancer, some scientists have claimed that this is due to substances produced by body fat cells, but the first of the mentioned substances happens to prevent and not to cause cancer.

The authors of the food and cancer report list other examples to prove a cause. Are they more convincing? Let's have a look at insulin, another key witness of the fat cancer prosecutors. They write:

"Obesity influences the levels of a number of hormones and growth factors. Insulin-like growth factor 1 (IGF-1), insulin, and leptin are all elevated in obese people, and can promote the growth of cancer cells."
Insulin is produced by pancreas islet cells and not by body fat cells. Babies come from human mothers and not from storks. Both body fat cells and insulin are abundant in some human organisms, and both storks and babies are abundant in some countries. This looks like a perfect analogue but we still have to consider the possibility that body fat cells, by some substances, trigger the pancreas cells to produce more insulin. Such a mechanism is a mere speculation, and recent research suggests that both high insulin and high body fat are guided by the same genetic causes and are independent of each other, just like storks and babies.

Why lab values may be misleading

Far from being a proven cause, the link between body fat and cancer is not even a direct one. At best, body fat may be linked to some lab values such as insulin level and this lab values in turn may be linked to the cancer risk. If the links to the lab values are not very clear and strong, we have a cascade of weak effects, resulting in an overall effect that is no longer detectable: Here is a case where biomarkers failed to predict stroke.

The Mrs Jones Trick

Those who have read my earlier post about snake oil tricks may wonder if this is such a case. You will need some fantasy but then you may see it: The snake oil peddler (body fat cancer researcher) claims that snake oil (body fat) helps to fight pain (makes cancer grow). He presents Mrs Jones who has applied snake oil and lost her pain (a correlation between fat and cancer) and says this is the prove that snake oil works (body fat causes cancer). When asked how this may work, the peddler (researcher) tells people that genuine Chinese snake oil (body fat) contains (enhances) poly unsaturated fatty acids (cell hormones, insulin) that promote healing (cancer).

I may not be finished with the food and cancer report yet, but it's high time now to deal with other health issues. I'll feel free to come back later with more points and a final conclusion.

Photo credit: flickr.com/photos/yeliseev/646936102/

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