I have hypothesized that both sides are right in this debate – 5 or more servings of fruit and vegetables a day can reduce the likelihood of getting cancer, but the effect is net small and variable. Consequently about a third of studies flat out miss the effect.
- The effect is a net effect – a net effect of a number of influential compounds, each of which has a net effect. Some compounds (and not just the obvious – man-made pesticides) in fruits and vegetables increase the odds of getting cancer, while others decrease the odds. Most compounds both increase the odds and decrease the odds and in different ways, affecting the likelihood of some combination of the initiation, promotion, and propagation of cancer, as well as their effects on many complex immune responses.
- All of the effects are net and all are highly variable – thus the disagreements in the scientific literature.
- Different fruits and vegetables contain widely different amounts and different chemical forms of the influential compounds, and they vary with growing conditions, and for the same concentrations, they may have different biological activities.