This comes to mind because I was just reading a little about the effects of pesticides on plants:
Pesticide residues in plants are regulated to protect human health. They are measured when plants enter the market. However, this procedure does not consider that pesticides modulate secondary metabolism in plants when they are applied. The question arises whether it is conceivable that pesticide-induced changes in the chemical composition of plants influence human health. The examples resveratrol, flavonoids, and furanocoumarins indicate that plant phenolics may have subtle effects on physiologic processes that are relevant to human health. These effects may be beneficial, e.g., due to the inhibition of the oxidation of macromolecules and platelet aggregation or by their pharmacologic properties. Depending on concentration and specific chemical composition, however, plant phenolics may also be toxic, mutagenic, or cancerogenic. The consequences of a modulation of plant phenolics on human health are complex and cannot be predicted with certainty. It may be that the modulation of plant phenolics at the time of application and not the usually low level of pesticide residues at the time of consumption is critical for human health.
Put another way, pesticides can actually alter the nutritional properties of plants by removing environmental stress, stress which would have caused the plants to produce nutrients that may be important to humans. I hadn't considered that.