Dear Dr. Blonz: There is a periodic argument in my circle that our vitamin- and mineral-depleted soil has been worn out from overfarming and the use of chemical fertilizers, resulting in a lesser ability for nutrients to get into plants and the foods we eat. Are the whole foods we eat today providing the same level of nutrition they used to? Are we slowly starving ourselves, and this is the rationale for why we need supplements? I know it sounds suspiciously like a sales pitch, but what about it?

— S.S., Jacksonville, Florida

Dear S.S.: Plants are genetically programmed to require a specific set of nutrients to enable their growth and reproduction. If these are not in the soil — or added as fertilizer — the plant won’t grow and reproduce, or it will look sickly (off-color, wrong size, etc.), just like humans don’t look well when malnourished. The “vitamin-depleted” element also must be buried, as plants do not get their vitamins from the soil. Rather, vitamins, along with all beneficial plant phytochemicals, are synthesized in the plant. The amount of a particular vitamin found in a fruit, vegetable or grain is determined by the plant’s genes and environmental factors, not by the amount of that substance in the soil. After harvest, vitamin content can decline with time; some are also affected by cooking.

I remain a supporter of organic agriculture and programs such as integrated pest management (IPM). I buy locally and shop at farmers’ markets to support local agriculture whenever possible. It also allows me to buy foods that are as fresh as possible. We should all do what we can to encourage farmers to be good stewards of the soil and our environment. And, while I support all forms of sustainable farming, eating conventionally grown produce is better than limiting your intake of fruits and vegetables and counting on supplements to fill the gap.

Dear Dr. Blonz: I read your articles with great interest. My question is: It is my understanding that foods of animal origin have no fiber. How could your body form stool if you ate only animal foods and no plant foods? And if you did, where would it come from?

— K.M., Dover, Delaware

Dear K.M.: “Fiber” doesn’t refer to one substance. Rather, it stands for a variety of indigestible materials that are found in plant foods. That makes you correct in your statement that animal foods have no fiber. It doesn’t follow, however, that foods containing no fiber are 100% digestible. The stool would consist of whatever cannot be broken down or absorbed, the sloughed-off cells from the lining of the digestive system that get replaced every three to five days, and any secreted and un-reabsorbed digestive fluids.

Kensington resident Ed Blonz has a PhD in nutrition from UC Davis. Email him at cctimes@blonz.com.