DEAR DR. BLONZ: I am an advocate of farmers markets. While shopping at one organic booth recently, I overheard a discussion that there are more nutrients in homegrown and market produce than in the items at larger stores. Can you tell me if this is true? -- J.E., San Diego
DEAR J.E.: This discussion usually revolves around the "field to plate" time for a given food. It's true that some nutrients in fruits and vegetables can decrease over time -- mostly certain vitamins and phytochemicals; mineral values, for the most part, remain unchanged. Assuming no form of food preservation has been used, such as freezing or drying, the shortest "field to plate" times are indeed found with homegrown and farmers market offerings.
Keep in mind, though, that it's often tough to make direct comparisons: For example, many flavorful varieties of produce aren't even grown by the higher-volume commercial agricultural operations. Many varieties are simply better suited to homegrowing or production by small, local farms.
Nutritional values are analyzed by organizations that take multiple samples. This might involve picking up products from stores around the country. As there are different varieties and growing areas, and the nutrient content may vary throughout the growing season, it's best to consider posted nutrient values as nothing more than an average.
Soil conditions can also affect the nutrient value of a crop, but it is not as straightforward as you might think. Minerals can end up in plants because they are essential for their growth, or they can end up there because they are passively taken up from the soil. A deficiency in an essential nutrient might result in a lower overall crop yield, but not a decrease of that nutrient in each individual item. Nutrient levels can vary from soil to soil and region to region. It's one of the best arguments for eating a wide variety of fruits, vegetables and grains.
So, while there can be nutrient differences between supermarket produce and that at farmers markets, there is no evidence that these differences will result in significant health impacts. The bottom line is that fresh or fresh-frozen produce will always be your best nutritional bargain -- regardless of its source. All the better if you can find products that are sustainably grown.
DEAR DR. BLONZ: Please explain why BHT is in breakfast cereals. I thought it was used to help prevent oils from going rancid, but there is little, if any, oil in breakfast cereal. -- C.C. Baton Rouge, Louisiana
DEAR C.C.: BHT stands for butylated hydroxy toluene. It is an antioxidant that helps prevent oil rancidity, as you correctly point out. In low or no-fat cereals, FDA-approved BHT can help protect the destruction of fat-soluble vitamins that may have been added to the cereal. This compound can also help preserve the ability of the packaging material to remain an effective barrier between the cereal and the outside air, which is a particularly important function in warmer climates.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.