Studies over the last 15 years, The Times reported, reveal that much of our produce is low in phytonutrients, the compounds that are supposed to reduce the risk of the four diseases that plague modern life: cancer, heart disease, diabetes and dementia. And the decline in the health benefits of our food is not a recent development. Source
The mass production of vegetables and fruit will gravitate to the best tasting, hardiest, cheapest, and easiest to grow versions of the product. It comes down to profits over nutritional value. This may have several consequences.
First, variety may be jeopardized. Rather than having six or seven types of tomatoes, we may only see two or three. Second, the lowest cost, highest volume version of a particular vegetable may not be the most nutritious type. For example, blue or purple corn has more anti-oxidant capacity than white corn, but white corn is the type we see most often in stores. Third, over time, studies have shown that the strain of a specific type of vegetable may lose its phytonutrient potency sacrificed for stronger, more robust strains that are easier to grow. For example, the original cabbage the grew in the wild before it was cultivated probably had a different nutritional profile than the cabbage we buy for $0.59 / lb in the stores today. Fourth, which is a more well know controversy, pesticides are a common ingredient in our non-organic produce which may or may not cause health problems, though proponents of pesticides will argue that there is no cause for alarm.
An example given in the article is that research on native peoples of the Americas who first foraged and then cultivated some of the original vegetables had fewer of the health problems and lower instances of the allergies that we experience today.
There are a few things that can be done to optimize your selection of good produce. Go to a farmers market once in a while and check out the different varieties of squash, potatoes, melons, peppers, tomatoes, kale, and mushrooms so that your ingredients stay dynamic and not stuck on the typical vegetables at the big box grocery stores. Try to buy local ingredients when possible, to minimize degradation during transportation. Buy organic if the price is manageable. And lastly, if you have the time, resources, and space, try planting your own garden and make 'farm to table' a reality!