Farming can deplete soil of valuable nutrients. What’s the effect on your health?
Last week, we got into a discussion about nutritional supplements on the Nutrition Diva Facebook page. A couple of people made the comment that fruits and vegetables aren’t as nutritious as they used to be because the soil has become depleted. I thought that would be an interesting topic to investigate further.
Is Our Soil Depleted of Nutrients?
If you’ve been reading this column for any length of time, you probably know that I believe that you’re usually better off getting your nutrition from real food than from dietary supplements. There are some cases where supplements make sense. (For more om supplements, see my articles Multivitamins, What are the Benefits of Vitamin D?, and Fish Oil and Omega-3s.) For the most part, though, if you’re eating a healthy diet, you really shouldn’t need to take handfuls of vitamins as well. But what about this idea that we need supplements to make up for the fact that fruits and vegetables are less nutritious than they used to be? Has our soil become depleted of nutrients and rendered our food supply nutritionally bankrupt?
It is true that growing crops removes nutrients from the soil. Over time, soil that’s farmed intensively and constantly can become depleted of certain nutrients. Although farmers add nutrients back to the soil in order to maintain the productivity of the land, they might not always replace everything that’s been depleted.
For example, fruits and vegetables absorb minerals from the soil that aren’t required for healthy plant growth but do contribute to the health of the animals and humans that eat those plants. Over time, these nutrients will become depleted. But if they don’t noticeably affect crops, farmers might not bother to replenish them. As a result, the level of nutrients in fruits and vegetables could decline. That’s the theory, anyway. So, what’s the evidence?
What’s the Evidence that Fruits and Vegetables Have Gotten Less Nutritious?
A couple of studies, one in England and one in the U.S., attempted to compare nutrient data collected in the and 50s and 60s with more recent nutrient analyses. Both studies found differences. For example, the British study found that the calcium content of modern vegetables was about one-fifth lower than what was measured in the 1960s and average copper content declined almost 80%. The U.S. study, which was more carefully controlled, found that amounts for a few nutrients like vitamin C, iron, and riboflavin declined somewhat, several were the same, and a few actually increased.
There are a lot of factors that influence the nutritional value of fruits and vegetables—and I think many of them are actually trending in a positive direction.
These studies are widely—but very selectively—cited in books, articles, and websites that sell nutritional supplements. You never see any mention of the fact that the level of some nutrients has apparently increased in the last 50 years, for example. Instead,
the 80% decline in copper levels observed in the British study is frequently translated as, “Fruits and vegetables have lost 80% of their nutritional value,” which is obviously a gross mischaracterization of the findings.