Most of us are familiar with the much-maligned Western diet and its mainstay of processed food products found in the middle aisles of the grocery store. Some of us beeline for the salty chips and others for the sugar-packed cereals. But we are not the only ones eating junk food. An awful lot of crops grown in the developed world eat a botanical version of this diet—main courses of conventional fertilizers with pesticide sides.

It’s undeniable that crops raised on fertilizers have produced historical yields. After all, the key ingredients of most fertilizers—nitrogen (N), phosphorus (P), and potassium (K)—make plants grow faster and bigger. And popular insecticides and herbicides knock back plant enemies. From 1960 to 2000, a time when the world’s population doubled, global grain production rose even more quickly. It tripled.

But there is a trade-off. High-yielding crops raised on a steady diet of fertilizers appear to have lower levels of certain minerals and nutrients. The diet our crops eat influences what gets into our food, and what we get—or don’t get—out of these foods when we eat them.

Agronomists who analyzed archived wheat samples collected from 1873 to 1995 found significant declines in iron and zinc. A 2009 study of nutrient levels in United States crops concluded that there was strong evidence for 5 to 40 percent declines in the mineral content of fruits and vegetables over the previous 50 to 70 years.

There are multiple factors at play in declining nutrient levels. Among them is the trend in plant breeding for larger seed, grain, fruit, or vegetable size. Picture a big russet potato next to a small fingerling potato, both grown in the same soil and containing the same total amount of iron. Thanks to modern breeding techniques, the larger russet can contain less iron per unit of biomass than the smaller fingerling, making the russet less nutrient-dense.

Modern agriculture also influences phytochemical levels in food. These powerful bioactive compounds made by plants confer innumerable health benefits to themselves and the people who eat them. In general, the closer a crop type is to its wild ancestor, the higher its phytochemical levels. Yet NPK fertilizers translate into lower phytochemical levels. When plants grow explosively they tend to cut back on making phytochemicals.

Central to the problem of declining mineral and phytochemical levels is what goes on in the out-of-sight world of a plant’s roots. From our human perch we marvel at what we think a plant’s life consists of—growing. The gnarly seed that sprouts into a soft green thing and the sapling that becomes a behemoth, understandably, catch our eye.

But the things that fuel plant growth on today’s farms, chiefly NPK fertilizers, are not the same things that plants need to stave off disease, heal from injuries, and fend off pests and pathogens. In other words, our big human brains have long, and erroneously, conflated plant growth with plant health. And herein lies a pickle for modern agriculture.