In the last few decades scientists have noticed that nutrient content of our food is declining. A research from 2004 studied how the nutrient content changed in plants from 1950 to 1999. They noted significant declines of protein, calcium, phosphorus, iron, vitamin B and C in 43 different garden crops. What is causing this? As plants get their nutrients from soil, some suggested that the new agricultural practices have resulted in soil depletion. Monoculture and pesticide use significantly affect invertebrates and microorganisms living in the soil, causing beneficial ones to decrease in numbers, while maleficent ones are increasing. Pesticides can also interact with certain compounds in the soil, disturbing its chemical structure.
On the other hand, farmers have been using many methods to conserve and enrich their soils. Fertilizers, green manure and soil rest have shown to be quite effective. Pesticide use is optimized to leave as little residual as possible, so we cannot blame the decline of nutrients solely on overcropping.
If it’s not soil, maybe it’s selective breeding? Plants today look a lot different from their ancestors – bigger, sweeter and with more flesh. Did we somehow manage to breed out the nutrients by preferring other attributes, like resistance to low temperatures or diseases?
Answer to this question is not an easy one, because it’s quite hard to compare e.g. an apple from 1918 and 2018. But what scientists could compare is goldenrod, a plant native to North America which bees use as a source of protein. Smithsonian institute has been keeping hundreds of samples of this plant, first one being taken in 1842. With this material, scientists compared the 2014’s goldenrod with her more than century old ancestor and the result confirmed the trend – there was a 30% decrease of protein content. Since goldenrod is a wild plant, it’s pretty obvious that selective breeding and soil depletion are not to blame for the nutrient drop.
Irakli Loladze, mathematician with a big interest in biology, got immersed in this subject in 1998, when he was studying for his PhD at Arizona State University. He and other graduate students studied the effect of light and algae growth on zooplankton in the laboratory. What they discovered was intriguing.
Zooplankton are microscopic animals that live in the oceans and lakes all over the world. They rely on algae for food, and algae rely on photosynthesis like plants. Researchers found that when they shine more light on algae they grow faster (makes sense, right?), thus increasing the food supply for the zooplankton. If we follow the logic, we can conclude that zooplankton will flourish in such environment. The researchers expected the same result, but it’s not what happened. At some point zooplankton started struggling to survive in such abundance of algae.
The increased light made the growth of algae faster, but their nutrient content declined. Zooplankton had plenty to eat, but they were starving. This result got Loladze thinking – is the same thing happening to terrestrial life?
In real life conditions plants aren’t getting more sunlight than before, but they do not only use light in the process of photosynthesis. They also use CO2 and water.
Since the start of the Industrial Revolution CO2 levels have increased about 50%. So what do increasing levels of CO2 mean for plants? More food and more growth. In the process of photosynthesis plants use water and carbon dioxide to make glucose and oxygen. More carbon dioxide means intensive photosynthesis – more sugar and oxygen production. While some might think this is good as the crops are bigger and more oxygen is made, those fruits are not more nutritious than the ones grown in an atmosphere with less CO2. They just have more carbs. Increasing levels of carbon dioxide are literally making plant junkfood, as Loladze said: “We are witnessing the greatest injection of carbohydrates into the biosphere in human history – [an] injection that dilutes other nutrients in our food supply”.
Although the decrease in nutrients (especially proteins) is significant, it doesn’t mean that you should get some food supplements right away. For now, we can still get everything we need with a well balanced diet. But the problem that emerges then is the big quantity of sugar we are ingesting. Protein is what makes us feel full – decreased levels in food as a result have a need for more food. All those nice nutrients are diluted with sugar and you need more fruits to get them, thus ingesting more sugar. This could fuel, or maybe even be one of the causes of the obesity epidemic.
We thought that climate change affected the temperature, sea levels and atmosphere, but it also affects the food we eat. Every day we learn more about the scope of this change and how everything is connected. We cannot disturb one element without affecting thousand others.