Over the past 50 to 70 years, the concentration of nutrients in U.S. fruits and vegetables has been declining — by about 5% to 40%, according to researchers at the University of Texas. But the reason for those nutrient declines is where things get sketchy.
What is the primary cause of the decline?
Is our soil depleted? Has our addiction to pesticide and fertilizer use somehow altered the nutrient bioavailability of plants? Are modern cultivars inferior to heirloom varieties that were grown in generations past? Or is there something else going on that we haven’t even considered?
But perhaps more importantly there’s the question of what we — consumers — can and should do about it.
Since 2000, I’ve been studying and teaching nutrition as a registered dietitian nutritionist, certified diabetes educator, and self-care coach. In that time, there has been a definite cultural shift toward the use of manufactured nutritional products and supplements, which the FDA defines as a “…a product intended for ingestion that contains a “dietary ingredient” intended to add further nutritional value to (supplement) the diet.”
Likewise, I’ve noticed that individuals who sell these products often reference nutrient declines as a key selling point, and while I agree that there are instances where supplements are medically necessary, it seems like we’re missing the bigger issue at hand: Why is the quality of our food declining in the first place and how are we addressing it as a nation?
As I dug into the research, I found out there are only a handful of researchers studying this trend. One reason is that there isn’t much funding available, and that makes sense when you consider there aren’t many incentives. What would the booming food industry stand to gain from it?
Donald Davis, a now-retired professor at the University of Texas, is one researcher who has looked at this trend extensively. I first heard about his research on an NPR interview several years ago, when he referenced his 2004 landmark study, Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999, in which he pointed to several potential causes of the declines. His research compared the nutrient density of 43 raw fruits and vegetables, specifically those that were common in home gardens both in 1950 and in 1999.
But after reading the study, I still had questions. I wanted to know what he personally concluded from the findings in terms of what we should be doing differently as consumers. After all, he was closest to the data. So, I did the only logical thing a curious dietitian would do: I contacted him directly and crossed my fingers that he would agree to speak with me.
Fortunately, he was gracious enough to jump on the phone, and we spent more than an hour talking about the details of his research. That call led to another conversation with Ann-Marie Mayer, an independent researcher in the UK who has studied the topic as well.
What I discovered is that there’s probably not a single cause for the overall reduction in nutrient density, but I did learn some interesting facts that are outlined below. Let’s look at some of the possible causes for the declines:
Okay, let’s start with research methodology. Could sampling errors be contributing to the declines? Some critics have pointed out that researchers who collected prior samples left a significant amount of soil on the roots of some vegetables, making it seem as though the food itself contained more nutrients when compared to current samples.
But, as Davis noted, iron is the only nutrient that has been identified as being potentially problematic with regard to testing errors. That means sampling blunders probably aren’t playing a large role here.
Another popular suggestion for the decline is that soils have become depleted from overuse and repetitive mono-cropping, without adequately replenishing nutrients.
In past generations, and in some smaller communities still today, agricultural practices included allowing fields to lay fallow (not planting them) for a season as well as crop rotation (not planting the same crops in the same areas). These strategies prevented depleting the soil of the same nutrients over and over again.
It’s clear that placing high demands on the soil without replenishing nutrients does reduce the overall health of the soil, but so far research hasn’t shown that the reductions are significant enough to name soil as the sole culprit.
For example, side-by-side studies (where different plant varieties are grown in the same soil) still show an overall decline in nutrients — which means soil depletion can’t be the primary source either.
Okay, then. What about pesticides? The use of pesticides has become commonplace in large agricultural operations. For one thing, it’s easier than implementing natural forms of pest control, such as crop rotation and plant guilding.
Today’s large-scale farms are not configured the way smaller farms were at one time. Sure, planting a single crop in long, narrow rows makes it easier to harvest, but it also makes it easier for pests to harvest. And that’s why pesticide use has become so prevalent in recent years.
While there are many controversies related to the health impact of pesticides (which aren’t discussed in this article), it doesn’t appear that pesticides are a significant factor when it comes to nutrient declines either.
It’s well-known that the industry has grown reliant on the use of fertilizers in the U.S. Until around the 1960’s, manure and compost were still the primary fertilizers used on American farms. But when commercial fertilizers became en vogue, peaking in the early 80’s, there was a definite shift.
That’s because fertilizers produce greater yields and require less labor than traditional farming methods. Bigger is better when it comes to consumer buying behavior, but higher yields also increase plant dry matter, which dilutes the overall concentration of nutrients. This is sometimes referred to as an environmental dilution effect.
For example, earlier varieties of bunch broccoli had small heads and longer stems. Today’s cultivars grow so fast that the base is nearly hollow. In fact, as Davis explained, it’s so unsightly to consumers that producers usually cut it off, which is why most of the broccoli we buy at the store today has a short stem.
The sad truth is that nutrition is an afterthought for most large-scale operations.
According to Davis, these nutrient declines “are symptoms of breeding for high yield and fertilizing for rapid growth.” Because of the increase in plant dry matter, it’s likely that fertilizers are playing a significant role.
But it’s not the whole story.
How are modern plant varieties playing a role in the declines?
Just as fertilizers are used to increase plant yields, many farmers and large-scale producers have moved toward newer plant varieties, sometimes referred to as cultivars, to further increase yields.
In addition to the environmental dilution effect noted above, there’s something researchers refer to as a genetic dilution effect. Wheat is one example. Today’s wheat varieties have fewer leaves and shorter stalks, making them less likely to topple over with heavy fertilizer applications or intense rains.
But since minerals enter the edible portion of the plant from the leaves and stalk, the plant can’t draw up as many minerals when the leaves and stalks are small.
Side-by-side comparisons of high- and low-yield cultivars, such as in the 160-year Broadbalk Wheat Experiment, have found an inverse relationship between yield and nutrient concentrations.
In other words, the higher the yield, the lower the concentration of nutrients.
Today, plant breeding is focused on “high yield, post-harvest handling qualities, and cosmetic appeal,” says Davis. And it’s true. Consumers want big and pretty produce, so that’s what the industry is delivering. But it comes at a price. For example, zinc levels are lower today than they have been at any time throughout history, and that’s largely because of newer, faster-growing cultivars.
Rising Carbon-Dioxide Levels
Recently, it has been suggested that rising carbon-dioxide levels may also be playing a role, but very little research has been done to date in this area.
So, what does mean for Americans?
As consumers, we’re the ones who ultimately foot the bill when it comes to modern farming practices. And we pay in two ways:
First, we pay per pound. Because we drive the demand for bigger and prettier produce, that’s what the industry is growing and delivering — and that means we’re paying higher prices per pound for lower quality produce. Basically, we’re getting fewer nutrients for our dollar. Davis suspects that if we paid per nutrient rather than per pound, the industry would be more incentivized to select cultivars that maximize nutrients over size. But for now, the industry has nothing to gain from shifting priorities.
And second, we pay in terms of our health. All of this might not seem like a big deal on the surface, until you consider that we’re spending even more money on manufactured products that are marketed to close the gap and replace nutrients that have been lost in food. The nutrients and phytochemicals found in real, whole foods are still somewhat of a mystery. We don’t completely understand their synergistic properties yet, which means we can’t recreate them in the lab.
Davis believes (and I agree) that while today’s produce may be slightly less nutritious, the most important action we can take to improve our health is to reduce our consumption of sugar, white flour, and refined fats, and increase our consumption of fruits and vegetables.The most important action we can take to improve our health is to reduce our consumption of… Click To Tweet
As researcher Robin J. Marles stated in her review, “a diet rich in vegetables, fruits and whole grains, which continue to be nutrient-dense foods, will still provide all of the nutrients we need for good dietary health.”
Are Supplements Necessary?
So, are supplements essential for good health?
In fact, both researchers that I interviewed were surprised (and alarmed, quite honestly) when I mentioned that I’ve seen their findings used to justify product sales. From their point of view, that isn’t the answer.
Manufactured supplements were designed to fill dietary gaps for those who have medical conditions that interfere with nutrient absorption, or require significant dietary restrictions. But supplements aren’t necessary for the vast majority of people who consume a balanced diet.
From a practical standpoint, we’re talking about single-digit changes in milligrams here, which can easily be addressed through dietary adjustments. For example, as a 40-year-old female who requires about 18 milligrams of iron each day, I could easily make up for the ~16% decline by choosing foods that are higher in iron.
Certainly, the choice of whether or not to use supplements is a personal one. Learning to recognize our needs and choosing strategies that meet those needs is a foundational element of self-care.
But to do that, we first have to understand what we’re dealing with.
What You Can Do
Here are a few things you can do now:
- Ask Questions. Begin asking your local grocers and growers for more details about how their produce is grown. What kind of pesticides and fertilizers, if any, do they use? What varieties of broccoli and other produce are they growing? As long as we don’t care what they answers are, no one else will either. You don’t have to be a scientist; you just need to be an interested consumer.
- Buy Organic Produce. While the jury is still out as to whether organic produce is more nutrient-dense than conventional produce, it’s pretty clear that pesticides aren’t health-promoting compounds. (For me, that’s reason enough to buy organic.) Find out which fruits and vegetables contain the highest amounts of pesticides here.
- Buy Local Produce. Supporting local growers benefits our communities in a number of ways. First, it enhances food availability. The more demand there is for local produce, the more farmers will grow. Besides, have you ever wondered what might happen if the major food producers in this country suffered a loss? The number of U.S. growers has dwindled over the years, and many have turned to mono-cropping (only growing a single crop). If we ever experience a major crop failure, it could be devastating.
- Grow Your Own Produce. Grow some of your own produce, even if it’s in a pot on your balcony. It reminds us how much energy and effort goes into growing food, and it invites a sense of gratitude for the growers across the country who are doing this important work. Reconnecting with the food we eat is the most significant action we can take as consumers.
I know this is a LOT to process, but sometimes we make things more complicated than they have to be. Sometimes the answers are much simpler than we think.
We hold a great deal more power than we realize when it comes to our health. We can vote with our dollars and cause shifts within industries, and we can choose to support ourselves in ways that have a positive impact on our health — as individuals, as communities, and as nations.
But we have to pay attention — and take action.