Nov 12 2015

Nutrient Density of Crops Over Time

A new video is making the rounds on social media making the incredible claim that you would have to eat five grocery store apples today to equal the nutrient density (not calories, but other nutrients) of a grocery store apple from 1936. The video makes a second claim, that the decrease in nutrient density is due to poor soil. The video is little more that pro-organic propaganda, and neither claim is sourced – because they are not true.

However, the story of nutrient density of fruits and vegetables is a complex and interesting one. It is interesting to compare food plants from thousands of years ago (prior to any cultivation), 100 years ago, and today. First we need to ask – what are the differences? Then we can try to explain them.

Let’s compare first fruits and vegetable from today to 50 and 100 years ago.  A systematic review by Donald David found:

Recent studies of historical nutrient content data for fruits and vegetables spanning 50 to 70 years show apparent median declines of 5% to 40% or more in minerals, vitamins, and protein in groups of foods, especially in vegetables.

So there does appear to be a real decline, although not the 80% across the board suggested by the pro-organic video. The declines are significant for vegetables, and less so in fruits (so apples was a poor example to use). Averaging out all the declines, you get about a 20% decline in nutrient density for produce.

That decline is significant, and something we definitely need to pay attention to, but may not be having any health effect on the average consumer in an industrialized nation. It is more than offset by the increased availability of fruits and vegetables year round.

There appear to be two processes leading to this modest decline in nutrient density, a production dilution effect and a genetic dilution effect. The Davis review also concludes that the evidence suggests higher yields result in lower nutrient density – the production dilution effect. This makes sense – if you get more yield out of the same land, micronutrient density will tend to be diluted in the larger yield. This is the trade-off for producing more fruits and vegetables without dramatically increasing land use.

This dilution effect can likely be compensated for, the evidence also suggests. Differences in nutrient density differ from year to year, suggesting an environmental effect. Also, historically, when specific minerals were supplemented into the soil those minerals increase in the produce. While this is not a problem of degrading soil quality, if we are going to demand more from the soil with higher yields we will need to put more into it.

The second factor is perhaps more significant – genetic dilution. Essentially breeders have mainly selected crops for yield and properties that make them more marketable, such as shelf-appeal and durability for shipping. They have largely ignored nutrient density and have even sacrificed flavor in some cases in favor of yield or visual appeal.

This is almost certainly why people find that garden-grown vegetables taste better, because they are growing heirloom varieties that inherently taste better than the mass produced varieties in the store.

There is also reason to believe that this process is not new, but has been occurring for thousands of years. Many micronutrients are bitter or sour, and when our ancestors cultivated plants that were sweet, tender, with high yields and high caloric content, they also reduced the bitter phytonutrients in the wild cultivars.

I don’t buy arguments, however, that there has been a net negative health effect from this trade off. We are taller, healthier, and have greater longevity today partly because of overall better nutrition.

It does mean, however, that for optimal nutrition you should eat plenty of fruits and vegetables. They may not be as nutrient dense as wild or heirloom varieties, but they still contain plenty of vitamins, minerals, and other micronutrients. You could also eat plants that are closer to their wild origins, like arugula. These tend to be bitter, and some people have a hard time tolerating the bitter taste.

The evidence clearly shows that eating fruits and vegetables regularly has a health benefit. There is no evidence, however, that eating “super foods” with especially high nutrient density is necessary or beneficial. It may simply be overkill without a specific health benefit, but more data is needed to say definitively.

In any case, if we want to maintain or improve the overall nutrient density of our produce there are two things that can be done. Optimizing soil treatments to replace micronutrients does seem to have an effect. For efficiency, this can be targeted to specific minerals that are especially low.

The more intriguing intervention, however, is to reverse some of the trends in cultivation. If plant breeders measured and prioritized nutrients and flavor we could possibly develop cultivars that have the best of both worlds – good yield and great flavor with preserved nutrient density.

However, sometimes these trade offs were unavoidable, or at least difficult to avoid with standard hybrids and cultivation. Scientists are studying plants genetically to identify what specific genetic changes occurred between wild or heirloom varieties and the modern grocery store varieties, and how these genetic changes resulted in the desired traits as well as the undesired traits.

One goal of this research is to be able to make specific genetic changes that will undo the damage while maintaining the increased yield and other desirable properties – to put the flavor and nutrient density back into produce.

Conclusion

The evidence shows that there has been a modest overall decrease in nutrient density, mostly in vegetables and less so in fruits, both over the last century and compared to the wild ancestors of our modern crops. For the individual consumer, this is probably not something you need to worry about. Fruits and vegetables are still plenty nutritious, and if you eat enough of them you will be fine.

However, systemically this is a trend we should pay attention to, and hopefully reverse. As we push the limits of our ability to mass produce food without dedicating the entire planet to farming, we obviously need to continue to tweak and advance our farming technology. This is nothing new, and farmers already know they need to treat their soil to keep it producing, but we are pushing the limits of production.

Perhaps more significant is the possibility of breeding or genetically modifying plants specifically to increase their flavor and nutrient density. We might be able to reverse some of the accidental negative effects of plant breeding, or even exceed wild varieties. Golden rice is an example of this, fortifying rice with beta carotene, a precursor of vitamin A. It seems likely that over the next century our produce will become more nutritious, not less.

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