Posts

Posted on

Still important to eat up your fruit and veg

Fruit and vegetables sold in the UK are ‘half as nutritious’ as 80 years ago due to depleted levels of iron, magnesium, sodium and copper, study shows

That’s the headline in the Daily Mail. But is it true?

Well, the study in question didn’t actually measure anything. It looked at the UK’s Composition of Foods Tables ((Otherwise known as “McCance and Widdowson’s ‘composition of foods integrated dataset’ on the nutrient content of the UK food supply.”)) for 1940, 1991 and 2019, and compared the levels of 7 nutrients in 29 fruits and vegetables ((Cabbage – winter, carrots – old, cauliflower, celery, cucumber, leeks, lettuce, mushrooms, onions, peas, potatoes – old, radishes, runner beans, tomatoes, watercress, avocado, bananas, blackberries, cherries, eating apples, grapefruit, grapes, nectarines, oranges, pears, pineapple, plums, raspberries, strawberries.)) sold (but not necessarily grown) in the UK for which the data were roughly comparable. That is, for which results were presented in the tables for raw samples of the same part of the same sort of plant prepared in the same way: unpeeled eating apples, say.

To be clear, this analysis can say nothing about whether modern vegetable or fruit varieties are on average more or less nutritious than older ones. In the jargon, any differences between old and new varieties are confounded in this dataset with differences in growing conditions and agronomic practices, for example, and more besides. There’s no way to disentangle one from the other, and the authors of the paper make this clear.

So what can the study say? Is the “half as nutritious” thing justified? Predictably, it’s more complicated than that. I’ll reproduce the key findings verbatim (though ever so slightly edited) to preserve the nuance:

  1. In the first period, from 1940 to 1991, there were significant reductions (p < 0.05) in Na, Ca, Mg and Cu. The greatest reductions were Cu (60%) and Na (32%). There were also increases in water content. This is of interest because it shows that by 1991 the fruits and vegetables contained more water, and nutrient density (on a fresh weight basis) has consequently decreased...
  2. In the second period, from 1991 to 2019, there was a significant reduction in Fe (36%) and a significant increase in Mg (18%). There was also a further reduction in Na and increase in water that was not statistically significant (p < 0.05).
  3. The overall longer-term comparison of data from 1940 to 2019 shows that the mineral contents of fruits and vegetables remain lower than in 1940. The greatest overall reductions during this 80-year period were Na (52%), Fe (50%) Cu (49%) and Mg (10%). There was a 12% decrease in dry matter content that was not statistically significant.

Some notable reductions, then, but hard to say that fruits and vegetables are “half as nutritious” now compared to 80 years ago. Not for the first time, the Daily Mail somewhat overcooks the vegetables, as it were.

Do the reductions matter? That would, of course, depend on a bunch of other things, including whether people eat more or less of these (and other) fruits and vegetables, and whether any losses in nutrient supply from fruits and vegetables are made up from other sources. As the authors say: “For some vulnerable groups, and those with poor diets, these reductions are important because they make a bad situation worse – teenagers are at particular risk of inadequate diets.” But that assumes that teenagers are scoffing down the same amount or less of old carrots and unpeeled eating apples than formerly, which may in fact be likely but needs proof.

Anyway, there are some useful recommendations at the end of the paper, both for the UK and globally. I’ll just highlight a couple here:

  • With the seemingly systematic reductions, it is necessary to have a holistic approach rather than an approach that takes each nutrient one at a time. It is important that all foods are grown and processed in a way that optimises their nutrient content from production through to consumption.
  • Plant breeding should aim to improve a whole basket of mineral nutrients, not just targeted to one nutrient at a time, as is the current approach of biofortification programmes.

Perhaps it was too much to hope the Daily Mail would have gone for that in their headline.

Posted on

All maize, all the time

Thanks to Jay Bost for alerting us to a whole bunch of forthcoming maize talks. The first is by Dr Helen Anne Curry today, who will use her book…

…Endangered Maize, to discuss the history of efforts to conserve crop diversity from the turn of the twentieth century until today. Focusing especially on the case of maize, she will highlight the stories about agricultural change that have motivated scientists and states to save threatened varieties—and raise questions about the agendas ultimately served by these stories.

The others start next month:

The National Agricultural Library is hosting a three-part webinar series that will highlight global food staples and the intersections of global cuisines with USDA research, social sciences, and history. The series will focus on maize and corn and its past, present, and future role in food, culture, and society. Key areas of focus for the series will be sustainability, environmental justice, social justice, and nutrition security.

Posted on

Brainfood: Organic ag, Food systems, Seed systems, Breeding for value, Breeding for intercropping, Breeding for cider, Breeding with CWR, Breeding with imaging, Breeding with modelling, Ag & the state

Posted on

How diverse can croplands be?

A guest post from Fernando Aramburu Merlos on his recent paper with friend-of-the-blog Robert Hijmans.

Four species (wheat, rice, maize, and soybean) occupy half the world’s croplands. It has been argued that this means we cannot increase crop species diversity much without changing what we eat ((Renard, D. & Tilman, D. Cultivate biodiversity to harvest food security and sustainability. Curr. Biol. 31, R1154–R1158 (2021) )). Radically shifting our diets is a tall order, not just because changing habits is a challenge but also because we are so good at growing and processing the major crops. It’s an unfair race in which the major crops have a head start of millions of dollars and research hours.

We wanted to know how much crop diversity can be increased without changing the global food supply ((Aramburu Merlos, F. & Hijmans, R. J. Potential, attainable, and current levels of global crop diversity. Environ. Res. Lett. 17, 044071 (2022) )). So we estimated the attainable crop diversity, which is the highest level of crop species diversity you can get without changing the total production of each crop. To compute this, we “shuffled the cards and dealt again”: over 100 crops were distributed across the worlds’ existing croplands by allocating each to the most suitable land while considering the inter-specific competition for land.

It turned out that tropical and coastal regions can reach much higher levels of diversity than temperate and continental areas. Perhaps that is not especially surprising, but one implication is that we should not assume that all countries can achieve the same maximum levels of crop diversity ((This assumption was made for the agrobiodiversity index proposed by Jones, S. K. et al. Nat. Food 2, 712–723 (2021))). We also noted that attainable diversity cannot explain current diversity patterns very well. For example, the diversity gap,  the difference between the current and the attainable diversity, is much higher in the Americas than in Europe and East Asia.

Diversity gaps, expressed as a percentage of the attainable diversity, are greater than 50% in 85% of the world’s croplands. Thus, in principle, crop diversity could double in the vast majority of the world without changing our heavy reliance on a few staple crops. So there must be strong forces at work that make farmers and regions specialize. For example, at the farm level, a high crop diversity may be difficult to manage, reduce economies of scale, and be costly if it comes at the expense of the most profitable crops.

It would be interesting to better understand what specific factors limit diversification in the regions with the largest crop diversity gaps, and how to reduce them. But more important questions need to be answered first. How much diversity is enough diversity? And is that the same for all regions? Some very low diversity systems appear to be highly sustainable (the flooded rice systems in Asia come to mind). A more spatially explicit and species-specific, functional understanding of the effect of diversity at the field scale would be helpful. Without that, diversity gaps are just an interesting emergent property of specialization, but not something that necessarily must be reduced.