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YOU could be forgiven for thinking we are living in the midst of a nutritional apocalypse. “You’d have to eat 10 tomatoes today to get the same level of nutrients as one in the 1950s,” declared an activist on the radio recently.

On Twitter, there was more of the same: “One would have to eat eight oranges today to derive the same amount of vitamin A our grandparents would have gotten from one.” And at a farming conference, a speaker proclaimed that modern farming means that fruit and vegetables have been “drained of their nutrients”, showing falls of “up to 50 per cent over 50 years”. But what evidence are these claims based on? I thought I’d better take a closer look.

Perhaps the most commonly cited study used to support this narrative is a 2004 paper in the Journal of the American College of Nutrition. It analyses nutritional data for 43 garden crops in the US from 1950 and 1999. But scan the results and a rather different picture emerges to the popular idea that modern food is lacking.

Instead of showing a nutritional collapse across the board, the research found only about half of the 13 nutrients checked showed a statistically reliable decline, while others remained unchanged. For those nutrients that were found to have declined, the falls reported across all 43 crops ranged from a modest 6 per cent for protein to a 38 per cent drop for riboflavin, which is a B vitamin.

What about the 90 per cent reduction in the overall nutrient levels in tomatoes I had heard? Well, no such figure appears to exist in this study. The single largest fall in the study, which was in an individual tomato crop, appears to be a 54 per cent drop in calcium, however most other vitamins and minerals stayed pretty stable. What about the “eight oranges” claim for vitamin A? Oranges weren’t even part of the study, so it is unclear exactly where that statistic originated.

And the 2004 study is only so reliable. In the decades between the 1950 and 1999 data sets it used, everything from crop varieties and testing techniques have changed significantly. So this type of study is unlikely to be a like-for-like comparison. This was something the authors were careful to point out: “There is no way that you can reliably measure the decline for single foods.” This is the opposite of what I keep hearing.

“If the nutrient levels in modern crops had collapsed to the degree claimed, it would be clear in the human population”

Is there any other evidence on nutrient changes? The Broadbalk Wheat Experiment is a pioneering study that has been gathering samples of wheat grown in the same field in England for 175 years, making it the world’s longest running agricultural trial. Between the 1800s and the late 1960s, the nutrient levels in the grain grown there stayed relatively stable. However, from then onwards there have been significant falls, especially for minerals like zinc and iron, which neatly coincided with the introduction of a modern variety of wheat. These findings are potentially concerning.

But while it was an excellent review of the nutrient content for a single crop in a single field in one place, extrapolating its results as representative of all crops across the whole world, or frankly even the same wheat variety in the next county, are problematic. Trials have shown, for example, that identical types of wheat grown in two different fields in the same US state can show an eight-fold difference in key minerals like selenium. Such a difference far outweighs the declines observed in the English single-field study.

Arguably the best evidence comes from studies that grow historical and modern varieties side-by-side in the same fields, replicating the exercise at various locations. Results have been mixed. In one study by the US Department for Agriculture, broccoli didn’t show a clear trend nutritionally speaking either way in terms of differences between old and new varieties. While nutritional differences were recorded in terms of the size of the broccoli head, factors such as weather showed an effect on nutritional content up to 10 times greater than crop size. For wheat, while some nutrients did decline in newer varieties, many were stable. This suggests a far more complex picture than many have claimed.

Most pertinently of all, if the nutrient content of crops had indeed collapsed to the degree so frequently claimed, this would be clear in terms of human health. Yet nutrient deficiencies have actually declined worldwide by roughly 40 per cent since 1960, according to a University of California study, and by as much as 80 per cent in regions like east Asia. This was partially due to fortification of foods, but mainly attributed to modern agriculture resulting in a more diverse diet. It seems modern farming isn’t quite the dietary demon some say it is.

I for one can’t wait to see what further research uncovers, but there is no need to panic just yet.