Nutritional yield in the spotlight

by Luigi Guarino on July 29, 2015

Dr Jess Fanzo had a paper in the works on the topic when he asked a few days ago “How would you measure agricultural production?” But his pleas for measuring nutrition per hectare, rather than just calories or yield, certainly gets a boost from the article, and in Science, no less.

Here is what Prof. Ruth DeFries of Columbia University, who is the lead author, and others1 think:

We propose a metric of “nutritional yield,” the number of adults who would be able to obtain 100% of their recommended DRI [daily dietary reference intake] of different nutrients for 1 year from a food item produced annually on one hectare.

Why? Because…

…nutritional needs for a wide range of essential nutrients in the human diet have generally not been included in considerations of sustainable intensification. Access to food with high nutritional quality is a primary concern, particularly for 2 to 3 billion people who are undernourished, overweight, or obese or deficient in micronutrients.

They even provide a worked example, highlighting the fact that many neglected staples are more nutrient-dense than boring old rice, wheat and maize.

In 2013, for example, on average one hectare of rice produced 4.5 metric tons/year, which is the equivalent of providing the annual energy requirement for 19.9 adults. Millet produced only 0.9 metric tons/ha per year, the annual energy requirement for 4.0 adults. However, a hectare of rice fulfills the annual iron requirement for only 7.6 adults, compared with 15.3 for millet.

Leave aside for a minute that, depending on what particular millet is meant, rice vs millet is an unusual comparison to be making. This does sound like a promising idea; but here’s the problem I see. You have to do the calculation for each damn nutritional factor: protein, iron, zinc, whatever. How do you know which to pick for any given comparison you want to make? Is there no way to come up with a more synoptic nutritional yield score? One that takes into account multiple nutrients at once, rather than one at the time. How about this, for example:

the number of adults who would be able to obtain at least 50% of their recommended DRI of all of X nutrients for 1 year from a food item produced annually on one hectare

Where X is whatever nutritionists think is a sensible basket of nutrients. After all, people rarely need just iron.

  1. DeFries R, Fanzo J, Remans R, Palm C, Wood S, & Anderman TL (2015). Global nutrition. Metrics for land-scarce agriculture. Science (New York, N.Y.), 349 (6245), 238-40 PMID: 26185232 []

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