Monday, July 15, 2013

Scientists for sustainability.

As a planetary scientist, I spend most of my time thinking about the moons of Jupiter and the formation of the Solar System. It’s an exciting line of work, but it doesn’t give me much opportunity to help solve the problems currently facing humanity. That’s why I got involved with the Union of Concerned Scientists (UCS), a group of scientists and technical experts who help critically analyze proposed solutions to environmental problems. The UCS produces policy briefs and public outreach materials based on quantitative study in the areas of clean energy, climate change, and food systems (just to name a few).

One criticism of our current food system that I’ve highlighted before is that we devote a huge amount of land and resources to growing industrial grain. Because these grains are not directly edible by humans, the grains we grow are used mainly for ethanol fuel, animal feed, and heavily processed food and additives. While many researchers have investigated how we could use grains differently to produce more calories, I have found very little information on what we could grow instead of grains that might produce either more calories or more nutritious food. Recently, the UCS’ Food and Agriculture group produced a really interesting infographic that begins to address this important question.

Plant the plate.

The USDA and the CDC provide recommendations for the servings of fruits and vegetables that each of us needs to eat in order to stay healthy. Vegetables are particularly important because they provide so many micronutrients. According to the new MyPlate recommendations, fruits and vegetables should make up 50% of our daily food intake. The USDA’s food plan calculator offers more specific recommendations. It says I ought to eat 2.5 cups of vegetables a day, varying the kinds of vegetables I eat throughout the week, and 1.5 cups of fruit each day. My husband should get 3 cups of veggies and 2 cups of fruit per day. We actually aim for about 8 cups of veggies a day because that’s the best way to meet the recommended allotments of micronutrients, but 2.5 cups is a good minimum.

Interestingly, the Union of Concerned Scientists determined that we do not actually grow enough fruits and vegetables for every American to consume the recommended daily intakes. Currently, only 2% of the farm acreage in the US is used to grow produce. We would need to more than double that number in order to provide enough food for everyone to eat a healthy amount of produce. Even with these adjustments, the total acreage devoted to fruits and vegetables would only be 5.28% of our total farm acreage.

It’s unclear why we grow so little food that we know is essential for good health. Certainly, the government subsidies for grains play a role – driving down the price of grain, which then becomes an extremely profitable raw material for food companies. Demand also plays an important role, though. Have we become so accustomed to processed food and sugary beverages that we no longer demand produce, or is the price difference between fresh and processed foods turning people away?

Counting calories.

Pro-grain groups often cite world hunger as a justification for using any means necessary to produce more calories. However, in the United States, we have over 3700 available calories per person per day [1] – far more than any of us needs to consume. However, if we followed the UCS’ suggestion and switched 23 million acres of grain-producing cropland to the growing of fruits and vegetables, we probably would reduce the total number of calories we produce.

Grains go through so many changes before they are consumed that it’s hard to say how many calories would be produced on 23 million acres. Here’s my first attempt to estimate how much of an impact such a change would have on the caloric yield of our food. For simplicity, I’ll just focus on corn for this analysis.

According to the USDA’s crop statistics, the 2011 corn harvest was used for a variety of purposes: 40% went to ethanol fuel, 12% was exported, and 9% went to food sweeteners and additives, including high fructose corn syrup (HFCS), glucose, dextrose, food starch, and alcohol. Only 2% of the corn harvest was used to make corn-based foods (e.g. corn chips), while 37% went to animal feed, an indirect source of edible calories. That means 52% of the corn harvest did not contribute to the available calories in the US, and another 37% entered indirectly through consumption of meat, poultry, dairy, and eggs from corn-fed animals.

The whole point of switching from grains to fruits and vegetables is to enable people to eat the daily recommended values of these foods. So, presumably, 100% of the harvest from the additional 23 million acres would be consumed by humans. Because 52% of the corn crop does not contribute to edible calories, the new fruits and veggies could provide only 48% of the calories from the corn they replaced without changing the number of edible calories in the food system.

Of the corn that directly delivers calories, the largest portion becomes HFCS, which contains about 80 calories per ounce*. About 32 pounds – or 512 ounces - of HFCS can be produced per bushel of corn [2]. In 2011, about 25 bushels per acre were used for HFCS, yielding about a million calories over the year. The next largest portion went to glucose and dextrose. If these sugars have similar conversion rates (a big assumption), then the 6% of the corn crop used to make HFCS, glucose, and dextrose produced about 1.7 million calories. I was unable to find enough information to deduce the caloric yields per acre of food starch or alcohol, but these are likely negligible.

Edit (09/05/13): In the above analysis, I incorrectly calculated the number of bushels per acre that were devoted to each type of food product. The numbers should be about 6 bushels per acre for HFCS, 3 for glucose and dextrose, 3 for starch, and 1.5 for alcohol. I have also found the information for the corn starch conversion; one bushel of corn can be used to make 32 pounds of corn starch, which contains 107 calories per ounce. Hence, the total caloric yield of these "food uses" was only 531,000. I am still neglecting calories from corn-based alcohol in this analysis.

Jonathon Foley, of the Institute on the Environment at the University of Minnesota, stated that the caloric efficiency of converting corn to edible animal products ranges from 3% to 40%, depending on the product (e.g. steak vs. eggs). So the 37% of corn that is used for animal feed contributes far fewer calories than were initially grown. How many calories would the corn deliver if it wasn’t used for animal feed? Well, if it’s made into HFCS, as most of the corn is, the 50.5 bushels per acre devoted to feeding animals would produce approximately 62,000 to 825,000 calories depending on which conversion rate is assumed.

The 2% of the corn crop that is used for food goes into a wide variety of products, from corn chips to polenta. That makes it virtually impossible to determine the precise caloric yield per acre. However, according to the Corn Refiners Association, corn oil is the major food item produced with corn. One bushel of corn produces 0.7 pounds of corn oil [3], which contains about 240 calories per ounce. Making the simplifying assumption that all 11 bushels per acre that were used for food were delivered in the form of corn oil yields just under 30,000 calories.

Edit (09/05/13): As above, the bushels per acre is an over-estimate. The correct number is about 2,  which yields about 13,500 calories.

Based on these assumptions, I estimate that the 2011 corn crop supplied between 1.792 and 2.555 million edible calories per acre to the US food system, depending on the relative amounts of different animal products produced.

Edit (09/05/13): My revised estimate is 600,000 to 1.8 million calories. In the Foley article, he states that the US corn supply delivers about 3 million calories per acre per year, but there is no reference or data provided. I can only guess that my calculation includes some oversimplifications that account for the discrepancy. However, he also states that the corn crop is used to make polenta, which is actually made from sweet corn. The crop data from the USDA, upon which I have based my analysis, does not include sweet corn. So, perhaps we are using different data as well as different assumptions.

Also in 2011, the USDA reports that 1.76 million acres were devoted to the growing of vegetables and melons, which resulted in 43.2 billion pounds of food [4]. That’s ~24,500 pounds per acre. The top three crops were onions, head lettuce, and watermelon. Onions have about 12 calories per ounce, lettuce has 4, and watermelon has 9. Using the average of these three as representative of the caloric yield per pound of vegetables results in 3.14 million edible calories per acre.

It’s pretty surprising to think that vegetables and melons produce more calories per acre than corn. The reason is the way we use corn. If we instead used the 40% of the corn crop currently devoted to ethanol production to make corn oil or high fructose corn syrup, the corn crop would deliver significantly more calories than the vegetable crop. Of course, having more corn oil or corn sweetener may not have a significant benefit to human health.

We could also produce more edible calories if we did not use corn as animal feed. However, as long as we are growing corn, perhaps using it to create foods like eggs and pork is a nutritionally superior choice. Feeding corn to animals, especially cows, has many other drawbacks, though. Overall, the lack of an efficient pathway from the corn crop to nutritious food reinforces the idea that we ought to grow less corn, and use the land to cultivate nutritious foods instead.

The recommendation from the Union of Concerned Scientists is to convert 23 million acres of land from grain to fruits and vegetables in order to provide all Americans with their daily recommended intake of these foods. My analysis, which necessarily required a lot of simplifying assumptions, shows that this switch would actually deliver more edible calories to the food system, in addition to more micronutrients. It also shows how inefficient the corn-based system is at producing actual food. This makes me wonder just how much we could change the food system without a significant drop in calories. Could we switch to all organic production? Diversified farms? Farms that combine plants and animals? Given that we currently produce a surplus of calories, can more extreme changes in production practices (e.g. devoting more land to pasture for animals) still provide enough calories to feed our population? And would those calories provide superior nutrition to what we currently produce? Hopefully, with more research into sustainable farming practices, we can begin to answer these questions and design a food system that can sustainably produce nutritious, delicious food.

I think our food system should produce more fruits and vegetables instead of crops that are not used primarily for food. The Union of Concerned Scientists is doing a great job of showing how to make these changes and informing food policy decisions. You can learn more about their vision for the future of the food system in their recent policy brief, The Healthy Farm. You can also follow their blog, The Equation. If you like what you see, consider joining and taking action. Together, we can “plant the plate” and get on a better path to a sustainable food future.


Caveat to my analysis: More of the wheat crop is devoted to food products than the corn crop. Hence, switching from wheat to fruits and vegetables could result in a net drop in edible calories in the food system. Most farms cycle between wheat, corn, and soy, so it’s not quite as simple as switching out inefficient corn for produce. Although, perhaps fruits and vegetables could be added to the rotation instead of corn. This type of analysis is necessarily complicated, especially by the diversity of end products from corn, wheat, and soy. If you have ideas as to how it could be improved, or if you know of similar analyses elsewhere, please leave a comment!


[1] Data from FAO statistics website
[2] Fooducate article (32 pounds) and 2008 Iowa State Extension Service publication (33 pounds)
[3] North Dakota State University Extension Service website
[4] Data from USDA Economic Research Service website

* All calories determined from Calorie King


  1. Mark Shepard in Restoration Agriculture has an interesting solution. The idea is annual agriculture is an input based agriculture and perennial agriculture is a yield based agriculture. He does a thorough analysis of a perennial vs an annual based farming system and finds perennial farming can feed the world and wouldn't require the incredibly inefficient subsidy based agricultural system we have today. He goes into many of the topics you touch on here. Interesting stuff.

  2. I have heard in USA, big land lords own hundreds of acres of land where as in India, if they own 20 acres of land also, they are called big land lords. In USA they use large machines for all the operations and so only a single family is involved.Where as in India, many people are employed for doing various operations like sowing, ploughing,etc. I don't know how much is it true in the following point. The US, if they want to test any new variety they don't do it in their soil, but make poor countries like Indian food in Australia as testing ground. thanks

  3. Don't we grow so little because Mexico's basically our grocery store? I don't expect the USA exports much (any?) of its produce, thus that 50% stays local. Then, the rest of it comes from elsewhere. We seem to be able to get "everything" else relatively cheaply (or maybe my sense of price is disconnected, I'm open to that possibility).

  4. I'd also suggest re-hashing these numbers and land-yield and needed calories through the eyes of a reasonable (not Texas-sized) diet ... you know, to see what we could do if in response to our Mexican guide's assertion that they are now the second fattest country in the world, all us gringos hadn't been able to bust out chanting "we're number one!"