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Research intends to enhance lettuce nutrient content

Issue Date: April 15, 2020
By Bob Johnson
Researchers seek new ways to make lettuce more nutritious.
Photo/Kevin Hecteman

The next generation of lettuces could be higher in such important nutrients as vitamin C, antioxidants and beta carotene, as researchers and plant breeders take advantage of constantly advancing understanding of plant genetics.

These improvements in the nutritional value of lettuce could make a world of difference, researchers say, because people are not likely to begin eating enough vegetables any time soon.

"Nobody eats enough fruits and vegetables, and that is worldwide," said David Still, director of the agricultural research institute at Cal Poly Pomona. "We eat so much lettuce, it is a major source of nutrients in U.S. diets. People will not change their diets. People don't eat much spinach or broccoli, but we can change the nutrients in lettuce."

Still made his remarks during the Future of Lettuce Symposium, an event put together by the University of California, Davis, Genes to Growers project that featured presentations by university, U.S. Department of Agriculture and other agricultural researchers.

The event was originally scheduled for mid-March in San Luis Obispo County, but was moved to a video conference in order to avoid a large social gathering.

Though most vegetable crop breeding focuses on yield and pest or disease resistance, much of the research presented at the symposium aimed at breeding lettuce that contains more nutrients or lasts longer after harvest.

"Lettuce is one of the most consumed fresh market vegetables in the U.S.," Still said. "Consequently, increasing the nutritional content of lettuce would have positive impacts on health without asking consumers to change their dietary habits."

Still has already identified some of the genetics that make for health-promoting lettuce, and he has also learned that how the crop is grown impacts its nutritional value.

"The ascorbic acid and beta carotene are higher in furrow irrigated than drip," he said after conducting a series of trials in San Luis Obispo and Yuma, Arizona. "Anti-oxidants are higher under drip. There are also differences depending on whether you apply high or low levels of nitrogen."

A long-term goal of this research is to develop lettuce varieties that are uniformly high in important nutrients under different growing conditions, and are capable of conserving both water and fertilizer.

"We were screening by thinking future lettuce should use less water and less nitrogen and the current lettuce genomics are not well adapted," Still said. "There is a huge amount of difference based on environmental conditions, and that is a problem. We should dial in as much consistency as we can. We have candidate genes. We're going to end up stacking the traits and doing them one at a time."

Breeding and growing lettuce with more nutritional value would fit with a more general trend in vegetables.

"We are seeing a shift in vegetables in general and lettuce in particular toward quality characteristics," said Richard Howitt, UC Davis professor emeritus of agricultural and resource economics.

As one group of scientists works to breed better plants, other researchers are looking for ways to help retailers entice people to eat more vegetables.

"Very few Americans eat the recommended amounts of vegetables," said Gary Thompson, University of Arizona professor of production economics. "Less than 10% of us eat the recommended daily amount of fruits and vegetables. There is growing evidence that eating just a little more may help with health questions."

Thompson has conducted a survey of which shoppers are price sensitive in their vegetable purchases and would presumably respond to promotional pricing, and which are not, and would likely respond better to information about nutrition or how to use vegetables in interesting ways.

"Improvements in lettuce and leafy green production and processing leading to lower prices at retail will stimulate purchases by price-sensitive consumers," he said. "But segments of consumers not sensitive to price changes must be targeted with effective public policies and adept advertising. Using prices and quantities purchased would be good for targeting price-sensitive households. For price-insensitive, it might be more a matter of how to use them."

Thompson used data on the produce buying habits of 46,000 households, collected by Nielsen during a decade, in order to learn how to predict which shoppers would respond to lower prices.

"The whole point is to identify price-sensitive shoppers," he said. "If we were to promote more double-up offers on food stamps, we might be able to increase the consumption of fruits and vegetables by those shoppers."

Thompson said he learned a lot about differences in fruit and vegetable purchasing patterns via the 46,000 shoppers who agreed to take a scanner with them every time they went to the produce department.

In research conducted before stay-at-home orders related to the COVID-19 pandemic, there was a huge difference in how often people went to the market, as some shopped almost every day whereas others went to a supermarket barely more than once a month.

And there was also a very significant difference in the amounts of fruits and vegetables households purchased.

What he did not find, however, was the demographic characteristics of shoppers who would buy more produce if it were offered at lower prices.

"Much to my surprise, findings suggest that targeting consumers using demographic and geographic attributes alone will not be effective at stimulating demand for vegetables," Thompson said. "The number of trips is also not a good indicator."

Though the study revealed much information about produce buying habits, it left unanswered the question of why some people buy more vegetables than others.

"We can only speculate why demographics are not a good indicator of how much vegetables households consume," Thompson said.

(Bob Johnson is a reporter in Sacramento. He may be contacted at

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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