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PubMed Food Problem: Cruciferous Vegetables

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To do a PubMed search for cruciferous vegetables that includes such species as Radish and Arugula, each species must be done separately.

By Eric Rumsey, Janna Lawrence and Xiaomei Gu

In order to do successful searches for cruciferous vegetables in PubMed, it helps to know exactly what “cruciferous” means, which makes it easier to understand what vegetables are considered “cruciferous” and the botanical relationships among them. We have discussed these topics in a companion article.

In general, cruciferous vegetables are considered to be any plants in the family Brassicaceae that are edible. Most of these, especially the more popular ones (cabbage, broccoli, cauliflower, brussel sprouts) are in the genus Brassica. A few others are in other genera in the family, the most notable being Radish (Raphanus), Daikon (Raphanus), Arugula (Eruca), Horseradish (Armoracia), White mustard (Sinapis), Garden cress (Lepidium) and Wasabi (Wasabia). With most edible members of the family Brassicaceae being in the genus Brassica, then, searching for that genus works well for most cruciferous vegetables. But without including the MeSH terms for all of the other edible genera in the family, there is no easy way to do a comprehensive search for them as a group.

With edible species in several genera in the Brassicaceae family, it might seem like a way to include all of them would be to search for the family name, since it’s an explosion that contains all of the genera in the family. We have seen this done by MeSH indexers in some cases, but it has problems. For one thing, the family is very large, containing 372 genera, so searching for the family name can retrieve many inappropriate citations. This is especially a problem because one of the genera in the family is Arabidopsis, a very commonly used research subject in plant genetics, having nothing at all to do with nutrition. Arabidopsis is something like the Drosophila of the plant world. So of course searching for the exploded MeSH term Brassicaceae gets a flood of articles on Arabidopsis; approximately 80% of all articles retrieved from this search are indexed to the narrower term Arabidopsis.

We found another problem in how cruciferous vegetables are treated in PubMed indexing when we looked at sample of 30 articles with “cruciferous” in the title.  Twenty-eight of the 30 articles actually had the phrase “cruciferous vegetables” in the title, but  in about ⅓ of the 30 articles, there was no indexing term at all correlated with the word “cruciferous,” and the indexing term used was just “vegetables,” ignoring the word “cruciferous.” Another problem we found in this sample is that, of the articles that had an indexing term correlated with “cruciferous,” the term that was usually used was the family name, Brassicaceae, which retrieves many non-food-related citations, as discussed above.

Suggestions for improving indexing of cruciferous foods

Because there is currently no way to search for cruciferous foods as a group, we would suggest that NLM should add a new MeSH term <cruciferous foods>. This would not only put all of these foods under one term, it would also provide a term to use for articles that use the term itself in the title or abstract.

Image at top of article is from Wikipedia.

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The meaning of cruciferous

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To modern ears, “cruciferous” is all about vegetables. But the word’s rich history shows that it was formerly used in a much broader sense.

By Eric Rumsey, Janna Lawrence and Xiaomei Gu

In a Google search for the word “cruciferous,“ 9 out of the top 10 retrievals contain the phrase “cruciferous vegetables.” This certainly does fit the predominant modern usage of the word. As a game show host might say, “what do you think of when I say ‘cruciferous’?” Well, of course, “vegetables”! But it hasn’t always been this way. As the Google Ngram chart below shows, the phrase “cruciferous vegetables” only came into prominent use about 1980. Before that, the word “cruciferous” was widely used in other contexts.

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To understand the real meaning of the word, it’s important to understand what these other contexts are. This is important for more than simply historic reasons; it’s also important to understand the meaning of the word to understand its connections to nutrition, and because it helps to search for the subject in databases such as PubMed (as we’ve discussed in a companion article). Additionally, it’s a surprisingly interesting story.

The key to understanding “cruciferous” is a knowledge of its rich botanical history. The chart below gives a hint of this. The chart is a comparison of the use of the words Cruciferae and Brassicaceae. These are names that have been assigned to the plant family that contains “cruciferous vegetables” and many other plants as well. As the chart indicates, Cruciferae was the name of the family until the early 20th century, when it was officially changed to Brassicaceae. Since then, botanists have gradually been switching the word they use, with continuing widespread use of the older name Cruciferae.

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This seemingly arcane naming distinction is important because when the family name was Cruciferae, the word cruciferous was used to include all plants in the family, not just the edible species that we call “cruciferous vegetables,” which helps explain the common use of the word in the chart above. (Examples from Google Books of the broad botanical use of the word “cruciferous” in the 19th century are here, here, and here.) The significance of this is magnified by the fact that the family is very large, containing 372 genera and 4060 species, making it one of the largest flowering plant families. This and other details of the family are well-covered by a Wikipedia article on it. Another detail that gives an idea of the size and variety of the family and helps explain the widespread use of “cruciferous” is that, in addition to cruciferous vegetables, it also includes decorative flowers, weeds, and Arabidopsis thaliana (“a very important model organism in the study of the flowering plants”).

Relating to the image of three flowers at the top of the article, another help in understanding “cruciferous” is the etymology of the word itself. The word comes from the word “cross,” because the 4-petaled flowers have the appearance of a cross. The flowers in the image above are (from left) Raphanus sativus (Wild radish weed), Brassica oleracea (Broccoli) and Arabidopsis thaliana. (Images are from Wikipedia).

In conclusion, the word “cruciferous” is confusing because the word has its origins in a time when the large family Brassicaceae was called Cruciferae, which meant that all of the plants in the family (most of which are not edible) were referred to as “cruciferous.” In the last generation, as botanists have switched to calling the family Brassicaceae instead of Crucuferae, and as people have become more aware of nutrition, the word “cruciferous” has gradually come to be used most commonly in the context of “cruciferous vegetables.” As we’ll discuss in a companion article, it’s important to know about this history and the taxonomic relationships of cruciferous vegetables in order to do successful searches in research databases like PubMed.

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Plant-Based Foods – A Tricky PubMed Search – Revised 2016

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By Eric Rumsey, Janna Lawrence and Xiaomei Gu

As we discussed in an article earlier this year, searching for nutrition in PubMed has improved greatly since NLM brought the subject together in one explosion (Diet, Food, and Nutrition). This ability to search the field of nutrition easily has helped in searching for plant-based foods [PBFs] in some ways. But in other ways, it’s still as difficult as it was when we wrote our 2013 article on the same topic.

The basic problem in searching for PBFs, just as it was before the addition of the new explosion, is that a large proportion of PBFs are not in the Food explosion, but are only in Plants, and not in Food. So the fact that Food is part of the new inclusive explosion doesn’t make it any easier to search for PBFs.

In addition to the fact that most fruits and vegetables are treated as plants instead of foods, another problem in searching for them is that almost all of them are put under their botanical, Latin names, that are not recognizable to most people. Here are some examples, all of which are in the plant-taxonomic branch of the MeSH tree:

  • Kale is Brassica
  • Sweet potato is Ipomoea batatas
  • Plum is Prunus domestica
  • Almond is Prunus dulcis
  • Apple is Malus
  • Cranberry is Vaccinium macrocarpon
  • Strawberry is Fragaria
  • Kidney Beans is Phaseolus
  • Chocolate is Cacao
  • Turmeric is Curcuma

If you’re searching for specific food plants, the Latin botanical MeSH terms are usually not a problem, because when you search for a common name, it’s mapped to the botanical MeSH term (e.g. if you search for Grapes, it maps to Vitis). The problem comes if you want to browse the Plants explosion to pick out the edible plants from the many plants that are not edible, because only the botanical names are listed. The Rose family (Rosaceae) of plants, for example, has several edible species within it. There are 19 genera listed in MeSH in the family, and 6 of them have edible species. But to find them, you have to be able to pick out the genera with edible species (e.g. Malus, Prunus) from the others (e.g. Agrimonia, Alchemilla).

If you’re interested in learning about how to search for PBFs in PubMed, see our companion article, which includes an updated “search recipe,” or hedge.

[Image above is public domain, from WikiMedia]

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US Lags Behind The World In Plant-Based Food Research

By Xiaomei Gu, Eric Rumsey and Janna Lawrence

In our explorations of plant-base foods (PBFs) in PubMed, it’s often striking that there are many excellent articles from non-US countries. So we did a survey in PubMed to measure different countries’ authorship of articles on PBFs, and we found that, indeed, several countries have a much higher proportion of their total articles on PBFs than the US.

The charts below show our data for all PBFs and for four specific foods or food groups. The charts are based on the percentage of articles from each county, not the total number of articles. So even though the total number of articles on PBFs by US authors may be higher than other countries, the proportion of articles on PBFs is substantially lower. [The charts are from a poster presented at MLA in 2016. For more details on our survey methods, see the poster.]

hardinlibPosterPBFcountriesLeadPubMed search strategy used to find plant-based foods in chart above is described here.

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Nuts as a Healthy Food: How to Search in PubMed

By Eric Rumsey, Janna Lawrence and Xiaomei Gu

This article is based on a poster presented at the Medical Library Association annual meeting, Toronto, May 2016.

Introduction

Searching for nuts as food is difficult. As with most plant-based foods, MeSH terms for specific types of nuts are in the Plants explosion instead of in the food explosion. Nuts are especially tricky because the MeSH term Nuts is not an explosion, and most articles on specific types of nuts are not indexed to the term Nuts. So it’s necessary to search for specific nuts to retrieve articles on them.

A caveat—As with nutrition topics in general, and plant-based foods in particular, searching in PubMed is complicated, largely because many plant-based substances are used as foods and also as medicines or experimental organisms. A list of articles on specific nut types is likely to contain some articles that are not food-related.

Searching for Nut Types

The general idea of searching for specific types of nuts is simple: Do an OR search that includes the common name and botanical name. In most cases, articles on a specific nut type will be indexed under the botanical name, but using the common name is always a good idea. See the example below for searching walnuts.

walnut [tiab] OR walnuts [tiab] OR juglans [MeSH]

It is necessary to restrict the search for the common names to the title and abstract [tiab] fields because there are many streets in the Address field that are named after nuts (e.g., 975 Walnut St.).

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Image 1. Almonds

 

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Image 2. Walnuts

 

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Image 3. Hazelnuts

 

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Image 4. Cashews

 

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Image 5. Pecans

 

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Image 6. Brazil Nuts

 

Peanuts Are Different!

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Image 7. Peanuts

Peanuts are a special case. Unlike the other nuts here, they grow on herbaceous plants instead of on trees and, as members of the bean family, they are nutritionally more closely related to beans than to other nuts. There is also a separate MeSH term, Peanut Hypersensitivity, dealing with peanut allergies.

Because peanuts are commonly used as experimental plants, many of the articles about them are not related to nutrition. To  focus on nutritional aspects, we suggest incorporating the Diet, Food, and Nutrition explosion into the search:

(peanut [tiab] OR peanuts [tiab] OR arachis [mh])

AND Diet, Food, and Nutrition [mh]

Citations: 2932