The cause of celiac disease remains a puzzle. The prevalence of the disease has increased dramatically over the past few decades; but, contrary to some of the claims in the popular media, there is no clear evidence that changes in wheat or changes in wheat consumption can account for the major increase in prevalence of celiac disease.

In my previous article (Ref. 1), I discussed some of the current ideas for the huge increase in celiac disease that has been reported, including changes in childhood infection or breastfeeding. This blog focuses on the idea that the amount of gluten that we consume might be important.

In the 1600′s and 1700′s, it was very expensive to produce wheat, so wheat bread was mainly consumed by the wealthy. In the 1800′s, improvements in machinery for agriculture and milling reduced wheat production costs, and expansion of the railroad system enabled transportation costs to be reduced dramatically, especially over long distances in the U.S. By 1900, U.S. wheat consumption had increased to 226 lbs/year for an average person (see the Figure and Ref. 2).

In the 20th century, there was a steady decline in consumption, with an all-time low of 110 lbs/year in 1975. More recently, dietary concerns about the health effects of dietary fats, plus an increase in fast-foods, led to a resurgence in wheat consumption. This may also have been influenced by dietary recommendations from the USDA. In 2011, U.S. per capita consumption of wheat was about 133 lbs.

The prevalence of celiac disease is estimated to have increased about 4-fold over the past half-century, but there is no obvious relationship between the dramatic rise of celiac disease and the fairly modest changes in wheat consumption over the same period.

A recent paper by D. Kasarda (Ref. 3) discusses this idea, based on available information about U.S. wheat over the past century. Two main types of wheat are consumed: “hard” wheat has a higher gluten content, ideal for bread making, while “soft” wheat has lower gluten, and is more suited to cakes and pastry. Hard wheat contains about 12-14% total protein, while soft wheat has 7-11%. Durum wheat, used for pasta, has a high total protein content, but less gluten than bread wheat.

According to Dr. Kasarda, no major changes in wheat protein have occurred for the years where data is available. The only slight changes are for years in which there was a drought, but it is common practice to blend wheat produced in different years in order to achieve a consistent gluten content.

Agricultural practices have changed over the years, with increased use of fertilizer, and changes in crop rotation patterns. However, these changes have focused on increasing the overall yield of wheat, rather than changing its gluten content.

There are literally hundreds of varieties of wheat grown around the world. Breeding efforts have focused on increased yield, and adaptation to different environments—not altered gluten content. Interestingly, wild varieties of wheat can have roughly twice the gluten content of modern versions (Ref. 3). So far, genetic improvements have involved traditional breeding approaches, and the use of modern “genetic engineering” technology to improve wheat has not been applied on a commercial scale. (In principle, genetic engineering technology might be used to reduce the immune-stimulating activity of wheat, without sacrificing its bread-making properties, but this approach has not been tried yet).

Another way to examine the possible role of gluten consumption is to look at celiac disease prevalence in different countries. For example, the prevalence of celiac disease in Germany is roughly one tenth that in Finland, even though Germans eat plenty of bread. Of course, there are many other differences between these two countries, including their different ethnic backgrounds. However, genes can’t be the critical factor, since people in Karelia (who are ethnically Finnish, but live in Russia) have a much lower celiac disease prevalence than their Finnish relatives.

While there are some people who would like to blame modern wheat agriculture for the rise in celiac disease, the available evidence simply does not support this idea.

Personal comment:

Wheat currently provides about 20% of calories for the world’s food supply, and is a critical part of the world’s nutrition. From a social perspective, the 20th century “green revolution”, with its dramatic increase in wheat yields certainly saved the lives of millions across the world. In the future, changes in climate and population will put increasing stress on our ability to feed the world. The challenge will probably be to maintain current productivity, let alone address the increasing demand, so I personally hope that we haven’t exhausted ways of improving wheat strains and agricultural methods. What do you think?

References:

Ref. 2:  Wheat’s Role in the U.S. Diet Has Changed Over the Decades. http://www.ers.usda.gov/topics/crops/wheat/wheats-role-in-the-us-diet.aspx#.UVyUo6tOx8M

Ref. 3:  Can an Increase in Celiac Disease Be Attributed to an Increase in the Gluten Content of Wheat as a Consequence of Wheat Breeding? http://pubs.acs.org/doi/full/10.1021/jf305122s  Kasarda, D.