Incidence of celiac disease is on the rise but scientists have yet to identify why. One leading theory is that it is a result of wheat breeding that has created higher gluten content in wheat varieties.
However, a research article published in the Journal of Agricultural and Food Chemistry has shunned this popular idea.
"I have not found clear evidence of an increase in the gluten content of wheat in the United States during the 20th century, and if there has indeed been an increase in celiac disease during the latter half of the century, wheat breeding for higher gluten content does not seem to be the basis," said Donald Kasarda, physical science collaborator for the US Department of Agriculature (USDA) and author of the article.
Kasarda said that changes in the per capita intake of wheat and gluten were likelier factors that could have played a role in the rise of celiac disease, as both increased during the 20th and 21st centuries, although he said there was a lack of suitable data on the incidence of celiac disease by year to test these as possibilities.
He also said the rise of celiac disease could have been driven by increased consumption of vital gluten - a wheat flour fraction used as an additive to improve characteristics like texture.
He noted that this additive features a lot in increasingly popular whole wheat products.
Historical data and crude estimates
The research article cited statistics on wheat flour consumption throughout the two centuries.
Per person, wheat flour consumption (from all classes of wheat) was at a high of 220 lb (100kg) in 1900; declined steadily to a low of around 110 lb (50kg) in 1970; gradually rose to about 146 lb (66kg) in 2000 and has since decreased to about 134 lb (61kg) in 2008.
"Although wheat flour consumption seems to be decreasing slightly in recent years, there was an increase in the yearly consumption of wheat flour of about 35 lb (15.9kg) per person in the period from 1970 to 2000, which would correspond to an additional 2.9 lb (1.3kg) of gluten per person from that extra flour intake," Kasarda said.
Using 'crude estimates', the scientist also suggested that vital gluten consumption has tripled since 1977.
"This increase is of interest because it is in the time frame that fits with the predictions of an increase in celiac disease," he said.
However, he noted that it remains difficult to attribute this directly to the rise of celiac disease, especially as consumption of wheat flour increased far more significantly in the same time frame.
Wheat breeding for increased gluten: Shunned
Kasarda rejected the theory that farmers have been breeding wheat to ensure higher protein and therefore gluten content over the years.
"The earliest farmers were selecting for many traits, but protein content was not one of them," he said, suggesting seed size and starch content as likelier traits targeted.
"Various studies have compared the protein contents of wheat varieties from the early part of the 20th century with those of recent varieties. When grown under comparable conditions, there was no difference in the protein contents," he said.
Improved diagnosis: Another factor?
Another factor put forward for the rise in celiac disease is that more people are being diagnosed, and chief executive of Coeliac UK Sarah Sleet said that diagnosis is rising rapidly and noticeably.
Sleet told BakeryandSnacks.com that research undertaken in the last ten years has shown that 1 in 100 people across the UK have celiac disease, but it is estimated that less than one in five of these are diagnosed. The average figure of celiacs in Europe is the same.
"So it is likely that the number of people being diagnosed is rising rapidly. We don’t know if the numbers of people with the disease itself is rising rather than just more people being diagnosed - there is not enough evidence yet to give an accurate picture although there are two studies, one in the US and one in Finland that suggest the prevalence of the disease may be on the rise," she said.
In light of Kasarda's article, Sleet said: "A lot more research is needed, first of all to show that there is a real rise in the prevalence of the condition and secondly to understand how it relates to levels of gluten consumption over time."
Source: Journal of Agriculture and Food Chemistry
Published online ahead of print, doi: 10.1021/jf305122s
"Can an Increase in Celiac Disease Be Attributed to an Increase in the Gluten Content of Wheat as a Consequence of Wheat Breeding?"
Author: Donald D. Kasarda