No clear link seen in new wheat breeds, celiac disease
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KANSAS CITY — A researcher who explored the hypothesis that modern strains of wheat produced by special breeding might be linked to the rise in cases of celiac disease in the United States has concluded that evidence is lacking to support the theory.
Writing in the September 2013 Journal of Agricultural and Food Chemistry, Donald D. Kasarda, a U.S. Department of Agriculture staff member at the Agricultural Research Service’s Western Regional Research Center in Albany, Calif., said that “if there has indeed been an increase in celiac disease during the latter half of the (twentieth) century, higher gluten content does not seem to be the basis.”
Celiac disease is an immune reaction to consumption of gluten, a plant protein found in wheat, barley and rye. Symptoms involve damage to the small intestine that ultimately may lead to most vital organs being starved of nourishment. No cure exists but a strict gluten-free diet may help manage symptoms.
A key starting point in Mr. Kasarda’s research was his assertion that little evidence exists that either winter or spring wheats have consistently trended toward higher protein — or gluten — levels since they were introduced to American farmers from Europe and Asia in the early years of the 20th century. He acknowledged there is a dearth of relevant data, especially from the first-half of the 20th century, which has not been digitized. But he added that “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.
Furthermore, manufacturing practices in the production of both bread, which typically uses hard winter and spring wheat varieties, and baked goods, which utilize lower-protein soft wheats with good starch qualities, keep protein levels within the same predictable ranges long used by bakers.
Mr. Kasarda noted that flour blending occurs to keep protein levels at uniform levels in the manufacture of bread and baked goods.
“To maintain a uniformity of quality characteristics from year to year, flour mills usually blend wheat flour that is intended for commercial use by specific customers, for example, bakeries,” he said. Therefore, even when especially high-gluten wheat is available, it would be blended with lower-gluten varieties to create the same baking properties that have been in place for decades, well before the surge in celiac disease cases that began about 50 years ago.
But Mr. Kasarda acknowledged that a variety of factors might contribute to the development of celiac disease symptoms “such as per capita vital gluten intake, variations in individual diets with regard to the amount and types of wheat consumed, wheat genetics and agronomic practices (such as nitrogen fertilization) could contribute to the level of toxicity of wheat for people genetically predisposed to celiac disease.” He recommended further study of the subject.
Mr. Kasarda examined the development of wheat from its beginnings as a domestic food crop about 10,000 years ago. He pointed out that wheat was bred with more complex genomes as early farmers and breeders selected for seed size, among other traits, because larger grains were easier to recover during threshing. Because there was no way to test for actual protein levels until late in the 19th century, protein considerations did not count for centuries of wheat breeding. Mr. Kasarda said the protein content of domesticated wheat probably steadily declined because of trait selection that involved an inverse relationship to protein, such as seed size and starch content.
He noted that, today, there are no bioengineered varieties of wheat being cultivated; all current breeds are descendants of early wheat, although they have split into many varieties and possess more complicated genomes than early diploid wheat. Evidence exists that one of the genomes in bread wheat is especially likely to aggravate celiac disease, he said. Other varieties such as durum appear to be less toxic to celiac patients than bread flour.
Mr. Kasarda raised the question of whether increased consumption of wheat or vital gluten, an ingredient often used in whole wheat products, may be responsible for the increase in celiac disease.
He doesn’t fully answer this line of inquiry because he said data is lacking. But he pointed out that the gluten in a slice of bread so far exceeds the very small amount of gluten considered safe for celiac disease sufferers that it appears to obviate any effects from a variation in protein content.
He noted that U.S.D.A. Economic Research Service statistics indicate that consumption of wheat flour per person reached a high of about 220 lbs per person in 1900, to a low of 110 lbs per person in 1970 and then gradually has risen to about 146 lbs per person in 2000. Vital gluten consumption has tripled per capita since 1977. This ingredient, added to certain whole wheat products, is 80% imported, and there is a lack of accessible information about it relating to celiac disease.
He said further research into the mechanisms of celiac disease itself would be useful.
“One cannot rule out that the process by which the immune system switches from tolerance of wheat gluten protein to intolerance (celiac disease) might be dependent on the total amount of gluten encountered,” Mr. Kasarda said. “Development of immune system tolerance to food proteins in general is an as yet imperfectly understood process — as is the loss of immune system tolerance to gluten proteins that is characteristic of celiac disease.”