1. Introduction
Celiac disease (CD) is a chronic small intestinal immune-mediated enteropathy, observed in genetically susceptible individuals in response to exposure to dietary gluten [
1]. Gluten is the main structural protein complex of wheat with equivalent proteins found in other cereals including rye and barley. The gluten toxic protein fractions for people with CD include prolamins and glutenins [
2] but the alcohol-soluble fractions (prolamins) of wheat (gliadin), rye (secalin) and barley (hordein) are considered to be the protein constituents of most concern to celiac individuals [
3]. The word “gluten” is often considered as a generic name given to storage proteins in wheat, barley, rye and other closely related cereal grains. Thus, it is the gluten in wheat flour that binds and gives structure to bread, baked goods and other foods making it widely used in the production of many processed and packaged foods.
Presently, the only treatment for celiac disease is a strict exclusion of gluten sources including wheat, rye, barley and their hybridized forms from the diet [
4,
5]. However, a very low amount appears to be tolerated by most of celiac individuals. The available scientific literature addressing safe levels of gluten intake for individuals who suffer from celiac disease essentially relies on either the analysis of results of intestinal biopsies carried out on these individuals or on strictly clinical criteria [
6,
7]. Although there is no evidence to suggest a single definitive threshold for a tolerable level of gluten intake for those with CD, there is evidence to suggest that, for most affected individuals, exposure to less than 10 mg/day is unlikely to cause histological changes to the intestinal mucosa while exposure to 50 mg/day is likely to do so [
8,
9].
Typically, the diet that is consumed by individuals who suffer from celiac disease is based on a combination of: (a) foods that naturally contain no gluten and are unlikely to have been contaminated with gluten (meat, fish, milk, eggs, etc.); and (b) specially formulated substitute gluten-free grain-containing products (labelled “gluten-free”). However, because naturally gluten-free (GF) grains can become contaminated with gluten-containing grains, there may be some concern about the safety of individuals with CD using naturally gluten-free flours and starches made from cereal grains (e.g., corn), legumes (e.g., peas, beans) or other plants to prepare grain-based foods such as bread and baked goods at home.
The potential for gluten to be present in grains that do not naturally contain gluten is related to the way that grains are grown, harvested and transported. This unintended presence of gluten is to be expected in the context of current industry practices, and is allowed in Canada under the Canadian Grain Standards. There are processes in place for cleaning grains but these can only reduce, and not completely eliminate, the presence of gluten in flours and starches made from cereal plants that do not naturally contain gluten.
The objective of this study was to estimate the level of incidental gluten potentially present in GF diets consumed in Canada, including its potential variability across factors such as presence/absence of a GF package label and varying levels of fiber content in GF grain-based ingredients.
3. Results
Estimated intakes of grain-containing foods (g/day) by average eaters (50th percentile) and by heavy eaters (97th centile) in the CCHS 2.2 survey are presented in
Table 3. Estimates are presented for both single day intakes and for usual intakes, as well as for both “as-consumed” weights and “as-purchased” weights. “As-purchased” weights are reported because section B.24.018 of Canada’s
Food and Drug Regulations applies to GF foods as sold/purchased.
Table 3.
Estimated intake (g) of grain-containing foods among CCHS 2.2 participants.
Table 3.
Estimated intake (g) of grain-containing foods among CCHS 2.2 participants.
Categories | 24-h Intake | Usual Intake |
---|
50th | 97th | 50th | 97th |
---|
Grain-containing foods, as-consumed weight (g) | 154.0 | 618.5 | 189.2 | 391.0 |
Grain-containing foods, as-purchased weight (g) | 133.5 | 433.3 | 151.4 | 299.6 |
Estimated levels of gluten exposure under Scenarios 1 and 2 (hypothetical gluten contamination levels of 5, 10, 20 and 50 ppm) among all survey respondents are presented in
Table 4. Estimates are presented separately for a single 24-h period and for usual intake; for average eaters (50th percentile) and for heavy eaters (97th percentile). Looking at the results for Scenario 1, hypothetical contamination levels of 5 ppm and 10 ppm in all ready-to-eat GF grain-containing foods was associated with an estimated gluten exposure levels below 4 mg/day, among both average eaters (50th percentile) and heavy eaters (97th percentile). At a hypothetical contamination level of 50 ppm the estimated total daily intake at the 97th percentile is 19.31 mg/day for one-day and 14.98 mg/day for usual intake, both higher than the 10 mg/day tolerated by most individuals with celiac disease. A hypothetical contamination rate of 20 ppm was associated with one-day and usual gluten exposure estimates for heavy eaters (97th percentile) below 10 mg/day (7.72 mg/day and 5.64 mg/day respectively).
Table 4.
Estimated percentiles of gluten exposure (mg/day) assuming hypothetical levels of gluten contamination of 5, 10, 20 or 50 ppm in as-purchased products.
Table 4.
Estimated percentiles of gluten exposure (mg/day) assuming hypothetical levels of gluten contamination of 5, 10, 20 or 50 ppm in as-purchased products.
Gluten Levels | Scenario 1 Food Purchased Ready-to-Eat | Scenario 2 Ingredients Purchased for Home Preparation |
---|
24-h Intake | Usual Intake | 24-h Intake | Usual Intake |
---|
50th | 97th | 50th | 97th | 50th | 97th | 50th | 97th |
---|
5 ppm | 0.63 | 1.93 | 0.76 | 1.50 | 0.48 | 1.55 | 0.55 | 1.08 |
10 ppm | 6 | 3.86 | 1.51 | 3.00 | 0.97 | 3.11 | 1.09 | 2.16 |
20 ppm | 2.54 | 7.72 | 3.03 | 5.64 | 1.93 | 6.21 | 2.19 | 4.32 |
50 ppm | 6.34 | 19.31 | 7.57 | 14.98 | 4.84 | 15.53 | 5.47 | 10.80 |
Table 5 provides separate gluten exposure estimates for 14 age-sex groups under the 20 ppm hypothetical level of gluten contamination used in Scenarios 1 and 2. While exposure estimates vary across these population sub-groups it can be seen that the highest estimated exposure levels among heavy eaters (97th percentile) are for males 19–30 years of age and males 14–18 years of age. While estimated exposure for these two sub-groups is slightly over 10 mg/day when a single day’s food consumption is considered (10.31 mg/day and 10.12 mg/day respectively), it is below 10 mg/day when usual dietary intakes are considered (8.45 mg/day and 4.92 mg/day respectively). Exposure estimates are generally lower for Scenario 2 than for Scenario 1, with 97th percentile values for Scenario 2 of 8.45 mg/day (one day) and 4.92 mg/day (usual) for males 19–30 years of age and values of 8.33 mg/day and 5.75 mg/day respectively for males 14–18.
Table 5.
Estimated percentiles of gluten exposure (mg/day) in different age-sex groups assuming hypothetical levels of gluten contamination of 20 ppm.
Table 5.
Estimated percentiles of gluten exposure (mg/day) in different age-sex groups assuming hypothetical levels of gluten contamination of 20 ppm.
Age-Sex Groups | Scenario 1 Food purchased Ready-to-Eat | Scenario 2 Ingredients purchased for Home Preparation |
---|
24-h Intake | Usual Intake | 24-h Intake | Usual Intake |
---|
50th | 97th | 50th | 97th | 50th | 97th | 50th | 97th |
---|
1–3 years | 1.59 | 4.60 | 1.73 | 3.65 | 1.25 | 3.89 | 1.35 | 2.91 |
4–8 years | 2.71 | 6.90 | 2.94 | 4.67 | 2.06 | 5.27 | 2.28 | 3.66 |
M: 9–13 years | 3.30 | 8.48 | 3.75 | 5.66 | 2.52 | 7.18 | 2.89 | 4.31 |
F: 9–13 years | 2.88 | 6.86 | 3.19 | 5.06 | 2.16 | 5.78 | 2.46 | 3.90 |
M: 14–18 years | 3.67 | 10.12 | 4.13 | 7.12 | 2.78 | 8.33 | 3.22 | 5.75 |
F : 14–18 years | 2.75 | 7.58 | 2.95 | 5.33 | 2.07 | 6.13 | 2.30 | 4.25 |
M: 19–30 years | 3.35 | 10.31 | 3.71 | 6.30 | 2.55 | 8.45 | 2.96 | 4.92 |
F: 19–30 years | 2.34 | 6.80 | 2.49 | 4.28 | 1.82 | 5.66 | 2.00 | 3.56 |
M: 31–50 years | 2.89 | 8.95 | 3.31 | 6.47 | 2.21 | 7.15 | 2.57 | 4.56 |
F: 31–50 years | 2.23 | 6.33 | 2.43 | 4.14 | 1.71 | 4.84 | 1.90 | 3.48 |
M: 51–70 years | 2.70 | 7.10 | 2.86 | 5.36 | 2.06 | 5.92 | 2.19 | 4.22 |
F: 51–70 years | 2.06 | 5.88 | 2.22 | 4.01 | 1.55 | 5.02 | 1.74 | 3.35 |
M: ≥71 years | 2.51 | 6.75 | 2.72 | 4.81 | 1.91 | 5.26 | 2.08 | 3.80 |
F: ≥71 years | 2.03 | 4.83 | 2.16 | 3.83 | 1.53 | 3.97 | 1.65 | 2.97 |
Overall | 2.54 | 7.72 | 3.03 | 5.64 | 1.93 | 6.21 | 2.19 | 4.32 |
Table 6 presents results for the two lower fiber scenarios (Scenarios 3 and 5) in which many grain-based foods are prepared at home with packages of traditionally used GF flours and starches (for example, rice flour, corn starch, potato starch). In Scenario 3 all packages of flour/starch had GF labels. As can be seen on the left side of
Table 6, estimated gluten intake is consistently below 10 mg/day, for a single day’s intake and for usual intake, for average eaters (50th centile) and for heavy eaters (97th centile), overall and in each of the 14 age-sex groups for which intake levels were estimated.
Scenario 5 was similar to Scenario 3 except that in Scenario 5 none of the packages of GF flour/starch had GF labels. Results for Scenario 5 are similar to those for Scenario 3. As can be seen on the right side of
Table 6, values for the (97th percentile for a single day ranged from a low of 2.81 mg/day for females 71 years of age or older to a high of 7.03 mg/day for males 19–30 years of age. Corresponding values for usual intake were somewhat lower (from 2.05 for females 71 years of age or older to 4.21 for males 14–18 years of age).
Table 7 presents results for the two higher fiber scenarios (Scenarios 4 and 6) in which many grain-based foods are prepared at home using packages of GF flours and starches that can be used to increase the fiber content of a GF diet (for example, bean flour). In Scenario 4 all packages had GF labels. As can be seen on the left side of
Table 7, estimated gluten intake is below 10 mg/day, for both a single day’s intake and for usual intake, for average eaters (50th percentile) and heavy eaters (97th percentile), overall and in each of the 14 age-sex groups for which intake levels were estimated.
Table 6.
Estimated percentiles of gluten exposure (mg/day) in different age-sex groups when many grain-containing foods are prepared at home using traditional lower fiber GF flours and starches.
Table 6.
Estimated percentiles of gluten exposure (mg/day) in different age-sex groups when many grain-containing foods are prepared at home using traditional lower fiber GF flours and starches.
Age-Sex Groups | Scenario 3 Lower Fiber GF Flours and Starches Labelled GF | Scenario 5 Lower Fiber GF Flours and Starches NOT Labelled GF |
---|
24-h Intake | Usual Intake | 24-h Intake | Usual Intake |
---|
50th | 97th | 50th | 97th | 50th | 97th | 50th | 97th |
---|
1–3 years | 0.52 | 2.94 | 0.70 | 1.91 | 0.59 | 3.13 | 0.80 | 2.39 |
4–8 years | 0.86 | 4.35 | 1.20 | 2.44 | 0.98 | 4.52 | 1.39 | 2.88 |
M: 9–13 years | 0.79 | 6.04 | 1.29 | 2.95 | 1.01 | 6.09 | 1.52 | 3.19 |
F: 9–13 years | 0.74 | 5.06 | 1.17 | 2.43 | 0.92 | 5.06 | 1.38 | 2.70 |
M: 14–18 years | 0.83 | 6.55 | 1.44 | 3.69 | 1.04 | 6.65 | 1.70 | 4.21 |
F: 14–18 years | 0.54 | 4.67 | 0.86 | 2.90 | 0.73 | 4.83 | 1.11 | 3.25 |
M: 19–30 years | 0.18 | 7.01 | 1.05 | 5.65 | 0.61 | 7.03 | 1.24 | 4.10 |
F: 19–30 years | 0.46 | 4.26 | 0.78 | 2.16 | 0.60 | 4.48 | 0.96 | 2.65 |
M: 31–50 years | 0.21 | 5.90 | 0.97 | 2.92 | 0.57 | 5.99 | 1.18 | 2.58 |
F: 31–50 years | 0.29 | 3.71 | 0.63 | 2.33 | 0.50 | 3.91 | 0.82 | 2.48 |
M: 51–70 years | 0.29 | 4.22 | 0.61 | 2.97 | 0.56 | 4.40 | 0.86 | 2.80 |
F: 51–70 years | 0.29 | 3.10 | 0.53 | 2.08 | 0.48 | 3.40 | 0.70 | 2.23 |
M: ≥71 years | 0.53 | 3.27 | 0.66 | 2.55 | 0.70 | 3.62 | 0.87 | 2.58 |
F: ≥71 years | 0.43 | 2.43 | 0.54 | 1.72 | 0.56 | 2.81 | 0.74 | 2.05 |
Overall | 0.51 | 4.54 | 0.76 | 2.94 | 0.68 | 4.74 | 1.00 | 3.19 |
Table 7.
Estimated percentiles of gluten exposure (mg/day) in different age-sex groups when many grain-containing foods are prepared at home using higher fiber GF flours and starches.
Table 7.
Estimated percentiles of gluten exposure (mg/day) in different age-sex groups when many grain-containing foods are prepared at home using higher fiber GF flours and starches.
Age-Sex Groups | Scenario 4 Higher Fiber GF Flours and Starches Labelled GF | Scenario 6 Higher Fiber GF Flours and Starches NOT Labelled GF |
---|
24-h Intake | Usual Intake | 24-h Intake | Usual Intake |
---|
50th | 97th | 50th | 97th | 50th | 97th | 50th | 97th |
---|
1–3 years | 0.56 | 3.02 | 0.74 | 1.95 | 0.96 | 22.96 | 2.73 | 9.44 |
4–8 years | 0.93 | 4.46 | 1.25 | 2.42 | 1.68 | 29.89 | 5.29 | 12.30 |
M: 9–13 years | 0.92 | 5.98 | 1.40 | 2.59 | 2.06 | 41.47 | 7.44 | 12.59 |
F: 9 –13 years | 0.86 | 5.06 | 1.28 | 2.12 | 1.75 | 33.70 | 6.23 | 11.52 |
M:14–18 years | 0.94 | 6.46 | 1.53 | 3.46 | 2.22 | 51.50 | 8.81 | 17.05 |
F: 14 –18 years | 0.66 | 5.05 | 1.03 | 2.76 | 1.47 | 38.91 | 5.69 | 13.22 |
M: 19–30 years | 0.47 | 7.12 | 1.20 | 3.85 | 1.77 | 49.43 | 7.58 | 14.96 |
F: 19–30 years | 0.56 | 4.72 | 0.90 | 2.28 | 1.24 | 32.54 | 4.94 | 9.77 |
M: 31–50 years | 0.47 | 6.39 | 1.12 | 2.33 | 1.56 | 47.42 | 6.37 | 17.99 |
F: 31–50 years | 0.44 | 4.05 | 0.78 | 2.10 | 1.05 | 32.10 | 4.61 | 10.73 |
M: 51–70 years | 0.47 | 4.79 | 0.84 | 2.56 | 1.42 | 41.17 | 6.50 | 14.19 |
F: 51–70 years | 0.43 | 3.76 | 0.70 | 1.86 | 1.08 | 30.16 | 4.79 | 10.31 |
M: ≥71 years | 0.65 | 4.03 | 0.86 | 2.27 | 1.46 | 34.24 | 5.89 | 11.87 |
F: ≥71 years | 0.52 | 3.12 | 0.71 | 1.71 | 1.13 | 27.48 | 4.68 | 10.52 |
Overall | 0.61 | 4.87 | 0.96 | 2.56 | 1.42 | 37.66 | 5.71 | 13.65 |
Scenario 6 was similar to Scenario 4 except that in Scenario 6 none of the packages of GF flour/starch had GF labels. However, results for Scenario 6 are quite different to those for Scenario 4. As can be seen on the right side of
Table 7, values for the 97th percentile for a single day ranged from a low of 22.96 mg/day for children 1–3 years of age to a high of 51.50 mg/day for males 19–30 years of age. Corresponding values for usual intake were somewhat lower (from 9.44 mg/day for children 1–3 years of age to 17.99 mg/day for males 31–50 years of age).
4. Discussion
For people with celiac disease, the main concern regarding the use of “gluten-free” prepackaged products and the use of naturally gluten-free food is the doubt that these products being “contaminated” with the main sources of gluten, i.e., wheat, rye and barley.
The adoption of a single gluten threshold for gluten contamination at 20 mg/kg (ppm) is suggested by several authors [
8,
22]. Thus, in Canada, risk evaluators consider that the presence of gluten at levels which do not exceed 20 ppm in products that are labelled “gluten-free” does not pose a risk for the vast majority of individuals who suffer from celiac disease [
23]. The choice of the 20 ppm level for the purposes of risk management reflects also an international standard that has been initially established by the Codex Alimentarius Commission based on scientific premises [
24]
. A number of western countries have ruled on this matter, and have implemented the 20 ppm level indicated in the Codex Alimentarius standard. Thus, the measure is effective since January 2012 in the European Union (
Commission Regulation (EC) No 41/2009 of 20 January 2009) and was announced in August 2013 by the US-Food and Drug Administration.
The 20 ppm level is used to express the concentration of gluten present in a given food, but the measurement of total exposure to gluten each day is what constitutes the threshold in terms of prevention (10 mg/day). Therefore, by applying the 20-ppm level for gluten-free foods, with the understanding that total gluten intake must be limited to no more than 10 mg/day, it would be possible to consume 500 g of gluten-free foods on a daily basis. However, this calculation should take account the exposure to flours made from cereal grains and plants that do not contain gluten naturally and that are frequently used by celiac consumers to prepare daily foods.
Overall, the question is to know whether the limit of 20 ppm is a realistic threshold to protect most of the Canadian people with CD taking account Canadian consumption data including “gluten-free” prepackaged products but also naturally gluten-free food notably flours and starches used at home by celiac consumers for GF cooking and baking.
Our results show that for a hypothetical level of contamination of 50 ppm the estimated usual daily intake at the 97th percentile was 14.98 mg/day in Scenario 1 (ready-to-eat) and 10.80 mg/day in Scenario 2 (mainly prepared at home). Both are above the maximum safe level of 10 mg/day gluten intake for individuals with celiac disease. We conclude that, given the consumption levels of grain-containing foods by Canadian in the general population (levels that may not currently be consumed by Canadians with celiac disease, but could be in the future, to the extent that the perceived quality of GF grain-based products increases and their cost decreases), from a safety perspective this level of gluten contamination is too high for prepackaged GF foods or ingredients labelled as GF and sold in Canada.
For a hypothetical level of contamination of 20 ppm, estimated usual daily intake at the 97th percentile (heavy Canadian consumers) averaged 5.6 mg/day for Scenario 1 (ready-to-eat) and 4.3 mg/day for Scenario 2 (mainly prepared at home) (
Table 4). While exposure estimates are fairly similar for each of the hypothetical levels of gluten exposure examined in Scenarios 1 and 2, exposure estimates are consistently lower in Scenario 2. This can be explained by the fact that the hypothetical levels of gluten contamination were applied (in most cases) to ingredients such as flours and starches in Scenario 2 while they were applied to ready-to-eat foods in Scenario 1. The dry weights of the flours and starches used as ingredients in Scenario 2 are less than the weights of the corresponding ready-to-eat grain-containing foods in Scenario 1, thus exposure estimates are expected to be lower.
While there was variation in intake across the different age and sex groups, the 97th percentile estimates did not exceed 10 mg/day in any group: the highest 97th percentile values were 7.1 mg/day and 6.3 mg/day for males 19–30 years of age and males 14–18 respectively. On the basis of these results we conclude that a maximum of 20 ppm of incidental gluten in pre-packaged GF grain-containing foods and ingredients that are labelled as GF and sold in Canada does not pose a health risk for the majority of Canadians with celiac disease.
In Scenarios 3 to 6, instead of using hypothetical levels of gluten contamination, we used data our team had previously collected on levels of gluten contamination of a range of pre-packaged GF flours and starches sold in Canada [
18]. We then estimated dietary exposures using these measured values in GF grain-based foods that can be prepared at home relatively easily (bread, cake, cookies), while continuing to assume that GF grain-based foods that are more difficult to prepare at home (e.g., pasta, crackers) were contaminated at levels of 20 ppm (as-purchased).
Considering results by age-sex group (
Table 5) and assuming a gluten contamination level at 20 ppm, the highest estimated exposure levels among heavy eaters (97th percentile) are for males 19–30 years of age and males 14–18 years of age and are slightly over 10 mg/day considering a single day’s food consumption (10.12 mg/day and 10.31 mg/day respectively). With a contamination level at 20 ppm, this category of consumers is susceptible to consume a little bit more than 500 g of prepackaged products per day and with a diagnosis of celiac disease, young male adults should be encouraged to reduce their consumption of food ready-to-eat (
i.e., prepackaged food with a “gluten–free” statement). However, considering usual intake measurements which correspond to a more realistic situation than a single day’s food consumption, the highest estimated exposure level is below 10 mg/day for the same categories of consumers (7.1 mg/day and 6.3 mg/day respectively). Moreover, the values of 10.1 mg/day and 10.3 mg/day are very close to 10mg/day observed with 24-h intake assessment. On the basis of these results, we would consider that the limit of 20 ppm defined as a threshold value for celiac disease risk management should not be questioned from a public health point of view.
Lower fiber GF flours and starches traditionally used in GF cooking and baking were used in Scenarios 3 (packages labelled as GF) and 5 (packages NOT labelled as GF, with no precautionary statement, i.e., “may contain”). Gluten exposure at the 97th percentile was only slightly higher in Scenario 5 (3.19 mg/day) than in Scenario 3 (2.94 mg/day). Possible explanations for the similarity of these results include the fact that grains such as rice and corn are generally grown, transported, processed and sometimes packaged in different regions of the world than wheat is. Consequently, the level of cross-contamination is low even with non-GF products. Until this finding of similar levels of gluten contamination in lower-fiber GF flours and starches labeled GF and comparable products not labeled as GF are demonstrated to be a consistent characteristic of lower-fiber GF flours and starches not labeled as GF, we recommend that Canadians with celiac disease continue to use only pre-packaged lower fiber GF flours and starches that are labelled as GF.
Looking at diets with GF grain-containing foods prepared at home using higher GF fiber flours (table 8) and starches with GF labels (Scenario 4), estimated usual intake of gluten at the 97th percentile is well below 10mg/day in all age-sex groups (1.71 to 3.46). In contrast, results of the modeling for Scenario 6 (higher GF fiber flours and starches with no GF label), show that all but two of the 97th percentile values for usual intake by age-sex are greater than 10 mg/day (10.31 to 17.05). While usual intakes among average eaters (50th percentile) were, as expected lower (2.73–7.58), they were also considerably higher than the corresponding 50th percentile estimates for lower fiber GF flours and starches not labeled as GF (0.74–1.70), suggesting that concern should not be restricted to individuals with the highest consumption of GF grain-containing foods. We recommend that individuals with celiac disease who wish to increase their fiber intake by using higher-fiber flours and starches purchase only packages that are labeled as GF.
In preliminary results of this study, Koerner
et al. [
18] have shown that traditional ingredients (considered here as lower fiber content) have a lower contamination compared with those with higher fiber content such as soy, millet and buckwheat. As it was initially suggested in Koerner’s study, our exposure scenarios confirm that among the naturally gluten-free flours and starches tested that do not contain a gluten-free label, the higher fiber ingredients would constitute the greatest probability of being contaminated with gluten above 20 mg/kg and should be avoid by celiac consumers.