Food sources of energy and nutrients among Canadian adults following a gluten-free diet

Introduction

Celiac disease (CD) is a systemic, autoimmune disease triggered by the ingestion of gluten in genetically susceptible individuals (Leonard et al., 2017). The inflammatory process targets the intestine, leading to progressive villi damage and, consequently, malabsorption of nutrients, particularly iron, folate, calcium and fat-soluble vitamins (Theethira, Dennis & Leffler, 2014). Multiple micronutrient deficiencies are common at diagnosis and frequently persist despite adherence to gluten-free diet (GFD) (Rondanelli et al., 2019). A recent review reported rates of up to 40% for iron and zinc deficiency, 30% vitamin B₁₂ deficiency, and 20% folate deficiency in adults with CD with over 2 years of good GFD compliance (Rondanelli et al., 2019). While recovery of nutritional status has been linked to intestinal healing, mucosal healing may be incomplete despite GFD adherence (Theethira, Dennis & Leffler, 2014). For example it has been estimated that only 57–76% of newly diagnosed CD cases achieve intestinal healing following initiation of a GFD (Ludvigsson et al., 2014). Thus, long-term nutritional status may be influenced by refractory disease, inflammatory processes and inadvertent gluten exposure, in addition to dietary choices, and requires monitoring.

A strict, lifelong GFD is the only treatment currently available for CD. This involves the elimination of all gluten-containing foods and ingredients derived from wheat, barley or rye (Vici et al., 2016). This restriction can be problematic as wheat is a major contributor of carbohydrate, dietary fibre, protein, B vitamins and phytochemicals in Western diets (Shewry & Hey, 2015). Wheat also serves as the mandatory fortification vehicle in Canada for iron, folic acid, thiamine, riboflavin and niacin in all refined white (wheat) flour (Government of Canada, 2019a). Conversely, whole wheat and whole grain flours are not enriched, creating a different nutrient profile that provides fibre, magnesium, protein, zinc and selenium (Government of Canada, 2015). Packaged gluten free (GF) grain products such as breads and cereals may be voluntarily enriched by manufacturers, however this practice is not required (Government of Canada, 2019a), and the nutritional quality of such products has been established as inferior compared to fortified wheat staples (Elliott, 2018; Jamieson, Weir & Gougeon, 2018; Kulai & Rashid, 2014). This is likely related to reliance on corn and rice as base ingredients for GF foods, which are high in starch but low in micronutrients and fibre (Pellegrini & Agostoni, 2015). While pseudocereals, legumes and oilseeds may have useful functional, as well as nutritional, properties, incorporation into GF foods may be limited due to cost or availability (Gobbetti et al., 2018). Therefore, in addition to gluten avoidance, nutrients provided by wheat-based staples must be replaced with nutrient-dense food choices to ensure adequacy on this long-term, restrictive diet.

The modern food environment, with an ever-growing abundance of food choices, as well as changing food labels and health claims, is complex (Slater, 2017). For people with CD, the ability to accurately identify safe foods from a nutrition label is necessary for diet adherence (Downey et al., 2015). In fact, adherence and avoiding cross-contamination is the main focus of GFD management in current clinical practice guidelines for CD (Ludvigsson et al., 2014; Rubio-Tapia et al., 2013, Downey et al., 2015), while guidance on healthy GF eating and nutrition education are lacking. Understanding GF nutrient sources in today’s food landscape is important for designing strategies to meet dietary guidelines. While there is a growing body of evidence reporting low nutrients intake for people with CD (Gonzalez et al., 2018; Martin et al., 2013; Wild et al., 2010), few studies have used a dietary pattern approach to analyse food sources of nutrients. To address this gap, a secondary analysis of food records collected from participants on GFD enrolled in the MOVE-C lifestyle intervention pilot study (Dowd et al., 2019) was conducted to identify food sources of energy and nutrients of concern. Findings will inform patterns of dietary adequacy for people requiring a GFD.

Materials and Methods

Results

Discussion

The GF food environment is complex and rapidly changing, with new and diverse food options for emerging populations of consumers and patients seeking GF foods. While the poor diet quality of packaged GF foods has been previously established (Elliott, 2018; Jamieson, Weir & Gougeon, 2018; Kulai & Rashid, 2014), actual food sources of nutrients in the GFD have not been thoroughly explored. Thus, this study presents novel findings on the top nutrient sources for a sample of Canadian adults diagnosed with CD or gluten intolerance.

In agreement with GFD assessment studies (Vici et al., 2016), lower mean intakes of dietary fibre, calcium and iron (for women) from food sources were observed in this study, but most mean nutrient intakes met recommendations. Macronutrient balance was shifted from the recommended ranges towards lower energy intake from carbohydrate (with half of participants consuming less than 45%) and higher energy intake from fat (with over half of participants consuming more than 35%). This is exemplified by lower mean intake of dietary fibre and the higher ranking of energy from MPF over grains. The mean 45% energy from carbohydrate is lower than previously observed in Nova Scotia (NS) adults consuming a GFD (50%), despite a similar sex balance in study samples (Jamieson, Rosta & Gougeon, in press). Similarly, a study of diet-experienced people with CD (n = 55) in Australia reported 45.8 ± 0.7% energy as carbohydrate (Shepherd & Gibson, 2013), whereas a British diet study (n = 49) reported a 48% average (Wild et al., 2010). Thus, average carbohydrate intake in the present study is at the lower end of observed intakes in CD. This may partly be related to the regional dietary pattern which trends toward lower relative carbohydrate intakes than the national average (Statistics Canada, 2019). Additionally, this could reflect other participant characteristics such as lack of food skills or literacy with respect to wheat replacement or lack of support and dietary guidance for those requiring GFD, as previously noted (Jamieson & Gougeon, 2019).

Approximately two-thirds (67.9%) of the energy consumed by this sample was derived from five food groups (MPF, grain products, dairy products, desserts and sweets and beverages). Notably, this resulted in a higher ranking of MPF and lower ranking of fruits and vegetables in this sample compared to the NS GF study (Jamieson, Rosta & Gougeon, in press) and was reflected in the nutrients with lower mean intakes (fibre, iron). The high-ranking contribution of dairy foods (third) to energy intake is not reflected in the mean calcium intake observed. However, this may be explained by the emphasis on cheese and eggs (4.9% and 3.0% of energy, respectively) and lesser emphasis on yogurt and milk. LNS ranked quite low (eighth) on the contribution to energy intake, in agreement with the NS GF Study (seventh) (Jamieson, Rosta & Gougeon, in press).

Of all grain products, cereals were the top contributor of carbohydrate, dietary fibre and iron in agreement with the NS GF Study (Jamieson, Rosta & Gougeon, in press). At the same time, grain products were fifth in contribution to total sugar intake, with cereals as the top source. Cereal as a top source of fibre is likely related to frequent consumption of oats and unenriched, ready-to-eat cereal brands which tended to be made from whole grains and ‘natural’ ingredients. In contrast, enriched ready-to-eat cereals were also frequently consumed, likely contributing to micronutrient intake, but not fibre. Thus, GF cereals appear to represent key foods with two distinct nutrient profiles, varying with enrichment practices and fibre-rich ingredients. Notably, vegetables, fruits and nuts were greater dietary fibre contributors than cereals.

Gluten-free breads were also a key contributor to carbohydrate and dietary fibre, and to a lesser extent, iron intakes, despite being primarily unenriched (89.3%). This may be related to the growing food trend to incorporate ancient grains and seeds in the North American market (Roesler, 2018). Thus, while GF breads often use rice or starch as the first ingredient, other whole grain flours (e.g. amaranth, quinoa) and seeds (e.g. chia, flax) may be added as secondary ingredients, improving nutrient density. However, while ranking highly amongst grain products, the absolute contribution of iron was still relatively small for breads.

A mixed grain dish category (rice or pasta-based) was the other top grain sub-category source of carbohydrate, dietary fibre and iron. However, nutrient contributions from this category are difficult to interpret since additional ingredients (e.g. meats, vegetables) are also included. In Canada, the enrichment of rice and non-wheat pasta is voluntary (Government of Canada, 2019a) and thus not a reliable micronutrient source. The selection of brown rice, brown rice noodles, and whole grain-based GF pastas could enhance fibre and select micronutrient (e.g. magnesium, zinc) intakes (Government of Canada, 2015). In addition, non-grain key contributors of iron (e.g. LNS and select vegetables) could be emphasised to improve intakes for those following the GFD. In fact, these suggestions align well with Canada’s Food Guide, which emphasises a central role for vegetables and fruits, along with whole grains and plant-based protein foods such as beans, lentils, nuts and seeds (Government of Canada, 2019b). In the present sample, LNS made a small contribution (<8%) to energy, carbohydrate, iron and protein, but a moderate contribution (13.3%) to dietary fibre. Most LNS choices in the present study were from various seeds, nuts and seed/nut butters, contributing more fat than fibre. In the present study, and in the NS GF Study (Jamieson, Rosta & Gougeon, in press), infrequent legume consumption was observed, an especially rich plant source of naturally occurring vitamins and iron (Government of Canada, 2015).

This study has several important limitations. Due to the nature of convenience samples, the dietary patterns observed cannot be generalised. However, the large number of diet records collected over several time points helps to counter this problem. The lack of ingredient-specific data was a limiting factor in food categorisation. The lack of brand specific GF nutrient composition data (e.g. B vitamins, minerals) limited the number of nutrients that could be reliably analysed. A control group was not available for comparison purposes, however some national data on food sources of nutrients are available for the general Canadian population (Garrigeut, 2011; Langlois & Garrigeut, 2011; Statistics Canada, 2017). As with any food coding system, results are affected by categorisation choices and thus, comparisons between studies should be done with caution. However, this study did follow the same protocol as the NS GF Study and is comparable in that respect. Finally, there were some missing diet records (19%) which may have influenced the types of foods reported in this sample.

Conclusions

Although carbohydrate accounted for only 45% of energy intake, on average, in this sample of adults following a GFD, grain products were still a top source of nutrients including carbohydrate, dietary fibre and iron. Top grain contributors included cereals and yeast breads, despite few of the brands reported being fortified or enriched with micronutrients. Thus, while GF grains are a source of fibre, they are less reliable as key sources of vitamins and minerals. Given this and the lack of nutrient composition data for micronutrients (other than iron) in GF foods, it would be prudent to re-evaluate enrichment and fortification policies, which presently are optional for GF flours in Canada. In addition, improvements in the nutritional quality of GF food formulations could contribute to nutrient adequacy for those requiring long-term GFD. Findings also suggest that legumes, a good source of folate, potassium, minerals, fibre and protein, were not a key nutrient source in this study. As people with CD are at increased risk of vitamin and mineral deficiency (Rondanelli et al., 2019), nutritional adequacy of the GFD will require dietary planning and appropriate replacement of nutrients provided by enriched wheat products. Without reliable exposures to key micronutrients through population-level fortification, nutritional monitoring and dietary guidance from a registered dietitian appears even more critical. Further research is needed on nutrient composition data in novel GF foods and ingredients, as well as in regard to the accessibility of registered dietitians to support people requiring long-term GFD management.

Supplemental Information