Systematic Review With Meta-analysis

Dietary Intake in Adults With Inflammatory Bowel Disease

Kelly Lambert; Daniel Pappas; Chiara Miglioretto; Arefeh Javadpour; Hannah Reveley; Laura Frank; Michael C. Grimm; Dorit Samocha-Bonet; Georgina L. Hold


Aliment Pharmacol Ther. 2021;54(6):742-754. 

In This Article


The aim of this systematic review and meta-analysis was to synthesise data on the usual dietary intake of adults with IBD and compare usual intake to those of healthy individuals matched for age and gender. Compared to recommended requirements, adults with IBD consumed inadequate energy and fibre. Fat-soluble vitamin intake was inadequate for many subgroups of adults with IBD, and intake of important nutrients such as folate, vitamin B1, B2, B3, B6, calcium potassium, magnesium and phosphorus were determined to be frequently suboptimal in adults with Crohn's disease, females, those in remission and those with active disease. Compared to healthy controls, adults with IBD consumed less fibre. For adults with ulcerative colitis, they were found to consume significantly more fat and copper compared to healthy controls. Adults with Crohn's disease consumed significantly less protein, iron and fibre compared to healthy controls. For fibre, this was equivalent to a daily mean intake −4.04 g (95% CI: −4.77, −3.30) lower per day than healthy controls.

The other important finding of this review was that intake of major food groups considered core to a healthy diet such as breads and cereals, legumes, fruit, vegetables and dairy were determined to be inadequate in people with IBD. This finding is consistent with recent systematic reviews investigating the diet quality and associations between dietary components and the development of IBD. Milajerdi et al[10] found that dietary intake of fruits and vegetables were inversely associated with the risk of developing IBD. A "Western style" diet characterised by a high intake of refined grains, processed meat, animal protein and low consumption of fruit and vegetables was also found to be associated with the development of IBD.[65] Similarly, Hou et al found that the high intake of total fat, meat and low intake of fibre and fruit was associated with the development of IBD.[66] Recent research has also found in Dutch adults with IBD that a dietary pattern that was high in grains, oils, processed meat, sugars and confectionary was associated with disease exacerbation[67] and a microbial environment characteristic of inflammation.[68] Further research to describe how diet quality may change during the disease course, and how these associations between diet quality and gut microbiota profile change would be useful. These insights may help elucidate disease mechanisms and guide future therapeutic interventions and management.

Inflammation in the small bowel, particularly when widespread, is known to impair absorption of many micronutrients.[69] Micronutrient status is also impacted by disease severity, disease location and previous surgical treatment, which may reduce surface area for absorption.[70] In addition to any effect of the disease on absorption, this study indicates that the intake of micronutrients in adults with Crohn's disease was suboptimal. This included most B vitamins, vitamin A, E, K, and D, calcium, magnesium, iodine, and selenium. A recent review of micronutrient absorption and outcomes in IBD indicated deficiency in these micronutrients leads to deleterious downstream effects such as impaired immune response within the gut, and inflammation as a result of increased production of reactive oxygen species.[70] Anaemia[71] and osteoporosis[72] are also common in people with IBD. These findings suggest that additional attention should be made by clinicians to identifying those with particularly poor intake and implementing dietary strategies to improve the long-term intake of these nutrients as part of the therapeutic management of the disease. Given that polypharmacy in IBD is common[73] and the burden of many medications among these patients is associated with reduced adherence[74] and higher disease activity,[75] attention to improving diet quality may reduce patient pill burden.

This review has clearly identified nutrients, food groups and subgroups of adults with IBD at risk of malnutrition. What remains unclear at this point is why adherence to basic healthy eating guidance, especially in those in remission is suboptimal. Understanding how patients perceive their health and experience their disease is fundamental to providing patient-centred care. Unfortunately, qualitative research is limited,[76,77] and further research of this type that explores food-related behaviours, preferences and factors impacting adherence to diets in groups identified as consuming inadequate intake would be of great benefit. Information from these studies may inform clinicians about how to enhance dietary adherence and address the psychosocial concerns of patients.

There are several limitations to this review. Studies were restricted to articles in English and other potentially eligible articles in other languages were excluded. Several studies that reported data in a metric not able to be converted to mean were excluded and their exclusion may affect interpretation of the data. Insufficient or unclear reporting of dietary intake in several studies precluded their inclusion in the meta-analysis. Some studies also had clear under reporters of energy intake,[52] implausible nutrient values[31,32,57] or unusually small intake.[42,58] Importantly, the large range of dietary assessment methods and tools used in the different studies reviewed makes it challenging to interpret "usual" intake. Twenty eligible studies used food records or recalls of period less than or equal to 1 week; while the remainder used food frequency questionnaires varying from 1 week to 1 year. Only two studies[36,49] used the gold standard of weighed food records and only one of these required this method of data collection for participants with IBD.[49] Variation in collection of dietary data relies on recall of intake and is thus subject to recall bias, especially when recalling long periods such as 1 year. The reporting of differences in intake between adults with IBD and healthy controls as SMD and not natural units such as grams or milligrams may also make interpretation challenging for readers. A lack of standardised reporting of disease activity and surgical history also makes it challenging to compare the similarity of individuals between studies. The use of meta-regression in future studies could be used to identify factors influencing dietary intake such as IBD type, disease activity and geographic location. Despite these important limitations, there are several strengths including the comprehensive analysis of all available nutrient data from macronutrients to vitamins, minerals and food groups. Severely unwell patients or those taking oral nutritional supplements or enteral nutrition were excluded, making the results more generalisable to the broader IBD population. Similarly, inclusion of cross-sectional and cohort studies increases the generalisability of findings to people with IBD, rather than specially selected participants of randomised controlled trials.

Based on the available evidence, it is apparent that significant efforts are required to improve the diet quality and resulting nutrient intake of adults with IBD. Longitudinal observational studies will provide useful insight into "problematic" nutrients and dietary patterns associated with disease activity or dysbiosis. The use of technology such as mobile apps to collect prospective dietary intake data has been shown to be acceptable, reduce recall bias and improve accuracy.[78] Many apps also link directly with food composition software and can improve reporting of micronutrients, which many studies in this review failed to include. Future research should also consider incorporating multiple methods to capture dietary intake as well as potentially including the use of objective biomarkers such as carotenoids[79] to objectively gauge fruit and vegetable consumption.

Overall, the findings of this review provide clinicians and researchers with important information and some clarity about the dietary intake of adults with IBD. Suboptimal intake of energy, protein, vitamins and minerals can result in increased inflammation, poorer recovery from illness and decreased quality of life. Future attention is required to improve diet quality and to improve understanding of dietary adherence so that clinicians can provide appropriate patient-centred care.