Amid reports of patients with gastrointestinal (GI) conditions combining dietary regimens, a practice dubbed “diet stacking”, clinicians are advised to familiarize themselves with the variety of diets recommended for key conditions and inquire about patients’ dietary practices during consultation, according to a new review.

“As dietary therapies become increasingly legitimized and widely used across gastrointestinal and non-gastrointestinal conditions, clinicians need to be more aware of not just whether a patient is following a therapeutic diet, but how many dietary interventions they are using at the same time,” Sarah L. Melton, first author of a review published in JGH Open, told Medscape Medical News.

Evidence-based dietary therapies can have important roles in the management of GI disorders, with strategies ranging from short-term induction therapy, such as exclusive enteral nutrition for Crohn's disease, to a long-term monotherapy approach, such as the gluten-free diet for celiac disease.

Diet stacking, a term coined by the review authors, is loosely defined as an accumulation of at least two concurrent dietary strategies. The practice can result from various scenarios, a key one involving a patient seeing different specialists, such as a gastroenterologist and a cardiologist, and being recommended entirely different diet strategies by the clinicians who are unaware of the other specialist’s recommendation, the authors note.

In another scenario, patients may be intentionally recommended a combination of dietary therapeutic strategies, such as those with celiac disease and co-existent irritable bowel syndrome (IBS) who are recommended a gluten-free as well as a low FODMAP diet (a dietary restriction of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols).

Still another — possibly common — scenario could involve patients receiving advice based on questionable evidence from either alternative practitioners or from the wide array of unreliable sources found online and through social media.

“Patients might be directed by advice from sources external to the managing clinician's advice, such as alternative practitioners or from online sources with limited or questionable evidence, or for a clinical scenario where an evidence-based diet is inappropriate, without appropriate guidance and support,” the authors note.

Finally, patients who are recommended dietary strategies may incorporate key elements from other dietary restrictions, such as a gluten-free diet combined with a low-fat or dairy-free component, they add. 

“Patients may accumulate diet strategies by layering them with additional restrictions [without] ever discontinuing an inefficacious diet, which may in fact worsen symptoms, reduce diet quality, and precipitate disordered eating,” they write.

Common Combinations

“In clinical practice, one of the most commonly observed examples of diet stacking is the combination of a gluten-free and dairy-free diet,” said Melton, who is a practicing dietitian with the Department of Gastroenterology, Monash University, in Melbourne, Australia.

“We also frequently see individuals combine the low FODMAP diet — an evidence-based, short-term dietary therapy for irritable bowel syndrome — with additional dietary restrictions,” she noted.

“These extra restrictions are often layered on top of the low FODMAP diet without clear clinical indication, increasing overall dietary complexity and restrictiveness.”

In the Research

Although the prevalence of patients combining multiple dietary strategies has not been well addressed in the medical literature, studies documenting such practices include a Canadian study. The study found that as many as 52% of patients attending a gastroenterology clinic for IBS reported simultaneous use of other dietary manipulations during their trial of the low FODMAP diet, and with only 30% seeing a dietitian for guidance after a mean of 2.5 visits.

Another study of patients using a low food-chemical diet for symptom management reported that 52% (26/50) of patients followed at least two dietary interventions, and 12% (6/50) followed three or more diets simultaneously.

Key Concerns

Such dietary combinations, particularly among patients already experiencing GI disorders, can carry a multitude of risks.

“The most potentially risky combinations are those with overlapping or conflicting food exclusions,” Melton explained. 

“For example, combining a low food-chemical diet with a low FODMAP diet can substantially limit food variety and increase the risk of nutritional inadequacy, making it particularly challenging to implement safely,” she said.

With underlying eating disorders common among patients with GI disorders, another concern is that combining or layering diets may further exacerbate that risk, the authors speculate. 

“Diet stacking, especially when self-imposed and not undertaken in collaboration with a dietitian, is likely to be a significant risk factor for the development of eating disorders, although this has not been formally studied,” they note.

“Given this, screening for disordered eating when individuals engage in diet stacking is recommended,” they add.

Of note, some dietary combinations may be appropriate when there is a clear medical indication, Melton added. 

“For instance, a gluten-free diet in someone with celiac disease can be implemented alongside a low FODMAP diet if clinically indicated and appropriately supervised,” she said.

Managing Diet Stacking

With issues of diet stacking potentially related to complex medical, psychological, and nutritional factors, suggested management of the behavior could likewise involve the multidisciplinary help of a gastroenterologist, gastropsychologist, and/or gastroenterology dietician, the authors say.

In the first-line setting, gastroenterologists should familiarize themselves with the various diets that may be recommended by specialists and/or prone to be experimented with by patients, the authors note.

Further, gastroenterologists should “be vigilant to the existence of diet stacking and actively enquire if the patient is following any dietary restrictions, including asking the patient if they would like more information or referral to a dietitian with gastroenterology expertise,” they recommend.

At their first visit, patients should be asked about any concerns with their nutritional needs and if they have experienced unintentional weight loss. 

“The physician may determine that a micronutrient screen is required to measure key nutrients including specifically plasma albumin and serum vitamin B₁₂, iron studies, and folate levels,” the authors explain.

Psychologists could benefit by conducting assessments regarding any potential psychological comorbidities that could contribute to dietary combinations.

And dieticians could further play a key role by providing patient education on each dietary strategy and helping patients maintain the most important medical strategy, such as a gluten-free diet in celiac disease.

Ultimately, increased awareness of diet stacking in research is needed to better understand its prevalence and nuances, Melton added.

“While diet stacking appears to be commonly observed in clinical practice, it is rarely reported explicitly in research studies,” she noted.

“By defining and naming ‘diet stacking’, we hope to highlight this as an emerging issue and encourage future studies to report on the frequency and clinical implications of multiple concurrent dietary interventions in gastrointestinal populations,” she added.

Melton had no disclosures to report.