Review Article

Biological Mechanisms for Symptom Causation by Individual FODMAP Subgroups

The Case for a More Personalised Approach to Dietary Restriction

Xiao Jing Wang; Michael Camilleri; Stephen Vanner; Caroline Tuck


Aliment Pharmacol Ther. 2019;50(5):517-529. 

In This Article

A Hypothetical Model for a Personalised "Bottom-up" Approach to Implementing the FODMAP Diet

The low-FODMAP diet is designed as a three-phase approach, whereby patients restrict all FODMAP subgroups for a 2–8 week period, followed by strategic re-challenge of subgroups to test tolerance, and then follow an individualised long-term maintenance phase with periodic re-challenge of poorly tolerated foods[5] in a "top-down" approach. There are advantages of this approach such as providing more rapid symptom relief through initial FODMAP reduction, and that it can be easier to identify trigger foods following the symptom improvement seen in the initial phase. However, it requires a more restrictive diet in the initial phase with potential for disruption of microbiota and nutritional status. This strategy may also lead to patients being on a prolonged restrictive diet unnecessarily if phase 2 and 3 are not implemented. This may be most beneficial in patients who may have more severe symptoms, lack of identifiable patterns for symptom generation with food intake.[63] Other approaches have been suggested including a "bottom-up" approach as shown in Figure 1.[63]

Figure 1.

Top-down vs bottom-up approach to the low-FODMAP diet

Implementation of the "Bottom-up" Approach

While this approach has not been well studied, the "bottom-up" approach starts with a more liberalised diet, and only restricts a few specific foods or FODMAP subgroups thought to potentially cause symptoms in the individual based on baseline diet history and patient reported triggers. It is important to keep hypolactasia in mind especially in those with ethnic risk profiles and therefore a first approach may include a lactose-restricted diet, for example a patient of Asian background who has not previously restricted dairy may benefit from a trial of lactose restriction. In implementing lactose restriction, evidence from meta-analyses such as that by Shaukat, Levitt and colleagues, suggest that low amounts of lactose are tolerable (12–15 g, approximately one cup of milk),[17] and thus total restriction may be more burdensome to the patient without providing more symptom relief.

Beyond this first measure, choice of foods or subgroups to restrict is tailored to the patients' usual food intake and suspicions of potential food culprits. For example, a patient with symptoms of diarrhoea and bloating who consumes large quantities of fruits and fruit juices may benefit from restriction of only excess fructose and polyols to start. Conversely, a patient consuming large amount of wheat, onion and garlic with symptoms of gas and abdominal pain may be more likely to benefit from restriction of fructans. Following the initial restriction of one to two foods or subgroups for approximately 2 weeks, symptom response is re-evaluated. If symptoms have improved no further restriction is necessary. If symptoms continue, then additional foods or subgroups are added to the dietary restriction until either symptoms resolve, or lack of response is noted.

Patients who might benefit most from this more liberalised approach would be those with milder symptoms, or those already at risk of nutritional deficiencies.[63] A dietitian with time and expertise to evaluate usual dietary intake and potential triggers is likely to be very important to the ultimate impact of such an approach. Advantages of this strategy include potentially lower likelihood of nutritional inadequacies, but this remains to be proven and follow-up with a re-challenge strategy will be key to avoid prolonged nutritional deficits.

Having these two options, that is, "top-down" vs "bottom-up" available may allow for more individually tailored dietary advice, account for patient preference, and could reduce the level of dietary restriction necessary. Currently, no evidence exists to know which patients may respond best to each type of treatment plan. While it is possible that the microbiome, VOCs or genetic variants may allow clinicians to predict response, further data are needed prior to implementation into clinical practice. Regardless of the type of approach used, it is important that both clinicians and patients are aware from the outset, that should symptoms not resolve, patients should return to their usual diet and investigate other treatment modalities. In addition to modification of FODMAP intake, other general dietary modifications should be considered such as those suggested in the NICE guidelines, of ensuring regular meal intake, as well as adequate fluid and limiting caffeine and alcohol consumption.[4] Dietitians can play an important role to ensure the patient appropriately navigates dietary modifications and avoids over-restriction of the diet.[5]