Editorial: Emulsifiers and thickeners in our food—Do they alter gut permeability?

Changing from a traditional home-cooked diet to a ‘Western diet’, high in ultra-processed foods (UPFs), may play a role in the recent increase in Crohn's disease observed in many countries where it was previously rare.^{1, 2} Fitzpatrick et al hypothesised that diets high in UPFs increase gut permeability, allowing access of pro-inflammatory bacterial products such as lipopolysaccharide (LPS) to the immune system leading to IBD.³ Studying this involved creating a high emulsifier diet (HED) and a low emulsifier diet (LED), with 70% and 29% calories from UPFs, respectively.⁴ They identified 30 different emulsifiers and thickeners in the HED, which have very varied chemical structures and properties with the common aim of preventing phase separation. For example, surfactant-type emulsifiers (e.g. soy lecithin) lower surface tension, whereas biopolymer-type thickeners (e.g. pectin) increase viscosity.⁵ The dominant thickener in the HED was acetylated distarch adipate (E1422), accounting for 60% (1614/2815 mg/day) of total emulsifier/thickener content. Acetylated starch is a resistant starch, which increases colonic short-chain fatty acids although extensive human feeding studies do not show any deleterious effect.⁶ By contrast, the emulsifier polysorbate 80 was present in minute amounts (0.00002 mg/day) with other additives in the range 5–100 mg/day each.

The HED and LED diets were fed in a randomised single-blinded, cross-over study to assess the effect on the upper small bowel permeability as assessed by the lactulose/rhamnose ratio (LRR)⁷ and blood levels of LPS. The results were somewhat surprising in that the HED actually decreased the LRR and LPS. However, when stressed, those on the HED had a rise in LRR while those on the LED had a fall. Unfortunately, there was an order-effect meaning this stress-induced increase in LRR on the HED was only observed if HED was consumed first. While the authors should be congratulated on tackling an important question, the results raise more questions than answers. The HED initially appeared to decrease LRR; was this due to a response to injury incurred on starting the HED, or does it reflect adherence of fibres consumed the night before to the mucus layer impeding paracellular uptake of a large molecule like lactulose?

Pre-clinical studies using IBD models such as that of Ogulur et al.⁸ have tended to focus on somewhat atypical emulsifiers, which are actually consumed in very small amounts. What this study teaches us is that future studies should test substances that predominate in UPFs and have a specific mechanism, for example emulsifiers such as lecithins^{9, 10} or thickeners such as modified starch. Human studies should avoid a cross-over design and be less ambitious, using just one agent, such as acetylated starch or soy lecithin as an intervention. Such a study is more likely to obtain a clear answer as to whether specific emulsifiers or thickeners do significantly alter human gut permeability when taken as part of a normal diet, something that is at present unclear.

Joshua Reid: Conceptualization; writing – review and editing. Robin Spiller: Conceptualization; writing – review and editing.

Supported by NIHR Nottingham BRC (NIHR203310).

JR declares no conflicts of interest. RS has recieved research grants from Sanofi and Nestle and is consultant to Enterobiotix.

This article is linked to Fitzpatrick et al papers. To view these articles, visit https://doi.org/10.1111/apt.18172 and https://doi.org/10.1111/apt.18266