Editorial

At the mercy of our microbes?

Andrew Moore Editor-in-Chief The next time you crave a piece of chocolate, think of the teeming billions of microbes in your intestines, for they might be craving it too! As Alcock et al. [1] note in this issue as part of a larger discussion of microbiota-driven dietary behaviour, the spectrum of microbial secondary metabolites found in the urine of ‘chocoholics’ differs from that of chocolate-indifferent people. And if you read that study [2], you will see that this is not because of some crass oversight such as metabolism of residual chocolate in the chocoholics compared with the ‘chocolate-indifferents’. Apparently, even without having consumed chocolate, people differ in intestinal microbiota in a way that cosegregates with chocolate preference; and when both groups are fed chocolate in the study, the chocolate-indifferents do not become more similar to the chocoholics in terms of urinary content of microbial secondary metabolites. Is this, as Alcock et al. imply, suggestive of a particular human food preference being associated with differences in intestinal microflora between individuals, and hence potentially being influenced by microbes? It is an interesting conjecture indeed, and in the authors’ larger thesis it fits nicely: essentially the dietary predilections of humans are partly dictated by our intestinal microbial commensals. In this context, the word commensal can hardly be more apt – meaning ‘at the same table’ (via Old French from medieval Latin: com, with þ mensa, table), because our tiny companions in life do, more or less, eat at the same table as we. However, that is not all we

do together, and almost as a silent vow of marriage – one that lasts longer than any between two humans, ‘in sickness and in health … until death us do part’ – we have an evolutionary bond with our intestinal microbiota. The case of chocolate consumption might be quite appropriate for investigating the other side of the relationship: how we influence our intestinal microbiota. We know that very crude insults, such as a course of antibiotics, can have striking effects, but what of more subtle things such as mood? It need not be mediated via neurotransmitters – though it is beyond doubt that certain intestinal microbes produce neuroactive compounds and probably respond to them too [3]: rather, mood can influence the physical properties of the gut, for example intestinal motor function and hence transit times [4]; ‘butterflies’ in the stomach – a temporary change in the status of the gut caused by brief anxiety/excitement – are not caused by microbes, but rather the brain. Mood without doubt influences eating behaviour, and chocolate is a convenient ‘mood modulator’ that tends to be consumed – independently of calorific value-related effects – more by depressed than non-depressed people [5]. Might this confound the explanation for inter-individual differences in gut microbiota, revealing chocolate-derived metabolites to be an incidental byproduct? The factors governing gut colonization are interesting in their own right [6], and could it be that, as a result of prevalent mood, the intestinal function of depressed people selects a slightly different microbiota compared

Bioessays 36: 905, ß 2014 WILEY Periodicals, Inc.

with non-depressed? Well, with such a speculative argument it would be foolish to negate the converse – that microbes influence mood, leading to consumption of a conveniently packaged ‘booster’. But why not in everyone? Investigating why only some people have a particular craving might elucidate the question of who feels happy dining at our table, and placing orders, in the first place…

References 1. Alcock J, Maley CC, Aktipis CA. 2014. Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms. BioEssays 36: 940–9. 2. Rezzi S, Ramadan Z, Martin FP, Fay LB, et al. 2007. Human metabolic phenotypes link directly to specific dietary preferences in healthy individuals. J Proteome Res 6: 4469–77. 3. Lyte M. 2011. Probiotics function mechanistically as delivery vehicles for neuroactive compounds: microbial endocrinology in the design and use of probiotics. BioEssays 33: 574–81. 4. Gorard DA, Gomborone JE, Libby GW, Farthing MJ. 1996. Intestinal transit in anxiety and depression. Gut 39: 551–5. 5. Rose N, Koperski S, Golomb BA. 2010. Mood food chocolate and depressive symptoms in a cross-sectional analysis. Arch Intern Med 170: 699–703. 6. El Aidy S, Van den Abbeele P, Van de Wiele T, Louis P, et al. 2013. Intestinal colonization: how key microbial players become established in this dynamic process. BioEssays 35: 913–23.

Andrew Moore Editor-in-Chief

www.bioessays-journal.com

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At the mercy of our microbes?

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