Com­ment & Anal­y­sis


BBC Earth (Asia) - - Contents - Dr Michael Mosley is a science writer and broad­caster, His lat­est book is The Clever Guts Diet

He­len Cz­er­ski on frost

One of the hottest topics in 2017 was the microbiome, and I’m pre­dict­ing that gut mi­crobes will con­tinue to stir the emo­tions of sci­en­tists and con­sumers in 2018.

For those who are not fa­mil­iar with the more in­ti­mate con­tents of your bow­els, the gut microbiome is a term that cov­ers the one to two kilo­grams of as­sorted mi­crobes that live in your guts and are es­sen­tial to your health. There are at least 1,000 dif­fer­ent species down there, made up of tril­lions of dif­fer­ent cells.

Although that is a big num­ber, in the past it was wildly ex­ag­ger­ated. We are not ‘90 per cent bac­te­ria’ and ‘10 per cent hu­man’, as many books and ar­ti­cles have claimed, but more like 50:50. In fact, one re­searcher who helped ex­plode that par­tic­u­lar myth claimed the pro­por­tions are so sim­i­lar that “each defe­ca­tion event may flip the ra­tio to favour hu­man cells over bac­te­ria”.

As a med­i­cal stu­dent, I was taught that the main role of our gut mi­crobes was to pro­tect us from dan­ger­ous in­vaders and syn­the­sise a few vi­ta­mins. Now we know they do far more than that. Among other things (like in­flu­enc­ing our mood and weight), those lit­tle mi­crobes help reg­u­late our en­tire im­mune sys­tem. Big claims? Cer­tainly.

Over the last half-cen­tury we have seen a mas­sive rise in al­ler­gic dis­eases, such as asthma and eczema, caused by an over­ac­tive im­mune sys­tem. We have also seen a surge in au­toim­mune dis­eases, rang­ing from in­flam­ma­tory bowel dis­ease (IBD) to type 1 di­a­betes, which are pri­mar­ily caused by an im­mune sys­tem that has got out of con­trol. One of the rea­sons for this rise seems to be that over time we have laid waste to a par­tic­u­lar pop­u­la­tion of mi­crobes that live in the gut and are known to im­mu­nol­o­gists as the ‘Old Friends’. They’ve been given that name be­cause they have evolved with us over mil­lions of years, and are vi­tal for our health. Without enough of your Old Friends around, so the the­ory goes, your im­mune sys­tem be­haves like a drunken teenager, smash­ing up its own home. A re­cent study, for ex­am­ple, found that one of the Old Friends, a gut bac­te­ria called Bac­teroides, helps pre­vent IBD by re­cruit­ing white blood cells to kill a cell of the im­mune sys­tem that can trig­ger IBD.

So why did it all go wrong? What has hap­pened to the Old Friends? Well, a diet of an­tibi­otics and junk food hasn’t been good for their long term health. We also know that chil­dren who are born by Cae­sarean section (which is in­creas­ingly com­mon) are far more likely to de­velop al­ler­gic dis­eases later in life, pos­si­bly be­cause they are less likely than those born vagi­nally to in­herit their mother’s Old Friends.

The good news is that it’s never too late to try and give your Old Friends a bit of a boost. I am now a big fan of home-made fer­mented foods like sauer­kraut, which are rich in liv­ing bac­te­ria. I have also switched to a diet that has more of the foods that will help my microbiome thrive (mainly those that con­tain plenty of fer­mentable fi­bres).

I’m also steer­ing clear of the pre­bi­otics, pro­bi­otics and sup­ple­ments that are sold in the shops. From what I’ve learnt, few have cred­i­ble science be­hind them and most of what is sold is based on hype. That may change, though. Watch this space.

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