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Kimchi,
kombucha, sauerkraut, miso and kefir – all fermented foods and drinks –
have been around for centuries, but suddenly they are all the rage. The
reason? They are supposedly packed full of gut-healthy microorganisms,
and we are finally waking up to just how much the trillions of
microorganisms that live in our guts (AKA the gut microbiome) contribute
to our mental and physical health.
True, probiotic products such as Yakult –
sweetened skimmed milk fermented with a single strain of friendly
bacteria – have been shifting hefty units for some time: the global probiotic market, dominated by yoghurt drinks, was worth $45.6bn (£33bn) last year.
But Yakult is fairly bland and sweet. Traditional and home-fermented
delicacies are another, more pungent matter altogether: kombucha (a
naturally fizzy cocktail of green tea and sugar) tastes vinegary; kimchi
(vegetables fermented Korean-style) is sour and fiery; sauerkraut,
which is fermented cabbage, whiffs of sulphur. All can intimidate
palates used to highly processed western blandness.
Because of how they are prepared, they all contain microorganisms that boost the diversity of good bacteria,
yeasts and fungi living in our guts. Harbouring a flourishing gut flora
has been linked to lower obesity, fewer autoimmune conditions and
digestion problems, longer lifespan, good brain function and happiness.
Some very big companies are beginning to take
this on board. If you could never quite trust the mouldering kombucha
you once nurtured in your airing cupboard, now you can buy some from
Whole Foods instead. Step forward brands such as Eaten Alive, Bio-tiful –
whose flavoured version of the fermented-milk drink kefir is now
stocked in Sainsbury’s – and the Urban Fermentary, whose
bacteria-riddled pickles and drinks come in appetising packaging. (It is
unlikely, however, that mass-produced, pasturised ferments will contain
as many of the desired microorganisms as those made using traditional
methods, so it’s worth checking how a product was made before you buy.)
Take sauerkraut, the pickled cabbage beloved of
central Europeans.
Unlike the majority of supermarket-bought pickles,
which are preserved in vinegar and have no “live” element, the cabbage
in sauerkraut is massaged in salt until the juices are drawn out and the
healthy microorganisms living on it produce lactic acid. This stops it
going off, while adding a vinegary twang. The result, says Tim Spector,
professor of genetic epidemiology at King’s College London, where he
also directs the British Gut microbiome project, is “a really good
combination of a pro- and prebiotic”. Spector’s 2015 book, The Diet
Myth, revealed that much of what we eat is digested by our microbes,
which in turn produce vitamins and unlock other nutrients for us (and
are influential in many other ways). As with live yoghurt, the
probiotics are the friendly bacteria food contains, whereas prebiotic is
the word for substances that feed your gut flora. “The cabbage actually
feeds other microbes in your gut, so I’m definitely a fan of kraut,
kimchi, all those kind of things.”
But unless you are fermenting foods yourself,
these products are not cheap – a 375g jar of sauerkraut from Eaten Alive
will set you back £6. It’s good to know, therefore, that bog-standard
live yoghurts aren’t a total waste of time. All yoghurt is fermented and
the milk used to make products for sale is legally required to be
pasteurised to kill off pathogens, after which a few strains of
lab-produced friendly bacteria are added. “We’ve done some
[not-yet-published] research ourselves,” says Spector, “showing that
[this] yoghurt definitely does have an effect on the microbes.” The
added bacteria aren’t the same as the ones that live in our guts, he
says. “The [former] are moving through the body, but
they can have an effect on your existing microbes and we also know they
produce substances that are beneficial. So, in a way, they’re energising
your gut microbes as they go through, producing some chemicals that
look as if they’re good for weight loss as well.” However, he reserves
the title of “super yoghurt” for kefir. “It has about five times as many
microbes, with more diversity, and also has extra fungi in there and
they’re all good.”
Sourdough bread is extolled for its natural wild fermentation, harvesting diverse yeasts and Lactobacillus bacteria from the environment, but they then all perish in the oven. The main health benefits come from microbes
having chomped away on lots of fibre, breaking down the gluten
proteins, releasing tasty, mould-deterring acids, rendering the
nutrients more digestible and lowering the glucose spike after
consumption. “But if you make it yourself,” says Spector, “the extra
microbes go on your hands and there’s increasing likelihood that people
who make sourdough are potentially healthier because they have greater
microbe diversity.”
Of course, alcoholic drinks are fermented, too,
and red wine in moderation is actively gut-friendly. This is partly to
do with the polyphenols in red wine, which you may have already heard
about in their capacity as antioxidants, but they have the added benefit
of being rocket fuel for good bacteria. It seems to be the combination
of alcohol and polyphenols that is especially good. “If you compare
grape juice and wine and gin’s effects on the microbiome,” says Spector,
“gin isn’t very good, but red wine is better than grape juice. So,
alcohol plus the fruit is good.”
Not surprisingly, warns Spector, “microbes don’t
cope very well if you drink too much, and liver damage also causes
problems for your microbes”. But he does hypothesise that beer and cider
in moderation “are probably also of some benefit”. The alcohol has
killed off the fermenting microbes before you drink, but you still get
the tasty and useful chemical byproducts from fermentation. “A lot of
these things that are thought to be bad for you,” says Spector, “have so
many polyphenols that they might be overcoming any potential
downsides.” He also recommends a little polyphenol-packed coffee and
dark chocolate.
If you were to view your microbiome as a garden,
fibre would be your fertiliser. Spector reckons that most people need
to double their intake. Foods containing the best fibre types for your
microbes – AKA prebiotic foods – include artichokes, jerusalem
artichokes, leeks, celery, chicory, onions and garlic. Variety is the
top priority. “So, it’s not just focusing on one or two of these
examples,” warns Spector. “Our latest research is showing that it’s not
necessarily someone who calls themselves vegetarian who has the most
healthy gut – it’s the person who eats more diversity of plants in a
week. Having the same salad every day isn’t going to be as healthy as
eating a rich diversity of food with occasional meat.” This could just
as easily be a way of describing the Mediterranean diet, with its
kaleidoscope of fruit, veg, nuts, grains and legumes.
The exciting news for carb lovers is that you
can render potatoes, rice and pasta more prebiotic by cooking and then
cooling them and then either eating them cold or reheating them (be
careful with rice, which can potentially harbour unhealthy bacteria). In her book Gut, gastroenterologist Giulia Enders writes
that, as they cool, some of the starch crystallises, making it more
resistant to human digestion, “so your potato salad or sushi rice
reaches your microbes untouched”.
Fasting – a dietary habit as ancient as
fermenting – is also beneficial to gut health. “When you’re not eating,”
says Spector, “a whole different set of microbes comes and cleans up
your gut wall, eating the sugars and things there, and that’s important
in keeping a good immune balance.” We are not talking extreme
abstention. In fact, animal studies have shown microbes nibbling through
the gut’s protective lining if starved for too long. But intermittent
fasting with low-calorie days, or simply leaving long gaps between
meals, is beneficial for your gut microbes. You are even allowed to skip
breakfast – Spector says it’s a myth that this makes you gain weight.
“There are now at least six randomised control trials showing that.
Skipping breakfast has generally been shown to be good for adults and
helps you lose weight. Basically, in southern Europe, their breakfast is
an espresso and a cigarette, if they’re lucky, and they don’t snack.
Whereas we are told to always eat breakfast and continual snacking is
encouraged.”
Junk food is the gut microbes’ nemesis. In the
introduction to a new book, The Healthy Gut Handbook, by Justine
Pattison, Spector writes that after he put his student son on a fast
food diet (chicken nuggets, burgers, soft drinks etc) for 10 days, the
boy had lost 40% of his microbe species and felt sick and lethargic.
Emulsifiers, which keep texture consistent, are rife in heavily
processed foods and, warns Spector, “it has been shown in a couple of studies in rodents that they cause disruption of the gut microbes,
which react differently and produce funny chemicals, in a similar way
to sweeteners. If you give animals lots of sweeteners, you get a
reduction in diversity of the microbes and they produce abnormal
chemicals – different metabolic signals which have been shown to be more
likely to give you diabetes and make you put on weight.” There’s no
hard evidence yet in humans, but Spector has seen enough to make him
wary of regularly eating these additives.
Refined sugar is another culprit, although we
don’t fully understand the reasons. One simple answer, he suggests,
could be: “If you’re eating junk food, you’re having a surge of fat and
sugar that are absorbed before they reach the gut microbes, so you’re
starving the guys of fibre lower down. Then they send out signals that
promote obesity.”
Make Slow Changes to Avoid Discomfort
If
you are inspired to consume more fibre, Pattison offers a word of
warning: “It’s best to start slowly” – especially if you have digestive
problems – or you could end up with uncomfortable bloating and wind.
Each gut is unique and one diet doesn’t fit all, so if you change your
eating habits to no avail, try something else. You are on the right
track, says Spector, “if you notice a change in your bowel habit. After a
couple of days, your stools will get softer and you’ll be going more
regularly. That’s a sign your microbes have changed for the better, and
though they are working harder, they are happier.”
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