As a new book says processed food is killing off ‘friendly’ bacteria in our gut… Can eating home-made pickles fight off infections – and obesity?
- Nine out of every ten cells in our bodies belong to microbial species
- These microbes maintain the health of the gut wall
- They constitute one of the human body’s most important organs of defence
- Western diets don’t contain enough foods that nourish this bacteria
- Eating more probiotic foods (yoghurts, cheese, pickles) will improve health
By MICHAEL POLLAN
PUBLISHED: 20:39 EST, 10 June 2013 | UPDATED: 20:39 EST, 10 June 2013
Non-pasteurised pickled vegetables – and the fibre in them – feeds our guts’ microbial residents
For more than a century we have been engaged in a war on bacteria. We deploy an arsenal of antibiotics, hand sanitisers, pasteurisation and food regulations to tackle the moulds and bacteria and so, we hope, hold off disease and death.
I grew up on that field of battle. My mother instilled in our family a deep fear of botulism, and countless other unnamed germs possibly lurking in our food.
A touch of white on a wedge of cheese was enough to condemn it.
The slightest dent in a can of food consigned it to the rubbish, no matter that the dent came from being dropped on the floor. You never know, could be botulism; better safe than sorry.
In the decades since Louis Pasteur discovered bacteria, medical research has focused mainly on their role in causing disease.
The bacteria that reside in and on our bodies were generally regarded as either harmless freeloaders, or pathogens to be defended against.
But then in the early 2000s, researchers discovered hundreds of new species of bacteria in the human gut doing all sorts of unexpected things.
To their surprise, microbiologists discovered that we are made up of 90 per cent bacteria. Nine out of every ten cells in our bodies are not human but belong to these microbial species (most of them residents of our gut).
As one scientist put it to me, we ‘stand on the verge of a paradigm shift in our understanding of health as well as our relationship to other species’.
Metaphors about it being a ‘war’ no longer made much sense.
So what exactly are the 500 or so distinct species and countless different strains of those species that make up the kilogram or so of microbes in our gut doing there?
For most of these microbes, their survival depends on our own, and so they do all sorts of things to keep their host – us – alive and well.
Perhaps their most important function is to maintain the health of the gut wall, or epithelium. In the course of a lifetime, 60 tons of food pass through the gastrointestinal tract, an exposure to the world that is fraught with risk.
It appears that much of that risk is managed, most of the time brilliantly, by the gut bugs.
Taken as a whole, the organisms in the gut constitute the largest and one of the human body’s most important organs of defence.
So why would the body enlist bacteria in all these critical functions, rather than evolve its own systems to do this work? One theory is that because microbes can evolve rapidly they can respond with much greater speed and agility to changes in the environment.
Though we’ve tended to think of bacteria as agents of destruction, they are invaluable creators as well. Gut bugs manufacture essential vitamins (including vitamin K as well as several B vitamins) and a great many other compounds scientists are only just beginning to recognise.
Too much to process? Overly-processed foods typical of Western diets don’t contain enough fibre to sustain our gut bacteria – unlike probiotic foods such as yoghurt and other fermented food
Some of these compounds act on the central nervous system, moderating our appetite and the mechanisms that determine how we store fat.
So might changing the composition of our gut bacteria in turn change our weight?
Possibly: the researchers have found that when they transferred bacteria from the guts of fat mice into mice with no gut bacteria, they gained nearly twice as much weight as those that received gut bacteria from skinny mice.
But under the pressures of broad-spectrum antibiotics, food pasteurisation and a modern diet, the human microbe community has probably changed more in the past 100 years than in the previous 10,000, when the shift to agriculture altered our diet and lifestyle.
Children are exposed to fewer bacteria and the theory is that their immune system isn’t then ‘trained’ to accurately distinguish between good and bad microbes, which may explain the escalating rates of allergy, asthma and autoimmune disease in the developed world.
The average child in the developed world has also received between ten and 20 courses of antibiotics before their 18th birthday, an assault on the gut bugs the implications of which researchers are just beginning to calculate.
And then there is the diet. Put in a more scientific way, the diet should include both probiotics – beneficial bacteria – and prebiotics – something good for those bacteria to eat (such as fibre).
Probiotics are what you should expect to find in fermented food, such as pickled vegetables, sauerkraut, cheese, yoghurt, breads, vinegar, soy sauce and beer.
But we’ve worked hard to eliminate bacteria from the diet, by sterilising our food, and by processing it we’ve removed much of the fibre – precisely the component of greatest value to the microbes.
With the exception of yoghurt, foods that contain live bacteria have all but vanished from our plates (the bacteria in sauerkraut, ketchup, pickled vegetables etc are killed off by pasteurisation).
The Western diet, with its refined carbohydrates, highly processed foods, and dearth of fresh vegetables, preserves foods by killing bacteria and then deprives our gut bacteria of much that is good for them to ferment and grow.
‘The big problem with the Western diet,’ Stephen O’Keefe, a gastroenterologist at the University of Pittsburgh, told me, ‘is that it doesn’t feed the gut, only the upper GI [gastrointestinal tract]. All the food has been processed to be readily absorbed, leaving nothing for the lower GI.
‘But it turns out that one of the keys to health is fermentation in the large intestine.’
The lack of fibre in our diet is, in effect, starving our gut and its microbial residents.
O’Keefe and many others are convinced the myriad intestinal disorders that have become common among people eating a Western diet can be traced to this imbalance.
We have changed the human diet in such a way that it no longer feeds the whole superorganism, as it were, only our human selves. We’re eating for one, when we need to be eating for a few trillion. But intestinal problems may be the least of it.
Populations that eat a Western diet consistently develop high rates of diseases such as heart disease and stroke, obesity, cancer, and type 2 diabetes. What remains subject to debate is exactly what about this diet makes it so lethal.
Lately, some researchers are beginning to suspect the problem is to do with inflammation, something in which our gut bugs may turn out to play a crucial role.
The case for getting more live-culture foods (especially of children) is already compelling and growing more so. Consider the research that has come out in the past decade or so.
Probiotics – beneficial bacteria ingested either in fermented foods or in supplements – have been shown to calm the immune system and reduce inflammation; shorten the duration and severity of colds in children; relieve diarrhoea and irritable bowel syndrome; reduce allergic responses; stimulate the immune response; possibly reduce the risk of certain cancers; and improve the health and function of the gut.
Mysteries remain, obviously, but the case for eating live-culture foods seems strong, perhaps strongest for fermented vegetables.
For in addition to bringing large numbers of probiotic guests to the party, the vegetables themselves also supply plenty of prebiotics – nourishment for the bacteria already there.
That’s why I have been busy with my pickling, working to perfect my sauerkraut – without pasteurisation.
Adapted from Cooked by Michael Pollan, published by Allen Lane, £20. © 2013 Michael Pollan. To order a copy for £14.99 (including p&p), call 0844 472 4157.