The market for pills and yoghurts containing ‘friendly’ bacteria is
worth $28bn, but do claims for them stack up? Can they really alter our gut
flora? And are we healthier if they do? You may find the answers surprising.
The chances are, you think you are an individual. Within a few social,
economic and legal constraints, you probably see yourself as pretty autonomous.
The reality, however, is that you are more of an ecosystem than an individual.
There are 10 times more microbial cells in your body than human ones.
In recent years, scientists have developed a greater understanding of
the important roles played by the 100tn or so bugs the average person carries.
After decades of focusing on how to kill bacteria with soap and antibiotics, we
are coming round to a more nuanced appreciation of the symbiotic relationship
we have with them. While some can make us sick, others help to break down the
nutrients in our food, teach our immune systems to recognise enemies, fight off
food poisoning and even produce chemicals that determine our moods.
As our knowledge of the importance of the microbes in our bodies grows,
the big question is whether it is possible to give our gut flora a helping
hand. In fact, it is the $28.8bn question – the projected global value of the
probiotics market for next year. The ads are certainly seductive. All that harm
from takeaways, boozy nights and work stress can be put right with a daily dose
of live bacteria. But do probiotics have real health benefits?
Studies have documented that people with a wide range of diseases
including Parkinson’s, Alzheimer’s, type 2 diabetes and cardiovascular disease
have different gut flora from those of healthy people, but it can be hard to
tell whether this is a cause or a consequence of the illness. Microorganisms
play important roles in regulating immune system responses, and can therefore
affect the chances of people developing auto-immune diseases such as multiple
sclerosis, inflammatory bowel disease, irritable bowel syndrome and allergies.
Numerous studies, including one published last year by Swedish scientists, show
that babies born by caesarean have lower levels of good bacteria and chemical
imbalances in the immune system that make them more susceptible to allergies
and eczema.
Research also suggests that healthy gut bugs can improve the
effectiveness of some cancer therapies. In a study published last year,
Professor Laurence Zitvogel, of the Gustave Roussy Institute in France, gave
cyclophosphamide, an anti-cancer drug, to mice with skin cancer and sarcoma.
The drug made the lining of the mice’s small intestines porous, allowing gut
bacteria to escape and encourage immature immune cells to develop into T-cells
capable of attacking tumours.
Those who have had “gut-wrenching” experiences or butterflies won’t be
surprised to hear that there are also strong connections between the gut and
the brain. Gut bacteria produce neurochemicals such as serotonin and dopamine
that regulate basic psychological processes and mental states. Altering the
balance between beneficial and disease-causing bacteria can change the brain
chemistry of animals in ways that can make them either bolder or more anxious.
Of course, understanding that gut microbes have major influences on
health does not necessarily mean we can do anything about it. “Working out
potential effects involves doing large, long-term population studies, and
that’s expensive and difficult,” says Kristian Bravin, a spokesman for the
British Dietetic Association.
The best evidence to support the use of probiotics is for reducing
cases of infectious diarrhoea, especially that associated with the use of
antibiotics. Around 30% of patients given antibiotics get diarrhoea, with
potentially serious symptoms. When scientists at the California-based Rand
research organisation combined the results of 63 studies, they found people who
took probiotics alongside antibiotics almost halved their risk of diarrhoea.
There is also good research supporting the use of probiotics to treat ulcerative
colitis and pouchitis, a complication patients can suffer following surgery.
When it comes to mundane colds and respiratory infections, the evidence
is mixed. A German study published in 2006 did find probiotics shortened the
average duration of cold symptoms from nine to seven days and reduced their
severity, but had no effect on incidence. However, a Cochrane review, combining
the results of 10 studies, found those given probiotics were 8% less likely to
get colds, but that probiotics had little effect on symptom severity.
There is little convincing evidence to support the many other health
claims made for probiotics, such as helping with weight loss, lowering blood
pressure and cholesterol, and preventing or alleviating skin conditions,
urinary tract infections, anxiety and depression.
The idea behind probiotics is to increase levels of beneficial
bacteria, but another approach is to help those already there. That is what
prebiotic supplementation is for. Prebiotics are non-digestible carbohydrates
that provide food for friendly bacteria. Food sources include beans, garlic,
onions and leeks, but they are also added as supplements to food, and
increasingly to formula milk for babies. Last year, a large study found no
evidence that putting prebiotics in baby formula prevents babies getting asthma
or hives, but did find some evidence that they could reduce the chances of
developing eczema.
Hundreds of applications to make health claims for probiotic products
have been rejected by the European Food Standards Authority in recent years on
the grounds of lack of conclusive evidence, though some scientists believe this
is more to do with faults in the claims process than lack of evidence. Others
are sceptical that probiotic products containing a few million live bacteria
can even survive exposure to gastric acid in the stomach.
“If someone is buying a probiotic,” says Bravin, “I’d say go for
good-quality live yoghurts, consume them every day, and select those that
contains several different species of bacteria. And ideally it should be
something with a prebiotic as well.”
http://www.theguardian.com/lifeandstyle/2014/nov/30/probiotics-myth-or-miracle-prebiotics
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