36 | New Scientist | 7 September 2019
Megan Rossi is a research fellow at King’s
College London and a dietician and founder of
the Gut Health Clinic at Harley Street in London.
Her background as a clinical dietician and sports
nutritionist in Australia helped her realise the
depth of the link between what we eat, the
bacteria in our gut and how we feel, subjects she
now researches at King’s. Her book Eat Yourself
Healthy is published on 19 September.It made me laugh when you said in your book
that “intimate kisses” can transfer bacteria
between partners. Are there consequences?
There are millions of bacteria in our saliva, so we’d
like to see if these impact our partners’ health in
some way. In observational studies, there’s an
increased risk of being obese if you have an obese
partner. Of course, this may just be down to your
shared eating environment, but there’s a theory
that you might also be sharing bacteria that are
associated with obesity.How did you become The Gut Health Doctor?
It’s not the most glamorous specialism.
I’ve always had a huge passion for food. During
my dietetic degree, my grandma passed away of
bowel cancer. I had a very negative relationship
with the gut, for making her go through all that
pain. But when I was working as a clinical dietician,
I realised all my patients were complaining of gut
problems even though they actually had kidney
disease. I couldn’t find any information that
linked the kidneys and the gut, so I did a PhD to
see if there was a way to improve the health of
these patients by giving them prebiotics, which are
dietary fibre that feed gut bacteria, and probiotics,
which are the actual bacteria. My work showed
that this decreased the toxins in their blood that
were associated with kidney disease and helped
their gut problems.
At the same time, I was the nutritionist for
the Australian Olympic synchronised swimming
team and I saw that the girls who had the most
performance anxiety had the most gut issues.
All these things showed me how essential the
gut was to every organ in the body.How is it that gut bacteria can affect our brain?
It has been known for ages that there is a
connection between our gut and brain via nerves,
but now there is a new player, gut bacteria. They
communicate with the brain in three different
ways: they send signals up the vagus nerve
directly into the brain; they influence immunecells in the gut, which produce a range of
chemicals that affect the brain; and they produce
chemicals that travel in the blood. Some can
get through the blood-brain barrier to the brain.
And it works in both directions.What is the effect of this gut-brain
communication?
This is an area that scientists are desperately
trying to understand. There are studies in people
that suggest that bacteria can affect hormones
and neurotransmitters like GABA, which has a
calming effect on some areas of the brain, but
the exact mechanism is something we don’t
quite understand. However, if we give just theright bacteria for six weeks, we can see an
increase in activation in parts of the brain
associated with mood and emotions, compared
with a placebo group. Gut bacteria can influence
symptoms of depression, too.So should we all be taking prebiotics and
probiotics regularly?
You don’t need to take a prebiotic supplement:
prebiotics are found in thousands of foods
we would normally eat. If you’re generally
healthy, you don’t need any extra probiotics
either, but there is really good evidence that
people with certain conditions will benefit from
taking a probiotic supplement. One example
is when you’re taking antibiotics. Probiotics
can significantly reduce your risk of antibiotic-
associated diarrhoea, which affects about
30 per cent of people.How do we make sure we’re feeding our
gut bacteria the right kinds of foods?
It’s not about taking supplements, but about
having a wide range of plant-based foods in
our diet. Things like whole grains, nuts, seeds,
legumes, fruit – all these things should be
part of our daily diet. There are beneficial
chemicals like polyphenols in plant-based
foods too. They are found in nice things like
dark chocolate and red wine.What are the easiest dietary changes
we can make?
We know that people who have at least
30 plant-based elements in their weekly diet
have a more diverse range of bacteria in their
gut, which is associated with better weight
management, better heart health and better
mental health. One easy change is to get a packet
of mixed seeds and put a teaspoon on your
breakfast – that’s four extra elements right
there. Or get a packet of mixed leaf salad, rather
than a single lettuce, because each different
type of lettuce has different plant chemicals
that feed different bacteria.Do we need to keep an eye on what comes
out of our bodies, as well as what goes in?
Yeah. You don’t need to talk about it at the
dinner table, but listening in to our gut health,
keeping an eye on our poop every few weeks
and talking about what we’re eating to help
our bowels are definitely things we should be
more open about. ❚Dietician Megan Rossi tells Helen Thomson how the food we
eat can have a big effect on our mental and physical healthEat your way to happiness
DAVID STOCK FOR NEW SCIENTIST“ People with
30 plant-based
elements in their
diet have better
mental health”