This is 6 Minute English from

BBC Learning English.

I'm Sam.

And I'm Neil.

In recent years new diets with names

like 'vegan', 'keto' and 'paleo' have

become very popular.

Are you a

vegetarian, Neil?

Do you follow

any particular diet?

Well, I eat lots of fresh fruit

and vegetables and only a little

meat from time to time.

Well, while many diets claim to

improve health or help you

lose weight, recent research

shows that what counts is not

what you eat but how

your body reacts.

Yes, and that reaction doesn't

happen where you might think - not

in the brain, or tongue, or even

the stomach, but in the gut - another

name for the intestines - the

long tube inside your body

which digests food.

Inside everyone's gut are millions

of microbes - tiny living organisms,

too small to see without a

microscope.

Some of them are good

for us, some bad.

Microbes help digest food, but

they influence our bodies more

than we know.

Think of them as

chemical factories that cause our

individual reaction to

the food we eat.

This mix of gut microbes is

unique and different for everyone,

even identical twins.

And it's the reason why some

doctors now recommend a

personalised diet, one that

perfectly fits your own unique

combination of microbes.

We'll hear more soon, but first

I have a question for you, Neil,

and it's about the gut - the

tube which includes the large and

small intestine.

It's very

long - but how long exactly is

the average adult's gut?

Is it:

a) 3 and a half metres?

b) 5 and a half metres?

or,

c) 7 and a half metres?

Well, everybody is different

of course, but I'll say on average

the gut is b) 5 and

a half metres long.

OK, Neil, I'll reveal the answer

later in the programme.

Among the first to investigate gut

microbes was Dr Tim Spector, author

of bestselling book, The Diet Myth.

He wanted to check whether the

dietary advice he had heard and

believed, advice like 'eat little

and often' or 'avoid fat',

was really true.

Listen as Dr Spector explains

how he started to doubt some of

this advice - 'food myths', he

calls them - to BBC Radio 4

programme, The Life Scientific:

All these so-called myths that

I'd believed, whether it was

about calories, about fats,

when to eat, how to eat, were

based on flimsy or no evidence,

very old, very poor quality,

and had been repeated so much

that people didn't

think to question them.

One of the food myths Dr Spector

questioned was counting calories - the

units which measure the amount

of energy food provides.

He discovered that much of

the dietary advice he had

heard was either incorrect or

based on flimsy evidence.

If

evidence is flimsy, it's

weak and unconvincing.

As Dr Spector questioned these

food myths, he remembered an

earlier study involving

identical twins, pairs of brothers

or sisters with the same genes.

It was the surprising differences

in weight between one twin and

another that made Dr Spector

realise that no two people

have the same gut - even

identical twins' guts are different.

But, as he told BBC Radio 4's,

The Life Scientific, the discovery

came in a very smelly way - by

asking his volunteers to send

samples of their poo in the post!

We collected lots of these

samples, sequenced them,

and looked at twins where

one was overweight and one

was skinny... and we found

in every case, the skinnier

twin had a more diverse

microbiome, greater numbers

of different species and

they also nearly always had

high numbers of a couple

of microbes that just

stuck out of the crowd - and

one was called christensenella

and the other was

called akkermansia.

Although genetically identical,

one twin was overweight, while

the other twin was skinny,

or very thin.

Because the weight difference

could not be explained

genetically, Dr Spector

suspected the microbes in

the skinnier twin's gut

held the answer: the more

diverse someone's microbes,

the better their gut was at

digesting food, regulating

fat and maintaining health.

Two microbes, christensenella

and akkermansia, were especially

effective.

Dr Spector says these

microbes stuck out of the crowd,

meaning they were easy to notice

for their positive effect.

And since everyone's microbes are

different, it follows that a

personalised diet which selects

the friendliest food for

your gut, is best.

Right,

and all this talk of eating

is making me hungry, so tell me,

Sam, was my answer

to your question, right?

Ah yes, I asked about the

length of the gut in

the average adult.

I said it was 5 and

a half metres.

Which was... the correct answer!

Well done, Neil - that took 'guts',

which is the second meaning

of the word: courage.

OK, let's recap the vocabulary we've

learned starting with gut - an

informal word for the intestines,

the tube which digests

food from the stomach.

Microbes are microscopic organisms

living inside the body.

A calorie is a unit measuring

how much energy food provides.

If an argument or evidence is

flimsy, it's weak

and hard to believe.

A skinny person is very thin.

And finally, if something

sticks out of the crowd,

it's noticeable in a good way.

Unfortunately, our six minutes

are up, but remember:

look after your gut, and

your gut will look after you!

Goodbye!