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Ever
wondered why some days all you want to do is snack, yet on other
days you don’t feel the slightest bit hungry?
Under
normal circumstances we feel hungry when we have burnt up the food we
have eaten as energy and our blood sugar and insulin levels begin to
drop. Ghrelin, a hormone connected to appetite, then communicates this
to the brain, which is how we feel the need to eat.
But all sorts of
things can interfere with this process. Earlier this month, researchers
from Aberdeen University revealed that brain cells vital to regulating
appetite slow down as we age, leading to middle-aged spread.
Researchers revealed that brain cells vital to regulating appetite slow down as we age
This,
they said, is because it takes us longer to feel full, so we eat more
than we should – and our weight creeps up, usually at a rate of about
1lb a year.
So what else has an impact on how hungry we feel?
Here,
with the help of experts, we look at what could be influencing our
appetite without us so much as looking at a slice of cake…
You get peckish when you’re tired
We all know that we feel a bit more hungry when we are tired, but the effects are more profound for women.
According
to a 2011 study by researchers at Columbia University in the U.S.,
those who are sleep-deprived eat almost 300 calories a day more than
those who get enough sleep.
This is because levels of the hormone
ghrelin, which tells the brain we need to eat, increase when we don’t
get enough sleep, so we are more hungry than usual.
However, the
Columbia researchers also noted that the women who didn’t get enough
sleep were hungrier than the men, with their average intake of fat
rising by around 30g on sleep-deprived days – four times as much as the
average increase for men. ‘It’s possible that when we are awake we need
more energy to sustain that state of wakefulness, which is why the body
may want food,’ says Professor Russell Foster, director of the Sleep and
Circadian Neuroscience Institute at Oxford University.
Levels of the hormone ghrelin, which tells us we need to eat, increase when we don’t get enough sleep
‘It seems that the body especially craves carbohydrates and sugars such as bread and cake, which are energy-giving foods.’
The problem with eating on the go
If you tend to bolt down your toast as you run out of the house in the
morning, or have your lunch standing up at the kitchen counter, it could
make you hungrier.
Eating in this way tends to make us eat faster,
so there isn’t enough time for signals that tell us when we are full to
kick in.
‘When we eat we have to give enough time for the messages
and responses from the stomach to reach the appetite centres of the
brain,’ explains consultant cardiovascular epidemiologist Dr David
Ashton, medical director of the Healthier Weight Centres. ‘This usually
takes about 20 minutes from when we finish eating. But eating quickly
overwhelms this mechanism, so the body doesn’t get the chance to feel
full and therefore there is an increase in appetite.’
Menopause makes women ravenous
Fluctuations in levels of the hormone progesterone in the lead-up to the menopause can make women more hungry.
‘Levels
of progesterone vary in the perimenopause – the two to five years
leading up to the menopause – and this seems to affect appetite,’ says
Leila Hannah, a gynaecologist at Queen Mary’s Hospital, Sidcup.
Progesterone
relaxes the body’s smooth muscles – these are the ones that work areas
such as the bladder and gastrointestinal tract. When levels are higher,
it increases the need for energy. This is what causes the craving for
food, especially energy-dense carbohydrates.
However, Miss Hannah adds that this tends to level out after the menopause has passed.
Feeling
unusually hungry can also be a sign of pregnancy. ‘Pregnancy is a time
when tissues are being laid down for the growth of the embryo,’ explains
Manchester GP Dr Jude Gunasekera. ‘This uses up a lot of energy, which
is why women who are pregnant may feel so hungry.’
Taking antidepressants can stimulate hunger
It could be your hay fever pills
It’s
common for people to go off their food if they are depressed, as
sufferers become so overwhelmed by feelings of bleakness that they lose
interest in food.
However, taking antidepressants – and especially
those containing the drug mirtazapine, for reasons that are not clear –
can stimulate hunger.
‘Antidepressants disturb the function of the
hypothalamus, the part of the brain that controls and regulates
appetite, and this is why appetite can increase when people take them,’
explains consultant psychiatrist Professor Jonathan Chick, medical
director of the Castle Craig rehabilitation clinic in Peeblesshire,
Scotland.
Antihistamines, given for allergies and taken by many for
hay fever, also affect the hypothalamus and therefore increase our
appetite, though this tends to be cumulative, rather than happening
after a single dose.
There is no easy way to combat the problem if
your medication is making you hungry – but simply being aware that this
may happen can help you keep an eye on your food intake.
Blame the Today programme
Politicians
may talk about tightening our belts during lean times – but hearing
about economic hardship on the news actually makes us want to eat more,
according to scientists at the University of Miami.
In a 2013 study,
they found that people who were primed to expect ‘tough times ahead’ ate
more food when they were told it was high in calories than people who
listened to neutral messages.
When the bad news group was given the same food but told it was low-calorie, they ate 25 per cent less.
‘Taste
[for a particular food] was not what caused the reactions, it was a
longing for calories,’ said lead researcher Professor Juliano Laran.
It’s
thought that hearing about troubled times causes a survival instinct to
kick in, making us want to ‘seize the day’, leading to cravings for
high-calorie snacks such as chocolate. The researchers went so far as to
suggest that people should ‘tune out [the] news for a while’ if they
are looking to cut back.
Tempted by that extra biscuit? Then just enjoy it
‘Naughty’ foods fuel cravings
Tempted by
that extra biscuit? Then just enjoy it – as researchers have found that
when you feel guilty about a pleasurable experience, the guilt itself
becomes pleasurable, so encouraging you to do it more.
In a 2012
study involving 1,000 people, researchers from Northwestern University,
in Chicago, gave volunteers sweet treats, and primed them to experience
feelings of guilt before eating them by talking about occasions when
they had felt guilty in the past.
This group was shown to enjoy the treats more and eat more of them than the volunteers who were not urged to feel guilt.
‘If
we consider something a naughty pleasure, it can psychologically drive
the appetite and the guilt may make you want to eat more,’ says Cary
Cooper, professor of psychology and health at the University of
Lancaster.
The appetite centre of the brain also lies very close to
the area governing mood – the limbic system – which is why changes in
the way we feel may affect appetite.
Mobiles muddle your metabolism
The bright blue light emitted by devices such as smartphones and tablets may give an unwelcome boost to your appetite.
Research this year found that exposure to the light increases hunger levels for several hours – even if you have just eaten.
Scientists,
again from Northwestern University, asked volunteers to be exposed to
dim light for three hours in the evening, then on the next day to blue
light for three hours. They found that those exposed to the blue light
had a marked increase in appetite 15 minutes after initial exposure to
the light. Their appetite continued to be increased almost two hours
after eating their evening meal.
It also altered their metabolism, as blood tests showed that the blue-light subjects had higher insulin and glucose levels.
One
possible explanation is that bright blue light at night confuses our
body clock, which has a role in controlling when we feel the need to
eat. Natural light is made up of different colours, including blue
light, and it is this type that sends the strongest signal to the brain
to let it know whether it is day or night.
…And the things that can kill your apetite
Eggs are a particularly dense form of protein, which is why you feel fuller for longer
PICKING A POSH RESTAURANT
Adding
softer lighting and mellow music in restaurants can reduce the amount
that diners eat, according to U.S. research. People ate nearly 20 per
cent fewer calories and were more satisfied with the quality of the food
when they ate in a ‘fine dining’ environment, complete with soft
lighting.
This was the opposite to what the researchers at Cornell
University Food and Brand Lab were expecting. They thought that the
relaxing environment would entice people to eat more.
The reason why
they didn’t could be because the relaxing atmosphere enabled them to
savour their food and eat slowly, which would make them more responsive
to signals from their brain that told them when they were full.
In
another study this year, Cornell researchers found that people who paid
more money found their meal more satisfying than diners who had the same
food but paid half as much.
THE COLOUR OF YOUR CROCKERY
Dieters
should eat from red plates, as the colour can actually make you feel
less hungry, according to research by scientists at the University of
Parma, in Italy.
For the study earlier this year, researchers gave
240 participants snacks of popcorn and chocolate chips served on either
red, white or blue plates. Those eating from the red plates ate less
overall.
Researchers suggest that this is because we generally
associate the colour red with stopping and caution (for example, traffic
lights). This subconsciously encourages us to eat less if our food is
on red dishes.
HAVING AN EGG FOR BREAKFAST
Eggs are a
particularly dense form of protein, says independent food scientist and
nutritionist Dr Sam Christie, ‘which is why you feel fuller for longer
after eating them’.
According to a report in the Journal of the
American College of Nutrition, eating two scrambled eggs for breakfast
resulted in people eating fewer calories for the rest of the day – in
fact, for the next 36 hours.
Sprinkling cinnamon on food can also make you feel fuller for longer.
‘It
seems to have an effect on both insulin uptake and blood glucose
levels, which is why you don’t get a spike and then drop in how full
you feel,’ says Dr Christie.
When not being hungry is something serious
Even
the common cold can make you lose your appetite – a bunged-up nose can
make food less appetising, as 75 per cent of what we think is taste is
actually smell.
However, in some cases a prolonged loss of appetite can be a sign of cancer.
There
are two reasons why this can signal the disease, explains Justin
Stebbing, professor of cancer medicine at Imperial College London. ‘It
can be a local effect – such as a tumour in the stomach which causes the
person to feel full. On a broader scale, cancer can cause secretion of
various hormones that suppress appetite.’
He adds the size of the
tumour may not make any difference. ‘A pancreatic cancer the size of a
5p piece can cause a person to lose their appetite, yet a melanoma the
size of a football inside the pelvis may not.’
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