What are you hungry for?

Feature
your appetites — yes, appetites plural.
According to entomologists David
Raubenheimer and Stephen Simpson,
authors of Eat Like the Animals, (see
p.25), living organisms — including
humans — do not eat just to silence
a growling stomach. Instead, they are
responding to finely tuned appetites for
specific, essential nutrients. The number
of these appetites depends upon the
animal, from three appetites identified
in locusts (protein, carbohydrate and
sodium) and five in human beings
(protein, carbohydrate, fat, sodium and
calcium). Of these, the most dominant
is for protein, driving organisms to
prioritise it over other nutrients and, if
need be, overeating just to get enough.
This doesn’t mean that we should
all start eating masses of protein —
according to Raubenheimer and
Simpson, just 15-20% of our calories
tends to come from protein. What it does
mean, however, is that this appetite is
stronger, so many animals — including
humans — will seek out protein over any
other nutrient, and will keep eating until
that 15-20% has been satisfied.
Raubenheimer and Simpson first
observed this in locusts. When locusts
were presented with adequate food
sources, they would eat the locust
equivalent of a nutritionally balanced
diet. But when protein was in short
supply and carbohydrate-rich, low
protein foods were on the menu, the
locusts would overeat until they got
enough protein — even if that meant
becoming overweight.
From slime mould to humans, ancient appetites for specific
nutrients keep us eating — especially when protein is scarce
D
o
you often eat only to feel
oddly unsatisfied and hungry for
something more, maybe going
on to raid the kitchen cupboards for a
snack to fill the gap? If so, it could be
that your food choices aren’t satisfying
On humans and locusts
According to Raubenheimer and
Simpson, this phenomenon has also
been observed in humans. In studies
carried out in Switzerland, Jamaica
and Australia, it was found that protein
made up about 18% of what volunteers
ate. But like the locusts, if volunteers
were presented with low protein foods,
they ate more calories — around 35%
more, even though their protein intake
remained the same.
When it comes to understanding our
own food preferences, it may be hard to
comprehend how such innate appetites
might work to drive us towards certain
nutrients: carbohydrates may be sweet,
protein is usually associated with a
savoury taste, and fats tend to have a
creamy mouth-feel. It’s possibly harder
to imagine what calcium tastes or feels
like. Yet, says Raubenheimer, the five
appetites are controlled partly by taste
and associated receptors located across
the gut and throughout the body. “The
14 OPTIMUM NUTRITION | AUTUMN 2020

Feature
This could explain why it may
sometimes be so hard to put
down that bag of crisps — not
because it tastes so good…
calcium receptor (CaR) is among these,
and sodium and calcium receptors are
widespread in the nervous system and
elsewhere,” he says. “There are also
associated hormonal signalling systems.”
Raubenheimer and Simpson go on to
suggest that our five appetites may also
be a factor in the growing obesity crisis.
As people across the globe increasingly
consume an ultra-processed diet, high
in carbohydrate and fat, our ancient
appetite for protein is going unsated —
or is being sated less quickly. This could
explain why it may sometimes be so hard
to put down that bag of crisps — not
because it tastes so good, but because
our appetite for protein isn’t being
satisfied. They suggest that the umami
taste of many processed foods tricks the
brain into perceiving them as a source of
precious protein.
Omega-3s
It has been suggested elsewhere that
a need for omega-3 fatty acids could
also be driving consumption through a
similar mechanism. However, Simpson
does not think this is likely. “There is a
fat appetite,” he says.
“More likely that a balance of free
fatty acids is what is being regulated,
not one component [such as] omega-
3s.” The need for a balance of fats,
he suggests, is similar to the need for
a balance of amino acids, which are
obtained from protein.
What Raubenheimer and Simpson
suggest is that rather than focusing on
calories, we should consider the type of
food that we are eating. However, for
anyone struggling with obesity or insulin
resistance, which disrupts ‘normal’
healthy appetite signals, this may need a
reset.
“In some animals [nutrient imbalance]
happens naturally as part of the
seasonal shifts in food abundance and
temperature,” says Raubenheimer. “The
biochemistry simply shifts into states that
support the conditions — hibernation,
fruit abundance, [etc.]. The orang-utans
we discuss in the book is an example;
we’ve studied several other examples
including grizzly bears.
“Evidence in humans is that metabolic
dysregulation in type 2 diabetes can be
reset by a period of fasting and very low
calorie intake.”
A FASTER TRACK
TO METABOLIC
FLEXIBILITY?
F
asting has increased in
popularity as a means to
improve metabolic health and
— as a by-product of that — to lose
weight. It may follow time restricted
feeding, when meals are eaten within
a set time frame (e.g. 12 hours or
four hours) or a pattern of fasting
days. However, whatever form it
takes, Amanda Swaine, a registered
nutritional therapist and author of
Intermittent Fasting for Beginners, says it
is not the same as a low calorie diet.
Switching from feast to famine
“Intermittent fasting works
differently… by switching between
periods of very few calories (fasting)
to periods of abundant calories
(feasting),” she says. “This…stops
the body from thinking starvation is
coming and slowing the metabolic rate
as a protection mechanism.”
One of the benefits, she says, is
“metabolic flexibility”, with the body
being able to transition between using
carbohydrates, fats or proteins for
energy — so “the body can meet its
energy needs in accordance with how
it evolved; using glucose-based energy
as the main fuel for short term needs
and internal fat stores for longer term
energy needs”.
Other benefits include helping to
resolve chronic inflammation and
increased sensitivity to the hormones
insulin and leptin. This, she explains,
enables cells to use blood glucose
more effectively and enables the brain
to ‘see’ and utilise fat stores from
around the body.
Whatever plan you choose, however,
Swaine says to eat during or as
close to daylight hours as possible.
“Interestingly, the body adapts more
easily to skipping a meal than having
one at a wildly different time than
usual,” she says.
Pack in good nutrition
She also emphasises the importance
of not adopting a diet mentality. “It is
important to focus on eating enough
and eating healthily during the eating
phase,” she says. “Some people notice
they aren’t as hungry…after they have
adjusted to their fasting regime and
eat a lot less than normal, thinking this
will speed up weight loss and the other
benefits of fasting.
“If this becomes a regular
occurrence, over time they could
experience a similar effect on their
BMR (see p.10) to that experienced
during long term, low calorie diets.”
She also warns against eating
ultra-processed foods. “Some people
think they can eat whatever they like
during the eating phase,” she says.
“If the diet is low in nutrients and
highly processed, you may be driven
to overeat as the body sends out
strong hunger signals in an attempt to
get the nutrients it needs.” She also
recommends adding in some weight
training to help boost the BMR.
However, while she says fasting
may benefit most adults she adds that
it is not suitable for people who are
underweight, who have or previously
had an eating disorder, are pregnant,
chronically stressed, experience
hypoglycaemia or low blood pressure,
have type 1 diabetes or need to take
medication with meals several times a
day at set times that can’t be adjusted.
She advises that anyone taking
medication, such as for type 2 diabetes
or thyroid conditions, should seek
medical advice before starting a fasting
regime. She also recommends that
women who are breast feeding or
people over 70 work with a practitioner
to ensure they are getting adequate
nutrients.
For those who have a history of low
calorie dieting, she says that weight
related benefits may take longer to
achieve. “The good news for those
people is, with the right fasting
and eating plan…their body will be
becoming more metabolically flexible.”
WHAT TO WATCH OUT FOR
• Do not adopt a ‘diet’ mentality
• Do not cut food to speed weight loss
• Avoid ultra-processed foods
• Aim for good quality nutrition
• Seek medical advice beforehand
• Consult your GP about any
medication you are already taking
OPTIMUM NUTRITION | AUTUMN 2020
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