PROTEIN POWER
Protein is one of the more popular and
positive nutrition buzzwords today, with a myriad packaged processed
foods declaring that they are high in protein. But what exactly is
protein, what are the best sources, how much are we consuming, and do we
really need those protein balls and shakes?
Proteins are chemical compounds made up chains of amino acids
which themselves are composed of the elements carbon, hydrogen, oxygen
and nitrogen. There are 20 amino acids that are important to humans, and
nine (histidine, isoleucine, leucine, lysine, methionine,
phenylalanine, threonine, tryptophan, and valine) of these are
considered essential in that they must be obtained from foods and drinks
in our diets, whereas the other non-essential amino acids can be
synthesised within our bodies. Amazingly, all of the proteins in our
body are made from these 20 amino acids.
Proteins are
essential parts of the structure and function or every cell in our body
and the body of an average 80kg adults will contain about 13g of
protein, with 43% found in muscle, 16% in blood and 15% in skin. The
protein in our cells are constantly turning over, over a period of
minutes to months, through the process of protein synthesis and
degradation, which is one reason why we ideally need to obtain a range
of proteins from foods and drinks each day. In addition to being used to
make proteins, amino acids can be used for specific purposes within
cells, like the formation of nerve transmitters and hormones. Amino
acids also can be used as a source of energy – particularly when other
sources of energy like carbohydrate and fat are restricted.
In
the great scheme of things, our body’s top priority is to meet its
energy requirements, and when energy from other sources is limited, it
will break down protein to meet its needs. It does this by stripping off
the nitrogen from the rest of the amino acid molecule, leaving carbon,
oxygen and hydrogen skeletons to be used as fuels, just like
carbohydrate, and provides 17 kJ per gram of protein. On the other hand,
if you consume adequate carbohydrate and fat, your body spares protein
from being used for energy. When amino acids are used for energy, the
nitrogen molecules are converted to urea and excreted in your urine.
Most
people eat a variety of foods containing many different proteins. Some
foods contain all 9 essential amino acids in amounts suitable for humans
and these are called complete protein foods. Commonly eaten foods that
are complete proteins include animal foods like meat, poultry, seafood,
eggs, and dairy foods and in addition, soy protein is considered to be
complete. Proteins in plant foods (vegetables, grains, legumes, nuts and
seeds) are rarely complete, but when they are eaten in combination,
either at the same meal (e.g., rice and beans, or bread and peanut
butter), or another time of the day, you nearly always end up with a
complete source of protein, which is one of the reasons why vegan diets
(where you do not eat any animal foods) can meet all of our nutritional
requirements if well designed.
Unfortunately, most
people don’t realise that both low and high protein intakes are
detrimental to health. Low intakes can impair the functioning of our
immune systems, making us more prone to infections, and of course will
stunt the growth of children and adolescents, and slow the healing of
wounds and rates of recovery after surgery, for example. It is also
possible to eat too much protein as our kidneys don’t have an unlimited
capacity to remove urea from our blood. The upper limit of protein
consumption in humans is estimated to be 35% of energy from protein,
which for a typical person consuming 8,700 kJ (2080 Calories) a day
would be 179 grams a day. Needless to say, this rarely occurs under
normal circumstances, but has been observed in populations where food is
scarce, and people are forced to rely heavily on eating wild animals
like rabbits for food, and that’s why it is known as rabbit starvation
or mal de caribou. Symptoms include diarrhoea, headache, fatigue, low
blood pressure and slow heart rate, and a vague discomfort and hunger
that can only be satisfied by consuming foods that are high in fats or
carbohydrates.
The Estimated Average Requirement (the
daily nutrient level estimated to meet the requirements of half the
healthy population) for protein for men is 0.68g per kg body weight per
day and for women it is 0.60g per kg body weight per day. Australia’s
most recent nutrition survey (part of the Australian Health Survey, or
AHS) in 2011/12 determined that men consumed an average of 104.6 g of
protein per day or 1.2 g per kg body weight and women consumed 77.9g of
protein per day or 1.1g per kg body weight. In other words, the average
Australian adult consumes nearly twice as much protein as the estimated
average requirement each day.
Perhaps unsurprisingly,
Australians have increased the amount of protein they consumed each day
since the last national nutrition survey in 1995 – as low-carbohydrate
diets have become more fashionable, people have replaced some of the
carbohydrate with protein. The primary sources of high quality protein
in the Australian diet are lean meats, poultry, seafood, eggs and
alternatives (e.g., soy-based products, other legumes, nuts and seeds,
etc…) and milk, yoghurt, cheese and alternatives. The AHS found that
only 17% (less than 1 in 5) of Australian adults consumed the
recommended number of serves of meats and alternatives and less than 14%
(around 1 in 7) consumed the recommended number of serves of milk,
yoghurt, cheese and alternatives. Legumes are also a good source of
protein, but again, less than 10% of Australians consume the recommended
number of serves. Overall, these results suggest that most of the extra
protein Australian adults are consuming is coming from discretionary
foods. This may be highly refined protein devoid of other nutrients – or
in other words “junk” protein.
In Australia at least,
we should beware the high protein health halo – we don’t need to eat
more processed foods high in refined proteins. We should instead be
eating more of those high-quality protein-containing foods like lean
meats, poultry, seafood, dairy and alternatives that generally don’t
make protein claims on their packaging.
Read more:
• This edited extract is based on text from Dr Alan Barclay’s book Reversing Diabetes
• Australian Health Survey – Protein
Alan Barclay, PhD is a consultant dietitian and chef (Cert III).
He worked for Diabetes Australia (NSW) from 1998–2014 . He is
author/co-author of more than 30 scientific publications, and
author/co-author of The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).
Contact: You can follow him on Twitter or check out his website.
