There
has been a resurgence of diets emphasizing increased protein intake
to promote weight loss or to improve health, so the topic of protein
and its role in a healthy
diet is worth reviewing.
What
is protein and why is it important? Protein contains nitrogen and
provides amino acids that are essential for building body proteins.
Protein is used to build muscle and maintain/repair lean tissue, including
muscle and body organs.
There
are nine essential amino acids: histidine (essential for children),
isoleucine, leucine, lysine, methionine, phenylalanine, threonine,
tryptophan, and valine. These amino acids must be supplied by food;
the body cannot make them. There are also 12 nonessential amino acids,
which are important, but called nonessential because the body can
make them from the essential amino acids.
Proteins
come from plant and animal sources. Animal proteins more closely match
the amino acid composition of human proteins, however people who do
not consume animal foods can get all of the protein needs from plant
sources, (they just need a larger amount of plant protein versus animal
protein to fulfill the body’s requirement for protein).
According
to the Food and Nutrition Board of the National Reseach Council (who
establish dietary recommendations for the population), the body’s
need for protein is met when protein intake is at .8 grams of protein
per kilogram of body weight. (Divide your body weight in pounds by
2.2 to get the equivalent in kilogram weight). This meets the needs
of about 90% of the population of adults. For men, this translates
to about 63 grams of protein per day, and for women, it is about 50
grams of protein per day.
Protein
needs increase for growing children, nursing mothers, severally injured
or seriously ill people, and athletes. Athletes, in particular, pay
special attention to their protein intake and often supplement with
protein powders. In fact, the typical diet consumed in industrialized
countries already contains more than enough protein to cover the needs
of most athletes and any additional protein above the body’s needs
is either used for energy or converted to body fat. A typical diet
should contain between 10-20% of calories as protein. What athletes
and others expending great amounts of physical energy need are additional
calories, (in the proper balance of fat, protein, and carbohydrate,
not just protein).
So,
if we already get enough protein, why are high protein diets like
the Atkins diet so popular right now?
In the past few years,
there has been a swing towards hatred of carbohydrates, and carbohydrates
are being blamed for the obesity problem. The option on low-carbohydrate
diets is to increase fat and/or protein in the diet to make up for
a low-carbohydrate intake. What’s wrong with this is that high protein,
high fat diets severely limit sources of carbohydrates that provide
essential vitamins, minerals and other protective factors against
serious diseases such as cancer, heart disease, and high blood pressure.
And, at very low levels of carbohydrate intake, the body produces
ketones, which is a potentially dangerous condition. Beside the dangers
of a low carbohydrate intake, a high protein intake produces waste
products containing nitrogen that require a lot of water to flush
out of the body. Excess protein taxes the liver and kidneys, and does
nothing to increase muscle mass because the excess that is not used
for energy is converted to fat.
The
fact is, the body needs all of the nutrients that supply energy: fats,
proteins, and carbohydrates. Each have a unique purpose and are
essential in the right amounts, and taxing to the body in the wrong
amounts. Too much of any of these nutrients will lead to an increase
in body fat.
For
people who are following a reduced calorie to
lose weight, the protein intake should be at least 75 grams
per day. This is a higher protein level than the typical intake of
a diet that supplies calories to maintain weight. This is because
when energy balance is negative (i.e. fewer calories taken in than
are needed, causing weight loss), the body’s nitrogen requirement
is greater to maintain nitrogen balance when other sources of energy
(fat and carbohydrate) are not enough to provide energy balance. This
amount of protein can be adequately supplied with a reduced calorie
diet (of more than 1000 Calories) comprised of 15-20% of calories
as protein. Therefore, protein intake above 20% of calories is not
necessary for a properly reduced calorie diet and has no additional
health benefits.
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