What is PKU?
by Dr. Tracy L. Beck, Ph.D.
Have you ever looked at the label
on a diet soda can and seen the warning: Phenylketonurics
- contains phenylalanine? I personally know of several people who refuse to
drink diet soda because the word "phenylketonurics" sounds too scary!
What does "phenylketonurics" mean? Is it something you can catch from
diet soda?
Well, let me take the opportunity
to answer these questions.
"Phenylketonurics" is NOT something
you can catch from diet soda! This long, scary-sounding word is included in a
warning at the end of the ingredients list on some products, but it is NOT an ingredient these
products. "Phenylketonurics" is the term used to refer to people that
have the metabolic disorder Phenylketonuria, or PKU for short. So - kind of
like how the word "diabetics" refers to people that have
"diabetes", "phenylketonurics" refers to the people that have
"phenylketonuria". I myself, am one of these phenylketonurics and the
warning on diet soda cans is included merely to inform people like me that the
product contains the synthetic chemical ASPARTAME . People
that have the disorder PKU cannot consume any product that contains aspartame,
for reasons which I will elaborate on below.
Two additional questions that
people often ask when they learn of the true meaning of the warning label on
diet soda are - Do I have PKU? How do I know that I don't have PKU? Well, if
you have reached an age where you have the desire to drink diet soda and you
still have the mental capacity to question whether or not you have PKU, the
odds are that you don't have the disorder.
Phenylketonuria is a genetic
metabolic disorder that results when the PKU gene is inherited from both
parents. When babies are born in the United States, a heel stick blood test is
done to test for various disorders - PKU is one of the disorders that is tested
for. It is very rare, in the US an average of 1 in 15,000 babies is born with
the disorder (this number varies from region to region). If a baby is tested
positive for PKU at birth, a follow up test is done a few days later. Out of
500 babies which do test positive for PKU on the first test, on average only
one will actually have the disorder.
So, what is PKU? What happens to
people that have it?
People with PKU have a deficiency
of an enzyme which is necessary for the proper metabolism of an amino acid
called Phenylalanine (i.e., the component in diet soda included in the
warning). Phenylalanine is an essential amino acid and it is found in nearly
all foods which contain protein: meat (of all kinds), dairy products, nuts,
beans, tofu... the list goes on and on. Additionally, phenylalanine is found in
aspartame, the sweetener found in most diet soft drinks and sugar-free
candies/gum - hence the need for the warning on the labels of these products.
Those of us that have PKU must follow a strict "low protein" diet to
avoid all food sources that have high phenylalanine content. To get adequate
amounts of other amino acids found in protein (without the damaging phenylalanine),
people with PKU also have to take a special formula which is usually in the
form of a liquid beverage.
If those of us that have PKU do
not follow a strict low protein diet, phenylalanine is not adequately digested
in our bodies and it builds up in our blood in the form of an acid called
phenylpyruvic acid. High levels of phenylpyruvic acid damage the brain and can
cause an array of side effects - mental retardation, the loss of pigmentation
in the skin/hair/eyes (people with untreated PKU often have light skin, blond
hair and blue eyes), a "mousy" or musty odor, muscle aches and pains
and in extreme cases, even seizures. Depending on the severity of the PKU,
babies who were not treated for the disorder and put on the special diet at
birth run the risk of suffering irreversible mental retardation within the
first year of life.
PKU is certainly a detrimental
disorder if not treated properly, but the prognosis isn't nearly as grim as the
preceding paragraph suggests. If babies are put on the low protein diet at a
young age, and they follow the diet throughout life, there is no evidence that
their PKU will be a major hindrance in their accomplishments. In fact, in some
cases, (myself included) people with PKU view their disorder as being a
positive trait, one which has taught them to be more self-disciplined.
In the past, children were taken
off the low protein PKU diet at age 5 or 6 because it was believed that at this
age the brain had developed to the point where elevated levels of phenylpyruvic
acid in the blood would not cause severe health problems. These children are
now adults; many of them have noticed health problems and have decided, of
their own accord, to return to the PKU diet. These days, most doctors that
provide care for PKU patients preach that the low protein PKU diet should be a
way of life and, if we value our health and well-being, those of us with the
disorder should never stray from it.
One question that I often get
asked by people who read this webpage - "Is phenylalanine harmful to people
that don't have PKU?". If phenylalanine is in it's natural form, then the
answer to this question is a great big resounding NO. Phenylalanine is an
essential amino acid that is in nearly all proteins - meats, dairy products,
eggs, nuts, legumes... etc. Some researchers claim that the amino acid
phenylalanine is a natural muscle relaxer and sleep aid. & I've heard a
rumor that this could be why turkey, which is a high phenylalanine food, always
seems to make people sleepy (in addition to the amino acid tryptophan, which is
also a natural sleep aid). For people without PKU or other metabolic disorders,
it is very important to eat a balanced diet, and this certainly includes high
protein (high phenylalanine) foods.
The synthesized chemical called
ASPARTAME is the artificial sweetener that is used in many kinds of diet soda,
sugar-free candies and gums, and many other sugar-free products. Aspartame has
phenylalanine as an ingredient, but is itself a completely different chemical.
It is believed that aspartame can cause a wide range of side effects - from
stomach problems, to headaches, nausea and skin rashes. This chemical is
considered to be very unsafe by many people (including medical professionals).
I have seen the effects of aspartame toxicity and have discussed symptoms of
aspartame poisoning with literally hundreds of people who have found this
website. Based on the number of emails I have received from people like
yourself who have found this webpage, I believe that aspartame poisoning is
much more common than people realize.
I want to note that I am NOT a
medical professional (my Ph.D. is in Astronomy, not medicine), and you should
never make important decisions about your health without the guidance of a
medical specialist. However, if you think you may be experiencing effects of
aspartame poisoning, I recommend an easy test - avoid all aspartame containing
products for 1 month. If your symptoms are caused by aspartame poisoning then
you should feel better within this month. However, if your symptoms persist and
do not disappear in this time, then you should seek immediate medical
assistance to determine the true nature of your problems.
I hope this helps! I hope this
webpage has answered some of the questions you originally went searching for
regarding the scary-sounding warning: Phenylketonurics - Contains
Phenylalanine! Please feel free to send me an email:kineala@mac.com with
comments/suggestions on your case or on improving this website. Thanks for
visiting!
Thanks Dr. Tracy L. Beck, Ph.D. for sharing
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