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 and it is considered to be unsafe by many people (including medical professionals). Some people seem to be particularly sensitive to aspartame, though the incidence and range of detrimental effects are presently unknown. The adverse reactions that seem to be caused by aspertame sensitivity include headaches, muscle pains, skin rashes, hypertension, lethargy and heart palpitations. 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, I believe that the effects of aspartame toxicity are more common than people realize. However, because of the many reports of adverse reactions, aspartame is one of the most rigourously researched chemical food additives known. The American Cancer Society has investigated this chemical's use and has not found any direct correlation between aspartame consumption and cancer.

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!

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