- With Mayo Clinic nutritionist
Katherine Zeratsky, R.D., L.D.
read biographyclose windowBiography of
Katherine Zeratsky, R.D., L.D.
Katherine Zeratsky, R.D., L.D.
As a specialty editor for the nutrition and healthy eating guide, Katherine Zeratsky helps you sort through the facts and figures, the fads and the hype to learn more about nutrition and diet.
A Marinette, Wis., native, Katherine is certified in dietetics by the state of Minnesota and the American Dietetic Association. She has been with Mayo Clinic since 1999.
She is active in nutrition-related curriculum and course development in wellness nutrition at Mayo Clinic in Rochester, Minn., and nutrition education related to weight management and practical applications of nutrition-related lifestyle changes.
Other areas of interest include food and nutrition for all life stages, active lifestyles and the culinary arts.
She graduated from the University of Wisconsin-Madison, served a dietetic internship at the University of Iowa Hospitals and Clinics, and worked as a registered dietitian and health risk counselor at ThedaCare of Appleton, Wis., before joining the Mayo Clinic staff.
Nutrition basics (31)
- Water softeners: How much sodium do they add?
- Fat grams: How to track your dietary fat
- Yerba mate: Is it safe to drink?
- see all in Nutrition basics
Healthy diets (10)
- Canola oil: Does it contain toxins?
- Butter vs. margarine: Which is better for my heart?
- Detox diets: Do they work?
- see all in Healthy diets
Healthy cooking (7)
- When the heat is on, which oil should you use?
- Moldy cheese: Is it OK to eat?
- Food poisoning: How long can you safely keep leftovers?
- see all in Healthy cooking
Healthy menus and shopping strategies (8)
- Calories in sushi: What are the low-cal options?
- What is BPA? Should I be worried about it?
- Brominated vegetable oil: Why is BVO in my drink?
- see all in Healthy menus and shopping strategies
Nutritional supplements (18)
- Ground flaxseed: Better than whole?
- Fiber supplements: Safe to take every day?
- Chocolate: Does it impair calcium absorption?
- see all in Nutritional supplements
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Question
Phenylalanine in diet soda: Is it harmful?
My favorite diet soda has a warning about phenylalanine. Is phenylalanine bad for your health?
Answer
from Katherine Zeratsky, R.D., L.D.
Phenylalanine isn't a health concern for most people. However, for people who have the genetic disorder phenylketonuria (PKU) or certain other health conditions, phenylalanine can be a serious health concern.
Phenylalanine can cause mental retardation, brain damage, seizures and other problems in people with PKU. Phenylalanine occurs naturally in many protein-rich foods, such as milk, eggs and meat. Phenylalanine also is sold as a dietary supplement.
The artificial sweetener aspartame (Equal, NutraSweet), which is added to many medications, diet foods and diet sodas, contains phenylalanine. Federal regulations require that any food that contains aspartame bear this warning: "Phenylketonurics: Contains phenylalanine." This warning helps people with PKU avoid products that are a source of phenylalanine.
If you don't have PKU, you probably don't need to worry about harmful health effects of phenylalanine — with certain important exceptions. Aspartame in large doses can cause a rapid increase in the brain levels of phenylalanine. Because of this, use products with aspartame cautiously if you:
- Take certain medications, such as monoamine oxidase inhibitors, neuroleptics or medications that contain levodopa
- Have tardive dyskinesia
- Have a sleep disorder
- Have an anxiety disorder or other mental health condition
If you aren't sure if phenylalanine or aspartame is a concern for you, talk to your doctor.
Next questionDiet soda: Is it bad for you?
- Bodamer OA, et al. Overview of phenylketonuria. http://www.uptodate.com/index. Accessed Aug. 20, 2012.
- Phenylketonuria. National Human Genome Research Institute. http://www.genome.gov/25020037. Accessed Sept. 18, 2012.
- Position of the Academy of Nutrition and Dietetics: Use of nutritive and nonnutritive sweeteners. Journal of the Academy of Nutrition and Dietetics. 2012;112:739.
- Aspartame.Electronic Code of Federal Regulations. http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=e057b68f0345a6d44b25b082c07ffa91&rgn=div8&view=text&node=21:3.0.1.1.3.9.1.3&idno=21. Accessed Aug. 20, 2012.
- Zeratsky KA (expert opinion). Mayo Clinic, Rochester, Minn. Aug. 20, 2012.
- Phenylalanine. Lexi-Interact. Lexi-Comp. http://www.uptodate.com/crlsql/interact/frameset.jsp. Accessed Aug. 20, 2012.
- Magnuson BA, et al. Aspartame: A safety evaluation based on current use levels, regulations, and toxicological and epidemiological studies. Critical Reviews in Toxicology. 2007;37:629.
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