Aspartame - also known as Nutrasweet - breaks down in the body to 50% phenylalanine. While phenylalanine is found in milk and bananas, many people are sensitive to this. The claim by pro-aspartame people that "phenylalanine is fine because it's found in nature" is playing a bit loose with the quantities. They usually quote bananas and milk. So here we go:
Bananas contain 0.03g of phenylalanine per 100g of banana.
Milk contains 0.17g of phenylalanine per 100g of milk.
Aspartame contains 50.00g of phenylalanine per 100g of aspartame.
You might notice that many foods in the US carry warnings that the food contains phenylalanine even if it's in tiny amounts. There is a proven danger for many people. But what does phenylalanine do?
Studies have shown that when phenylalanine enters the brain, it interferes with how serotonin works. Serotonin is a chemical in the brain that helps keep your mood even. Without serotonin working properly, the person can have serious problems with depression and mood swings. This is true for most people in general, and PKU-sensitive people in particular.
Here is a study reported on the National Institute of Health website:
"This study was designed to ascertain whether individuals with mood disorders are particularly vulnerable to adverse effects of aspartame ... the project was halted by the Institutional Review Board after a total of 13 individuals had completed the study because of the severity of reactions within the group of patients with a history of depression ... We conclude that individuals with mood disorders are particularly sensitive to this artificial sweetener and its use in this population should be discouraged."
NIH Govt Website on this Research
Amusingly, pro-aspartame people have said this study should be discounted because only 13 people completed it. But the whole REASON that the study was halted was because the results were too dangerous to keep the study going!
Some pro-aspartame sites promote the 1987 study by Schiffman (partially funded by Nutrasweet) with 40+ patients that found no link bewteen aspartame and headaches. It was done for ONE DAY ONLY with capsules (delayed release). However, a year later, in 1988, a study by Koehler had patients given aspartame in a more standard way for four weeks. The placebo group had NO headaches. But half of those taking aspartame reported LARGE increases in headaches.
Find out for yourself if you are sensitive to phenylalanine and aspartame. If you normally are a big diet-soda drinker, or ingest other products with aspartame, cut them ALL out for 4 weeks. Instead, drink 8+ glasses of water a day and substitute in other low carb foods. See for yourself if you feel better at the end of the 4 weeks.
Basics of Aspartame
Lisa Shea's Library of Low Carb Books