Aspartame has been the subject of controversy since it was first approved by the Food and Drug Administration. It does not become poisonous when added to soda drinks, but because of its common usage in diet soda drinks, opponents warn against drinking sodas that use it as a sweetener. Aspartame has been blamed for a number of illnesses, but further study has been inconclusive.

Aspartame is made of two amino acids called phenylalanine and aspartic acid. It is a white and odorless and retains its sweetness when used at low temperatures. The two amino acids are broken down like protein in the body and its calorie count is very low at 4 kilocalories per gram. When it is heated, it loses some of its flavor.

According to Colorado State University, aspartame is 200 times sweeter than sugar. This sweetness is the reason it is so popular in diet drinks. The aspartame does not have the same calories as sugar and can be used in much smaller doses than sugar to achieve a sweet flavor, allowing the manufacturers to advertise a product as "calorie free." However, people with the genetic disorder phenylketonuria should avoid soda with aspartame as they cannot properly absorb phenylalanine.

There are some health fears around aspartame. Opponents believe it can cause memory loss, headaches, allergic reactions, changeable moods and seizures. Aspartame has been tested by the FDA on numerous occasions and has been approved as safe to use. However, the FDA recommends that you should not consume more than 50 milligrams per kilo of your body weight a day. This equals about 20 cans of diet soda a day.

Some scientific study would appear to indicate that aspartame may not be as safe as thought. Studies in Europe found that aspartame may have contributed to cancer in lab rats, but more study is needed to establish a definite link. The FDA responded to the study by saying that it would continue to monitor the health effects of aspartame but it was satisfied that the 100 toxicological studies it had conducted on aspartame supported its safety.