Aspartame crystal. Coloured scanning electron micrograph (SEM) of a crystal of the artificial sweetener aspartame. This chemical is nearly 200 times sweeter than sugar but has a very low calorific value. It is used to sweeten foods and soft drinks, and is used by diabetics as a sugar substitute. Aspartame contains phenylalanine, so products must carry a warning as people with the disease phenylketonuria (PKU) are unable to metabolise this amino acid. Alleged connections of aspartame consumption with brain lesions, tumours and lymphoma have made the chemical the centre of a public controversy. Magnification: x86 when printed 10 centimetres wide.