LONDON( Reuters)-The sweetener aspartame is a" possible carcinogen" but it remains safe to consume at already agreed levels, two groups linked to the World Health Organization( WHO) declared on Friday.... In a press conference ahead of the announcement, the WHO's head of nutrition, Francesco Branca, tried to help consumers make sense of the seemingly conflicting declarations, especially those who seek out artificial sweeteners to avoid sugar.... After undertaking its own comprehensive review,