The World Cancer Research Fund (WCRF) is trying to encourage people to give up an unhealthy vice, such as chocolate or crisps.
It hopes that those who take part in the Dump The Junk campaign will feel the benefits of eating a healthy diet while raising funds for cancer prevention.
Being overweight or obese increases the risk of 11 common cancers such as bowel and breast cancer, the WCRF said.
The charity estimated that around 25,000 cancer cases could be prevented in the UK every year if everyone was a healthy weight.
Sarah Toule, head of health information at the charity, said: "Many people don't realize how much sugar, fat and salt can be found in a lot of the food they eat on a daily basis and it's not just the usual suspects.
"These ingredients are particularly bad for us and can lead to people becoming overweight or obese which increases the risk of cancer.
"Continuously eating sugary food and drinks will gradually lead to a dependency on sugar. So why not Dump The Junk and kick that habit this June?"
• To find out more visit: www.dumpthejunk.org.uk