Unemployed obese people will have to diet or lose their benefits under Tory proposals dubbed "a stupid little stunt".
Alcoholics, drug addicts and others with "treatable conditions" also face being stripped of their sickness payments.
Prime Minister David Cameron said it was "not fair" that taxpayers were being asked to fund welfare for those who refused help.
Around 100,000 with treatable conditions are receiving sickness benefits and there is currently no requirement for them to undertake treatment.
Obese people on benefits could be forced to diet or lose their sick pay
Former Labour spin doctor Alastair Campbell, who had a well-publicised battle with booze and is an Alcohol Concern ambassador, said the Prime Minister was "pathetic" and was not taking the problem of addiction seriously.
The Prime Minister said in a statement: "Too many people are stuck on sickness benefits because of issues that could be addressed but instead are not. Some have drug or alcohol problems, but refuse treatment. In other cases people have problems with their weight that could be addressed, but instead a life on benefits rather than work becomes the choice.
"It is not fair to ask hard-working taxpayers to fund the benefits of people who refuse to accept the support and treatment that could help them get back to a life of work.
"The next Conservative government is determined to make sure that the hardest to help get the support they need to get them back to a fulfilling life. That is why I have asked Professor Dame Carol Black to undertake a rapid review in to how best to support those suffering from long-term yet treatable conditions back in to work.
"In particular, I have asked her to consider whether people should face the threat of a reduction in benefits if they refuse to engage with a recommended treatment plan - it is vital that people who would benefit from treatment get the medical help they need."
Dame Carol, an adviser to the Department of Health, said: "I am deeply interested in trying to overcome the challenges these types of benefit claimants pose.
"These people, in addition to their long-term conditions and lifestyle issues, suffer the great disadvantage of not being
engaged in the world of work, such an important feature of society."
But many on social media said such harsh measures punished people for "poverty-induced" issues.
Medics have often opposed such proposed measures in the past. In January 2013 when Westminster Council proposed unhealthy people who refuse to attend exercise classes should have their benefits cuts. GP Dr Lawrence Buckman told the BBC the idea was "draconian and silly".
Speaking to radio station LBC, Campbell branded the announcement "embarrassing" at a time when other world leaders were focusing on issues like the fighting in Ukraine and the Greek economy.
Describing addiction as "an illness, not a lifestyle choice", he said the Prime Minister should instead invest in treatment and minimum unit pricing. Campbell added: "I actually do think when you have got real leaders like (German Chancellor Angela) Merkel doing the things that they are doing, it is embarrassing that we have a PM who does this sort of stuff. The fact that he is making a speech about it is pathetic."
He added: "People that are walking around London and the rest of the rest of the country today, as they walk over people in sleeping bags on the streets, just ask themselves if those people really, really chose to be there. They did not choose to be there - they are alcoholics or drug addicts because it is a disease, it is an illness, that is how it should be treated.
"To say we are not going to give you benefit because you are fat, we are not going to give you benefit because you drink too much, just think about what we have become as a country that that is our Prime Minister and that is how they treat a serious illness."
Susannah Gilbert, of obesity support group Big Matters, said a "blanket ruling" stripping people of sickness benefit would not work. "I think it's naive to think people don't want to change their lives. Most people aren't happy with their weight and would like to change," she told the BBC Radio 4 Today programme. "Many of them have tried every diet under the sun and they still have a weight problem. So to think that they don't want to have help isn't true."