We know that around 30% of all cancers are preventable. We also know that there is clear evidence of the causal relations between obesity and cancer. This means that there could be lifestyles that could prevent obesity and, thus, cancer. Yet, who legitimises these lifestyles and on which ground? Should citizens be free to accept or not to accept policies concerning them? This is a problem faced within what has been named libertarian paternalism. We discuss it, also proposing a version that we call deliberative libertarian paternalism, showing how important this problem is for a proper framing of the lifestyle policies concerning obesity and, thus, cancer prevention.