Limbic system is one part of the brain. Here the sentiments originate, and one feels happiness or unhappiness and cheerful etc. Human sentiments cannot be controlled so long as the limbic system is not brought under control. It is the brain that controls and keeps the sentiments under check.
Without the control over the brain, it is not possible to exercise self-restraint on one's diet, or for that matter, to exercise control of any kind. People know that consumption of tobacco, alcohol, etc. are harmful to health, but they are unable to get over their addiction. The clear reason for it is that there is no brain-control. If there is brain-control, all such addictions can be given up in no time.