Some research has been done concerning the risk for a heart attack when the weight goes up and down in the way you describe and this shows that it increases by % compared with that for someone whit a steadier weight.The disadvantage of fasting is that no new eating habits are learnt, so that when the fast ends weight goes up again. In order to solve an overweight problem the attention must first of all be directed towards permanently improving your eating habits so that the desired weight, once achieved, can be maintained. If you think it is too difficult to change all your habits at once, then change them one at a time. It is also necessary to accept a completely new attitude towards food, i.e., you only eat the vegetables and protein your body needs and not the fat and sugar you merely long for. This new attitude will gradually feel natural and acceptable. You can plan your diet so that you gradually find it pleasant to eat wholesome food.
Scientific investigations have revealed that those with overweight eat far more fat than others and you can probably go down in weight just by drastically reducing your fat intake. The fact that you went up after finishing with Weight Watchers may have been caused by your regarding the period with them as a temporary cure. You accepted their diet plan without really being convinced. Instead of this, you must find a diet which you feel is permanently acceptable to live with. You will be surprised at the large improvements you will be able to make if you take it gradually and find changes which are acceptable to you.