Please avoid the 'very low calorie diet' approach. I'm talking less than 1200kcals for the average person.
If one were to consistently consume say 700 calories on a regular basis; there would be a huge weight loss in the beginning and then the metabolism will adjust accordingly. Not only are such diets a metabolism killer, but it is highly unlikely that nutrition is well absorbed on such a sparse diet.
Ultimately, once such a diet is discontinued, quick weight gain is expected. This is due in part by the body's ability to rebound from the survival from starvation mode to the fact that the basal metabolism is at a sluggish rate.
Often those who gain weight "just by looking at food" so to speak, fall in the category of a continual low calorie diet, even when the desired weight loss has not been achieved. Furthermore, those on VLCD often find there progress 'stuck' and the scale unmoving regardless of strict adherence to the VLCD. This is due to metabolic disorder/ body's natural survival from starvation mechanism kicking in.
I often find this pattern particularly true among those who have prior drug use, namely methamphetamine, whereby VLCD are the norm. The nature of the drug causes an anorexia to the user which rapidly deteriorates the individual to a sickly-skinny appearance. Once incarcerated, the subjects eat three meals a day, but gain weight extremely rapidly. This is not due to an exceptionally high calorie diet. In fact, the diet may only consist of 1200-1500 calories. However, if the metabolism is only adjusted to 500-700 calories, the subject has DOUBLED the norm even when many here would actually LOSE weight on a 1200-1500 calorie diet.
Moderate decrease in calories (250 a day), moderate daily exercise to expire 250 calories a day. This will safely and effective lead to about a pound loss every week without a future rebound.