Gaining weight/losing weight is all about calories in versus calories out.
If you have more calories coming into your body, you will gain weight. If you are offsetting your calorie load with excercise and strict eating during the week, it would depend on how many calories you have to 'play' with.
There are various calorie counters you could us. But if you stuffed yourself completely full of salad, I doubt that would cause weight gain. However, if you stuffed yourself full of donuts then, yes, you'd gain weight.
