On the day following a fast day, people usually eat more (“compensatory eating”), but only about 20% more than usual; anything more than that is just not comfortable.
On a fast day you eat 25% of your normal daily caloric intake. On the next day you take in 120% of your normal daily intake. Combining the two days (when normally you eat 200% your daily amount) you take in only 145% of your daily intake. Each fast day results in a reduction of 55% of your daily calorie intake.
How much weight would you lose? Daily caloric intake differs for everyone. For males, it is around 2400 calories; for females, it is about 2000 calories. Suppose we have someone whose daily calorie level is 2200 cal. Each fast day result in a reduction of 55% of 2200 kcal, which is 1210 kcal. Two fast days in a week means a reduction of 2420 kcal per week which is 0.7 pound of non-water tissue (3500 kcal is equated with a pound of non-water tissue). That and the associated water means you lose about a pound per week.
Do Intermittent Fasting for 10 weeks and you will certainly notice a 10 pound weight reduction!