had a discussion with my friends regarding weight gain
friend reckons that you can eat your three meals a day and not gain any weight even if you do no form of exercise

i however argued that you would put on weight eating your three daily meals if no exercise is done. afterall calories in vs calories out.

what do you think? please elaborate when you explain aswell

I expect if you modified your diet slightly to not eat over your BMR ( your bodies resting rate) but still ate 3 meals a day but did not eat over your basal metabolic rate you would not gain weight theoretically.
All the organs require certain amount of calories to function. Your BMR maybe around 1,200 calories if you are a woman.

Calorie Need Calculator | AHealthyMe.com

The theory of energy in V energy out is a fair comment... but its not just about three meals a day, its also about what is in thosee three meals (the mix of carbs, protein and fats) and also what time of day you are eating this stuff.

The 1200cals per day for women is way of the mark for most women as the BMR needs to be based on gendeer/height/weight/age and activity level.. to this end as a man of 90kg at 1.70cm (this produces a BMI of 31.5 which is also way off the mark by labelling me as clinically obese, yet I only have 15% body fat). My BMR is 2490cals but from my normal day to day stuff is actually 3900cals and during heavy training and competitive sports can reach 6500cals per day.

I would imagine that eating a sensible 3 meals a day would not lead to excessive weight gain especially if your body type is of a smaller frame person.