I'm just trying to get my head around various weighs of losing weight and I realised I don't really get how calories counting works. If someone eats 1500 calories worth of balanced diet and then someone else eats 1500 worth of balanced diet plus a load of junk but exercises the equivalent calories, would they both lose the same weight? Or is there more at play with the weight loss when calories counting like the types of foods etc?
Yes all other things being equal they will both lose the same weight.
Eg both are 40 year old women in sedentary jobs, both 5'4" and both weigh 12 stone. So would need 1700 cals/day to maintain current weight (this is called the TDEE - total daily energy expenditure)
Then person A eats 1500 healthy cals does no exercise so a deficit of 200 cals/day.
Person B eats 1500 healthy cals, 400 cals of junk but does a 45 minute spin class which uses 400 cals so a deficit of 200 cals/day.
It would take both of them about 17 days to lose 1 lb.
If however person A weighed 14 stone and had a moderately active job then they would need 2400 cals/day to maintain and so would have a deficit of 900 cals/day and would take 4 days to lose 1lb. Person B remains unchanged so still takes 17 days to lose 1 lb.
This obviously takes no account of water retention etc.