calories in versus calories out for weight loss .
energy has to come from somewhere for you to walk, talk , breathe , pumping the heart with blood , scratching your head , thinking etc .
you can eat all the healthy foods , nuts , salmon, brown rice, salads , but if you eat more calories than you are expending each day you will gain weight.
you could eat nothing but deep fried chicken and lose weight , so long as you are expending more energy than you take in
google "john cisna teacher weight loss "
food is the main source of energy for the body
if food is scarce the body will use it's reserves ( fat and muscle ) for energy ( when you are on a diet )
when fat is depleted it will start eating itself to preserve life ( muscle and tissue )
to keep as much muscle as you can on a diet it is wise to do some form of resistance training and to eat a high protein diet .
you need to be in a calorie deficit which you create by eating less, exercising more ( swimming ,running , walking etc ) or both . track the calories you consume and be under your maintenance figure by about 500 calories a day . walk 4 times a week for 30 minutes to an hour . you could easily lose 1 - 2 pound a week . i lost 10 kg doing this and drinking beers every weekend , going to restaurants etc
go on a bodybuilding forum and you will receive loads of good advice on how to do it
good luck