scribbles

It would be awesome if selective weight loss existed, but unfortunately, that's not the way the body works. Doing sit-ups can only strengthen the muscles underneath the fat, but it won't stimulate the muscles to favour fat loss in that area.

Aerobic exercise, the best fat burner, stimulates your fat cells to release its fat stores for fuel, but you can't choose which fat cells as it's not up to you. The fat loss "pattern" is partly genetically determined, and some fat cells are more "stubborn" than others. But with regular exercise over time, you'll lose fat from all over your body, so eventually, the fat from your thighs, stomach, etc., will also decrease -- one of the first areas most people show signs of weight loss is in their face.

By negative calorie diet, I'm assuming you mean foods that require more calories to digest than they contain -- celery's the well-known one. You can still eat these foods, but I think that since the few extra calories it uses is negligible in the big picture, I would rather focus on getting adequate nutrients from a balanced diet (a variety of food).

If weight loss and long-term maintenance is the goal, I would suggest that in conjunction with regular aerobic and resistance exercise, you should also pay attention to your energy intake, ie. burn more calories than is consumed.