Negative-calorie foods are foods that boost your metabolism and help you lose weight post pregnancy. These are usually plant-derived fruits and vegetables, high in water content and locked in a fiber matrix.  Many vegetables, like celery, for example, are water-rich negative-calorie foods. Apples, grapes and watermelons are considered water-fruits as they are loaded with water. A diet of negative-calorie foods is filling because of its water content and is an effective means of controlling the appetite.

Here are some best negative-calorie foods that you can consume as part of a post-pregnancy weight loss diet:

1.  Apples, grapefruits, and watermelons: These fruits are rich in dietary fiber and water. Count on an apple as an effective negative-calorie snack option.

2.  Celery: Celery is power-packed with nutrients, but contains no contributing calories. You can eat as much celery as you want, and you won't gain body fat. Celery juice is a powerful anti-inflammatory drink. Perfect as a crunchy snack, celery is also delicious in salads, soups, or juice.

3.  Lettuce, onions, and salad greens: These foods are rich in water and fiber, antioxidants as well as immune-boosting nutrients. You can munch on salads as much as you desire and still never gain body fat.