weight-loss efforts a boost with 'negative-calorie' foods With just 18 calories per celeriac is one of the lowest-calorie vegetables around.With just 18 calories per celeriac is one of the lowest-calorie vegetables around. Fall Vegetables, Different Vegetables, Celeriac Soup, Negative Calorie Foods, Liquid Meals, Cream Of Celery, Celerie Rave, Calories, Light Recipes