This idea has been around for a long time, and though I understand its appeal, it's an incomplete solution to losing weight. The thermogenic (energy burning/heat producing) effects of some high-fiber foods come close to their total caloric content, but keep in mind that many such foods provide little in the way of nutrients. It doesn't take that much energy to digest even the most fibrous food, so what you're really banking on is that the food contains very few calories to begin with. Celery and iceberg lettuce are two such examplesthey have little else besides fiber and water. They may help you feel full, but your body will only be fooled for a little while. Then you'll be ravenous and you're more likely to binge on high-calorie and high-fat foods.
Now, a better option would be to look for high-fiber foods that also contain usable calories and beneficial nutrients. Think beans, spinach, and citrus fruits. You can also include some of the high-fiber, low-nutrient foods, like celery and iceberg lettuce, in dishes that contain high-quality nutrients from other sources. Essentially, you're looking for ways to increase your fiber intake because fiber helps you feel full faster. But your body knows the difference between energy it can use and food that it can't, and taking the ideal of increasing your fiber intake too farwhich is really what the search for "negative-calorie content" foods is all about, approaches weight loss from the wrong angle.
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