There are three guarantees in life: death, taxes, and hunger when you're on a diet. Expanding your tummy through voluminous food, however, can help keep your grumbling stomach at bay.
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Examine.com discusses why any means of expanding the stomach will lead to appetite suppression:
The body naturally produces a variety of peptides and hormones that suppress hunger. One class of receptors, called mechanoreceptors, are located in the stomach and intestines and are not actually activated by any specific molecule, but by the stretching of tissue. That means that expanding the stomach will result in appetite suppression, regardless of what is causing the expansion.
Eating low-calorie food that results in intestinal bulk is a good way to limit caloric intake while suppressing the urge to eat more. While vegetables with a high water content will shrivel and shrink after consumption, foods high in soluble fibre will 'gel' and expand in the stomach. Vegetables high in cellulose, an indigestible carbohydrate, will also result in increased intestinal bulk.
So how do we accomplish this? Consume foods such as broccoli, cabbage, brussel sprouts, kale, cauliflower, and other foods on our "free food list" when you need to satiate your hunger.