The feeling of hunger is very much influenced by hormonal signals, and the hormone ghrelin particularly. I think of ghrelin like the hunger gremlin; it pushes and grumbles for more food. Researchers found that when study participants chewed more, their ghrelin levels were reliably lower after meals. So, the longer food is chewed, the less ghrelin is released, and the longer you feel satiated. Now, that's something to chew on!
How many chews, you might ask? In the experiment, participants who chewed 40 times rather than 15 times consumed fewer calories; but I'd rather you not worry about counting your chews. The point is that when you eat high-fiber whole foods, you must chew. By their very nature, the foods require that you masticate well before swallowing.
And before we move on from hormones, a study at the University of California–Davis in 2002 found that eating fiber causes the release of a hormone in the stomach called cholecystokinin, and that hormone plays a direct role in letting your brain know that you are fine, that you got what you need.
In so many ways, fiber is critical for healthy weight loss. It makes us feel full and satiated, turns off the hunger signal, and it also cleans out our bodies like a powerful internal scrub brush. I have a friend who used to be constipated for a week at a time; she thought she ate well and avoided fatty foods, but she never quite got around to eating fruits. She started eating an apple a day (sometimes even two or three) and now her bowels move twice a day. (Once is just fine, by the way; let's call the second time a bonus!) Her tummy flattened out, her skin took on a glow, and she has a lot more energy without that stuffed-up, compacted feeling she used to walk around with.
On top of that, apples are a rich source of a particularly powerful type of fiber called pectin. It's what's used as a gelling agent to make jams and jellies, and in our stomach it can delay stomach emptying through a similar mechanism. Researchers at UCLA showed that by swapping in pectin for regular fiber they could double the time it took subjects' stomachs to empty from about 1 hour to 2 hours, which meant subjects felt full that much longer.
In fact there was even a study entitled "Weight Loss Associated with a Daily Intake of Three Apples or Three Pears among Overweight Women" published in the journal Nutrition. Researchers found that instructing women to eat an apple or pear before each meal resulted in significant weight loss.
Pretty cool, no? They were told, in effect, to eat more food, to add the fruit on top of their regular diets, and what happened was, the fruit crowded out less healthy choices; they ended up eating fewer calories overall and they started shedding pounds.
Other great sources of this superfiber include citrus, peaches, peas, and carrots. So yes, you can have an apple. Or a pear. Or an orange. You can even have two or three. But at the very least, have an apple before the day is done.
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