By Maureen Callahan, M.S., R.D.
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Many of us worry about overeating when we sit down for a meal. But what, beyond overindulgence, makes people feel full -- and how can we leverage foods' filling powers to help control portions?
"It's a complex sequence of events that starts with the eyes, the mouth, the stomach, and the gut," says Barbara Rolls, Ph.D., professor of nutritional sciences at Pennsylvania State University and author of "The Volumetrics Eating Plan." "But hunger and satiety, the scientific term for that full feeling that comes after eating, are also influenced by our environment."
Armed with insight about the environmental cues that compel you to eat and the foods that offer the most satisfaction, you can make smart choices that will fill you up, and not out. (How not to pig out at that Super Bowl party. )
Mind over matter
"People are not like gas tanks. Our bodies do not tell us, 'Stop now, you've eaten 375 calories,' " says Janet Polivy, Ph.D., professor of psychology at the University of Toronto, Canada, who studies the connections between food and feeling. "Eating is much less determined by biology than by psychology." The size of the portions you eat and whom you eat them with have a direct effect on your intake. (Learn the top habits of the world's healthiest countries. )
When you're served larger portions, you'll most likely finish them and then some, according to University of Illinois researchers, who invited subjects to eat soup from bowls equipped with hidden refilling devices that kept the amount of soup in each bowl constant. Subjects who supped from these bowls consumed 73 percent more soup than those who used ordinary bowls; however, they didn't rate their feelings of satiety any higher than those who consumed less.
The presentation of portions can also influence the amount of food you eat. Most of us are likely to eat considerably more than usual from a buffet-style table. One study showed that just increasing the variety of foods available increased intake by 60 percent. In other words, you really do eat with your eyes.
Eat with friends or coworkers, and chances are you'll model the amount you eat based on their plates. "As long as you have a big eater in the room, our research suggests people then feel free to eat a little less than whoever sets the pace," Polivy says. She and her colleagues tested the hypothesis on people who had been deprived of food for 24 hours and found that subjects regulated their food intake by keeping an eye on their colleagues' plates, eating more when in the presence of someone who ate heartily.
The flexible physiology of the stomach helps place us at the mercy of environmental stimuli. Although ordinarily about the size of a closed fist, the stomach expands as food enters. "Our stomachs can hold about three pints of food," explains Julie Schwartz, M.S., R.D., coordinator of nutrition services at Emory Bariatric Center in Atlanta, Georgia. "That's about the size of a football." While useful in the event of food scarcities that plagued our ancestors, the stomach's ability to expand can undermine our best sensible-eating intentions.
Fill the stomach too quickly, and your body won't have time to recognize messages from the hormones that help regulate appetite. Insulin, leptin, cortisol, and ghrelin are some of the chemical messengers that send signals between the stomach and the brain, inducing hunger and registering satiety. "We don't have immediate feedback from our bodies telling us we've eaten enough," Polivy says. "It takes about 20 minutes for food to be digested enough that glucose gets into the bloodstream and the hormones start working." If you have already consumed most of a meal in 20 minutes' time, your brain will receive satiety signals too late to slow your eating.
How nutrients help
Although environment is a powerful factor that drives people to eat, certain nutrients -- most notably protein, fiber, and water -- can help tilt our internal scales toward "full" before we reach the red line. (Experts pick their perfect food )
Protein is the most satiating nutrient, says former Harvard University researcher Thomas Halton, Ph.D., who recently co-wrote review of 50 satiety studies in The Journal of the American College of Nutrition. Something about protein tells our bodies to stop eating it after a while. Researchers aren't quite sure of the mechanism but believe that part of protein's advantage may come from its thermic effect, the rate at which calories are consumed simply by the act of digesting food. "The digestion and absorption of protein takes more work than the digestion and absorption of fat and carbohydrates," Halton says. About 25 to 35 percent of protein calories are used as the body converts protein to energy; only five to 15 percent are used when carbohydrates are converted.
Carbohydrates are the next most satiating foods. "The type of carbohydrate plays a role," Halton says. "Whole grains are more satiating than refined sugars and refined white flour." Whole grains, along with fruits and vegetables, tend to be filling because they contain higher levels of fiber. Unlike other food substances, fiber is not digested. It adds bulk to foods, which helps fill the stomach, slowing the rate at which food is digested. The result: You notice feelings of fullness sooner.
Fruits, vegetables, and grains also have another satiety-related benefit: Because these foods contain high percentages of water, they generally have a lower energy density, the number of calories per gram, than meats, dairy foods, and confections. That means you can eat more of them without the consequences that high-calorie foods can bring. A number of studies coordinated by Rolls show that eating salads and other low-calorie foods can help people eat less without feeling deprived. In one study, Rolls found that eating a salad with low energy density before a meal enhanced satiety enough that subjects consumed 12 percent less food from the meal.
While fat's palatability certainly provides satisfaction, it isn't technically "satiating," according to Dana Gerstein, M.P.H., R.D., specialist at the University of California at Berkeley's Center for Weight and Health. "I think of 'satisfying' as fulfilling a desire," Gerstein says. "Fat fulfills desire but is not satiating. Satiation is a physiological process."
All of this information yields a plate containing a small amount of fat, a lean source of protein, and a variety of fiber-rich fruits, vegetables, and whole grains. "This is pretty much what we know we should be eating anyway, but it also helps with satiety," Rolls says. "It's a new way to encourage people to practice good nutrition."
Maureen Callahan, M.S., R.D., is an award-winning food journalist and recipe developer. She lives in Colorado.