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updated 5/20/2005 9:29:56 AM ET 2005-05-20T13:29:56

How do we know when to stop eating? Our bodies do have an intricate system that prompts us to eat when we’re low on fuel and sends signals to stop when our needs are met.

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Yet a new study shows that for most of us – whether we’re overweight or not – the overwhelming influence on how much we eat is the size of our portions.

In this study, soup bowls with holes were attached to special tables that allowed the bowls to slowly refill as soup was consumed. People who ate from the self-refilling bowls ate 73 percent more soup than those eating from normal bowls.

Yet despite eating so much more, this group did not believe they had consumed more and did not feel any fuller than those eating from normal bowls.

In another recent investigation, researchers compared how much people ate of the same foods served in different portions on different days.

First, people selected food from a buffet. On another day, when the people were given 25 percent more food, they ate 24 percent more, or an extra 165 calories.

On yet another day, when given 50 percent more than they ate from the buffet, they consumed 39 percent more, or an extra 270 calories.

No compensation for overeating
Once again, the study participants thought they consumed equal amounts on the different days and felt the same each time. The researchers wondered if eating more of the larger portions occurred because those people really were hungry for more and had taken smaller-than-necessary portions from the buffet to avoid any appearance of overeating.

This explanation is unlikely, since none of the participants were overweight or on a diet. Most people also tend to overeat at buffets.

You might think that eating more of larger portions at one meal would be balanced by less eating at the next meal.

But several studies have shown that people do not compensate for overeating at one meal by eating less at the next. In fact, in a third study, despite portions that doubled over two days at all meals, people still ate more. There was a 26 percent increase in calorie consumption per day – an extra 530 calories per day for women and 803 for men.

Fortunately, an awareness of how huge portion sizes affect us can help us eat better.

If you are trying to cut calories to lose weight, serve yourself smaller portions instead of hoping you will have the willpower to leave food on your plate. You can start with portions that are one-half to two-thirds of your usual size and eat more later if your physical hunger is still unsatisfied. You can also use smaller dishes and bowls. And try smaller glasses for all drinks, except water.

More vegetables, fruits
Today’s giant portions at restaurants warrant special strategies to avoid overeating. Share entrées where you can. Or ask for a take-out box as soon as your food comes. Box up what you think will be excess before you start eating, or you may clean your plate as usual. Even a “small” size at restaurants can be too big.

Understanding how large portions impact our eating habits can help us achieve a positive goal: eating more vegetables and fruits that so many of us overlook.

One way to do this is to place large serving bowls of vegetables and salads on the table, encouraging everyone to eat these foods abundantly. Or try putting a double portion of vegetables on your plate. If you prepare vegetables and salads with a variety of interesting textures and flavors, you may enjoy these healthful dishes more than you expect.

For dessert, set a big bowl of fruit on the table – more than you think people will eat – and they may really surprise you.

Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.

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