How much food should I eat?

Cookies as big as frisbees. Muffins the size of flower pots. Bowls of pasta so deep, your fork can barely find the bottom. One reason people's waistlines have expanded over the past few decades is because food portions have too.
Portion Distortion
People today eat way more than they used to — and way more than they need to. This means that they're constantly taking in more calories than their bodies can burn. Unfortunately, lots of us don't realize that we're eating too much because we've become so used to seeing (and eating!) large portions.
Portion sizes began to increase in the 1980s and have been ballooning ever since. Take bagels, for example: 20 years ago, the average bagel had a 3-inch diameter and 140 calories. Today, bagels have a 6-inch diameter and 350 calories. One bagel that size actually contains half a person's recommended number of grain servings for an entire day!
The price of such overabundance is high. It's common knowledge that people who consistently overeat are likely to become overweight. But they also risk getting a number of medical problems, including high blood pressure, high cholesterol, type 2 diabetes, bone and joint problems, breathing and sleeping problems, and even depression. Later in life, people who overeat are at greater risk for heart disease, heart failure, and stroke.
It's easy to understand why the food industry tends to serve way more food than is necessary: Customers love to feel like they're getting the best value for their money! But the value meal is no deal when it triples our calories and sets the stage for health problems.
So what can you do to take back control? A good place to start is knowing about two things that can help you eat smart: serving sizes and recommended amounts of different foods.
Help Yourself: The Truth About Serving Sizes
Look at the label on any product package and you'll see a nutrition information section that gives a serving size for that food. Contrary to popular belief, this serving size is not telling you the amount you should be eating. It's simply a guide to help you see how many calories and nutrients — as well as how much fat, sugar, and salt — you get from eating a specific quantity of that food.
Sometimes the serving size on a package will be a lot less than you are used to eating. In some cases, it's perfectly OK (and even a good idea) to eat more than the serving size listed on the package. For example, if you're cooking frozen vegetables and see the serving size is 1 cup, it's no problem to eat more because most vegetables are low in calories and fat yet high in nutrition.
But when it comes to foods that are high in calories, sugar, or fat, the serving size can alert you that you may be getting more than is healthy. If you buy a 20-ounce bottle of soda and drink it all at once, the amount you consumed is 20 ounces. But if the label shows the serving size is 8 ounces, not only did you have 2½ servings, you also had 2½ times the listed calories as well as 2½ times the sugar.
Eat Smart: What's Recommended
Serving sizes tell you how much nutrition you're getting from a particular food but they don't tell you which foods you need to stay healthy — and how much of those foods you should eat. That's where the U.S. Department of Agriculture's MyPyramid comes in.
MyPyramid divides foods into six groups:
grains
vegetables
fruits
oils
dairy
meat and beans
MyPyramid then offers guidelines to help people figure out how much of these foods they should eat based on age, gender, and activity level.
Once we know the types of foods and quantities we should be eating, it's easier to figure out how much of that heaping plate of food our bodies actually need as opposed to how much they want. Instead of going along with what your school cafeteria or favorite restaurant puts on your plate, you can take control by eating only the amount you need.

Using Visual Cues
Serving sizes on food labels and recommended amounts on MyPyramid are usually given in grams, ounces, or cups. Of course, most of us don't carry around food scales and measuring cups. So how can we translate those amounts into quantities we can relate to? That's where the following visual cues come in. (Just be warned: Some might seem small, especially to recovering super-sizers!)
One easy way to size up portions if you don't have any measurements is to take a look at your hand. A clenched fist is about a cup — and a cup is the amount experts recommend for a portion of pasta, rice, cereal, vegetables, and fruit. A meat portion should be about as big as your palm. And limit the amount of added fats (like butter, mayo, or salad dressing) to the size of the top of your thumb.
Another great way to visualize appropriate portions is to use the concept of the "divided plate." Think of your plate as divided into four equal sections. Use one of the top quarters for protein. Use the other top quarter for starch, preferably a whole grain. Then fill the bottom half with veggies. None of the foods should overlap — or be piled high! Not only will dividing your plate like this help you keep portions under control, it can also help you to balance your meals.

Portion-Control Tips
Being aware of realistic portion sizes and visualizing portions or using the "divided plate" concept will help you avoid overeating. But sometimes these visual cues can be hard — especially when foods are difficult to measure, like a sandwich, or they're foods like chips and cookies that we tend to eat right out of the bag.
More tips for portion control:
*Eat your meals on a smaller plate so your meal looks larger. A sandwich on a dinner-size plate looks lost; on an appetizer plate it looks downright hefty.
*Avoid taking an entire bag of chips or a container of ice cream to the couch. You're far less likely to overdo it if you serve yourself a portion in the kitchen first.
*Try single-serving size foods (like those cute little 8-ounce cans of soda!) to help your body learn what an appropriate portion size is. These days all kinds of snacks and beverages are available in "100-calorie" portions. Of course, the key is to eat just one!
*Eat three well-rounded meals (with vegetables, proteins, and carbs) and one or two healthy snacks at regular times throughout the day. Skipping meals or waiting too long between them can make you more likely to overdo it at the next meal.
*Add more salads and fruit to your diet, especially at the start of a meal. This can help control hunger and give a sense of fullness while controlling calorie intake.
*Try not to rush through your meals. Eat slowly and chew well — giving yourself a chance to feel full before you take more. If you do want seconds, go for more salad or veggies.
*Be aware that most restaurant portions are three or four times the right serving size. Try sharing meals with friends, ordering an appetizer as a main dish, or packing up the extra to take home before you begin to eat.
*Don't be tempted to go for the giant value meal or the jumbo drink just because they're only a few cents more than the regular size.
Most important, make it a habit to let your stomach rather than your eyes tell you when you're done with a meal.  
   The key to maintaining a healthy weight is to listen to your body's natural signals about when it's hungry and when it's full. Sometimes these signals can be confused by constant overeating or constant dieting, which is why it pays to watch portion sizes and make smart food choices.