Numerous studies have shown that people tend to eat what is put in front of them, regardless of the portion size. (Bartley Kives/Canadian Press)

When it comes to healthy eating, how much you eat is just as important as what you eat. But with portion sizes on the rise, it's not always easy to know what an appropriate amount of food is.

There are ways to keep your intake in check, but the first step is to understand the difference between the terms 'serving' and 'portion.' Although sometimes used interchangeably, their meanings are quite different.

There are ways to keep your intake in check, but the first step is to understand the difference between the terms 'serving' and 'portion.' Although sometimes used interchangeably, their meanings are quite different. (Melissa Golden/Associated Press)

A serving is a standardized way of measuring food — for example, half a cup of rice or one ounce of cheese. Serving sizes are based on energy and nutrient requirements and are used in dietary guidelines, such as Canada's Food Guide.

A portion is the actual amount of food that is being served for a snack or meal. It can refer to the amount of food on your plate or the amount of food in a package. In other words, portion size is the amount of food a person chooses to eat at one sitting.

For example, Canada's Food Guide advises that Canadian adults need between six and eight servings of grain products every day. According to the Food Guide, one serving of rice equals half a cup. Therefore, if you eat 1 cup of rice —which isn't an uncommon amount to see served as part of a meal — that's one portion, but it actually counts as two servings toward your daily nutritional requirement.

Portions on the rise

There is no doubt that average portion sizes for snacks and meals have increased in North America in recent decades. In fact, a 2003 study published in the Journal of the American Medical Association found that portion sizes of all foods, including salty snacks, soft drinks, hamburgers and French fries, increased between 1977 and 1998. In some cases, such as salty snacks, the portion size increased by more than 50 per cent.

Not only have the portion sizes of packaged foods increased; our own perceptions of appropriate portions are on the rise along with them. This means we're serving ourselves more food compared to 20 years ago, in many cases without even realizing it.

A study published in the Journal of the American Dietetic Association in 2006 found that young adults consistently chose larger portions of food when asked to select a meal, compared to a similar study conducted in the 1970s.

Eating with your eyes

Numerous studies have shown that people tend to eat most or all of what is put in front of them, regardless of the portion size.

In a 2005 study, researchers at Cornell University instructed two groups of participants to eat soup from a bowl until they felt full. In one group, the bowls were "bottomless" and secretly kept refilling themselves. In the end, the group that ate from the bottomless bowls ate 73 per cent more soup. Yet, the participants in that group did not perceive themselves to be any more full than those who ate from the normal non-refilling bowls.

Another study by researchers at Cornell University found that people unconsciously ate more when presented with larger portions. Moviegoers were given large or medium bags of popcorn to snack on, and the people with the larger bags of popcorn ate 45 per cent more than people with the medium-sized bags. This might not seem noteworthy — except that even when the popcorn was stale and not very enticing, people still ate 33 per cent more when eating from the larger bags.

So what does all this mean?

The research indicates that larger portions translate into an almost certain increased intake of calories. So, simply being aware of how much you are actually eating per portion during meals and snacks can go a long way when trying to keep your food intake in check.

What is an appropriate portion?

Canada's Food Guide provides an extensive list of appropriate serving sizes based on the different food groups. You can use these examples to help you choose an appropriate portion.

Look at the following serving sizes and try to use that as a reference next time you sit down to eat.

Food group	One serving looks like
Fruits and Vegetables (7 to 10 servings/day)	1 medium piece of fruit 1/2 medium potato 1 cup spinach 1/2 cup vegetable juice
Grain Products (6 to 8 servings/day)	1/2 bagel 1 slice of bread 1/2 muffin 1/2 cup cooked pasta 2 cups plain popcorn 1/2 cup rice 1/4 naan
Milk and Alternatives (2 to 3 servings/day)	1 cup milk (1%, 2% or soy) 1 1/2 oz. cheese 3/4 cup yogurt
Meat and Alternatives (2 to 3 servings/day)	2 eggs 1/4 cup nuts or seeds 2 tablespoons peanut butter 2 1/2 oz. chicken, beef or pork 1/2 cup tuna or salmon

Using everyday items for comparison can also be a handy method of figuring out what a serving actually looks like. For instance:

1 cup = a baseball or roughly the size of a woman's fist
1/2 cup = a small computer mouse
1/4 cup = medium egg
3 ounces of meat = a deck of cards or the area of the inside of your palm
1 ounce of cheese = 4 dice
1 teaspoon = 1 die

Keeping portions in check

Simply being aware of how much you are actually eating per portion during meals and snacks can go a long way when trying to keep your food intake in check. (Seth Wenig/Associated Press)

The following tips are some simple ways to help you keep your portions in check.

Controlling portions at home:

• Use smaller plates — not only will you serve yourself less; you'll eat less, too.
• Divide up single portions before sitting down to eat.
• When eating packaged food, put an appropriate portion in a bowl instead of eating directly out of the bag or box.
• Avoid eating in front of the television — you'll eat more than you realize if you're not paying attention to the food going into your mouth.
• If you are having trouble "eyeballing" it, get out the measuring cups until you have a better idea of what an appropriate portion is.
• Read food labels, and make note of the serving size. A package usually contains multiple servings.

Controlling portions when eating out:

• Order an appetizer and a salad as your main dish — they tend to be smaller than entrees.
• Share your meal, or request part of your meal be packaged to go before they even serve it to you — this way you won't be tempted to eat it all at one sitting.
• Ask for a doggie bag, and put aside enough to eat for lunch the next day.
• Avoid the temptation to get more bang for your buck — that means opting out of the biggie and super-sized meals.
• Avoid the buffet and order from the menu (unless you're very disciplined and comfortable with eyeballing proper portion sizes).
• Don't feel obligated to clear your whole plate — stop eating when you feel full.

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