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Judging by the proliferation of tiny packages of chips, cookies, chocolate bars and even soft drinks in the grocery store, Canadians like to snack.

And if you're a snacker who's also keeping tabs on the bathroom scale, 100-calorie packs of Doritos, Oreo cookies and Kit Kat chocolate bars might seem like a dream come true. But do these portion-controlled snacks really help people eat less?

According to researchers from Arizona State University, the answer is no. Rather than serving up pre-packaged willpower, 100-calorie snack packs actually boost consumption by people likely to buy these snacks - chronic dieters.

You'd think that pre-measured, calorie-controlled packages of treats high in sugar, fat and/or salt would be ideal for people who can't control the amount they eat from larger packages. Built-in portion control ought to prevent mindless eating (like munching your way to the bottom of the bag) - as long as you stop at one pack.

And 100-calorie snack packs could also aid portion control by helping people visualize what 100 calories of food looks like. But it seems such awareness doesn't necessarily prevent overeating.

In a study soon to be published in the Journal of Consumer Research, researchers measured the response to mini-packs of candy among dieters and non-dieters.

When faced with 200 calories' worth of regular-sized M&M's in one package versus the same caloric amount of mini-M&M's packaged into four small baggies, 18 per cent of dieters polished off all the mini-packages while only 4 per cent did so when the candies were in the larger package.

People who were not perpetual dieters did the opposite - they tended to polish off the regular-sized M&M's in the larger package rather than eating all of the smaller packages of mini-M&M's.

According to the researchers, we've been conditioned to think that when food is tinier, and comes in smaller packages, it's a "diet" food that helps control calorie intake. But when people see small pieces of food in multiple packages, they perceive those packages as containing more calories than the same amount of food in one package.

Scientists speculate the stress created by this conflict (how can diet food have more calories?) triggers chronic dieters to consume more food in smaller packages.

Non-dieters, on the other hand, ate in keeping with what researchers call "unit bias". Unit bias makes people feel that whatever unit (portion size) of food is served is the appropriate amount to eat. In other words, the larger the portion served, the more they eat.

Studies suggest there are other reasons why 100-calorie snack packs could lead to overeating. Once chronic dieters have eaten to a certain point, the "what-the-hell" effect kicks in. The feeling of failure to exert willpower makes people abandon any remaining resolve and keep on eating.

Other research suggests portion-controlled snacks can help people consume less than if they are presented with a super-sized package - but only for a short time.

A recent study from Washington University in St. Louis and the University of Toronto found that divvying food up into smaller portions created a "partitioning effect" and dramatically influenced consumption. Volunteers were given a box of 24 cookies and asked to record how long it took to eat them. Half were given cookies in bulk; the rest received individually wrapped cookies.

The group that received the 24 cookies in bulk gobbled them up in six days, compared with an average of 24 days for the participants with the individually wrapped cookies.

Singly packaged foods lead to a "transaction cost" - the cost of opening up a second package, which gives people the opportunity to think about how much they're eating. In this way, 100-calorie snack packs can prevent eating on automatic pilot. You're forced to decide whether or not to continue snacking by having to open up a second package.

But this partitioning effect diminishes as people grow accustomed to eating mini-me sized packages of snacks. As the novelty wears off, people may start eating more than one pack in a sitting.

If you like to snack and have difficulty limiting your portion size from larger packages, 100-calorie snack packs might be worth a try.

But before you stock your kitchen cupboards with these treats, there are other things to consider besides their ability - or inability - to cut your portion size.

For starters, you'll pay more for the extra packaging. A 100-calorie package (19 grams) of Doritos costs 67 cents. The same portion from a large bag costs only 17 cents - one quarter of the price.

The 100-calorie snacks might not satisfy your craving the same as the parent brands. Munching on Christie's Thinsations Chips Ahoy "crisps" isn't the same as biting into an original Chips Ahoy cookie.

When it comes to nutrition, these snacks don't offer much beyond white flour, sugar and, well, 100 calories. Each 100-calorie Coffee Crisp has two teaspoons of refined sugar. Ditto for 100 calories of mini-Oreos.

Most 100-calorie snacks are highly processed and lack appetite-suppressing nutrients such as fibre, protein and healthy fats. They don't fill you up the same way an apple and yogurt can, so you might be tempted to reach for a second package.

When the urge to snack hits, and only cookies or a bag of chips will do, 100-calorie snack packs can satisfy your craving for junk food. Just don't let them squeeze out nutritious snacks that help keep your appetite in check during the day.

Next week: Tips to downsize your portions.

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100-calorie snacks

Make your own snacks that contain some protein, fibre and carbohydrate along with a bit of fat.

1 small apple + 1 ounce skim-milk cheese (7 per cent MF)

7 baby carrots + 2 tablespoons hummus

1 tall (12 ounce) skim-milk latte

2 fat-reduced Triscuit crackers

+ 2 teaspoons of peanut butter

1/3 cup plain 1-per-cent yogurt

+ ½cup blueberries

15 plain almonds

3 dried apricots + 3 walnut halves