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Lose Weight with Portion Control

Meal replacements have long been a popular way to lose weight. Metrecal was one of the first meal replacement drinks, introduced in the 1960's as a high protein powder that could be mixed with water and drunk in place of a regular meal. Slim-Fast in liquid form was introduced in the 70's, and was soon followed by sports drinks, protein bars, and all the pre-made meal plans you see today.

Researchers have been divided on just why meal replacements work, however. Ordinarily reducing the number of calories at one meal results in increased consumption at the meals following, resulting in about the same number of calories consumed over the course of the day. Yet this wasn't the case with high protein meal replacements: dieters would eat the meal replacement and would not compensate for the reduction in calories by eating more at subsequent meals. They would then lose weight.

Then other researchers noted that having a bowl of high-fiber cereal would yield the same results: a standard size bowl of cereal in place of a single meal again resulted in lost weight (think of those "Special K Challenge" ads).

Researchers at Cornell University theorized that it was simply the smaller portion size of these meal replacement drinks, bars and the like that was resulting in weight loss (Appetite 2011;57(2):311-317). To test this theory, they recruited 17 adult men and women from the university campus to participate in a feeding study. For five weeks, the participants would eat all of their meals in the feeding lab during the week (Monday through Friday), and keep detailed records of what they ate on the weekends with an eye toward eating about the same number of calories on each weekend.

The participants were randomly assigned to one of two groups. For week one the participants ate all their meals and snacks, as much as they wanted, from a buffet prepared by the university's Human Metabolic Research Unit. The amount they ate was weighed and measured at each meal and the number of calories calculated for each participant's meal.

For weeks two and three, Group One chose one of four meals for their lunch:

1. Chef Boyardee Pasta
2. Smucker's Uncrustables
3. Kashi Bar
4. Lean Pocket
5. Campbell's Soup in Hand
   (Boy, the things people will agree to eat in the name of science!)

These meals averaged about 250 calories (with an optional apple), significantly less than the participants were used to serving themselves at lunch. Note that for both breakfast and dinner the participants could still eat all that they wanted.

For weeks four and five, Group Two had one of the four meals for lunch, while Group One went back to eating all that they wanted for lunch.

In addition to tracking the participants' caloric intake, the researchers weighed each participant before each meal, while the participant weighed themselves at home each morning and reported their weight daily.

They found that those who ate the meal replacement at lunch did not eat any more for their afternoon snack or at dinner, nor did they report feeling any hungrier later in the day than they did when they ate all they wished. Further, those who ate the meal replacement actually lost weight - an average of about 0.5kg, or 1.1 pounds over the ten days of eating the meal replacements.

What this means for you

The researchers note that this is a very small study performed on a fairly uniform population (college students) and that these college students were of normal weight (on average). So it's hard to say that the same results would obtain in the case of the more general population. That said, if you're working on your weight, this is a good argument for bringing your own portion-controlled lunch, whether it's a peanut butter and jelly sandwich or a convenience meal.

First posted: July 20, 2011