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A simple, inexpensive tool that takes the guesswork out of dieting could help obese people lose weight and help diabetics decrease their use of medications, finds a new Canadian study.

The tool is dishware marked with lines that delineate proper portion sizes for starches, meats and vegetables.

The dishes appear to help obese patients restrict their calorie intake, and restricting calories helps with weight loss and improves blood sugar control in Type 2 diabetics.

Dr. Sue D. Pedersen and colleagues at the University of Calgary, the study's authors, note that people tend to like to clean their plates. But with portion sizes in North America growing bigger all the time, we are ingesting more calories than ever, with the rates of obesity and Type 2 diabetes rising as well.

"The increasing prevalence of obesity is paralleled by increasing portion sizes in the marketplace," the authors write. "Portion sizes are an important determinant of energy intake; the number of calories ingested by subjects at a meal has been directly correlated with the serving size offered."

Dr. Pedersen's team conducted a six-month study of commercially available portion control plates and bowls in 2004. The plates were divided into sections that marked appropriate portions for carbohydrates, proteins, cheese and sauce, with the rest left open for vegetables.

"The weight loss that we saw in this study is similar to weight loss seen in studies of medications for weight loss -- but without the associated potential for side effects and at a fraction of the cost," Pedersen told Â鶹ӰÊÓnet from Calgary.

The sections approximately totaled an 800-calorie meal for men and a 650-calorie meal for women. The cereal bowl was designed to allow a 200-calorie meal of cereal and milk.

Pedersen said the guidelines are easy to follow because they don't require weighing, measuring the food, or counting calories. However, just because there are no height restrictions listed for the foods doesn't mean there are no limits.

For instance, "You can't pile steaks on top of each other," said Pederson. And the portion allocated for cheese on the dinner plate is restricted to one cube of cheese, "not a tower of cheese."

Half of 130 obese patients with diabetes were randomly assigned to use the plate for their largest meal and the bowl when they ate cereal for breakfast. The other participants ate off regular dishware and received usual care: dietary assessment and teaching by dieticians.

At the end of six months, 122 patients remained in the study:

• Those using the portion-control dishes lost an average of 1.8 per cent of their body weight;
• Those receiving usual care lost an average of only 0.1 per cent.
• A significantly larger proportion of those using the dishes -- 16.9 per cent vs. 4.6 per cent --lost at least 5 per cent of their body weight.

The authors note that a five per cent weight loss has been shown to help reduce the risk of death associated with obesity-linked disorders such as cancer and heart attacks.

In addition, more of those in the group using the portion-control plates were able to reduce their use of diabetes medications after six months (26.2 per cent vs. 10.8 per cent).

In fact, "some came off of diabetes medication altogether," said Pederson.

"On the other side of things, looking at the people who were in the control group --that's the group who did not receive the plate to use for the six-month trial -- they had an increased likelihood of needing more diabetes medication over the six months.