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If you want to keep excess snacking at bay, include enough protein in your diet. That's the take-away message from a new study that investigated how the amount of protein consumed affects calorie intake and hunger.

People who followed a lower protein diet – 10 per cent of daily calories – consumed more calories each day than when they consumed a 15-per-cent protein diet. What's more, the calorie increase was enough to cause a roughly two-pound weight gain each month.

It's thought that the protein content of our diet can determine our calorie intake and thus may play a role in the obesity epidemic. The "protein leverage hypothesis" contends that when we're faced with a lower protein diet, we increase our calorie intake in an effort to maintain a consistent protein intake.

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In other words, dilute the protein content of your diet with fat and/or carbohydrate and you'll gobble up more calories each day in search of missing protein and, ultimately, gain unwanted pounds. Given our increasing reliance on processed foods that are typically high in fat and refined carbohydrate, this theory may not be unrealistic.

To test the protein leverage hypothesis, researchers from the University of Sydney in Australia fed 22 healthy, lean men and women three diets, each for four days: 10-per-cent protein, 15-per-cent protein and 25-per-cent protein. The diets were made as similar as possible with respect to palatability, availability, variety and appearance.

Each four-day diet contained the same foods only differing in their protein content. "Meal time foods" were available only in a meal sitting whereas "any time foods" were snack foods to which participants had free access at all times.

Participants consumed an additional 260 calories each day on the 10-per-cent protein diet than they did on the 15-per-cent protein diet. Without an accompanying increase in calorie burning, those extra calories would lead to an annual weight gain of 26 pounds. (When on the 15- and 25-per-cent protein diets, participants consumed about 2,200 calories a day.) Seventy per cent of the extra calories came from "any time" foods not "meal time" foods. Providing constant access to snack foods, rather than restricting food to meal times, enabled participants to overconsume calories on the lower protein diet.

Increased hunger on the lower protein diet seemed to drive food intake. On the 10-per-cent protein diet, participants reported a greater increase in hunger one to two hours after eating breakfast than on the higher protein diets.

If protein puts the brakes on hunger, you may expect that moving from the 15-per-cent to the 25-per-cent protein diet would lead to a reduction in calorie intake. But this wasn't so. When participants were fed the 25-per-cent protein diet they ate the same number of calories each day as they did on the 15-per-cent protein diet.

It's becoming clear that protein plays an important role in weight management. Including protein at meals delays hunger and prolongs the time until your next meal.

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Getting enough protein also helps preserve muscle mass as we age. Having less muscle means your body burns fewer calories at rest – a recipe for incremental weight gain if you don't cut calories to compensate.

Protein-rich foods include meat, poultry, fish, eggs, beans, lentils, tofu, soy products, milk, yogurt and cheese. The acceptable healthy range for protein intake is 10 to 35 per cent of daily calories for adults (10 to 30 per cent for children and teens).

In this study, a 15-per-cent protein diet outscored a 10-per-cent protein diet when it came to curbing hunger and calorie intake.

What does a 15-per-cent protein diet look like? For a 2,000-calorie diet, you need 75 grams of protein a day – an amount you get by consuming six ounces of chicken, two cups of milk and one-quarter cup of almonds.

If you're a vegetarian consuming 1,800 calories a day, you need 67 grams of plant protein. To meet protein needs you'd have to consume one cup of lentils, one soy burger, three cups of soy beverage and one-quarter cup of roasted soy nuts.

A 1,400 calorie weight-loss diet would contain 52 grams of protein – the protein equivalent of roughly four ounces of salmon, one cup of Greek yogurt and two egg whites.

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Some people will benefit from eating more protein. Regular cardiovascular and resistance exercise drive up daily protein needs to repair muscle damage and to support muscle building.

In this case, it's best to calculate your protein requirements based on your body weight. Studies suggest that endurance athletes need to consume 1.2 grams of protein for each kilogram of body weight a day, while those doing regular strength exercise can increase protein to 1.7 grams for each kilogram of body weight a day.

Older adults should also ensure they consume one to 1.2 grams of protein for each kilogram of body weight to slow age-related muscle loss.

Include protein at all meals and snacks, especially breakfast. Eating lean protein at breakfast appears to keep your appetite in check longer than if eaten at other times of the day.

Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com .

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