For decades, we’ve been taught that maintaining (and losing) weight is a function of calories in versus calories out. In other words, it doesn’t matter whether you eat a 210-calorie candy bar or 210 calories of broccoli – as long as you burn those 210 calories, it’s all equal. Now scientists are turning that conventional wisdom on its head.

Research published in 2012 in Journal of the American Medical Association found that, even when calories are equal, dieters who consume greater amounts of protein and fat and fewer carbohydrates lose more weight than those who follow low-fat plans. Another study, published in 2005 in The American Journal of Clinical Nutrition, found that people who were on a high-protein diet with no calorie restrictions unknowingly reduced their calorie intake by 450 calories per day.

So while it's true that a 3-ounce skinless chicken breast has the same amount of calories as two slices of white bread (both have about 140 calories), those calories are not created equal in terms of how your body uses them. 

And according to dietitian Lona Sandon, assistant professor of clinical nutrition at University of Texas Southwestern Medical Center in Dallas, people who have arthritis need to be especially mindful of consuming calories from nutrient-dense sources. These types of foods, such as dark-green veggies, legumes and lean protein, contain important vitamins and minerals to nourish your joints and muscles – and are naturally low in fat.

Here’s how your body processes the big three nutrients – protein, carbohydrates and fat.

Protein (4 calories per gram)

Protein rebuilds damaged tissue and creates certain hormones and enzymes. A bonus: Your body burns more calories digesting and metabolizing protein than it does digesting other nutrients. Protein moves more slowly through your digestive system than other nutrients, thus slowing the time it takes for other foods to move through, and helping you feel full longer. Plus, getting adequate protein helps build and maintain muscle mass, and that burns more calories, boosting metabolism by as much as 30 percent (compared to fat and carbs' five percent calorie-burning spike). Protein's ability to not only burn calories, but also keep eaters satisfied, makes it a nutritional superstar in the weight-loss world.

Cautionary note: Over time, eating too much protein (and avoiding carbohydrates) can create myriad risks from cancer and heart disease to liver and kidney problems. In part, that's because many high-protein foods – such as beef and eggs – are also chock full of fat and often prepared with salt.

Carbohydrates (4 calories per gram)

Carbohydrates don't provide the same satisfied feeling as protein, but they're the body's main source of fuel, driving both organ function and physical activity. Trouble is, carbs that aren't used for immediate energy are stored as fat. Your best bet, experts say, is to get your carbs from fruits, vegetables and whole grains. "Carbs from these sources (unlike a sugary cookies or cake) contain a variety of anti-inflammatory compounds and antioxidants, including vitamins A and C, that help slow down the inflammatory process," explains Sandon.

Plus, fiber in fruits and veggies fills you up without weighing you down, keeps blood sugar levels in check, and prevents chronic diseases ranging from cancer to stroke.