Even with all the diet plans out there, weight management still comes down to the calories you take in versus those you burn off during activity.

Popular fad diets may promise you that not eating carbohydrates (carbs) or eating a pile of grapefruit is the secret to weight loss. But it really comes down to eating fewer calories than your body is using if you want to lose weight.

Calories are the energy in food. Your body has a constant demand for energy and uses the calories from food to keep working. Energy from calories fuels your every action, from fidgeting to marathon running.

Carbohydrates, fats and proteins are the types of nutrients that have calories and are the main energy sources for your body. No matter where they come from, the calories you eat are either converted to physical energy or stored within your body as fat.

These stored calories will stay in your body as fat unless you use them up. You can do this by cutting how many calories you take in so that your body must draw on reserves for energy. Or you can add more physical activity so that you burn more calories.

Your weight is a balancing act, but the equation is simple. If you eat more calories than you burn, you gain weight. And if you eat fewer calories and burn more calories through physical activity, you lose weight.

In the past, research found about 3,500 calories of energy equaled about 1 pound (0.45 kilogram) of fat. So researchers thought burning or cutting 500 calories a day led to losing 1 pound a week. But this isn't true for everyone.

In general, if you cut about 500 calories a day from your usual diet, you may lose about ½ to 1 pound a week. But this can vary depending on your body, how much weight you want to lose, your gender and activity level.

It sounds simple. But it's more difficult because when you lose weight, you usually lose a mix of fat, lean tissue and water. Also, because of changes that occur in the body as a cause of weight loss, you may need to decrease calories more to keep losing weight.

Cutting calories needs to include change, but it doesn't have to be hard. These changes can have a big impact on the number of calories you take in:

• Skipping high-calorie, low-nutrition items
• Swapping high-calorie foods for lower calorie choices
• Cutting portion sizes

Skipping one or two high-calorie items is a good place to start when cutting calories. For example, you could skip your morning latte, soda at lunch or that evening bowl of ice cream.

Think about what you eat and drink each day and find items you could cut out. If you think that skipping your treat will leave you with a craving, swap it with a low-calorie choice.

Simple swaps can make a big difference when it comes to cutting calories. For example, you can save 60 calories a glass by drinking fat-free milk instead of whole milk. Instead of having a second slice of pizza, reach for some fresh fruit. Or snack on air-popped popcorn instead of chips. Eat more fruits and vegetables, which have many nutrients and are high in fiber. And they'll fill you up more than high-fat choices.

The sizes of your portions affect how many calories you're getting. Twice the amount of food can sometimes mean twice the number of calories. But some foods with fewer calories, such as many fruits and vegetables, can be eaten in larger portions.

It's common to guess that you eat less than you actually do, such as if you're dining out. Paying attention to your portions is a good way to control calories.

Try these tips to control portion sizes and cut calories:

• Start small. At the start of a meal, take a little less than what you think you'll eat. If you're still hungry, eat more vegetables or fruit.
• Eat from plates, not packages. Eating right from a container gives you no sense of how much you're eating. Seeing food on a plate or in a bowl keeps you aware of how much you're eating. Think about using a smaller plate or bowl.
• Check food labels. Be sure to check the Nutrition Facts panel for the serving size and number of calories per serving. You may find that the small bag of chips you eat with lunch every day, for example, is two servings, not one. This means it's twice the calories you thought.
• Use a calorie counter. Check out reputable resources that offer tools to count calories, such as websites or smartphone applications.

Replacing high-calorie foods with lower calorie choices and cutting your portion sizes can help you cut calories and improve weight control. For a successful — and lasting — weight management plan, you also need to increase your physical activity. Combining regular activity and healthy eating will best help you get to and maintain a healthy weight.