Are All Calories Created Equal?
For one, metabolism can be slowed down if you restrict your calorie intake. This means that the fewer calories you consume, the fewer calories your body will burn. So if you decide to cut your daily energy intake by 500 calories to try to lose a pound a week, you will likely lose a pound in that first week. However, in each of the following weeks, you may notice that you will lose less.
This is the body's way of preventing you from starving. Your body will respond by "running cooler" to conserve the reduced number of calories you are consuming -- which means your body will increase the value of each calorie.
A study done at the University of Washington School of Medicine showed that when participants switched from a low-protein weight maintenance diet to a high-protein diet, they felt fuller despite the fact that they were eating the same number of calories. In this study, the people who were on the high-protein diet reduced their daily consumption voluntarily (as they were not as hungry) by 441 calories a day and lost more weight and body fat than those in the other group who were on the low-protein plan.
Another thing to consider is that fiber can help reduce calorie absorption. Fiber is not absorbed into the human body; however, because it is a form of carbohydrate, it helps to satisfy hunger without contributing calories.
This means that a 100-calorie, high-fiber food will reduce appetite and help satisfy hunger better than a 100-calorie, low-fiber food. So if you increase your daily fiber consumption without making a conscious effort to eat less, you will likely wind up eating less due to a reduced appetite. Therefore, a calorie in a high-fiber food may not be equal to a calorie in a low-fiber food.
The time of the day you eat can also affect how your body processes calories. The energy used up as a result of digesting and absorbing a meal is called the thermic effect of food (TEF). A research study done by the American Journal of Clinical Nutrition showed that TEF is higher in the morning than in the evening, which means we tend to burn more calories in the morning.
In addition, the effect of calories on body composition is also affected by the size and frequency of meals. In general, when calories are consumed in excess of the short-term needs, they tend to be stored as fat and less likely to be used immediately for energy, stored as glycogen, or used to make new muscle proteins.
This means that eating six small meals a day that total 2,000 calories will not have the same effect in the body as eating two large meals that total 2,000 calories -- research has shown that those who ate six small meals a day had a significantly lower body fat percentage.
So planning when you eat can affect how your body will use that energy in the food. Food calories are most likely to be used immediately for energy (or stored as glycogen or used to make muscle proteins) when they are consumed at times where you are energy deficient, such as first thing in the morning or right after exercising. A number of research studies have shown that people tend to build more muscle and gain less body fat when they eat adequate calories within two hours after exercising than if they did not.