The body spends energy processing protein
A food calorie measures energy, but not every calorie is available to the body after digestion. Breaking down and handling protein takes more energy than processing sugar, a simple carbohydrate. This cost is called the thermic effect of food: some of the energy in a meal is used up digesting, absorbing, and processing it.
So, from two foods containing the same number of calories, the body generally uses more energy processing the chicken’s protein than the sugar’s carbohydrate. The difference is real, though it does not make chicken calorie-free or guarantee a particular change in body weight.
Protein has other uses besides fuel
After digestion, chicken’s protein becomes amino acids—the building blocks the body uses to maintain and repair tissues and make substances such as enzymes. If the body has more amino acids than it needs, it can use them for energy, but that requires additional processing. Sugar, by contrast, is readily used for energy; any surplus energy can contribute to stored body fat over time.
Protein also tends to make a meal more filling than sugar alone. That can affect what someone eats later, although it is separate from the calories in the original portions.
The difference is not a weight-loss loophole
The comparison concerns net energy after processing, not an automatic change on the scale. Body weight reflects energy intake and use over time, along with factors such as water and food still being digested. A 100-calorie portion of chicken therefore does not translate into a fixed amount of weight gain—and neither does 100 calories of sugar.
The useful takeaway is that equal calorie counts can have somewhat different effects inside the body: protein costs more to process and serves more bodily functions, while sugar is a readily available fuel. But the overall pattern of eating matters far more than treating either single 100-calorie portion as a direct measure of weight gain.
