In this short video lesson, you’ll learn what calories actually measure, how our bodies use them, and why the “calories in, calories out” equation is more complex than it seems. As you watch, consider how energy, metabolism, and digestion interact in your own life. Understanding the science behind calories can help you think more critically about nutrition labels, health advice, and your body’s unique needs.
Watch the video and answer the questions that follow:
What does a “calorie” actually represent in physical terms?
What are some reasons why the same food might provide different amounts of usable energy for different people? Give at least two examples.
Sample answers
Question 1:
Strong answer:
A calorie is a unit of energy. Specifically, one (large) calorie represents the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. This definition comes from physics and helps quantify how much energy is stored in food. When we talk about calories in nutrition, we’re really talking about the potential chemical energy our bodies can release and use from that food during digestion and metabolism.
Weak answer:
A calorie is something that tells you how fattening food is. Scientists use it to see how healthy food is and how much we should eat. It’s just the number on the label that shows energy.
Question 2:
Strong answer:
The same food can affect people differently because of individual differences in digestion and metabolism. For example, fibrous foods like celery take more energy to digest, so someone with more efficient digestion might absorb fewer net calories than someone with slower digestion. Another reason is gut bacteria—some people have bacteria that are better at breaking down certain foods, which can increase the amount of energy they extract from the same meal. Enzyme levels and even the length of the intestines can also change how much energy is actually absorbed.
Weak answer:
Different people get different energy from food because everyone’s body is different. Some people digest food faster. Also some foods have less calories even if they are the same size.
