TL;DR Science: Calories & Weight Loss

By Shang Chen
June 09, 2021 · 5 minute read

Everybody knows the basic tenants of weight loss: eating healthy and working out. However, if you ask people what calories are and how our bodies interact with calories, most people would be stumped. To begin this week's article, we'll take a look at an often overlooked but necessary term: the calorie.

What are Calories?

At the most basic level, calories are a measure of energy stored in foods and drinks. This energy can be measured in terms of heat generated when burned or processed by the body. More formally, the calorie counts we see on nutrition labels is the amount of energy it takes to raise the temperature of one kilogram (2.2 pounds) of water by 1 degree Celsius. This relates to our bodies as we break down the calories from foods into their basic components (usually sugars) that our cells use for energy. Our bodies are constantly burning calories to perform basic tasks like walking, breathing, and sleeping. Since our bodies are constantly depleting our energy supplies, we need to replenish our calorie stores every so often through the process of eating.

Obviously, not all foods are the same in terms of their calorie concentration. An entire salad can have the same amount of calories as a donut due to the different chemical compositions of different foods. This is why it is so important to think about how much you eat as well as what you eat. Some foods that are higher in fiber and protein take longer for our body to break down, giving us a sense of fullness and satisfaction versus sugary foods (soda, candy, cakes) that our body can process quickly but don't really fill us up.

Okay, calories make sense but how does exercise come into the picture?

Exercise is a way of ramping up the number of calories your body burns by performing periods of physical activity. While your body is constantly burning calories, it burns far more while running a marathon than sitting on the couch. Exercise is important for weight loss due to one simple equation: Weight Loss/Gain = Calories in - Calories out. It's that simple. If you eat fewer calories than your body burns, it will turn to its reserves which for humans are in the form of fat. After the body has used up all the easily available energy in the forms of carbohydrates and sugars, it begins the process of breaking down the fat in your body.

Think of fat as the energy your body stores for a rainy day. Historically, fat storage has been an adaptation for humans to go long periods without food or when we were being chased by predators. Obviously, we do not get chased by predators very often anymore, but our bodies continue to store excess calories in our liver, heart, and tissue. From a chemical perspective, our fat cells are extremely efficient stores of energy as they contain a large amount of energy but release it quite slowly. This is why the process of weight loss and burning fat is such a struggle for many people. Not only do you have to be in a caloric deficit (more calories burned than intake), but you need to be in a caloric deficit for a prolonged period of time to start burning fat. This does not mean that the best way to lose weight is to simply starve yourself for a couple of days. In fact, the opposite is true. When you don't eat for a long period of time, your body begins to slow down its metabolism which is the rate at which it burns calories. This is another adaptation that served us well historically as it allowed us to conserve our fat stores when food was scarce. Another danger of simply trying to not eat is that your body will actually begin burning lean-muscle mass before it burns fat. It turns out that fat is so hard for our bodies to break down that your body will break down muscle before its fat stores if it feels like it is starving.

If not eating isn't an option, how do you burn fat then?

The scientifically proven way to burn fat is a combination of dieting and exercise. I'm sure you've heard this phrase plenty before, but there is simply no other way for our bodies to begin breaking down our fat reserves. Specifically, the best way to burn fat without losing muscle is to maintain a small caloric deficit. Everybody has a baseline of calories burned each day that varies depending on age, weight, and physical activity. To lose weight, you should maintain a caloric deficit of 100-300 calories for a prolonged period of time. Caloric deficits larger than 300 calories can be a hindrance to weight loss as your body's metabolism will slow down and even begin to break down muscle instead of fat. Being in a caloric deficit often leaves people feeling hungry which is where the dieting aspect comes in. Eating foods that are high in protein and fiber allows your body to feel more full, limiting the urge to eat more. Going back to our previous example, a donut or two may only serve as a light snack or a treat while a salad filled with leafy green vegetables, chicken breast, and chia seeds will leave you feeling full for hours

For more tips on how to burn fat and lose weight check out this 5-minute video by PictureFit:


The science of weight loss is based on calories which are a measure of energy stored in foods/drinks. To lose weight, you should maintain a caloric deficit which means you burn more calories than you intake. However, caution should be advised as the caloric deficit needs to be small otherwise your body will begin burning muscle and slowing down its natural rate of burning calories which can make losing those stubborn love handles even more difficult.


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About The Author

Shang is a current undergraduate at UC Berkeley studying Economics and Data Science. His hobbies include cooking, hiking, and playing video games. Send him new article recommendations or suggestions at

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