Calories in vs. Calories out

Welcome to the latest edition of the Fueling Greatness Newsletter. Each week, I aim to decode the “science to application” of nutrition and related fields to help you optimise your performance, body composition and well-being. Be at the cutting edge of this knowledge, and subscribe to my newsletter.

This week, I want to discuss the much-cited and yet often much-misunderstood ‘Calories in vs. Calories out” principle as it relates to effective weight management.

When discussing weight management strategies, it's important to understand the underlying principles that influence our body weight and the key terms related to energy balance.

Understanding Energy Balance

Critical to this discussion is that the laws of physics have been well-established for a long time, and the laws of thermodynamics still apply. Despite the internet debates over whether all calories are created equal, in nutrition science, a calorie is undeniably a calorie, a unit of energy measurement. To avoid further confusion, we should also express the nutrition-related calories as kilocalories or kcals (1000 calories = 1 kcal). Now that’s stated, let’s dive in.

Our body weight is mostly determined by the balance between the kcals (energy) we consume and the kcals we burn over time. This is known as the energy balance equation:

OK, now let's take a quick moment to remind ourselves about the major macronutrients in our diet. We've got carbohydrates, fats, and proteins (and hopefully only a little alcohol!). Each has a different caloric value, which you now know is the energy they provide our body. Carbohydrate provides about four calories per gram, fat about nine calories per gram, and protein about four calories per gram, with alcohol providing about seven calories per gram.

If we want to lose weight, a basic interpretation of the energy balance equation tells us that we must burn more calories than we consume. On the other hand, if we want to gain weight, we must consume more calories than we burn. However, it's a little more complicated when it comes to the quality of the weight loss or gain because different foods have different properties that affect how our bodies use this energy and their subsequent influence on the composition of the weight gained or lost. This fact is very important if you want to impact the quality of your body composition rather than simply the quantity of the numbers on the weighing scale. I’m going to get into that in more detail shortly.

By now, it should be clear that the “energy-in” comes from the calories in our food and drinks. On the other hand, the “energy-out” (AKA “burn”) can be broken down into three components, as defined in the table below.

So, to be accurate, we should refer to a combination of all these three components when discussing energy expenditure. Now that we have defined some key terms, we can discuss how they integrate and can be manipulated to influence body weight and composition.

Interactions Between the Components Matter

The body stores energy as stores of carbohydrates, proteins, and fats. Carbohydrates are stored as glycogen in muscles and liver but only comprise a small percentage of total energy (about 1%). Proteins are stored in various tissues, with the majority stored in skeletal muscles (about 15%). Fats, specifically triglycerides, are the body's largest source of stored energy (about 84%). If there is an imbalance in the utilisation of these energy sources, it can lead to changes in body weight. The body is especially efficient in storing excess calories as triglycerides in fat cells, an evolutionary adaptation to ensure survival during food scarcity.

It's important to remember that storing and burning energy is a process that changes over time. Time, therefore, is a big factor in determining energy balance and changes in body weight. When we look at a person's 24-hour food diary, they eat multiple meals, adding to their energy balance. Then, they might do physical activities, which increase their energy expenditure. So, the amount of energy going in and out is always changing. People have different 24-hour patterns every day, so their energy balance changes daily. The main point here is that energy balance is determined over a long period, so changes in body weight take time.

Hopefully, you now understand the basics of energy balance and how they relate to body weight changes. The body is an amazing, highly complex, yet exquisitely organised biological machine. So, although the fundamental concept of calories in vs. calories out does a good job of explaining weight control, the body has some very impressive mechanisms to control the limits of this system. These are known as compensatory mechanisms. Two key examples are as follows: It is established that a greater body mass results in a higher RMR thus, as we gain mass (muscle increases RMR more than fat), we have an increased need for calories, which is considered a passive mechanism. Following exercise, there is an active mechanism, such as increased food and fluid intake. Yes, this topic is pretty complex and beyond this article's scope, so here are a few bullet points summarising the main interactions between the energy balance components:

• Exercise affects how much energy we use and how much we eat. Even when people exercise the same amount, some lose while others gain. This is because people compensate for their exercise by eating more or less. Differences in appetite after exercise might explain why some people eat more or less after exercising.

• What you eat affects how full you feel and how much you eat later. Eating protein and high-fibre foods makes you feel fuller for longer. But sometimes, liking or wanting food can make you eat more, even if you're not hungry. So it's important to pay attention to how you feel about food, not just what you eat.

• Food intake affects how much energy our body uses. When we eat less, our body uses less energy. This can cause us to lose weight, but it may be from muscle and fat. Muscle and fat help our body burn calories, so our resting metabolic rate (RMR) decreases when we lose them. The thermic effect of food (TEF) also decreases because our body needs less energy to process nutrients. On the other hand, when we eat more than we need, our body stores the extra energy as weight gain. This can increase our RMR, physical activity energy expenditure (PAE), and TEF.

Conclusion

While the "calories in vs. calories out" principle is foundational for weight management, our body is an intricate system with adaptive mechanisms. A comprehensive understanding of these principles can assist in making more informed decisions about diet, exercise, and overall health.

Take-Home Messages

1. Understanding Weight Loss & Gain:

   • Losing weight requires burning more calories than consumed.

   • Gaining weight necessitates consuming more calories than expended.

   • The quality of food and beverages consumed impacts body composition.

2. Energy Expenditure Components:

   • Our body expends energy through a combination of Resting Metabolic Rate (RMR), Physical Activity Energy Expenditure (PAE), and the Thermic Effect of Food (TEF).

3. Dynamic Nature of Energy Storage: Energy storage and usage in our body constantly changes. This means that body weight changes are gradual and reflect energy balance over a prolonged period.

4. Interactions between Energy Components:

   • Stored energy sources in the body include carbohydrates (as glycogen), proteins (in tissues like muscle), and fats (as triglycerides). An imbalance in their utilisation can influence body weight.

   • Our evolutionary biology prefers to store excess energy as triglycerides.

5. Compensatory Mechanisms in Energy Balance: Our body adapts in response to changes in energy balance. For instance:

   • An increase in body mass boosts RMR.

   • People might consume more food after exercising.

6. Influences on Energy Balance:

   • The type and amount of exercise can affect our energy consumption and intake.

   • What we eat impacts our satiety levels, potentially influencing subsequent food intake.

   • Reduced food intake can lower energy expenditure, affecting weight loss composition and metabolic rate.

Reference: IOPN Position Stand on Effective Weight Management

That’s it for today! I hope you found this of interest and value.

Have a great week, and see you next week for another edition of Fueling Greatness, in which we will continue to explore key topics in sport and exercise nutrition and unpack the “science-to-application” to help you achieve your performance, body composition and well-being goals.

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Dr Laurent Bannock