Is weight loss as simple as calories in vs. calories out? Learn the science behind losing weight and how to create sustainable fat loss.
This article will teach you the basics of metabolism and how to create a calorie deficit.
“It’s just calories in versus calories out!”
If you’ve been looking to lose body fat, you’ve probably heard this phrase spoken like it’s the holy grail of weight loss.
And in theory, it’s not wrong; if you burn more calories than you consume, your body weight will decrease. But just because the answer is simple doesn’t suddenly make weight loss effortless; an understanding of caloric intake is important, but knowledge doesn’t necessarily translate into action.
If you’re aiming for healthy, sustainable weight loss, there are a few key strategies to keep in mind that will allow you to implement the principle of calories in/calories out in a way that guarantees results. Today, I’m going to walk you through the science of metabolism and how to put it into action to achieve fat loss results.
But first, let’s take a trip back to nutrition school to learn the basics of weight loss – and what science has to say about it.
If you’re studying to become a dietitian, energy balance is one of the first concepts you learn about. Energy balance refers to the idea that when energy consumption (calories you eat) and energy expenditure (calories you burn) are equal, body weight will remain the same (1).
And that’s what we’re aiming for! We all hope to reach a weight where we are comfortable and confident and then maintain that weight throughout our lives.
But if you’re currently in a phase of your health journey where you want to reduce body fat, we have to alter the balance a bit to take in less energy than is burned, creating a negative energy balance – also known as a calorie deficit.
So before we go about creating that important deficit, we should probably answer a key question: what is a calorie anyway?
If you’ve been dieting for a long time, calories may be something you’ve come to fear and avoid. But a calorie doesn’t need to strike fear into your heart.
First, our bodies NEED calories to function. Like overeating, undereating is associated with many negative health outcomes, particularly in the long term.
Second, a calorie is just a way we measure energy in the form of heat, specifically, the amount of energy required to raise the temperature of 1 kg (2.2 lbs.) of water by 1°C (approximately 34°F). Doesn’t it seem a lot less threatening when it’s put like that?
This unit we use to measure the energy provided by our food is actually called a “kilocalorie”. So when people talk about the number of calories in the bagel they just ate, or the ice cream sandwich they’re having for dessert, they’re really talking about kilocalories, although most of the time we just shorten it to “calories”.
The body gets its energy by breaking down, or “oxidizing” the chemical bonds in food and converting this chemical energy into forms of energy the body can use to move and to fuel the body’s internal processes (1).
We can find some answers about how weight loss occurs by first looking at the calories that our bodies are taking in. Energy comes into the body in the form of the three macronutrients (“macros”): carbohydrates, proteins, and fats, as well as alcohol, which – if you needed some confirmation – is not a nutrient. Here is some key info for you to keep in mind:
As a side note, alcohol provides 7 calories per gram.
The number of calories on the packages of foods you eat or the values you see in MyFitnessPal and other nutrient tracking apps are determined using a tool called a “bomb calorimeter”. Essentially, this device measures the heat released from a food as it is burned and allows us to determine how much energy is in the food based on how much heat is released (1).
With this said, calories in food are highly variable and just because a product says it has X calories it does not necessarily mean that is the EXACT amount. Calorie measures are always very close approximations
“Calories out”, or the number of calories your body burns, depends on four factors.
Your basal metabolic rate, or BMR, makes up 60-70% of the energy you burn in a day. This is the rate your body burns energy to perform all the functions to keep you alive, including breathing, circulating blood, building tissues, and getting rid of waste. Even if you lay bed all day not moving, your body would still burn all these calories just to keep you alive (1). The term “BMR” is often used interchangeably with “RMR” or Resting Metabolic Rate.
In the fitness and nutrition industries, there’s a lot of discussion on metabolism, and particularly on “speeding up your metabolism”. This refers to increasing the amount of energy that your body burns at rest – your BMR.
While much of the talk around supplements and certain foods to speed up metabolism has no scientific basis, one reliable way you can speed up your metabolism is through weight training! Weight training increases muscle mass, and your body requires additional energy to sustain the muscle. Furthermore, muscle is more metabolically active than fat, so even if your weight on the scale stays the same, you will burn more energy when your weight comes from muscle rather than fat.
Eating a very low-calorie diet can cause your BMR to slow down as much as 10-20%, essentially adapting to starvation. So it’s important to nourish your body with sufficient calories to keep your BMR high (1).
Another contributor to the energy you burn each day is Exercise Activity Thermogenesis, or the calories burned through intentional physical activity, such as going for a run, hitting the gym, attending a fitness class, or playing a sport. This makes up 10-30% of your daily energy use, depending on how much time you dedicate to fitness and sports.
Outside of what we typically picture when we hear “physical activity”, there is also another form of movement that can burn a significant number of calories each day. This is what we call Non-Exercise Activity Thermogenesis or NEAT, which refers to all your other daily activities (walking, running errands, doing chores) that burn calories through movement, outside of planned exercise (1).
The fourth, and lesser known component of the energy we expend is the energy we use to digest food and absorb nutrients. About 10% of our energy intake is used for the process of digestion. More energy is used when you consume more food – but I’m not saying you should eat more to boost this form of calorie burn!
One thing you should keep in mind though is that proteins require more energy to digest and store, and fats require the least energy to digest, so you will burn slightly more calories from a diet that is higher in protein. (1)
So, in summary (and to throw a little math at you), our equation for energy balance looks like this when someone is aiming to maintain their weight:
Calories In = Calories Out
Energy Consumed from Food = BMR + EAT + NEAT + TEF
So in order to shift that equation in favour of weight loss (by creating a calorie deficit), we have to either reduce the energy consumed from food, or increase the energy burned on the “calories out” side.
In the long term, increasing “calories out” could mean increasing BMR through weight training, as described above. In the short term, you can consider getting more exercise, such as through circuit training or HIIT cardio. Furthermore, increasing NEAT is an excellent strategy to burn more calories without even realizing it, by doing things like:
1. Parking further away from work or the grocery store and walking
2. Taking the stairs instead of the elevator.
3. Playing outside with your kids or your pet.
4. Working at a standing desk.
However, you may have heard the phrase “you can’t out-train a bad diet”, which basically means that if you’re not nourishing yourself properly with food, it doesn’t matter how much exercise you do – you’re going to struggle to lose fat.
So if weight loss is dependent solely on calories in and calories out, maybe cutting weight by focusing on your nutrition isn’t so difficult after all? All you do is cut your calories, stick to a meal plan, and cut out all those “bad” calorie-dense foods, right?
No, no and ABSOLUTELY NOT.
If you start on a “diet”, the first mistake that is often made is slashing calories far too low. In the beginning, when motivation is high, you may see some success and the number on the scale will start to drop, or you’ll start seeing changes in the mirror.
However, eventually your results will stagnate, and you will get bored of eating the same foods day in and day out. Eventually, as you continue without additional results, you’ll get fed up with the restriction and go back to the way you were eating before, often reaching an even higher weight than your starting point.
The other issue with diets is that they usually demonize specific foods and food groups, recommending you completely remove these foods from your diet to achieve success.
But what usually happens when you tell yourself you can’t have something? That thing is suddenly on your mind ALL THE TIME. This can lead to overeating or binging.
How then, can you achieve sustainable fat loss without the restrictions of dieting?
The best approach is to create a sustainable calorie deficit, rather than trying to cut calories drastically. Aim to burn 200-300 more calories than you consume and over time, fat loss will occur. It’s not a quick-fix process, but it is what will be sustainable in the long term.
The stand-by advice of calories in versus calories out only gives us part of the picture when it comes to meeting weight loss goals. In order to optimize health and create sustainable change, we have to work on creating a sensible calorie deficit while considering the macronutrient breakdown of our food choices.
There are many strategies to do this, but one of the most effective is counting macros. In next week’s post, we will be breaking down how to determine the best calories and macros for your goals, so stay tuned!! In the meantime, if you’re struggling with a weight loss plateau right now, be sure to check out this episode of the Nutrition Blueprint Podcast.
1. Smolin LA, Grosvenor MB. Nutrition: Science and applications. Hoboken, NJ: Wiley; 2010.
2. Helms ER, Valdez A, Morgan A. The Muscle & Strength Pyramid – Nutrition. Independently Published; 2019
3. Bellisle F, McDevitt R, Prentice AM. Meal frequency and energy balance. British Journal of Nutrition. 1997 Apr;77(S1):S57-70.
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