What are calories? Are they bad for you? How many do you need? In this article I’m going to explain calories in the context of fat loss. I’ll cover what they are, why they are important, how many you need, and how to get started if your aim is to lose fat. If it all sounds like too much effort then bear in mind that the majority of the population don’t need to track their Calories this closely. Most people can reduce Calories (and lose fat) without the need for any tracking just by cutting down on processed foods & sugar, and increasing the amount of whole foods they eat, things like fruit, vegetables and lean protein sources.
Let’s start with a definition. A calorie is simply the unit of energy we use when we talk about food, and the number of calories represents the total energy it contains.* Some foods contain more energy than others and you’ll see it written on food packaging as “Kcals” – An apple contains about 100 Calories, an avocado about 200, and a portion of McDonalds fries is around 380 Calories.
We burn energy by breathing, moving, pumping blood around our body, digesting food, exercising etc and we get all of this energy from the food and drink we consume. No matter if your goal is fat loss or muscle gain the most important piece of the puzzle is getting the right balance of energy coming in through your diet vs the energy going out.
If your Calories in is more than your Calories out you’ll gain weight.
If your Calories in is less than your Calories out you’ll lose weight.
If your Calories in is the same as your Calories out then you’ll stay at the same weight.
Read over those last 3 sentences again, all the secrets of fat loss can be boiled down to this calories in vs calories out equation. It doesn’t matter as much what type of foods you eat, what times of day you eat or anything else, if you’re not losing fat the number one reason is almost certainly because you’re eating more calories than you are burning.
Let’s look more closely at the other side of the energy equation – how much energy you burn. The amount of energy that someone needs per day is called Total Daily Energy Expenditure or TDEE. TDEE is made up of 4 main elements:
BMR (Basal Metabolic Rate) is the energy needed to perform basic, life sustaining functions like breathing. If you were lying down all day and not moving, eating or speaking this is the energy you would burn and it makes up about 70% of your daily energy needs. Think about it as the energy you burn just to stay alive.
NEAT (Non-Exercise Activity Thermogenesis) is the energy spent doing all physical activity apart from exercise. This would include any walking or moving you do throughout the day, as well as things like gardening, housework, carrying your kids. This makes up about 15% of your daily energy needs, and you can think about it as energy burned by moving.
TEF (Thermic Effect of Food) is the energy required for digestion, absorption, and disposal of ingested nutrients. Its size depends on the composition of the food consumed but it roughly makes up about 10% of our energy needs. Think about it as the energy burned by digesting.
EAT (Exercise Activity Thermogenesis) is the energy required for formal exercise like lifting weights, doing a spin class, CrossFit or going for a jog. On average it makes up only about 5% of our daily energy needs. Think about it as energy burned by exercising.
Or to simplify. Your average daily energy needs look something like this....
The goal for fat loss is to set your daily Calorie intake below your TDEE so that your body is in a Calorie deficit. When this happens your body starts to tap into the fat stores in your body for energy and magical things happen (you literally lose the fat through your breath, urine and sweat). But how do you know your TDEE and how far below that do your Calories need to be? There are a number of ways to work this out, and you’ll find lots of calculators and fancy equations online if you want a much more detailed approach.
I’m going to give you a much simpler way to do it: To work out your fat loss Calories, take your bodyweight in pounds and multiply it by 9-14
Why is there a range? It isn’t an exact science and there are multiple individual factors at play. Consider two people, John and David who both weight the same 65 Kgs. John has 10% body fat, works as a waiter which means he’s on his feet all day, and on top of that exercises intensely 4 days per week. David also weighs 65 Kgs, but he is at 20% body fat which means he has more fat and less muscle mass. He has a desk job so doesn’t move much during the day, and he doesn’t exercise at all. This means that David will have a lower BMR as he has less muscle, he will have lower NEAT because he moves less and he will have lower EAT because he doesn’t exercise. As a result David’s caloric needs will be much lower than John’s.
When setting your own target you’ll need to take things like this into account, so if you have a sedentary job, don’t do much exercise, or have high body fat levels then you’ll go with the lower end of the scale (body weight in pounds x 9-11). If you have an active job, exercise multiple times per week, or have low body fat levels then you’ll go with the higher end of the scale (body weight in pounds x 12-14). If in doubt pick the mid point of 11.5 to start with and go from there.
It doesn’t matter too much where you start as you’ll adjust it anyway later. However you should never go lower than 1,000 Calories per day and for most of you it should be much higher. If you set your intake too low, your body won’t have enough energy to function properly, your metabolism will slow down, you’ll have low energy levels, your immune system won’t work properly and your fat loss will probably stall. This is why you can’t just drop your Calories as low as possible and hope for the best. The goal should be to eat as much as you can, to make sure your body is functioning optimally, while still losing fat.
Here’s a rough start guide based on your weight, and as mentioned already if you’re not sure where you should sit on the scale, pick the mid-point for your weight
Before you get started:
Before you make any drastic changes to your diet, you want to understand where you are now. To do this track everything you eat and drink for about a week using an app like Myfitnesspal and at the end of the week look at your daily Net Average Calories – let’s call this your base number. You might find that you eat and drink much more at the weekend than you do on a weekday but that’s fine as the average will account for any particularly high or low days. Don’t try and make any changes to your diet during this week, just eat as normal but track everything you put into your mouth. You’ll now have 2 numbers – a base number of daily Calories (from Myfitnesspal) and a rough target number of daily Calories (using the calculation & table above). You’ll also want to measure your Body weight at this point.
After your week of tracking you should have 1 of 2 scenarios:
1. Your base number is higher than your target number. Assuming they aren’t drastically different from each other then reduce your calories down to the target number. If your base number is a lot higher than the target number you’ve identified above (around 400 calories or more) then your body is probably used to this higher level and you’ll want to make changes gradually. Start by reducing from your base number by about 100-150 Calories per day, stick with that for 2 weeks and at the end of those 2 weeks measure your body weight again.
If your body weight is falling between 0.5 Kg and 1.5 Kg per week then great, keep everything as it is.
If you have no weight change or your weight change is less than 0.5 Kg per week then make another 100-150 daily Calorie reduction and monitor again for 2 weeks.
If your body weight is falling by more than 1.5 Kg per week then you’ve potentially reduced calories too much and are likely losing muscle as well as fat. In this case increase your daily intake calories again and keep monitoring. It can be tempting to keep your Calories down but any progress will stall quickly if you have gone too low.
2. Your base number is lower than your target number. This is actually quite common, especially with females who have been on a severe calorie restrictive diet. If this is the case you may need to eat more to get your body functioning properly and give your metabolism a kick start. Make gradual changes by increasing up from your base number towards the target by about 100-150 Calories per day, and stick with that for 2 weeks. After the 2 weeks measure your body weight again and see if it has changed.
If your body weight is falling between 0.5 Kg and 1.5 Kg per week then great, keep everything as it is, you might even increase Calories slightly more and see what the impact is. If you’re still losing weight, and feel good then great.
If you have no weight change or weight change less than 0.5 Kg then make another 100-150 daily Calorie reduction and monitor again for 2 weeks.
If your body weight is falling by more than 1.5 Kg per week then your Calories are too low and you’ve got plenty of room to eat more. Increase daily Calories by 100-150 per day and monitor again after 2 weeks.
Following this approach will allow you to get the right ballpark number for fat loss and then make changes up or down as needed. If you pair this with weight training 2-3 times per week and eating plenty of daily protein it will reduce your chances of losing muscle along with the fat.
* More specifically for all the fellow geeks out there: 1 calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water by 1 degree Celsius. A calorie is a tiny amount of energy; in a can of coke there are actually about 140,000 calories, so we abbreviate this as 140 kilocalories or 140 Kcals. To make our lives easier and avoid talking about kilocalories all day we usually just refer to this as 140 “Calories” with a capital C.