Google ‘how many calories should I eat a day,’ and you’re bound to come across many articles claiming that ‘you’ll slim down fast and still feel satisfied’ on a 1,200 calorie meal plan.
Just for reference, 1,200 calories is basically nothing – you’ll have to settle for salads during lunch and dinner.
Satisfied? More like starving.
If you genuinely care about long-term, sustainable results, you have to tailor your calorie intake to your individual needs.
And for that, you need to understand the science behind calories.
To help you derive how many calories (exactly) you need to eat a day, I cover everything you need to know about these little units of energy you consume daily.
Don’t worry; it’s not rocket science. Promise.
What is a calorie?
You might have seen that Flamin’ Hot Cheetos you dug into during last night’s stay-in Netflix date packs 680 calories – but what does that mean, exactly? What is a calorie?
Well, the calorie is simply a unit of energy needed to raise 1 gram of water by 1 degree Celsius (1, 2, 3).
So, when you think of calories, you can simply think of them as the fuel that keeps you going. They power your body’s vital processes, such as breathing, pumping blood, and even sleeping (4, 5, 6).
Obviously, you don’t want to overwhelm your body with too much fuel (by eating too many calories), but you also don’t want to run on empty (by eating too few calories).
What’s the difference between calories and kilocalories (kcal)?
If you’re a real stickler for reading the nutrition labels on the food you eat, you might have noticed that some are labeled in ‘calories,’ while others are labeled in ‘kilocalories.’ What’s the difference?
To understand this, you need to know that scientifically speaking, there are two types of calories (7, 8, 9):
- Large Calorie (with a big ‘C’): Refers to 1,000 small calories
- Small calorie (with a small ‘c’): 1,000 small calories make up 1 large Calorie
To tie everything together, 1 Calorie is equivalent to 1 kilocalorie, which is also equal to 1,000 calories.
Now, here’s the confusing bit: when we refer to calories from a nutritional standpoint, we are referring to kilocalories.
So, when the food label indicates that the Snickers bar on your dashboard contains 488 ‘calories’ per 100 grams, it means that it’s a chewy, melty bar of 488 kilocalories (488,000 calories).
But honestly, you don’t need to sweat the specifics.
On food labels, calories and kilocalories are used interchangeably to mean the same thing (even though they’re not – in the strictest scientific sense). In other words, it’s perfectly normal (and acceptable) to use the small ‘c’ instead of the big ‘C.’
If you’re still confused, don’t worry – this isn’t that big of a deal in the grand scheme of things.
Following popular convention, I’ll be referring to kilocalories as calories moving forward.
Summary:
- The calorie is a unit of energy needed to heat up 1 gram of water by 1 degree Celsius.
- Calories are energy that powers your bodily functions.
- On food labels, 1 calorie and 1 kilocalorie (1 Calorie) are used interchangeably to mean the same thing, even though they’re not. To be honest, it doesn’t matter.
How many calories should I eat a day?
Step 1: What is your Basal Metabolic Rate (BMR)?
When it comes to figuring out the answer to ‘How many calories should I eat a day,’ you need to figure out the number of calories your body burns at rest.
This number of calories is also known as the basal metabolic rate (BMR) – you can think of this as the bare minimum number of calories you’d need to stay alive even if you were to stay in bed all day (10, 11, 12, 13, 14).
The Müller equation
There are several different equations conventionally used to estimate BMR, but I’ll be focusing on the Müller equation.
That’s because the Müller equation accounts for 4 of the variables which have the most significant impact on metabolic rate: lean body mass (LBM), fat mass (FM), sex, and age (15).
You can choose other equations – such as the Mifflin St. Jeor formula – if you see fit.
Just note that LBM contributes to metabolic activity more significantly than FM – and, therefore, burns more calories at rest. So it’s crucial for any other equation you choose to account for LBM and FM separately (16, 17, 18).
Don’t worry if you’ve no clue what your LBM and FM are. You can easily calculate these figures from your body fat percentage, which many mid-range bathroom scales are already equipped to measure.
Of course, if you want more accurate results, you could go for DXA (Dual-Energy X-ray Absorptiometry) scan (19, 20, 21, 22, 23).
In general, though, a rough estimate of your body fat percentage will suffice.
- How to calculate FM:
- Fat Mass (FM) = Body Weight x Body Fat Percentage
- How to calculate LBM:
- Lean Body Mass (LBM) = Body Weight – Fat Mass
- Here’s the Müller equation:
- BMR = (13.587 x LBM) + (9.613 x FM) + (198 x Sex) – (3.351 x Age) + 674
- Note: For sex, female = 0 and male = 1
Example of the Müller equation in use
To see this equation in action, let’s assume the following information about me:
- Body fat: 25%
- Bodyweight: 65 kilograms
- Sex: Female
- Age: 28
Here’s how I’d make use of the Müller equation to get to my BMR:
- Calculate my FM:
- Fat Mass (FM) = Body Weight x Body Fat Percentage
- 65 x 0.25 = 16.25 kilograms
- Calculate my LBM:
- Lean Body Mass (LBM) = Body Weight – Fat Mass
- 65-16.25 = 48.75 kilograms
- Calculate my BMR:
- BMR = (13.587 x LBM) + (9.613 x FM) + (198 x Sex) – (3.351 x Age) + 674
- (13.587 x 48.75) + (9.613 x 16.25) + (198 x 0) – (3.351 x 28) + 674 = 1,398.75 calories
As you can see, my BMR falls above 1,200 calories. And if you take the time to calculate your BMR, you’d probably also need more than 1,200 calories per day just to stay alive – unless you’re quite small in size.
Step 2: What is your activity level and maintenance calories?
Exciting times. We’re now halfway there to figuring out the answer to your burning question: ‘How many calories should I eat a day?’
Now that you’ve (hopefully) calculated how many calories your body burns to stay functioning, you need to take into account everything else you do that burns calories.
Yes, that includes your morning commute to the office and those regular Thursday night yoga classes.
Obviously, if you’re up and about more, you’ll burn more calories in a day compared to someone who’s sedentary.
Activity level factor breakdown
The following is a rough guide to the factor you need to multiply your BMR with to arrive at the best estimate of how many calories you need daily (24, 25, 26):
- Sedentary: Multiply by 1.2
- You work a desk job
- You don’t exercise
- Light activity: Multiply by 1.37
- You work a desk job, and you get to the gym sometimes
- Or, you don’t exercise but are on your feet most of the day
- Moderate activity: Multiply by 1.55
- You work a desk job, but you’re in the gym about 5 times a week
- Or, you get to the gym sometimes and are on your feet most of the day
- Very active: Multiply by 1.725
- You practically live in the gym and are also on your feet most of the day
- Extra active: Multiply by 1.9
- You live in the gym, and you work an exceptionally physically active job
How does this apply to my situation, then? Well, let’s say I’m moderately active – I work a desk job but am in the gym 5 times a week.
Given that my BMR is 1,398.75, as calculated in the section above, I’d arrive at the figure of 2,168 calories.
That’s how much I’d need to eat if I want to maintain my weight. That’s more commonly known as my maintenance calories.
Step 3: What is your goal?
But what if you don’t want to maintain your current weight? What if you’re trying to lose weight or gain muscle?
Well, here’s how you can tweak your maintenance calories to achieve a specific body composition goal:
- Fat loss: Lower your maintenance calories by 20% to create a calorie deficit (27).
- This is a good starting point to lose weight at about 3.5 kilograms per month while increasing the chances you’ll retain muscle mass.
- Muscle-building: Increase your maintenance calories by 10 to 15% to create a calorie surplus (28, 29).
- This is a good starting point for you to gain weight at about 1.8 kilograms per month while keeping fat gain to a minimum.
As usual, let’s apply this knowledge to my situation.
If I intend to gain muscle, I’ll have to eat at 110 to 115% of my maintenance calories, which makes my required daily intake 2,493 calories (Math: 1.15 x 2168).
That’s twice the energy I’d get from a 1,200-calorie meal plan – nice.
Summary:
- Calculate how many calories your body needs at rest – also known as your basal metabolic rate (BMR).
- Then, you need to account for your activity level – based on how physically active you are – to arrive at your maintenance calories.
- If you’re looking to lose fat, you’ll need to be in a calorie deficit of 20%. And if you’re looking to build muscle, you’ll need to be in a calorie surplus of 10 to 15%.
Monitor your progress and tweak your calories accordingly
Now, bear in mind that the figure you’ve arrived at is not a ‘for-sure’ number.
It’s merely an estimate. Your body – due to its complexity – will almost certainly behave differently from the prediction of a mathematical equation (even though it can be quite close).
The best way forward would be for you to consume the number of calories you’ve worked out for yourself and monitor your progress closely.
If you’re not losing weight (despite having cut down on your maintenance calories), you could be underestimating the number of calories you’re eating throughout the day. Or – your calorie deficit is just not sufficient. You can try cutting 100 calories from your diet each week and tweaking the numbers from there.
If you’re not gaining muscle mass (despite having increased your daily calorie intake), it could be that you’re not eating as much as you think you are. Or, your calorie surplus is simply not big enough. You can try adding 100 calories to your diet each week and adjusting your intake from there.
Summary:
- Your body is bound to behave differently from a Math equation.
- You’d still need to monitor if your weight is indeed changing the way you expect based on the calculated intake.
- You’ll have to tweak your daily calorie intake accordingly.
That said, not all calories are the same
Even though your total calorie intake matters most for body composition, it’s still a drastic oversimplification to say, ‘a calorie is a calorie.’
Admittedly, it’s true that all calories have the same amount of energy. One calorie contains 4,184 Joules of energy. Always. In that respect, a calorie is a calorie.
But when it comes to your body, things are not that simple. Your body is a highly complex biochemical system with elaborate processes that regulate energy balance.
Different foods – with varying macronutrient profiles – go through different biochemical pathways and can exert different effects on the biological processes that control when, what, and how much you eat (30, 31, 32, 33, 34, 35).
For instance, protein has a more satiating effect than carbohydrates or fats – helping you feel fuller for longer. This can prevent you from overeating or feeling hungry all the same.
Also, no one would say that eating 100 calories of broccoli is the same as eating 100 calories of M&Ms, for example.
The former is full of healthful micronutrients and is challenging to overconsume.
And the latter, while thoroughly happiness-inducing, is awfully easy to eat in excess – just ask anyone who’s tried to stop reaching for another after 5 M&Ms.
So, in addition to keeping an eye on your total calorie intake, you’d also need to account for your diet’s macronutrients and micronutrients proportion.
Summary:
- It’s true that all calories give the same amount of energy, but it’s an oversimplification to say that ‘a calorie is a calorie.’
- For optimal health, you still need to take into account the macro- and micronutrient profile of the foods you’re eating.
Does calorie timing matter?
By now, you should know the answer to “How many calories should I eat per day?” You also know the importance of accounting for macronutrients and micronutrients in your diet for optimal health.
But – there remains a question yet to be answered. And that’s: ‘Does the time at which I eat my meals matter?’ In light of all the information provided thus far, it’d seem like it wouldn’t matter, right? Not exactly.
Well, to be more specific, if you eat fewer calories than your body burns, you’ll lose weight. No matter the time at which you eat your meals.
But calorie timing can influence the amount (keyword!) of weight you end up losing.
Confused? Let me explain.
Research shows that individuals who eat most of their daily calories earlier on (i.e. breakfast and lunch, instead of dinner and supper) experienced significantly (36, 37):
- Less hunger
- Fewer cravings for sweets throughout the day
- Greater overall energy levels
Because of the two-fold impact of them sticking to their diets and having more energy, they created a larger calorie deficit than if they had allocated most of their calories to later meals (i.e. a back-heavy approach).
How do these findings then apply to you?
Well, to make use of this weight loss hack, you can just eat heavier meals earlier on in the day. Just make sure that you make full use of the increased energy you experience from those meals.
Up the intensity of your workout sessions. Do 15 reps instead of 12. Go for 6 laps at the track instead of your normal 4. And you’ll be able to increase the number of calories you burn without even tweaking the number of calories you eat.
That, in turn, creates a larger calorie deficit – putting you on the fast track toward weight loss (38).
Summary:
Eating heavier meals earlier on in the day without tweaking the total number of calories you eat can help reduce hunger levels and increase energy levels. This can put you in a larger calorie deficit, helping you lose weight at an accelerated rate.
Should I count my calories? Is counting calories healthy?
What is counting calories?
When someone tells you they’re counting calories, all it means is they’re tracking the number of calories in every food they consume.
You can get the calorie-count of a particular food from its nutrition facts label or use a food or diet app, like MyFitnessPal.
Counting calories can foster an unhealthy relationship with food
For some people, counting calories can be a dangerous practice. The act of calorie-counting can get you hyper-focusing on the numbers instead of enjoying the food you’re eating.
It can be a slippery slope – from paying attention to calorie counts to obsessing over them (39, 40, 41, 42, 43).
In other words, the practice can foster an unhealthy relationship with food and eating, in general.
So for anyone with a history of disordered eating, counting calories might be something to avoid.
If you have or are in recovery from an eating disorder, it’s probably best to seek a professional medical opinion before changing your dietary habits or tracking your food.
But … it’s still an incredibly useful strategy
Otherwise, there’s no denying the role calories play for others. Of course, calories do count, since they’re what you consume every day.
When you eat more calories than you burn off, you’ll gain weight (44, 45, 46).
And when you eat fewer calories than you use, you’ll lose weight (47, 48, 49, 50, 51).
If you’re trying to improve on your body composition, calorie-tracking can be an incredibly useful tool. It quantifies your progress instead of merely telling you to ‘eat less.’
And it doesn’t advocate for the complete elimination of food groups – unlike the super-restrictive keto diet, which practically forbids you from eating carbohydrates (52).
If you’re keen to learn more, here’s an article on why the keto diet isn’t more effective for weight loss than other diets.
Summary:
- Counting calories can lead to an unhealthy relationship with food, especially if you have a history of disordered eating.
- Nonetheless, it is an incredibly useful tool that quantifies your progress. Unlike other diets, it doesn’t eliminate entire food groups or tell you to simply ‘eat less.’
Find what works for you
When it comes to the question, ‘how many calories should I eat a day?’, you can indeed do the math to figure out the exact numbers.
But here’s the important thing. You ultimately need to find an eating pattern that works for you and that you enjoy. No matter if that’s counting calories, intermittent fasting, or saying no to carbohydrates – you’ll realize that the underlying rationale behind all diets remains the same.
It is to create a calorie deficit.
Every diet plan will work if you stick to it. Because no matter what, diets work by inducing a caloric deficit.
As always, the best diet plan is a sustainable one – one that you can stick to for years to come.
