How Many Calories Do You Need? It depends.

When people want to manage their weight (most often weight loss), they often gravitate to calorie counting or have a number in mind of how many calories they should have.

And in my experience in working with people, their numbers are often way off.

How many calories a person needs varies by each individual based on several factors and can even change day-to-day.

To suggest that people need a certain number of calories based on sex alone is just wrong.

I often hear in media stories the number of calories a person should have based on just the fact that someone is a man or a woman. I hate this because this is just too general to suggest that ALL women have the same calorie needs or that ALL men do.

I have taught nutrition classes for years and explicitly state that I am using an example of 2,000 calories per day in the context of explaining calories, macronutrients, and weight. Still, that is not a recommendation for you or anyone unless you happen by chance to have this as your specific number.

To think that 20-year-olds and 50-year-olds both have the same calorie needs is just ridiculous. Don’t we wish we had the same calorie needs as we did when we were 20? But we don’t.

And this is one of those cases where I state, “don’t blame the messenger” – sheesh. It isn’t my fault that the human body has a natural decline in metabolism as we get older. Very slight, but it happens.

And I promise you that if you are an adult human, it is highly likely that you need more than 1,200 calories a day.

When it comes down to it, there are people on both ends of the spectrum when it comes to getting the appropriate number of calories for their needs. Some are getting way too few, and others way, way too much.

There are some “quick and dirty” ways of calculating a person’s needs, but again these don’t even consider the difference between men and women, age, height, and activity level.

In reality there are five things to consider when determining how many calories an (adult) person needs: height, weight, age, sex, and physical activity level. All of these pieces of information must be known to estimate someone’s daily calorie needs accurately.

Height Let’s face it, the taller someone is the more surface area and more body to fuel. A taller person needs more calories, not a lot, but it is a factor. Being off by a half-inch or so, won’t’ make a lot of difference, but claiming to be six-feet tall when actually 5’ 10” will make a difference.

Height and weight are important pieces of information.

Weight The more someone weighs, the more calories they need to support that mass. A 100-pound person does not need as many calories as a 200-pound person.

Think of these two things as the difference between a large SUV compared to a compact car. One needs more fuel than the other because of the size difference alone.

Age As already mentioned, age is a factor in how many calories one needs. It sucks, I know, but it isn’t as dramatic as people tend to think, and it doesn’t magically change each decade or even on a birthday. It just happens day-to-day. In the big picture, the average calories difference with age is about FIVE fewer calories per year after the age of 20. Seriously. So, with all else being equal (same weight and activity level), your 50-year-old self needs a whopping 150 fewer calories than the 20-year-old self. When clients tell me that they are doing the same thing today as they were 20 years ago, but the weight keep coming, perhaps this is part of it. And, I also wonder why they haven’t changed their exercise routine in 20 years.

Sex, male vs. female Biological females need fewer calories than biological males, even with all other things being equal. Two people with the same birthday, height, weight, and even activity level will have additional calorie needs if they are of different sex. Again, I am just the messenger. Women biologically have more body fat than men, and there are other physiological differences in which women have a slightly lower calorie needs than men. The exception being during pregnancy and lactation.

With height, weight, age, and sex, we can easily measure or identify. Simple. Using this information, we can know how many calories a person needs to function at the most basic level without activity – basal metabolic rate (BMR).

This last factor is more subjective. And often over-estimated.

Don’t over estimate your physical activity level.

Physical activity level Even someone who has regular physical activity will have rest days during the week and even seasonal differences if they are in an organized sport. So, again this is often an estimated activity level. And over-estimating activity? I see this all the time. I have people who tell me they work out at the gym for two hours. I ask, are you exercising the entire time? Yes, they insist. Continuously? Yes. I don’t think so. Of course, some people exercise continuously, like those on a bike or running or hiking. But at the gym? I don’t know. There are people there who are on their phones and resting more than doing actual activity. While I don’t undermine their exercise, I always have to clarify that being at the gym for two-hours is not the same as exercising or working out for two hours. NOT. The. Same.  

But someone who does a cardio-exercise for 60 minutes four days a week, does strength training three days a week, and yoga twice a week will have different activity levels depending on the day.

There is a need for higher calories on some of those days and fewer on other days.

So, we don’t get all uptight and recalculate calories each day. We average. The average physical activity each week helps get us an average calorie need for the day.

Now to plug these numbers into an equation. These are often complex, and people who don’t use them regularly may find them confusing. Luckily there are calculators that can help with this.

Which equation? The classic Harris-Benedict equation (HBE) is like using Styrofoam or avoiding eggs. People still do it, but it is outdated. HBE had its place at the time. But a newer equation, Mifflin-St-Jeor, is more accurate in estimating the number of calories you need to just function and do the essential body processes daily, without factoring activity.

Here are a couple of examples of how many calories a person needs each day.

Person A: 37-year-old woman, 135 pounds, 5” 7”

With this information, person A needs 1,330 calories per day, assuming she does no physical activity. If she is getting below 1,300 calories per day, she is not even supporting her body’s basic daily needs, and if she also includes exercise, then where is the energy for that?

Person B: 43-year-old male, 187 pounds, 5” 11”

Person B needs 1,765 calories a day for essential body functions and not factoring in any activity.

So, what does this all mean? I threw out a bunch of numbers and explained how we got there, but now what?

While calorie counting is not necessarily something that people need to do regularly, it does help people get an idea of where they are and what may need to be adjusted.  

If weight is stuck – not going in the direction you want, make sure you are getting in the appropriate range of calories for your personal needs.

Are you getting enough to provide for your body to meet its most basic needs? Then consider your activity level – are you doing something regularly, at least 4-5 days a week. Then the quality of those calories and the timing of those calories will also matter, but ensure you are getting the right amount. If you find that you aren’t getting enough, that is like expecting to road-trip 1,000 miles away with only half a tank of gas. You won’t reach your destination.

If you want to find out your basal metabolic rate using the Mifflin St. Jeor equation, use this calculator here.

Originally posted on my prior blog/website on January 22, 2021.