How Calories “Work”

The topic of appropriate caloric intake has been on my mind a lot recently. There is A LOT of confusion around “how many calories” people ARE eating, SHOULD BE eating, and what it all means.

I know many people who insist their caloric intake is very, very low: 1200 to 1500 calories per day. And they are sure their metabolism must be broken because they are now gaining weight (or not losing weight) on this very low calorie intake.

It’s not true. It’s not accurate. It’s not the way things work. You have to eat enough food to support your activity, energy levels, and overall health. If you don’t understand how that works, and you are setting a caloric goal that is ridiculously low for your actual needs, odds are good you’ll never actually get anywhere near it (and may end up eating way more than your needs).

Most of us really just don’t know how TDEE & calories “work”. We don’t really understand it. And that creates cognitive dissonance when we are confronted with the idea that “eating enough food to support your activity, energy levels, and overall health” means eating MORE than we *think* we should.

It blew my mind when I realized I had gotten it wrong all those years – that my understanding about energy (calorie) needs and how my body functions was totally skewed. What a shift in thinking to truly appreciate that I NEED calories from food for more than just “exercise” … but for simple, daily functioning. It had simply never hit me before that I had a basic level of functioning that required fueling – BMR – and that I needed to respect that, and fuel that, before I could even think about doing anything else.


Calorie: a unit of energy, used to account for energy in foods & energy burned by your body
TDEE: total daily energy expenditure (what you burn living, moving, exercising, ALL the calorie burn).
BMR: basal metabolic rate (the amount of energy used to keep your body alive, before accounting for any activity – essentially, the amount of energy to keep you alive in a comatose state)

I’m linking two blog posts from Amber Rogers. These two posts had a huge impact on my understanding of “calories”.

Go Kaleo: Putting The Calorie Pieces Together
Go Kaleo: Finding Your Ideal Weight

From Putting the Calorie Pieces Together:

“There’s a lot of confusion out there, so in the name of clarity, I’ll give you the basics on calorie intake, as simply as possible. A calorie is a unit of energy. Your body uses energy to fuel your daily activity. If you take in more energy than your body uses, it stores the excess, usually as fat, but if you’re lifting heavy and using your muscles it can and will use that excess energy to build muscle too. That’s what we want.


If you’re at a healthy weight and your goal is body recomposition, you need to eat AT LEAST as many calories as your body burns, preferably a little bit more. Your body needs raw materials to build muscle, and if it’s using all the calories you eat to fuel your activity there will not be any left to build muscle with. If you’re undereating at a healthy weight, your body will do whatever it can to burn fewer calories, so will slow down your metabolic processes and start burning muscle for fuel, because muscle requires more calories to maintain than fat. If you’re undereating, that muscle is taking up energy (calories) that your body would rather use to fuel your heartbeat and brain activity.”

From Finding Your Ideal Weight:

“First lets establish the basics: a person’s weight is the product of their energy and nutrient intake (what and how much they eat) and their activity level. The more active a person is, the more energy intake they will need to support their weight. For instance: at my activity level, a calorie intake of about 2800-3000 a day will support a weight of roughly 160 pounds. My height isn’t a factor here, as long as I maintain this activity level and consume around 2800-3000 calories a day, my weight will be fairly stable at 160 pounds. Whether I were 4 or 7 feet tall, this activity level and calorie intake would support 160 pounds. The kinds of calories a person chooses CAN have some impact on how many calories they need to consume to support their weight, but that’s a topic I’ve already discussed. The basic idea here is that your activity and calorie intake will determine your weight. So lets reframe this whole subject. Instead of trying to figure out what your ideal weight is, lets instead work on figuring out what your ideal level of activity and calorie intake is. Once you have that dialed in, your body will eventually normalize at the weight those two variables support.”

I’m also linking two of Dr. Joshua Kern’s blog posts. He discusses several studies on diet, metabolism, & calorie underreporting, and it’s all very enlightening.

Go Maleo: Metabolic Derangement
Go Maleo: Calorie Underreporting

From Metabolic Derangement:

“This older study showed that people reporting dietary intakes of 1200 kcal per day under reported calorie intake by an average of 47% and overestimated activity level by 51% (of note their measured TDEE and RMR were within 5% of that which would be predicted by body composition):


This newer study used doubly labeled water to compare the true expenditure and intake of women again reporting very low intakes. 8/10 women had TDEE and RMR within 15% of predicted and were simply greatly underestimating their intake. Those 8 people were estimating intakes between 600-1000, while their average intake was roughly 2200, underestimating by an average of roughly 50% (my estimate by looking at the figure). Consistent with the previous study. Three of those 8 were actually underestimating their calorie intake by almost 3 fold (two estimated 1000 calories intake and was consuming over 3000). Of note one of those 8 women who was the closest to estimating their real calorie intake did eat below TDEE during the two weeks of the study period, the rest all ate at their TDEE despite reporting intakes much, much lower than their TDEE.


Of the two women not discussed in the above section one had a normal RMR but a very low TDEE (19% below predicted), suggesting a very sedentary lifestyle, though the possibility exists for the “efficient metabolism” idea. She also underestimated calories consumed by 38%.”

Most of us simply do not understand A) that we require more calories to function each day than we think, and B) we have a very difficult time tracking our intake accurately.

It blew my mind again to realize that even when I was really thin, underweight for my frame, underfat for my health … I was probably still taking in about 2000 calories. I thought I was eating less! I was certain that I must have been down to about 1500-1600 calories daily during that time. But the FACT is: At 110 lbs, I was still managing 90 minutes of daily low intensity exercise, over many months – the only way I could have maintained that would be to average about 2000 calories a day. If my intake had been consistently lower, my weight and/or activity level would have gone down.

During one of my most difficult periods of undereating, I weighed 105 lbs, spent 12 hours a day sleeping & barely moved all day: I was exhausted and starving, and THAT is what 1500 calories looks like.

(EDIT: I actually had to go back and re-run these numbers, the previous uploaded picture was incorrect data, because I had selected “male” instead of “female”.)

This is what 1500 calories looks like.

My stats, when I finally was so exhausted from insufficient calories that I spent an entire month sleeping for 12 hours each day. I couldn’t leave the house, I could barely drag myself into the kitchen to get a piece of fruit. I lost the whole month of January, 2008.


 You can check your own TDEE here: It is a good, accurate calculator – but remember, the data output is only as good as the data input.

So believe me when I tell you: if you think you are eating 1500 calories and gaining weight, you are not. You are not eating 1500 calories, you are not gaining weight on a 1500 calorie diet, your metabolism is not broken. None of those beliefs are actually true.

Whatever weight you reach, you are eating the amount of food – taking in the amount of energy (calories)  at whatever activity level you have – to support that weight.

If you find it difficult to accurately track your intake, you are normal. If you insist you are tracking accurately AND you are eating 1500 calories a day AND you are gaining weight … you are wrong. I understand. That’s why I’m writing this. I get it. But you have to really comprehend down in your core what I am saying: you are normal, and you are wrong about your intake. It is not a moral failing to be inaccurate about food intake or calorie counts. You are just eating the amount of food that supports a higher expenditure of energy. Again, it is not a moral failing. It’s just what is. It is so much easier to tweak your habits once you can identify where the disconnect is.

If you think you are taking in only 1500 calories every day, over the long term, please know that your weight would ultimately be around 100 to 105 pounds (for a sedentary woman) …. and even that would depend on how much time you spend sleeping or completely sedentary.


This an example of what 1500 kcal TDEE looks like. Notice: NO ACTIVITY and that will only support 100 lbs in a grown woman. Height does not matter, age would only alter the assumed expenditure very slightly. I calculated for a generic 35 year old woman of average height.


You would not be running, nor hitting the weights, nor chasing toddlers, nor doing much of anything besides sleeping, on 1500 calories. Because 1500 calories per day will not support extra activity.

Yes, in the short term, if you have extra body fat, you will burn some of that for fuel. But that’s a ‘crash diet’ – and your body will downregulate activity fairly quickly to prevent losing much of its mass, as well as burn lean tissue like muscle because muscle is expensive to keep when you are starving.

Think of it this way: crash diets don’t really work, because the body wants to preserve itself. Body fat is there for more than just burning off during a diet – it also exists to cushion your organs, to provide building blocks for hormones. Your body wants to preserve itself. It doesn’t just burn off all the fat when it’s hungry – it downregulates metabolic processes, it burns off other tissues that are more expensive to maintain.

There may be a few outliers – but outliers are outliers because they are very rare. You are probably not an outlier, the odds are very much against it. Some people do have medical conditions that lower metabolism slightly, but most people do not. And even those with medical conditions that reduce metabolism slightly do NOT experience seriously suppressed metabolism so far outside the norm that they maintain or gain weight on severely reduced calories. It just does not happen.

So if you are convinced you are that one special snowflake who is accurately tracking 1500 calories and working out 2 hours a day and still gaining weight: YOU ARE NOT. You really really are not.

You are not eating 1500 calories and gaining weight. 1500 calories will ultimately maintain (barely) 100 lbs in a full grown sedentary woman. This is truth.

There will always be some slight variation and individual range, it is still estimation, nothing is EXACT, but the fact is 1500 calories will NOT maintain 120 lbs or 130 lbs or 180 lbs or 230 lbs. It will maintain right around 100 lbs in an exhausted and sedentary adult woman, and I can just about guarantee that if you are an adult above 4’9″, you don’t need to be anywhere near 100 lbs.



I initially posted a version of this at the “Eating The Food” Facebook group: Its main purpose: to support members in recovering from disordered eating and diet mentality. I am one of the moderators there, and we talk about healthy weight, healthy weight loss, healthy body image, and how to stay sane about food & diet. 

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