Your basal metabolic rate (BMR) is the minimum number of calories your body requires to sustain life (think like being in a coma on life support).

This number changes throughout life and is based off multiple variables– such as gender, age, and weight. This is also the number you never want to go below in regard to food intake. Why? Because if you do it on a regular basis you WILL slow your metabolism down and you will end up in a stuck cycle of not being able to lose weight.

I can not tell you how many people I’ve interacted with or worked with who are eating too little and yet they carry excess body fat.

This is especially common amongst women. It is precipitated by mainstream diet advice that tells people they must cut calories drastically to lose weight.

Yes- if you are eating 4000 calories a day and maintaining a very heavy weight we want to cut lots of calories. But where do you think we are gonna cut from if you are already so low that you are not even providing enough for “normal” functions (like breathing and having your heart pump!?).

I’m sorry I use this analogy so much– but just like when you are driving, and the fuel tank goes to empty– you slow down to conserve gas. Your body works the same way. If you are chronically undereating- especially if you are exercising- your metabolism WILL slow to manage what you provide it.

I understand it seems so counterintuitive to eat MORE. But let’s be real– even going from 1200 calories to 1700 calories is still NOT a lot of food. And this does not just apply to remarkably active people. If you’re working out 45 minutes to an hour 3 days a week I want you consuming at minimum 1500 calories.

Chronic undereating has lots of other effects that people don’t realize.

It affects recovery, your immune system, and your mental state (think brain fog and depression). It affects your sleep, your performance in the gym AND at work, it even can affect your sex drive.

Two side notes: First, when I refer to “chronic undereating” I am referring to eating below your BMR- i.g. for a woman eating 1000 calories a day. Caloric restriction is how we lose fat, chronic undereating is how we slow our metabolisms down. Second- chronic undereating and fasting are two COMPLETELY DIFFERENT THINGS. Don’t get the two confused.

Most people who diet have learned that excess fat is stored because you are consuming excess calories.

This is true in its simplest form, yes. But let me make it a bit more complicated for you– the fat storage system is hormonally linked. If your hormones are out of whack, you will end up with stored fat.

Ever hear about cortisol? The STRESS HORMONE? Guess what happens when you chronically undereat? Your cortisol levels go up. Want to know why? Because your body is STRESSED that is isn’t getting enough fuel. It raises cortisol levels to conserve whatever it can- as BODY FAT– so that it has RESERVES of energy to ensure it can maintain life. Make sense?

You might be reading all this and feeling extremely frustrated because you’re not sure what to do.

Here’s the simplest way I can break it down for you: you need to be eating above your BMR, with a calorie deficit of AT MOST 1000 calories a day (which will equate roughly to losing 2 pounds per week). For example, If you are a 150lb, 5’5 tall woman over 18 and under 65 your BMR is going to be somewhere between 1200 and 1400 calories.

Now, remember your BMR is what you would require calorie wise if you were in a coma. However, since you are reading this right now I am guessing you are NOT in a coma, which means you need to eat MORE than your BMR.

We also need to account for the other calories that you need throughout the day (such as the calories your body uses to break down food- yes that is a thing) and the calories you use to walk to the car, exercise, etc.

This ends up being somewhere between 400 to 1000 (or more) based on what you do for work, etc. Check out this calculator to help you calculate what you should be eating to maintain your current weight.

Then to lose weight, subtract a reasonable amount of calories from that number– again never dropping below your BMR (you can find out what that is estimated at using this calculator).

I like my athletes and clients to have at most a caloric deficit of 300 to 500 cals a day on training/exercise days. On rest days we can go a bit more. I don’t like big deficits on days when my clients train. You still need calories to repair the damage you did during exercise (muscles grow by being broken down and being built up stronger for next time. That “building up” requires protein (read FOOD)).

Yes, this is all complicated and overwhelming, but if you take away ONE thing from this article- take away this:

Chronic undereating and chronic caloric deprivation is not only making it harder to lose weight, it may be adding to your fat stores.

Find how many calories your body would need to maintain the weight you’re currently at, then create a small deficit, no more.

Trust me- if you fuel your metabolism it will be a game changer for your weight loss goals (and it will make a huge difference in your performance at the gym!)

Questions? Comments? Concerns? I’m a health and nutrition coach on a mission to help people become the healthiest, strongest versions of themselves! Feel free to shoot me an email or comment below!

Shawna Norton

My mission is to help everyone I can become the healthiest, strongest versions of themselves. I am a Crossfit coach, athlete, Health and Nutrition coach, Movement Rehab Specialist, and a grad student completing my masters in Kinesiology with a focus on integrative wellness.


Ren · March 13, 2018 at 4:57 pm

Really great read. I own a gym in Carlsbad specializing in individual programing for training goals, nutrition goals and of course aesthetics and experience so many cases of the classic undereater. Simply put, we’ve been brainwashed to think less is more when is not the case at all. I’ll be sharing this with my clients. Thanks Shawna.

Brenda · March 14, 2018 at 8:33 pm

Houston we have a problem!!
I’ve been a chronic under-eater for years/decades (entire weekends without eating, eat one meal per day etc) but the net result is being overweight significantly. I know you are correct. On the occasion I have tried to eat more regularly, I have lost weight. I would like to find out approximately how many calories I should be eating so I can try to regulate this because I obviously don’t know the cues nor can I guess or use portion sizes. I am too out of whack. This is too counter-intuitive to do without guidance.
I exhibit some of the numerous signs of chronic under-eating as well.
When I use the calculator, it suggests that to lose weight I eat approximately half of my BMR calculation. Changing my weight in the calculator as some sites suggest only worsens the issue.
To use the calculator I input 50 year old female. 5’7″ 197# (goal is 145#) Lifestyle now = sedentary (right now I am tired – get my diet on track some then I hope I will have some energy and start increasing my activity).

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