How Many Calories to Lose Weight?

by BusyMama on November 6, 2013

I have been getting a lot of questions about calories and macros in my email and on Facebook lately so I thought I should write up some nutrition blog posts and address some of the most common ones starting with calories.  I haven’t written one of these in a while – this might be fun!  Before I start, I’m putting up a disclaimer:  all information that I post are out of my nutrition books and/or online classes so my answers are all pretty general.  When it comes to how we eat, how we burn fat, how our bodies use food – this isn’t a one-size-fits-all kind of thing.  Many of us have different body types, metabolic types, genetic backgrounds… so what I post may not work exactly for you as it might for someone else.  Please keep this in mind.

How do I figure out how many calories I need to eat to lose or gain weight?

Well, I could take the time and write out the Harris Benedict equation so you could plug in your numbers and do the math yourself, but honestly there’s no point when this awesome website exists that calculates your BMR for you.   BMR stands for basal metabolic rate and in a nutshell, this is the amount of calories your body needs in order to keep you alive even if you just laid in bed all day.   Once you know your BMR, you can follow the link on that same website that lets you calculate your daily calorie needs.   Here’s where it gets tricky:  be honest with your activity level.  Calories are not something we should be afraid of, despite what so many ‘fitspo’ pictures and weight loss ads tell us.  We need to fuel our bodies with enough food.   Once you’ve calculated your daily calorie number with your activity level taken into account, then all that’s left is some simple math:  1 lb of fat = 3,500 calories.  Since there are 7 days in the week, we divide 3,500/7 which gives us 500 calories.  This is the amount of calories we need to add or subtract from our daily calorie number in order to gain or lose 1 lb a week.  Which brings me to the next question…

Why do I only want to lose 1-2 lb a week?

One of the things that makes me want to pull my hair out sometimes is all of the damage that media, weight loss ads, supplements, Fitspo, Biggest Loser, cleanses and all of the like has done on our understanding of how weight loss works.  When you first start tracking your calories, changing your diet or even begin a new workout program it’s really common for the first couple of weeks to see a big drop on the scale.  But then after a couple of weeks, the scale number starts to slow down and people start to panic that they’re plateauing or the diet isn’t working.   The truth is – the initial big change in the number on the scale was due to your body releasing water.  Actual fat loss doesn’t come in numbers that size unless there’s a knife and some suction involved.

When you start lowering your calories, a lot of changes take place in your body metabolically and a lot of ‘alarms’ sound.  Your body doesn’t want to burn fat – fat is a means of survival!  Your body would rather break down muscle and burn that as fuel before dipping into the fat stores and if your calories are too low, those ‘survival alarms’ are going to sound off.   Those survival alarms are your hormones and this is how they are affected if you aren’t eating enough.

Thyroid:  Your thyroid is in charge of metabolizing your macronutrients (fat, protein, carbs).  It does this with hormones called  triiodothyronine (T3) and thyroxine (T4).  When you start decreasing your calories too much, your thyroid output of T3 and T4 lowers which can slow your metabolism.  Low metabolism is NOT what we want when it comes to weight loss.Leptin:  Leptin is a hormone that tells us that we’re hungry or satisfied.  When our leptin levels are high, we’re full.  We don’t need to eat.   When your calories are too low, your leptin levels drop.  Low leptin levels means hunger signals even if you’re not truly hungry.

Testosterone:  Testosterone is another hormone that lowers when calories dip too low and testosterone is an important hormone for both men and women.   We need testosterone so that we keep our muscle mass (and so we can build it, if that’s the goal).  Muscle mass is another player in getting a high metabolism.  Did you know 1 lb of muscle can burn 15-50 calories a day even if you don’t workout?

Cortisol:  Cortisol’s function is stress management.  When calories are too low, cortisol levels elevate.  When cortisol levels elevate, growth hormones (linking that because that’s a whole can of worms in itself) and testosterone levels lower.  Cortisol can contribute to muscle loss due to stressful conditions (like not enough food), assisting in breaking down muscle tissue into carbohydrates to use as fuel.  ”Under stressful conditions, cortisol can provide the body with protein for energy production through gluconeogenesis, the process of converting amino acids into useable carbohydrate (glucose) in the liver. Additionally, it can move fat from storage depots and relocate it to fat cell deposits deep in the abdomen .”  (“Cortisol Connection: Tips on Managing Stress and Weight”, Christine A. Maglione-Garves, Len Kravitz, Ph.D., and Suzanne Schneider, Ph.D.)


So when you keep your calorie deficit within a 1-2 lb weight loss per week, you are more likely to keep your hormones balanced which means fat loss! What we want, right?   Along with this, you also fuel your muscles’ recovery from when you worked out.  Remember: you don’t just burn calories while you’re working out.  You also burn calories after your workout as your muscles go through their repair process.   Eating enough helps us get those results we’re chasing!

Please let me know if you have any questions about calories that I didn’t address and don’t fret – a post about macros and different diet types is coming!!!   Also, if you would like to know more information about calories and fat loss, please comment below and I can email you an ebook or write up an additional blog post with more info!




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