Weight Loss Math: How To Lose Weight
While many of you probably dread re-living high school math, I was always a bit of a math geek. Formulas always made a lot more sense to me than foreign languages or reading comprehension. So today I’m going to throw a weight loss formula out there and see if we can’t solve an age old question…how do you lose weight? Let’s do some math!
Let’s start with a simple equation for weight loss:
Calories Eaten – Calories Expended Exercising < BMR
That doesn’t seem so hard, does it? The big challenge is that we have to further define these variables.
Calories Eaten
Calories eaten may seem pretty easy to calculate. You simply add up the amount of food you eat in a day. Unfortunately that’s a lot more complicated than it sounds. While nutrition labels list an estimate of calories, portion size is a huge variable. Even for something as simple as chips, the package might say that 10 chips equals 100 calories. How big are those chips? Does that include any broken pieces? The 10 chips that you eat today may be different than the ones you eat tomorrow. Accounting for these differences could lead to a 20-30% difference in actual calories eaten.
To get an accurate number of calories, you would have to weigh all your food before you eat it. This is a major inconvenience. Even someone like me who used to be obsessed with calorie counting never incorporated this approach.
So, calories eaten is still a big variable. The best assumption we can make is that we’re within 20-30%. If you count 2,000 calories, then you might be off by 600 calories in either direction.
Calories Expended Exercising
Calories expended exercising is a little easier to calculate but not much. I like to assume that I burn 500-600 calories per hour of exercise. Let’s assume that the average daily exercise you get is 30 minutes. That’s 300 calories. Again though, the calories you burn during that half hour could be significantly different due to varying intensity levels. If you perform a half hour circuit training routine or HIIT, then you might really burn those 300 calories. A half hour strength training workout with long rest periods might only result in 150 calories burned. The issue here is that 100 calories doesn’t seem like a big deal on a daily basis. However, over the course of a year, a difference of 100 calories per day could equal 10lbs of weight gain/loss (100 calories/day * 365 days / 3,500 calories to lose 1lb).
Cardio machines are notoriously bad at estimating calories…900 calories burned in an hour is probably 50-75% too high!
Basal Metabolic Rate (BMR)
What about calculating BMR? BMR is the amount of calories you burn by not getting out of bed. You can calculate that here. Most people would recommend adjusting for an activity factor. For a sedentary lifestyle, you would multiply by 1.2. My BMR is 1,600 meaning that my BMR adjusted for a sedentary lifestyle would be 1,920. That’s a pretty big difference. I account for calories expended exercising separately above, but if you wanted to include that here, you could as well. For 3-5 days of moderate exercise, you multiple the base BMR by 1.55. That would put me at 2,480. In other words, this equation assumes moderate exercise adds an additional 560 calories per day above sedentary BMR. That’s essentially an hour of exercise per day which seems pretty high. That’s why I like to separate calories expended exercising.
Can we solve this equation?
Well it’s complex algebra with 3 unknowns so we can’t really solve it. However, we can work around this equation to optimize our ability to lose weight.
- Calories eaten: try to overestimate rather than underestimate calories eaten
- Calories expended exercising: eliminate this from the equation
- BMR: no adjustment for sedentary lifestyle or activity factor
So, what’s our revised equation to lose weight?
Calories Eaten < BMR
You know your BMR, so try to keep calories eaten to something less than this number. Yes, it’s low but nobody ever said losing weight was easy. The variability in calories eaten is hopefully offset by not adjusting BMR. As a final hedge, this equation no longer accounts for the calories you burn exercising. If all goes well, calories burned exercising will lead directly to weight loss. Questions? Comments? Concerns? Class dismissed!
Not Your Average Fitness Tips
- Weight loss is a simple equation: calories eaten < BMR
- It’s highly challenging to accurately calculate calories eaten and calories expended exercising.
- BMR is a great eating target…don’t adjust for any activity factor though.
- Any exercising will only accelerate weight loss.
- Experiment through trial and error to find out how much you should eat and exercise to lose weight.
Related posts:
- Weight Loss Myths: Does the Mainstream Media Finally Understand How To Lose Weight?
- Protein Sparing Modified Fast and Rapid Weight Loss Diets: How to Lose 10 lbs in 2 Weeks
- Why am I not losing weight? What to do to lose weight?
- Diet or Exercise? Which is better for weight loss?
- Meal Timing and How Many Meals a Day to Lose Weight
Posted in Best Fitness Tips
Good example on how weight loss isn’t as simple as doing a math equation. If it were only that easy. Like you mention there are too many unknown variables that you can’t draw a clear equation and simply plug in the right numbers, the viola. The truth is the human body is always gravitating towards a state of homeostasis or balance so the “numbers” are never consistent. What does work though is creating a slight enough caloric deficit for your body to access stored fat reserves for energy….but, not staying in the deficit for too long as your metabolism will evenutally de-regulate to the decreased energy. People will be most successful with weight loss when then focus on a healthy diet and exercise with occassional short phases of caloric restriction.
Charleston,
I agree that a healthy diet and exercise are key to weight loss. People who try to follow restrictive diets over the long term unfortunately fail more often than not. My personal diet preference is intermittent fasting which allows me to consume more on the weekends and still lose weight.
Dave
I agree with you that counting calories in and calories out is crazy difficult and variable. (I’ve never been a fan, but will occasionally throw some of my data into FitDay for a general idea.)
There are two misconceptions about the “calories in – calories out = weight change” equation that really changed my paradigm once I learned them.
First, we assume that “calories in” and “calories out” do not affect each other. It’s easy to say “eat less, exercise more,” but the truth is when people eat less, they get lethargic and have less energy to exercise. When they exercise more, they work up an appetite and tend to “reward” themselves. Instead of being a bunch of independent parts, the human body is an amazing homeostatic system.
Second, we assume “calories in” and “calories out” are the cause and “weight change” is the effect. What if it’s the reverse? Bear with me here. When a child is growing, for example, we don’t say that it is because they are eating too much and exercising too little. While these two conditions must be true for the second law of thermodynamics to hold, truth is hormones cause the child to grow, which causes them to have a caloric surplus. A growing body of evidence points to fat accumulation as mostly hormonal in nature.
Whew. Sorry to bogart the comments section, Dave! Just wanted to shed some new light on why people struggle so much with the current paradigm.
Hey Dave, great you are quantifying the jigsaw pieces. I tried to calorie count in/out for a while but got jack off it because it became too hard. I think at some stage you need to make an estimate then move on once you get a feeling for it.
Very true Darrin loosing weight is strange I always get hungrier when I exercise whilst trying to stay lean.
But the best thing I think is observe yourself over time say a week if you are hitting your goals like lifting heavier, loosing weight, whatever they are great! if NOT change something eat less, eat something different try a different lift or hit a different muscle group .. you got the idea …cheers!
Dave,
If the calories are less on a consistent basis you will lose weight. The problem is that most people underestimate how many calories they are eating on a consistent basis. They may be good some days and eat too much other days. This is why I love intermittent fasting so much, I don’t have to worry as much about what I am eating.
I do think though that the leaner you get, the more you need to be aware of what you are eating, if you want to look really ripped. If you are thirty pounds overweight, intermittent fasting will work wonders, even if you are not eating very clean. If you are only a few pounds overweight and plan on eating junk food every day but still fasting to get a caloric deficit, you may not get the look you are after. I still fast each week, but as I get leaner, I also clean up my diet on the days that I am eating.
Darrin,
You make a lot of excellent points. Don’t ever worry about commenting too much, especially with comments like these that add a lot to the existing post.
Raymond,
You’re absolutely correct that you can’t do calorie counting forever. I think you can get a good sense just by tracking for 1-2 weeks. It’s a great way to make yourself accountable in the short term too.
Kelly,
I definitely agree that the game changes a bit as you get really lean. In my opinion, it’s actually easier to clean up your diet at that point. By then you’ll be used to fasting which means you probably won’t be as emotionally attached to food and you’ll have seen great results as well which should help motivate you to continue working hard. That’s been my experience at least. I now fast Monday and Friday and skip breakfast on Wednesday. Tuesday/Thursday I try to eat around 2,000 calories. That leaves me relatively free to eat what I like on weekends. Over the summer, I’m planning on really cleaning up weekends to hit new lows on bodyfat.
Dave
Dave,
that’s the exact logic I follow when dieting: expend more than BMr.
Two things that work for me:
1. eat very little (training doesn’t really matter)
2. eat normal, but train very hard (2hrs per day)
Yavor,
Those are the 2 basic ways to do it. For me, eating very little is easier because training very hard takes up too much time. Training very hard worked in pre-family days though.
Dave
Okay, now…I’m officially confused. I was never really good at math but I just did my BMR and it came out to: 1290.85. Is this correct? I can burn almost 1300 calories just be getting out of bed in the morning? What does this really mean for me though? I don’t count calories, it’s boring and takes up too much of my already-limited time. Is knowing my BMR really all that necessary? I mean, as long as I eat cleanly and keep up the exercising isn’t that enough provided the scale doesn’t move upwards?
Toni,
I’d say your BMR sounds about right…and you actually burn that many calories WITHOUT getting out of bed! It’s really just a baseline starting point for someone who has been challenged with how much to eat to lose weight. I agree that it’s best not to count calories but some people need to micromanage what they eat to motivate themselves. I’ll bet in the back of your head you have a reasonably good idea of how much you eat as well. Some people even if they ate cleanly might still see weight gain because they still eat too much food. That’s why knowing this can come in handle sometimes.
Dave
Dave,
So am I to assume that my BMR is good? This seems to be something that people needing to lose a lot of weight need to know. I do have a rough idea of how many daily calories I consume; it would be unwise not to know IMO.
Micromanaging your diet seems like a lot of unnecessary work but I could see where it would be necessary for some people – at least in the very beginning.
I always hear people speak about their BMR but never paid much attention to it. Good to know though.
Toni,
BMR isn’t good or bad, it just is. It’s calculated based on height, weight, age, and sex. Your BMR actually goes down as you weigh less which is why people say your “metabolism” decreases as you lose weight. There are other factors that ultimately determine how many calories you burn in a steady state but this is just a simple starting point.
Dave
So, is this why as you get leaner you have to rev up your metabolism or trick it by having a cheat day so that you’ll lose the last few pounds or whatever?
Toni,
You got it. You will lose weight by eating 1,300 calories but eventually you’ll have to eat 1,200 calories and so on. Eventually it can get to a point where calories are too low to sustain for the long term without other health consequences. It’s not entirely BMR related since other factors affect metabolism but that can play into it.
Dave
Cal/day < BMR I've read leads to significant loss of muscle mass. No doubt you'll lose weight. I lost 34lbs. in 3 months months eating that way, but my wife complained I looked skinny. Now I'm trying a different approach. I chose a weight just under a 25 BMI, because over 25 is alleged to lead to a shorter life. I then calculated my ideal lean body mass based on a 10% body fat goal. Using the Katch-McArdle formula that considers lean body mass, I calculated my ideal BMR. I then multiplied that number by the activity factor for a sedentary lifestyle (1.2). Setting that number as my daily caloric goal, as long as I'm not sedentary, I should lose weight while (theoretically) at the same time be moving towards my ideal body composition. I hope to gain muscle mass while losing fat with this approach, as opposed to losing both.
Anonymous,
Any diet can potentially lead to muscle mass. However, my belief is that if you’re performing resistance training and getting stronger, you won’t lose muscle. Additionally, the reason I recommend calories less than BMR is partly because counting calories is so challenging. If you could perfectly count calories, then adjusting for an activity factor would be fine. The average person tends to underestimate how much they eat though.
Dave