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How Many Calories Should I Eat To Lose Weight? | Ask The Fitness Nerd

December 24, 2008 on 9:54 am | By Matt | In Ask The Fitness Nerd |

Looking to lose weight, but not sure how many calories you should eat to achieve your goal? It’s actually not that hard if you know what to do.

Dear Fitness Nerd,

My New Year’s Resolution this year is to lose some weight. Not a lot — about 10-15 lbs. I don’t want to try diet pills or any thing like that. I’d prefer to do it by getting my diet in order, believe it or not. However, I am a little unclear on how I should determine how many calories I should eat to lose weight. I know I’m not supposed to go under 1,000 calories, but how many should I eat? Can you help? Thanks!  –Madison H. (San Jose, CA.)

Great question, Madison. How many calories you should eat to maintain, gain or lose weight is one of those fitness and nutrition fundamentals that is pretty easy to figure out, once you know how to go at it.

The simple answer is that most females can lose weight by reducing their calories to around 1500 a day and males, to around 2000 calories a day. 

But this isn’t a very scientific, nor particularly effective, method of determining how many calories you should eat each day to lose weight. Taking a “one-size-fits-all” approach doesn’t take into account a person’s weight, height, age and activity levels which can all impact how many calories you should eat each day. And taking this approach can also cost you muscle, which you always want to try to spare.

A much better approach is to calculate your own specific calorie requirements, and use that to determine how many calories you should consume to lose weight.

Calorie In, Calorie Out: The Key To Weight Loss

While there are all kind of theories out there about tactics to lose weight that don’t necessarily involve calorie-counting (for example, changing your carbohydrate, protein and fat intake ratios like on the South Beach or Ketogenic diets), at the end of the day, the best place to always start is with calorie-in, calorie-out. 

Yes, changing your macro-nutrient mix can help for some people, but this violates the 80-20 rule: Focus 80% of your effort on the 20% of tactics that get you the best results. Once you’ve done that, you can try other approaches to shave off those last few pounds. For most people, controlling how many calories they eat will produce 80% of their weight loss results.

The good news is that figuring out how many calories you should eat to lose weight isn’t terribly hard — all you’ll need is bathroom scale, a pen, piece of paper and a connection to the Internet. By the time you are done, you’ll have a pretty good idea of exactly how many calories you should be eating each day to hit your weight loss and fat loss goals.

However, before we get started, it’s important to understand a couple of terms, including what a calorie is, something called your Basal Metabolic Rate (or BMR or “resting metabolic rate”)  and your Total Daily Energy Expenditure (TDEE.) This will help you make more sense of the discussion going forward.

What Is a Calorie?

A calorie is simply a unit of energy.

If you think back to Middle School science class, you’ll remember that a calorie is the amount of heat released when a food is burned. Scientifically, it’s measured as the amount of heat needed to raise the temperature of 1 gram of water  1 °C.  Since adopting the metrics system, the calorie has been replaced with the “joule” in many countries (and in science) – but for most nutritional labeling in the U.S., the “Calorie” is still the standard metric for energy in food.

In terms of the body and food energy, a calorie is just a measure of the amount of energy released from food during digestion.  Only carbohydrates, fiber, fats, protein, organic acids, polyols and ethanol (alcohol) contain calories.  All foods are made up of these macro-nutrients.

All other foods not containing these macro-nutrients are considered “non-caloric”  — things like teas and coffees (provided you aren’t adding sugar or cream), water, most spices, vitamins and minerals, zero calorie artificial sweeteners like Sucralose or natural sweeteners like Stevia — as well as other substances present in food like enzymes and antioxidants.

Functionally, when you eat foods that contain calories, energy is released to the body to assist in powering your basic bodily functions like breathing, keeping your heart beating, digestion, reproduction and cellular repair. Energy from food is also used to repair tissue, assist in basic cellular functions, power the brain and to help you move around during the day — whether that is exercising, walking to your car or typing at the computer.

If you don’t get enough calories, you will lose weight — but if your calories are too low for an extended period of time, these basic functions will also suffer. If you eat just enough calories, you’ll be able to meet your daily energy needs and maintain your current weight. If you drop calories slightly, you’ll lose weight — but not enough to interfere with the work of the body.

What Is Basal Metabolic Rate (BMR) and Why Does It Matter

Your Basal Metabolic Rate (BMR) represents the minimum amount of calories — or energy from food — that your body requires each day to fuel your basic bodily functions. It does not include extra calories you need to perform daily activities.

You should view your Basal Metabolic Rate as the minimum amount of “gas” you need to put in your tank each day to stay healthy. Your BMR does not take into account the amount of activity you perform on top of breathing, thinking, pumping blood and digesting food. It’s really just representative of the amount of food you need to eat just to stay alive, at rest.

When you think about how many calories you should eat to lose weight, you want to also consider how many calories you should eat just to stay alive and healthy. Typically, that will no less than 1,000 calories — which is why you hear the idea that you shouldn’t eat less than 1000 calories a day bandied about.

Measuring BMR usually involves the use of tests in a very controlled environment — where you are awake, but completely at rest. However, it is possible to estimate BMR (also known as Resting Metabolic Rate or RMR) based on gender, age, height and your current weight. Your Basal Metabolic Rate will typically account for 60-75 percent of your daily calorie expenditure. The remaining calorie-expenditure will come from activities and exercise. 

How Many Calories Do I Need? Calculating Total Daily Energy Expenditure (TDEE)

Everyone has different lifestyles and levels of activities. The amount of calories that an Olympic Swimmer needs each day is much higher than a couch potato or even weekend runner.

Your Total Daily Energy Expenditure (TDEE) basically takes your BMR and then “adjusts” it based on your daily activity levels. If you have a desk job and don’t exercise much, your TDEE will be lower than a construction worker who does a lot of physical labor as part of his or her job, or your cube-mate who does the same thing as you at the office, but is training for a marathon each night.

Determining your BMR lets you set a baseline for what you need to consume each day to stay alive. Once you have that, you then need to take into account how much activity you perform each day, and add those calories into the BMR to get your TDEE.  This will then give you an idea of how many calories you need to eat each day just to maintain your current weight. Once you know that, you can then adjust your calories down (or activity up) to lose weight.

How To Determine How Many Calories You Should Eat To Lose Weight: A Step-By-Step Guide

The first step is to determine how many calories you need to eat each day just to maintain your current weight (based on your BMR and TDEE.) Once you’ve done that, you can then subtract calories to hit your weight and fat loss goals.

There are two ways to calculate this:

1. Online using one of the many calorie calculators available, which typically use the Harris-Benedict formula, but do the calculations for you.
2. Manually using a formula developed by two researchers, also know as the Harris-Benedict BMR formula

I’ll show you how to do both, although using an online calorie calculator is the easiest, and will generally give you similar results to calculating your BMR and TDEE manually.

Method One: Using an Online Calorie Calculator

Using an online calorie calculator is the easiest, fastest way to determine how many calories you should eat to lose weight.

Step One: On a piece of paper, write down your gender, age, current scale weight and height.

Step Two: Go to this calculator from the Mayo Clinic and plug in your numbers. Choose your activity level and write down your results on a piece of paper. This is your BMR adjusted for daily activities, or Total Daily Energy Expenditure.

Method Two: Manually Calculating Your Calorie Requirements

If you like numbers and are interested in exactly how BMR is calculated, you can try manually calculating your BMR and TDEE using the Harris-Benedict formula. A calculator comes in handy here.

Step One: On a piece of paper, write down your gender, age, current scale weight and height.

Step Two: Choose one of the following formulas based on your gender and plug in your specific numbers for each of the items in italics. On a piece of paper, perform the math in the brackets first and write down the results on a piece of paper :

Harris-Benedict Method for Calculating Basal Metabolic Rate (BMR)

Women:
655 + (4.3 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years) = BMR (un-adjusted for activity)

Men:
66 + (6.3 x weight in pounds) + (12.9 x height in inches) - (6.8 x age in years) = BMR (un-adjusted for activity)

Step Three: Once you’ve done the above math, you’ll have your BMR, not adjusted for activity. Now you need to adjust it for your activity level in order to get your TDEE. To do this, choose which of the following five activity categories best describes you and multiply your BMR by the appropriate factor below:

Activity Factor for Calculating Total Daily Energy Expenditure (TDEE)

• If you are sedentary: BMR x 1.2
• If you are lightly active: BMR x 1.375
• If you are moderately active (You exercise most days a week.): BMR x 1.55
• If you are very active (You exercise intensely on a daily basis or for prolonged periods.): BMR x 1.725
• If you are extra active (You do hard labor or are in athletic training.): BMR x 1.9

An Example of Calculating BMR and TDEE with Harris-Benedict

Just so you can understand how this works, let’s use the formula above to calculate the BMR and TDEE for:

• a 38 year old male
• who is 5′ 11″
• weighs 180 lbs
• Has activity level of moderate (works out daily.)

Italics indicate the actual numbers we plug in:

66 + (6.3 x 180) + (12.9 x 71) - (6.8 x 38) = BMR

Here’s how it would look once you’ve performed the math in the brackets:

66 + 1134 + 915.9 - 258.4 = 1857.5 (BMR)

Now, we just need to adjust the BMR for his activity level, which is “moderately active.” To do that, take the BMR number (1857.5) and multiply it by the activity factor, which is this case is 1.55.

1857.5 x 1.55 = 2879 Calories

This represents the estimated amount of calories he has to eat each day to maintain his current weight, based on his BMR and activity levels.

Adjusting Your Daily Calories to Lose Weight

Now that you know your BMR and TDEE, it’s time to figure out how many calories you should eat each day below your TDEE in order to lose body fat.

To do this, you’ll need:

1. A weekly fat loss goal (lbs per week)
2. Your TDEE number

A pound of fat contains about 3500 calories. So if you want to lose 1 lb of fat per week, you need to create an average calorie deficit of 3500 calories per week below your TDEE.

So let’s say your TDEE is 2800 calories a day. You would want to come in at the end of the day at about 2300 calories.  You can do this one of three ways:

1. Reduce your average food intake across the week by 3500 calories (about 500 calories a day)
2. Burn an extra 3500 calories a week via exercise (or 500 calories a day)
3. Do a combination of the two: Reducing your dietary calories by 1750 a week and burning an extra 1750 calories with exercise for a total deficit of 3500 a week (Reducing daily dietary calories by 250 and burning 250 additional calories a day.) 

Remember, we’re not talking about reducing your calories 3500 a day. Rather, for the scenario above, you would spread that out over seven days, which would equal a 500 calorie deficit each day. This is generally pretty attainable for most people. 

Which Approach To Weight Loss Should I Take?

The method that you want to use to create your calorie deficit really depends on your schedule, goals and current diet.

In general, the third option, where you reduce your calories slightly and increase your exercise levels is probably the most effective for most people.  In scenario three, you would basically eat 250 less calories a day, and burn an additional 250 calories with exercise to arrive at a daily deficit of 500 calories below your TDEE. For most people, this would result in a loss of 1 lb of body fat a week.

Option 3 is ideal, because it combines both exercise and diet modifications, which can improve overall fitness, increase metabolism and prevent you from feeling hungry.

It’s also easier for people to swallow (no pun intended), because you aren’t making dramatic cutbacks in the amount of food you eat. And trying to burn an extra 500 calories exclusively through exercise each day can be hard for people who have schedules that limit the amount of time they can spend in the gym.

Weight Loss Example: Meet Sarah

Just so you can understand exactly how this would work, let’s take a look at another example.

Sarah is 28, currently weighs 145 lbs and is 5 foot 5 inches. She is pretty inactive. She doesn’t work out regularly and spends most of her day behind a desk. To maintain her current weight, Sarah needs to eat about 1750 calories a day (this is her TDEE). To lose one pound of fat a week, she needs to end the day at 1250 calories (1750-500=1250 calories), which means creating a daily calorie deficit of 500 calories below her TDEE.

Sarah has one of three ways she can lose a pound of fat a week:

1. She eats 500 less calories a day, but keeps her activity levels the same
2. She increases her activity levels each day (typically through exercise) to burn an additional 500 calories each day
3. She eats 250 less calories each day and increases her activity levels to burn an additional 250 calories above her normal activity levels

Any of these options will work, it’s really just a matter of what Sarah feels she can effectively commit to.

What If I Want To Lose More Than a Pound A Week?

Generally, you should aim for no more than 1-2.5 lbs of fat or weight loss a week. The more weight you try to lose in a short period of time, the more restrictive your diet has to become and/or the more exercise you have to perform.

Also, the leaner you are, the more careful you want to be when it comes to creating dramatic calorie deficits — especially anything that creates a calorie deficit of more than 1000 calories a day. Typically, this will result in accelerated loss of lean muscle mass, which is never a good thing. Likewise, the more body fat you have, the deeper you can cut into your TDEE. However, as you lose fat, you’ll need to adjust this.

Studies have shown that people who lose weight more slowly are more successful at keeping it off for the long-haul.

Also, losing fat and weight slowly reduces the chances that you’ll lose precious muscle mass along with the fat. Also, losing more than 2 lbs of fat a week can be very challenging from a diet and exercise perspective. To lose that much weight, you would have to create a daily calorie deficit of 1000 calories, which is very difficult to safely do with diet alone.

The caveat here is that if your diet is currently full of lots of calorie dense foods, like soda, sweets, fast food, snacks and simple carbs, you could be overshooting your TDEE by as much as 1000 calories. Simply reducing those foods could result in fairly dramatic fat and weight loss. Adding some exercise in as well can speed that up.

Four Tips for Calorie Counting and Losing Weight

Once you know your TDEE and the amount of calories you need to burn or reduce in your diet, there are some tips and tricks that you can do to help you hit your weight and fat loss goals:

1. Consider tracking your food using one of the great, free online websites like SparkPeople, The Daily Plate or Fitday. All of these sites offer calculators for determining how many calories you need to eat to lose weight (or maintain and even gain weight.) These sites make it easy to keep track of your food and exercise and make sure you are hitting your goals.
2. Learn how to substitute more-nutritionally dense, healthier foods for the junk food you might be used to eating. Again, getting soda, excess sugar and fast food out of your diet can trim off hundreds of empty calories a day with some basic adjustments to your diet. And because you’ll be replacing junk food with healthier alternatives, you’ll find you are less hungry than if you just try to cut calories across the board.
3. Get moving.Burning an extra 200 calories a day isn’t as difficult as it sounds. If you are sedentary or not as active as you’d like to be, try finding little ways to burn a few extra calories here or there. This could include taking the stairs instead of elevators, getting up from your desk and walking around the office more, or even forcing yourself to walk more by parking your car farther from the building. An inexpensive digital pedometer is a great way to track all of those extra calories burned, which can add up quickly over the course of the day.
4. Focus on reducing body fat levels, not just scale weight. You’ve probably heard it before, but scale weight alone is not a good indicator of body composition. It’s fine to use a scale to measure your progress, but use it in conjunction with inexpensive AccuMeasure body fat calipers, which will give you a much more accurate reading on whether you are losing body fat, versus muscle.

By getting a real sense of how many calories you need to eat each day to hit your weight loss goals, keeping track of what you eat, cleaning up your diet and adding some exercise in, it’s actually fairly easy to make ongoing progress at reducing body fat and improving your overall fitness levels … without resorting to fad diets or extreme calorie-restriction.

Have a Question for the Fitness Nerd? Want a Chance To Win Some Free Under Armour?

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Tags: Ask The Fitness Nerd, Basal Metabolic Rate, BMR, BMR Formula, Calculate Basal Metabolic Rate, Calculate BMR, Calorie Calculator, Calorie Counting, Calories, Fat Loss, Harris Benedict Formula, Harris-Benedict, How Many Calories Do I Need, How Many Calories To Lose Weight, How To Measure RMR, Resting Metabolic Rate, RMR, TDEE, Total Daily Energy Expenditure, Weight-Loss

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