Calculating Your Calorie Deficit Is A Key To Lasting Weight Loss

Korin Miller
·7 min read
Photo credit: d3sign - Getty Images
Photo credit: d3sign - Getty Images

From Women's Health

Once you decide you want to lose weight, it can be tricky to know what to do next. (Should you try keto or the DASH diet, for instance?) But no matter what kind of eating plan you follow, there’s one rule of weight loss that’s clutch: You have to create a calorie deficit, or when you expend more calories than you take in. Without it, you’re unlikely to lose weight.

It sounds super simple, right? Well, there’s some detective work involved at first to figure out how many calories your body needs, followed by a little math to calculate what you need to take in to be in a deficit. And then, of course, you’ve got to figure out what that actually looks like in the food department to help you reach your goals.

Of course, you’re not born knowing about calorie deficits, how to figure out yours, and what you need to do to put all this in action. Don't get overwhelmed, though: There are plenty of ways to approach this. Here’s everything you need to know.

First, what is a calorie deficit?

Some basics: A calorie is a measurement of energy. The calories in food supply your body with the energy you need to survive. When you eat food, it’s broken down by your body to release that energy to be used right away or stored for later, depending on what you need at that moment.

Your body needs to take in a certain number of calories to maintain your weight, says Keri Gans, RD, author of The Small Change Diet. And, so, “a calorie deficit is when you consume fewer calories than your body requires to stay at its current weight,” she explains. If you take in fewer calories than your body needs, your body will turn to the calories you have stored up to burn for energy. As a result, you’ll lose weight.

Every person’s caloric needs and deficits are different and depend on a bunch of factors, like how much you exercise, your genes, your hormones, and your metabolism, says Sonya Angelone, RD, a spokeswoman for the Academy of Nutrition and Dietetics.

How much of a calorie deficit do you need to lose weight?

It can be a little complicated to figure out your exact calorie deficit but, in general, it’s thought that shaving 500 calories from your daily intake should lead to one pound of weight loss per week.

“The classic definition is based on the fact that one pound of fat contains 3,500 calories,” Angelone says. “If you eat 500 calories less than the amount you need to maintain your weight, you will lose one pound in a week.” If you want to lose two pounds a week, you might try a 1,000-calorie daily deficit. You just typically don’t want to cut any more calories than that. “Healthy weight loss is considered one to two pounds per week,” Gans notes.

You don’t necessarily have to drop 500 calories a day from your diet to lose weight, though. “Any deficit will lead to weight loss,” Angelone says. “It will just take more time or less time, depending how great the deficit.”

Creating a calorie deficit isn't a perfect science, though. Your metabolism’s speed is a factor, along with the type of calories you take in, Angelone says. (Some nutrients, like sugar, are used up more easily and quickly than those with fiber, she explains.) Your body also compensates for short-term calorie changes, temporarily raising your metabolism if you eat more for a few days, and lowering it if you eat less.

How do I figure out my calorie deficit for weight loss?

There are a lot of different ways to figure out your calorie deficit, and some are more accurate than others. There are different ways of calculating calorie needs, but Angelone says she usually uses the Harris-Benedict Equation, Mifflin-St Jeor Equation, or Katch-McArdle Formula with clients. Here’s how to figure out your deficit in a few different situations.

With your doctor or nutritionist

Every practitioner has a slightly different approach. Angelone will take calculations based on body measurements like weight and height, along with exercise level. And Gans prefers a more low-key approach. “I try to leave math out of the equation and instead focus with my patient on making small changes that can naturally lead to weight loss,” she says.

But some practitioners may even send you for metabolic testing, which measures how many calories you burn at rest (like when you’re sitting around), to try to get an accurate number.

With a formula

There are several formulas out there to help you calculate your calorie needs, but a study published by the Journal of the Academy of Nutrition and Dietetics found that the Mifflin-St. Jeor equation is very accurate. That equation calculates your basal metabolic rate (BMR), which is the minimum number of calories your body burns at rest.

For women, the Mifflin-St. Jeor equation is: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161.

So, the BMR equation for, a 25-year-old woman who is 5'4" and weighs 150 pounds would be this: BMR= (10 x 68) + (6.25 x163) - (5 x 25) -161 = 1,413 calories

The Harris Benedict equation is often used for comparison. That equation is: BMR = 655.1 + (9.563 x weight in kg ) + (1.850 x height in cm) - ( 4.676 x age in years).

For the same 150-pound woman, the BMR using the Harris Benedict equation would be: BMR= 655.1 + (9.563 x 68) + (1.850 x 163) - ( 4.676 x 25) = 1,490 calories

The results are slightly different depending on which formula you use. And, Angelone stresses, “this is still an estimate, since so many factors affect weight loss.”

With an online calculator

Don’t feel like doing the math? There are plenty of online calculators that can help. The National Institute of Health’s Body Weight Planner is a good one to try, Angelone says. It looks at your current weight and fitness level, along with your weight loss goals, and helps map out how many calories you need to take in to lose the weight over the period of time you specify. A nice perk: It also tells you how many calories to aim for once you reach your goal weight to help maintain it.

Okay, so now how do I actually achieve this calorie deficit?

There are a few different ways you can go about creating a calorie deficit and, ideally, you’d factor in a combo of all of these changes:

  • Do more strength training. Exercise in general can help burn more calories, but strength training helps to boost your body’s energy needs, increasing how many calories you burn at rest, Angelone says. Muscles “require calories or energy 24/7, so if you have more lean muscle mass, you will need more calories to maintain weight. Thus, you won’t have to cut back on foods as much to create a deficit,” she says.

  • Reduce your carb intake. Your body converts most carbohydrates in your body to sugar, and those calories are always absorbed or stored in your body for later use, Angelone says. Cutting back on your carbs means your body will store less away for the future.

  • Add more protein, fiber, and healthy fat to your diet. “Build your meals with high-fiber foods, such as fruits and veggies, so you are still satisfied even though your entree size may be smaller than you are used to,” Gans says. Adding more fiber, protein, and healthy fat to your meals will “help you stay satisfied longer and help you eat less,” Angelone adds.

  • Stop eating after dinner. Angelone says this is usually “the best way” to get a deficit. “Most people have met their calorie needs by then, so eating after dinner or before bed just adds extra calories,” she says.

  • Keep a food journal. Yeah, you’ve heard it before, but it actually works. Writing down what you eat on a regular basis can be eye-opening, and can also help you plan where you can cut back. “Just monitor the amount eaten,” Angelone says. “Decrease it slightly from there to avoid getting too hungry, then overeating later.”

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