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Calorie Deficit: What To Know

Consuming fewer calories than your body burns is a ‘calorie deficit’ that can lead to weight loss

Plate of chicken, vegetables and grain

Does the word “diet” make you wince? You’re not alone. Many popular diets come with all kinds of rules — some of them nearly impossible to follow perfectly. You may lose some weight initially, but often, the lost pounds (and then some) creep back later.


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Losing weight essentially comes down to one thing: By burning more calories than you’re eating, a math solution called a calorie deficit.

You can create a calorie deficit by reducing your calorie intake or combining fewer calories with more exercise. But even with that, you could still have a hard time losing weight. (It’s never easy, right?)

To demystify the process and explain possible risks, we turn to registered dietitian Beth Czerwony, RD.

What is a calorie deficit?

A calorie deficit simply means you’re eating fewer calories than you’re burning. People use calorie deficit to lose weight and maintain weight loss.

“If you want to lose weight with a calorie deficit, I suggest tracking what you’re currently eating before making any changes,” says Czerwony. “It’s good to understand your starting point.”

Use a food diary app to record what you eat and how many calories you consume over a week or two. (An app is a very convenient way to track eating habits.) Then, you can use a calorie deficit calculator to figure out your daily calorie target to meet your goal.

How to calculate calorie deficit

First, you need to know your daily calorie requirement. Czerwony prefers the Mifflin-Saint Jeor formula for calculating your daily calorie needs.

“There are other tools, but the Mifflin-Saint Jeor formula considers your height, weight, sex, age and activity level — which makes it less generic than other calorie calculators,” notes Czerwony.

Once you know your daily calorie requirement, subtract your calorie deficit goal from that number. For example, if your daily calorie need is 1,800 calories and you want a 500-calorie deficit, your new daily calorie target is 1,300 calories (1,800 – 500 = 1,300).

Or you can find a calorie deficit calculator online that does both of these steps together.

What is a safe calorie deficit?

A daily 500-calorie deficit should allow you to lose about a pound a week — and possibly even a bit more, says Czerwony. “Eating 500 fewer calories per day is a good place to start,” she adds.

She says another option is to do a smaller calorie deficit — 200 or 300 calories a day — combined with increasing your daily exercise.

Losing one pound a week may not sound like a lot, but slower weight loss is more likely to stick in the long term. And it’s easier for your body to adjust to a smaller calorie deficit than a larger one.

If you start with too big of a calorie deficit, you’re likely to have some unpleasant side effects, such as:

Even with a 500-calorie deficit, it can take your body time to adjust. You may not lose any weight for the first week or two.

“If you do lose weight in the first week, you’re probably dropping water weight,” explains Czerwony. “This is usually due to cutting some of the junkier carbs and salt from your diet.” After that, the fat loss begins.


What are the dangers of calorie deficit?

If you have any existing health conditions, a calorie deficit can potentially cause problems. “You can harm yourself with a calorie-deficit diet,” warns Czerwony. Here’s what to know if you have:

  • Type 2 diabetes: Beware of your blood sugar dipping too low while on a calorie deficit.
  • Kidney problems: Water fluctuations while reducing your calorie intake may strain your kidneys.
  • High or low blood pressure: Changes in your hydration and water intake can affect your blood pressure.

It’s best to talk to your healthcare provider before starting a calorie-deficit diet. If they clear you to follow this eating plan, make sure not to fall into two common traps: eating too little protein and cutting too many calories.

Don’t cut too much protein (it’s bad for your muscles)

Cutting too much protein from your diet can make it difficult for your body to maintain muscle. And if you cut back too drastically on your food intake, especially protein, your body will break down muscle for fuel. “Your body does this first before turning to fat for fuel,” says Czerwony.

Muscle mass plays an important role in keeping your metabolism powered up, so losing muscle is doubly bad if you’re trying to lose weight. Your metabolism helps your body process food into energy. A slow metabolism burns calories slower, which means calories get stored as fat.

“You have to go into calorie deficit just enough to get your body to use fat stores but not go into starvation mode where you start burning muscle mass,” states Czerwony.

Keeping the protein and dropping the sugary carbs can help you hit this sweet spot.

People often ask if you can still build muscle while in a calorie deficit. The answer? Yes, you can build muscle mass on the diet.

But you need to protein-rich foods and the right amount of calories to give you the energy to exercise and to keep your body from burning muscle. A dietitian can help you find the right balance of foods.


Don’t cut too many calories (it leads to the dreaded yo-yo)

If you jump into a big calorie deficit right off the bat, you run the risk of bouncing back and forth between undereating and overeating.

“You might start out fine on a large calorie deficit,” says Czerwony. “But at some point, you may get overly hungry and eat too much. Then you overcompensate and restrict your food intake. Then you overeat again, and you end up yo-yoing.”

Over time, so-called yo-yo dieting may actually lead to more weight gain. It’s better to cut out a smaller amount of calories at first so you don’t get too hungry.

Why aren’t you losing weight on a calorie deficit?

It seems logical that if you’re eating fewer calories than you’re burning, you should lose weight easily. But several factors might be preventing your weight loss, says Czerwony.

These factors impact your metabolism, and include:

  • Medications: Many medications either promote weight gain or make it difficult to lose pounds. Examples include some hormonal birth control medicines, antidepressants, anti-psychotics and insulin for diabetes.
  • Poor sleep: If you’re not sleeping well, your cortisol levels are probably not optimal, affecting your metabolism.
  • Stress: Like poor sleep, prolonged stress can also mess with your cortisol levels.
  • Menopause: Hormonal changes can throw off your body chemistry, affecting metabolism.
  • Underlying conditions: Conditions such as polycystic ovary syndrome (PCOS) and metabolic syndrome impact metabolism and make it difficult to lose weight. Even sleep apnea, which contributes to poor sleep, can affect your ability to drop excess weight.
  • Too few calories: It may seem strange, but eating too little can sometimes make it hard to lose weight. A very low-calorie diet can actually slow down your metabolism.


So, what can you do if a calorie deficit doesn’t seem to be working? Don’t despair — and do seek expert help.

“It’s so discouraging when you’re doing everything right with diet and exercise and you still can’t lose weight,” recognizes Czerwony. “If that’s what’s happening, it’s time to work with your healthcare provider to peel back the layers of the onion. These situations can be complex.”

She says it’s good to start with some basic blood tests, especially if it’s been a couple of years or more since you’ve had them. And if medications are getting in the way of your weight loss, your healthcare provider can talk to you about possible alternatives to try.

Tips for losing weight while your body is in a calorie deficit

Czerwony offers these tips for weight loss success on a calorie deficit:

  • Stay hydrated: Sometimes, what feels like hunger is actually your body signaling thirst. Drinking plenty of water also helps your body adjust to fewer calories.
  • Get enough protein: Eating enough protein helps you feel fuller and stay active to retain muscle mass. Muscle keeps your metabolism firing.
  • Eat your fruits and veggies: Czerwony recommends five servings of fruits and vegetables per day. The bulk and water in these foods make you feel full, and the chewing also leads you to eat more slowly and feel more satiated.
  • Take a multivitamin: At the beginning of a calorie-deficit diet, a multivitamin can fill in any nutrition gaps as you’re easing into a new way of eating. Talk to your provider about the multivitamin that’s right for you.

Czerwony also cautions that if you go back to eating as you did before, you’ll likely gain back any weight you lost. So, work with a dietitian who can help you plan a safe and effective calorie-deficit diet and guide you in the maintenance phase after weight loss.

“You can do it on your own, of course,” she says, “but a registered dietitian will get you on track from the start and show you how to avoid going back to old habits.”


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