What Is a Calorie Deficit and How It Impacts Weight Loss

Craig Primack, MD, FACP, FAAP, FOMA

Reviewed by Craig Primack, MD, FACP, FAAP, FOMA

Written by Lauren Panoff

Published 04/06/2024

You’ve heard the saying “calories in versus calories out” when it comes to weight loss. This is referring to a calorie deficit. But what is a calorie deficit, exactly? Basically, you need to take in fewer calories than you burn to lose weight.

While it’s true that a caloric deficit helps drive weight loss, it’s not the most important thing. In fact, we recommend taking the spotlight off calorie counting and taking a more holistic approach.

We’re digging into what it means to create a calorie deficit to lose weight and other critical factors of healthy, sustainable weight management.

A calorie deficit essentially means eating fewer calories than your body burns. In more technical terms, it’s the state in which your energy intake is lower than energy expended.

A calorie deficit prompts your body to tap into stored energy reserves — primarily fat — to make up for the shortfall. This is what ultimately leads to weight loss. 

Creating a calorie deficit is a factor in most weight loss strategies, whether through changes in nutrition, increasing daily activity or a combination of both. There are healthy ways to approach it, but remember, it’s not everything.

Your body’s needs are going to be different from someone else’s. Learning how to calculate those needs with science can help you reach a point where you’re neither getting too much nor — more importantly — too little food.

Obsessing over low calorie intake not only makes weight loss — and eating, in general — a chore, but it can have lasting negative effects on mental health. Food should provide nutrition while bringing you joy!

We’d argue that it’s more important to have a general idea of your daily energy needs. And instead of counting calories, focus on mindful eating, making nutrient-dense choices, practicing portion control and listening to your body.

These skills — paired with exercise and other healthy lifestyle habits — work together for healthy weight management. Plus, you can keep using them in your everyday life even after reaching an initial weight loss goal. 

As for how to do a calorie deficit, around 500 to 750 calories below your estimated needs is typically recommended as a healthy calorie deficit for weight loss.

If you’re wondering, How many calories do I need a day?, you can use a formula that accounts for your basal metabolic rate (BMR) — your daily energy expenditure at rest — and your activity level.

There’s no shortage of online calculators for BMRI, but not all are created equal.

The Harris-Benedict equation is often used to estimate BMR based on gender, age, weight and height. Once you have your BMR, multiply it by an activity factor to determine your total daily energy expenditure (TDEE).

TDEE is the number of calories you need to maintain your current weight based on your activity level. From there, you can adjust your calorie intake to create a deficit for weight loss.

For instance, let’s say your BMR is 1,800. If you’re moderately active, your activity factor might be 1.2. Multiple 1,800 by 1.2 to get your TDEE, which would be 2,160. To create a 500-calorie deficit, you’d want to aim to eat 1,660 a day.

Is a calorie deficit healthy? It depends. A calorie deficit can be an effective tool for weight loss, but it’s not without its risks.

When considering how to go on a calorie deficit, consider the potential risks for:

  • Nutrient deficiencies. Eating fewer calories may lead to an inadequate intake of certain vitamins, minerals and protein.

  • Muscle loss. In severe or prolonged deficits, your body can start breaking down muscle tissue for energy, leading to a loss of lean muscle mass and reduced strength.

  • Decreased bone density. Inadequate calorie intake, along with low calcium and vitamin D intake, can increase the risk of bone fractures over time.

  • Reduced metabolism. Ongoing calorie deficits can slow down your energy burn. This can make losing weight more challenging. 

  • Fatigue and weakness. When you’re not eating enough calories to sustain your energy, you’re more likely to feel tired. This can impact your mental performance and ability to be active. 

  • Hormonal imbalances. Calorie deficits can disrupt hormones, especially those involved in metabolism, appetite and reproductive functions.

  • Impaired immune function. Inadequate calorie intake can weaken immunity, making you more likely to get sick.

  • Mental health effects. Ongoing calorie restriction could probably make anyone irritable. Not eating enough can lead to mood swings and increase stress.

  • Risk of disordered eating. Unsustainable calorie deficits could end up making someone overeat from hunger or cravings for restricted foods, leading to weight ups and downs and potential long-term mental health issues.

Risks of Eating Too Few Calories

Is a calorie deficit safe? It depends on the circumstances. There’s often a focus on how not to overeat calories, but not eating enough calories is also problematic — perhaps even more so.

Eating too few calories can pose risks to physical and mental health. Severely restricting calories can eventually lead to nutrient deficiencies and side effects like weakened immunity, fatigue, brain fog or trouble concentrating.

It can also result in muscle loss and a slowed metabolism, making it harder to maintain a healthy weight and reach your weight loss goals. Finally, extreme calorie restriction can contribute to an unhealthy relationship with food.

Sustainable weight loss goes far beyond only a calorie deficit. Rather than counting calories, we recommend prioritizing nutrient-density, mindfulness of portion sizes and the quality of the foods you’re eating.

Lean proteins, whole grains, fruits, vegetables, nuts and seeds are key in healthy meals and snacks.

Nutrition is a crucial component of healthy weight management that’s often overlooked when the focus becomes calories.

Besides nutrition, we suggest focusing on four factors for healthy weight loss: movement, hydration, sleep and potentially weight loss medication.

Movement

Exercise has countless benefits, such as improved mood and a lower risk of things like heart disease, type 2 diabetes and cancers. It’s important for weight loss because it helps create a calorie deficit by raising your energy expenditure.

Regular physical activity boosts metabolism so you continue to burn calories even after a workout. Exercise also helps preserve your lean muscle mass while you burn excess body fat.

Experts recommend a minimum of 150 minutes of moderate-intensity exercise or 75 minutes of vigorous-intensity aerobic exercise per week, plus resistance training at least twice a week for general health. For weight loss, this goes up to 200 to 300 minutes a week.

But these are just recommendations. It’s okay to start where you’re at and fit what you can into your schedule. All movement counts.

Find enjoyable ways to move your body that you can do long-term, like: 

  • Jogging with your dog

  • Walking around your neighborhood after dinner

  • Playing basketball or soccer with friends

  • Joining a group fitness class

  • Lifting dumbbells or using weight machines and resistance bands for strength training

Our blog covers how many steps a day you need to lose weight.

Hydration

Hydration is essential for wellness. It also supports bodily functions involved in metabolism, fat loss and digestion.  

Drinking water, especially before meals, can also help curb your appetite and prevent overeating. Stay hydrated during and after exercise to replenish fluid stores and support energy expenditure.

Keep a reusable water bottle with you to sip throughout the day. If you get bored of plain water, flavor it with lemon or cucumber slices or opt for unsweetened seltzer water or herbal teas sometimes.

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Sleep

Better sleep supports sustainable weight loss by regulating hunger and appetite hormones like leptin and ghrelin.

Adequate shut-eye helps restore energy levels for the next day’s activities. It also improves brain function and decision-making abilities. Also, sleep deprivation is associated with increased energy intake (i.e., eating more because your hunger hormones are out of whack).

Experts recommend adults get seven to nine hours of sleep nightly. To improve your sleep, try:

  • Creating a sleep-promoting environment in your bedroom, using things like comfy PJs, breathable bedding, blackout curtains, and white noise if needed

  • Avoiding technology close to bedtime, as the blue light emitted from screens disrupts melatonin production and can make it harder to doze off

  • Going to bed and waking up around the same time every day

See our blog on how sleep supports weight loss for more insight.

Weight Loss Medications

Combined with nutrition, exercise and other healthy lifestyle habits, weight loss medications can be a helpful tool. 

Some suppress appetite by targeting brain chemicals and reducing hunger. Others may increase calorie expenditure by boosting metabolism or limiting how much fat or carbs your body absorbs.

Some of the most effective weight loss medications include: 

  • Topiramate. Topiramate helps with weight loss by reducing appetite and increasing feelings of fullness. It might also affect certain brain chemicals involved in regulating food intake and metabolism, ultimately contributing to decreased calorie consumption.

  • Metformin. This medication is primarily prescribed to manage type 2 diabetes. By helping the body use insulin more effectively, metformin may decrease hunger and promote modest weight loss over time.

  • Contrave®. This is a combination of bupropion (an antidepressant) with naltrexone (a drug used for alcohol and opioid dependence). It reduces appetite and cravings by targeting reward centers in the brain.

  • Glucagon-like peptide-1 agonists. GLP-1 weight loss drugs mimic the action of GLP-1, a naturally occurring hormone that regulates appetite and glucose metabolism. They decrease appetite, slow digestion and increase satiety. Common examples include liraglutide (Victoza®) and semaglutide (Ozempic®).

Speak with your healthcare provider to see if weight loss medications might be a good option for you. To start exploring your custom medication kit, take our free online assessment.

We’ve rounded up some of the most commonly asked questions about calorie deficits.

How Many Calories Do You Naturally Burn in a Day?

The number of calories burned naturally in a day depends on factors like age, gender, weight and activity level. On average, an inactive adult may burn around 1,600 to 2,400 calories a day, while those with higher activity levels can burn more.

How Much of a Calorie Deficit Does a Person Need to Lose 1 Pound?

When it comes to how many calories to eat to lose weight, everyone is different. To lose one pound of body weight, you typically need to create a calorie deficit of roughly 3,500 calories. This can be achieved through reducing calorie intake, increasing physical activity or both.

Also, keep in mind the average calorie intake for men can be different from calorie intake for women. As noted, caloric intake by age can vary too.

How Much of a Calorie Deficit for Weight Loss Is Safe?

The safety of a calorie deficit for weight loss depends on things like your starting weight, overall health and unique nutritional needs. In general, a gradual calorie deficit of 500 to 750 calories a day is considered safe and sustainable for most people, leading to a weight loss of about one to two pounds a week.

Creating a calorie deficit is a factor in weight loss because, in order to lose weight, your body has to be taking in fewer calories than it’s burning. If you’re starting a weight loss journey and considering how a calorie deficit fits into it, keep these things in mind: 

  • Weight loss is more than just calories. We all have general calorie needs to lose weight — but this isn’t the only piece of the puzzle. The nutritional quality of your meals and snacks, exercise routine, sleep habits, hydration and mindfulness are also important. Rather than being laser-focused on calorie intake, we recommend a holistic approach for sustainable, safe weight loss that incorporates these other key components.

  • Getting too few calories also poses risks. There’s often a focus on eating more calories than we need. However, eating too few calories can be dangerous, posing numerous health risks. Not only can it prevent you from getting the nutrients you need, but it can also leave you fatigued and irritable — and eventually, it might alter your metabolism in a way that leads to a weight loss plateau. 

  • Don’t be afraid to ask for help. Weight loss is personal. We all have different needs, preferences and challenges. It can be overwhelming to come up with a weight loss plan on your own. Reach out to your healthcare provider for support, or meet with a registered dietitian who can help create a nutrition plan that works for you. 

Curious what a personalized weight loss plan might look like for you? Start by taking our free weight loss assessment.

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