Calorie Deficit – What is it, how much is safe, and how can you achieve it?

Key Takeaways

• A calorie is a measurement of the amount of energy found in food.

• To lose weight, you need to take in fewer calories than your body uses, which is known as a calorie deficit.

• An excessive calorie deficit leads to health complications like hair loss, infertility, mood swings, constipation, and feeling cold.

• The maximum safe calorie deficit is 500 calories per day.

• A calculator can give an estimate of how many calories you’re currently using each day, based on your height, weight, age, and sex, along with your current activity level. Subtract 500 to find the amount of calories needed daily for your calorie deficit diet.

• During your weight loss journey, your body’s calorie needs will change, as your weight and body composition change. Be flexible, and adapt your calorie consumption as needed.

• The support of a health coach can be very helpful in achieving a safe and effective calorie deficit. 

• In some cases, medications (such as GLP-1 RAs) are also helpful in achieving a calorie deficit.

What is a calorie?

A calorie is a measurement of the amount of energy found in food. In science, there are actually two different measurements that are both known as a calorie. The one that matters for health is the food calorie (also known as a kilocalorie), which is technically defined as the amount of energy needed to raise the temperature of 1kg of water by 1°C. This is the type of calorie that’s referred to when talking about food and body weight. (In chemistry, the definition of a calorie uses 1g of water instead of 1kg, but this is less useful for the purposes of measuring the energy used by human bodies.)

What is a calorie deficit?

Simply put, a calorie deficit occurs when you take in fewer calories than necessary to meet your body’s energy needs. This is known as a negative energy balance. To make up the difference, the body will rely on its energy reserves, such as fat tissue. This is how a sustained calorie deficit results in weight loss.

It’s important to recognize that your body needs energy for maintaining itself. If you have a moderate calorie deficit, your body is able to make up for this by using its energy reserves. However, if the calorie deficit is too large, then your body may not have enough energy to complete critical functions. The maximum safe calorie deficit is about 500 calories per day. 

Because 1kg of fat contains about 7000 calories of energy, a deficit of 500 calories per day will equate to losing about 0.5kg per week. This may seem slow, but it’s healthy and sustainable. Over time, if you stay consistent with this, you’ll achieve your weight loss goals.

In order to calculate your calorie deficit, you first need to know how many calories your body is using. You can then calculate how many calories you would need to consume each day to be in a 500-calorie deficit. Calories are used for your basal metabolic rate (BMR) in addition to any physical activity that you do. 

What is your basal metabolic rate?

Your basal metabolic rate, or BMR, is the amount of energy that your body burns at rest. It’s also referred to as the resting metabolic rate, or RMR. 

It actually takes a lot of energy simply to maintain a human body. Things like blood circulation, breathing, processing and transport of nutrients, tissue repair, immune system function, maintaining body temperature, and electrical activity of the nervous system all take quite a few calories. The energy to complete necessary functions like these is included in the BMR.

There are calculators online that can estimate your BMR, using data like your age, sex, height, and weight. However, it’s important to emphasize that individuals of the same size do vary in their BMR. Any calculator can only provide an estimate, not a precise calculation. 

To know for sure what your BMR is, you would need to measure it. This can be done using a method known as calorimetry. The most accurate method is known as direct calorimetry, but this is relatively expensive, and is generally only used as part of research studies. There is also a less expensive method called indirect calorimetry, which can be accessed at some health and fitness centers.

Keep in mind that your BMR can shift over time, as your weight changes and as you gain or lose muscle mass. After about the age of 60, it also declines a bit as a result of the aging process.

What are maintenance calories?

“Maintenance” refers to staying at the same weight. Maintenance calories refers to the amount of energy that you need to take in to stay at your current body weight.

To figure out how much you need to eat to have a 500-calorie deficit, the first step is to determine what your current maintenance calories are. You can use an online calculator to get an estimate of this. You then simply subtract 500 calories from that total, and that’s how many calories you’re aiming to eat each day during your weight loss journey.

You won’t need to stay in a calorie deficit forever. Eventually, after you achieve your goal weight, you’ll transition to consuming your maintenance calories. This will allow your body to stay at that goal weight. However, your maintenance calories at that time will be lower than your initial maintenance calories were. When you’re at your goal weight, you can calculate your maintenance calories again and use that as your daily target for the long term.

Calculating your exact maintenance calories can be challenging. Keep in mind that your maintenance calories will need to account for your basal metabolic rate as well as any physical activity that you do. It’s very challenging to determine exactly how many calories your body is using – and, of course, this can change from day to day. 

The best way to know what your current maintenance calories are is to keep track of everything you eat for two weeks before you start trying to lose weight. Do your best to eat as you normally do, but track it all closely. You can then calculate how many calories you’ve been eating on a daily basis, which will give you your current maintenance calories based on your current weight. Keep track of your physical activity too, so you know what your baseline activity level is. 

Ultimately, the best measure of whether you’re in a calorie deficit is whether you’re losing weight. Throughout your weight loss journey and even after it (in the maintenance phase), you’ll need to monitor your weight regularly, so you can adjust your caloric intake accordingly.

The idea of “calories in, calories out”

For many years, the model of weight loss has been very simple: “calories in, calories out.” Sometimes abbreviated as CICO, this is the concept that all you need to do to lose weight is to eat fewer calories than your body uses. Eat less, exercise more.

On one level, it’s impossible to argue with this model. Everyone who loses weight does so by consuming fewer calories than they expend. However, things are not nearly as simple as CICO makes them sound. Both sides of this equation are more complicated than they seem.

First, let’s think about calories in. The control of appetite is complex, and is regulated by many different hormones. When you start losing weight, your body responds by increasing your appetite, so that you feel hungrier. Adaptations like this can make it more challenging to achieve weight loss.

Beyond this, it’s not how many calories you put into your mouth that actually matters – it’s how many calories your body absorbs. Not everything we eat actually makes its way out of our digestive tract and into our body. Many factors can influence your absorption of calories, from cooking methods to stress levels to the balance of bacteria in your gut. 

Now, let’s think about calories out. Your body can adjust its expenditure of energy – in fact, it normally does this every day. When you’re eating less, your body will try to conserve energy and use less calories. This is sometimes known as having a “slower metabolism.”

The reduction in energy usage can show up in subtle ways. For example, people who are in a calorie deficit have been found to fidget less often. They make fewer of the little movements that most people make throughout the day without even thinking about them. Although each movement may seem too tiny to matter, less fidgeting actually adds up to significantly less calories used overall. People who are trying to lose weight may not even notice that they’re fidgeting significantly less than they used to.

Many other factors also play a role. For example, hormone levels play a role in controlling both appetite and the body’s use of energy. When women’s estrogen levels drop during and after menopause, this can lead to weight gain.

Body weight is also known to be influenced by genetics. Research has found that between 40 and 70% of a person’s tendency to be overweight or obese is controlled by genetics. Because of this, some people have a more difficult time staying at a healthy body weight than others do. Many different factors involved in controlling body weight may be working against them.

All of this means that, although the CICO model is ultimately accurate, it’s not simple at all. A lot of factors – beyond a person’s willpower – can influence both sides of this equation. Still, this doesn’t mean that achieving weight loss through reducing caloric intake and increasing caloric expenditure isn’t possible. People certainly do achieve lasting weight loss in this way. It’s important to understand the challenges, so you can be prepared to overcome them.

How can you safely plan a calorie deficit diet?

In general, it’s considered safe to have a calorie deficit of up to 500 calories per day. Reducing calories by more than this can impair the body’s ability to perform critical maintenance tasks, and is considered to be unsafe. If you reduce calories by too much, then you may experience symptoms like:

• Hair loss

• Infertility

• Mood swings

• Constipation

• Feeling cold all the time

If you start to experience these issues, then your calorie deficit may be too large. Consider increasing your food intake just a bit, to address the problem.

Get enough essential nutrients

It’s also important to keep in mind that calories aren’t the only thing you need from your food. As you reduce calories, it’s crucial to ensure that you’re still getting enough of the essential nutrients that your body needs. These include vitamins, minerals, protein, and healthy fats. When you’re eating less food overall, you’ll need to focus more on ensuring that you get enough of these nutrients.

Eat enough protein

Protein is one crucial nutrient. Our bodies use muscle tissue as a store of both energy and protein. When the body needs to dip into its energy reserves, it will take that energy from both fat and muscle. If you’re not eating enough protein, then your body will need to break down muscle to get it. Unfortunately, as you lose muscle, your BMR will also decrease, which can cause you to hit a weight loss plateau.

To combat this, you need to make sure that you’re eating enough protein. People who eat less than the recommended amount of protein have been shown to lose more muscle mass as they lose weight. Your body’s protein needs don’t change when you reduce your caloric intake – you still need the same amount of protein, even though you’re eating fewer calories. You’ll need to focus on including protein-rich foods, to make sure that you’re still getting enough protein.

Get enough vitamins and minerals

It’s also important to make sure that you’re getting enough vitamins and minerals. Your body’s need for these also doesn’t change when you’re eating fewer calories. In general, eating a balanced diet that contains plenty of fruits, vegetables, and whole grains will provide you with the vitamins and minerals that you need. In general, these foods are low in calories but high in nutrients, and should make up a significant portion of what you eat while you’re trying to lose weight. Some people choose to take a multivitamin to help ensure that they’re getting the micronutrients that they need.

There are various approaches that you can take to reducing calories. Some options include:

• Intermittent fasting. This involves reducing the window of time during which you eat. Commonly, people use an 8-hour window, but it can be a little longer or shorter depending on your needs. During the eating window, you should still focus on eating healthy, lower-calorie foods, but you can eat relatively normal-sized meals, because you’ve skipped at least one meal on this plan.

• Quitting snacking. It’s very common for people to eat between meals. Often, they’re not even snacking because they’re hungry, but rather for emotional reasons (such as feeling stressed or bored). Quitting snacking, and finding alternative ways to deal with these emotions, may be enough to reduce your food intake by 500 calories – as long as the size of your meals doesn’t increase to make up for it.

• Quitting sugary beverages. Many people consume several sugary beverages (such as soda or sweetened coffee or tea) throughout the day. Simply replacing these with herbal tea, flavored water, or unsweetened coffee or tea may be enough to reduce overall intake by 500 calories. It only takes about 3 cans of soda to reach 500 calories.

• Reducing the size of each meal. This can be challenging, because most people aren’t used to paying attention to exactly how much we’re eating. By tracking your food intake before your weight loss journey begins, and then paying close attention to what you eat at each meal, you can reduce the size of your meals in order to be in a 500-calorie deficit. For example, by eating less bread or rice with each meal, you could reduce your intake by 500 calories over the course of each day.

While some people choose to count calories in order to reduce intake, others choose to use weight loss medications known as GLP-1 RAs to help them achieve this. By reducing hunger and keeping you full for longer after meals, these medications make it easier for many people to achieve the calorie deficit needed for safe and sustainable weight loss.

Calorie deficit calculator

Clients in our NOVI Optimum and Optimum Plus weight loss programs frequently ask for help in determining the number of calories they need to consume to be in a 500-calorie deficit. To help with this, we developed a simple online calculator. This will give you an estimate of your maintenance calories, as well as the number of calories you need to eat to be in a 500-calorie deficit.

Always keep in mind that the calorie numbers provided by any online tool are only an estimate. Although this estimate is based on the best scientific research, there is still individual variation that an online tool simply can’t measure. In addition, a person’s caloric needs change as their weight changes, so your target won’t necessarily remain the same through your entire weight loss journey. The target provided by the calculator is a good place to start, but you might need to adjust your caloric intake a bit up or down.

The importance of exercise

If you’re trying to lose weight, it’s best to pay attention to both sides of the CICO equation. Watch what you’re eating, so you don’t consume too many calories. At the same time, start exercising more. Neither one of these is a substitute for the other. Instead, they work together to help support a healthy body weight.

Of course, physical activity takes energy, so your body uses more calories while you’re exercising. However, after you’re finished exercising, your body’s energy usage remains increased for more than 12 hours. Ensuring that you get exercise every day will significantly increase your body’s use of energy.

It’s also a good idea to do some strength training. Muscle tissue burns a lot of calories, even at rest. The more muscle tissue you have, the more calories your body will use. In addition, strength training has been shown to help combat the loss of muscle tissue as you lose weight. 

As you begin to lose weight, your body will compensate by trying to conserve energy. This is one reason why people may hit a weight loss plateau. They go into a calorie deficit and lose weight, but then their body slows down its use of energy, and now that calorie deficit has turned into maintenance calories. It can be frustrating. Exercise can help to keep your body’s use of energy up, so that you’re less likely to run into this problem.

How you will feel when going through a calorie deficit

When you’re in a calorie deficit, you’ll likely have some feeling of hunger, at least at first. When you’re consuming less energy than your body is using, then your body responds by sending hunger signals. The hunger shouldn’t be severe – if it is, then you might be in too large of a calorie deficit. However, the mild hunger is enough to bother some people. Over time, as you get used to eating less, you’ll likely feel less hungry. Many people find that their hunger adjusts, and they no longer feel any extra hunger on a calorie deficit compared with how they used to feel when eating significantly more food.

You might also feel a bit low on energy when you’re in a calorie deficit. This is related to your body attempting to conserve energy, since you’re not taking in as much. Although you may feel like you just want to sit on the couch, you’ll actually feel much better if you do some exercise. In fact, research has shown that exercise reduces fatigue and increases feelings of energy and vitality. This can help you to keep your energy levels up, while also assisting with weight loss.

If you feel extremely hungry, or if you’re experiencing symptoms like trouble concentrating, headaches, or trouble sleeping, then you might be in too much of a calorie deficit. A deficit of about 500 calories per day should not cause severe symptoms like these. You might need to add back a little more food, so that you feel more comfortable. This will help to ensure that your weight loss is healthy and sustainable.

Support in creating a calorie deficit diet

Creating a 500-calorie deficit is not complicated, but that doesn’t mean it’s easy. In addition, because of the adaptations that your body undergoes as you lose weight, you may need to adjust your plan as you go. It can be very helpful to have support from a health coach. This professional can help you to create a weight loss plan that will work well for your lifestyle and preferences, including a healthy diet and exercise. They’ll also help you to stick with it and stay consistent, so that you get the results you’re hoping for. 

If you’d like to try using a GLP-1 RA to help you achieve a calorie deficit, you’ll need a doctor’s prescription for this. Our physicians, who are experts in treating diabetes and obesity, can evaluate you for these medications, and prescribe them if appropriate. These medications have been shown in studies to be safe and effective for weight loss when used in appropriately selected patients.