What factor accounts for the greatest percent of the calories burned per day by humans?

Doing the Math With a BMR Calculator to Make Weight Loss Work for You

To lose a pound, you need to have a good idea of how many calories you burn (use for energy) on an average day. According to the U.S. Department of Health and Human Services, the average adult woman expends roughly 1,600 to 2,400 calories per day, and the average adult man uses 2,000 to 3,000 calories per day. (The average adult woman is 5 feet 4 inches tall and weighs 126 lbs, while the average man is 5 feet 10 inches tall and weighs 154 lbs.) Yet age, activity level, body size, and body composition all influence how many calories a person burns through each day.

To get a more accurate idea of your daily caloric requirements, you can turn to an online metabolic rate calculator. These determine basal metabolic rate (BMR), which refers to the number of calories that the body burns every day for energy just to maintain basic biological functions. It’s based on your height, weight, age, and biological sex, according to diabetes.co.uk. When multiplied by an activity factor (how much you move in a day), you get your daily metabolic rate, an estimate of how many calories you actually burn in 24 hours — and how many calories you need to eat every day just to keep your weight constant, says Sari Greaves, a registered dietitian nutritionist at LBS Nutrition in East Brunswick, New Jersey, and the author of Cooking Well Healthy Kids. Some BMR calculators allow you to enter your body fat versus lean mass, a percentage that accounts for a large amount of the variations between any two people’s basal metabolic rates. But using such a calculator, while more accurate than calculators that do not take into account your body fat versus lean mass will require that you have a tool like calipers (those fat pinchers your doctor may have used on you in the past) or a smart scale to estimate your body composition.

Once you know your current daily caloric requirement, you can create your own formula for losing weight. Simply put, as long as you are eating fewer calories than that number, or you increase your daily caloric burn with exercise, you will lose weight, explains Audra Wilson, RD, CSCS, a bariatric dietitian and strength and conditioning specialist at the Northwestern Medicine Metabolic Health and Surgical Weight Loss Center at Delnor Hospital in Geneva, Illinois.

For example, you might eat 500 fewer calories, work off 500 more calories through exercise, or do any combination of the two actions to achieve a deficit of 500 calories. For example, you might choose to eat 250 calories fewer than your daily caloric requirement and then do a workout that burns another 250 calories, she says.

In terms of the 3,500-calorie rule, that would mean that if you achieve that 500-calorie deficit at the end of each day, you would lose 1 lb of fat in seven days. Unfortunately, that equation tends to oversimplify — and overestimate losses, so don’t expect to lose that much that fast.

While the math is complicated, the Pennington Biomedical Research Center in Baton Rouge, Louisiana, one of the top nutrition research centers in the United States, has created a weight loss predictor to help you more closely estimate how much weight you would lose with a given daily calorie deficit. It uses mathematical models based on your age, height, weight, and biological sex, as well as the size of your daily caloric deficit. It also provides an estimate of how many calories you need to maintain your body weight (and likely are consuming right now).

RELATED: 9 Hard Truths About Weight Loss That Can Help You Slim Down

When It Comes to Losing Weight, Easy Does It

The size of your caloric deficit affects how fast you lose weight, with larger deficits leading to faster weight loss.

Yet experts typically agree that losing 2 lbs per week is the healthiest and most sustainable pace of weight loss, Wilson explains. If you are losing more than that in a given week, it is likely that you are significantly cutting into your lean muscle mass. By lowering your metabolic rate, this sets you up to eventually regain all of the weight you lost, and possibly then some. When losing more than a couple of pounds per week, you’re also at a higher risk of not having enough macronutrients (protein, carbohydrates, and fat) or vitamins and minerals in your diet, explains Greaves. That’s not because fast weight loss itself deprives the body of nutrients but because, when cutting calories to a point that such rapid weight loss is possible, overall food, and therefore nutrient intake, can be unhealthily low. A study published in January 2018 in Nutrients analyzed three commercial diet plans designed to result in rapid weight loss, and authors reported that participants experienced deficiencies in nutrients such as vitamin D, B vitamins, vitamin E, selenium, and zinc.

However, even with a conservative caloric deficit of a few hundred calories per day, if you are drastically cutting down on processed foods or carbohydrates, you may quickly lose water weight, Greaves says.

Factoring in Diet and Exercise to Shed Unwanted Pounds

Whatever your weight loss goal may be, losing 1 lb should ideally involve both diet and exercise. Pursuing one without the other is setting yourself up to regain the weight later on.

“Diet and exercise go hand in hand,” Wilson says. “Diet is more impactful for weight loss in the short term and exercise is more beneficial in the long term to maintain weight loss.”

Not to mention, most people find it easier to cut 500 calories from their diet than to burn 500 calories through exercise. But without exercise, a larger portion of any weight lost will be from lean muscle, meaning that as you lose weight, your body-fat percentage could actually decrease. In the long term, reduced levels of muscle lower your body’s metabolic rate, meaning that, over time, your body may actually gain fat, she explains.

One way to help keep yourself on target is to track your food using a journal or app. Many allow for you to keep tabs on both calories consumed and calories expended through exercise and everyday tasks, and according to a study published in May 2019 in JMIR mHealth and uHealth, that can be useful in the management of weight loss.

Again, unfortunately, it’s rare for calorie counters to get things perfect, and they typically overestimate energy expenditure, Wilson says. In fact, some research shows that women, on average, underestimate caloric intake by 25 percent.

And if you don’t weigh or measure every ingredient you eat (which can be a challenging undertaking), you can easily think you are in a large caloric deficit when you’re actually in a surplus, meaning you’re consuming more calories than you’re burning, thus effectively gaining weight, she says.

A study published in May 2017 in the Journal of Personalized Medicine, every fitness tracker studied incorrectly estimated caloric burn by at least 20 percent.

Greaves adds, “I don’t disregard the value of having a tracker. They can keep you accountable and reinforce healthy dietary choices. My advice, however, is to use these trackers as tools. Track for mindfulness, not for calorie counting.”

Small changes in your daily habits, designed to increase your activity and reduce your caloric intake to healthy levels for you, can lead to slow, steady, and lasting weight loss.

RELATED: Smart Health: I Tried Noom for Weight Loss — and It Worked

Diet and Exercise Tips That Help With Weight Loss

These diet and exercise tips can help you create the daily caloric deficit that will help you lose 1 lb:

Eat whole grains. They fill you up and take longer to digest than the simple carbohydrates contained in processed flour or white rice. Choose whole-grain bread, brown rice, and oatmeal. Whole grains also contain lots of healthy fiber, which may further aid weight loss, according to a wealth of research. According to the U.S. Department of Agriculture (USDA), a cup of brown rice offers 3.12 grams (g) of fiber, which provides 11 percent of the daily value of this nutrient.

Think before you drink. Sodas and fruit juices contain tons of calories and added sugar, which can contribute to weight gain and hurt your health in a variety of ways, according to the Harvard T.H. Chan School of Public Health. For example, the USDA notes that 8 ounces of fruit punch contains 110 calories and 26 g of sugar. Simply switching to water (plain or sparkling) can decrease your caloric intake almost effortlessly, she says.

RELATED: Thirsty? Try These 11 Refreshing Alternatives to Soda

Eat regular meals. “Skipping meals can cause dips in your blood sugar and make you more prone to overeating later on in the day,” Greaves says. Stick to three meals and one or two snacks per day. If you’re prone to forgetting or missing meals, set reminders in your phone for all meals and snacks.

Do regular strength training. Muscle at rest burns more calories than fat at rest. Increasing your muscle mass helps you lose weight more efficiently. The more muscle you have, the more calories you will burn, even at rest. What’s more, strength training will help ensure that you are losing the bulk of your weight from fat, rather than muscle, Foster explains. Yes, it’s possible to actively build lean muscle while still losing fat.

Break up your workout. Try to engage in at least 30 minutes of exercise a day, but current federal guidelines show that you don't have to do it all at once for weight loss benefits. For example, you could take a brisk 10-minute walk around the block in the morning, then do a 20-minute strength-training workout later in the day, Wilson says. This way, even the busiest of people can squeeze in calorie-burning activities. Top-rated app options for tracking activity include MyFitnessPal, Simple Workout Log, and FitNotes.

Now that you know what it takes to lose 1 lb of fat, your weight loss plan will be more effective and you’ll start building the motivation to lose more and more.

Additional reporting by Dennis Thompson Jr.

What burns the largest percentage of our calories?

What factors affect the number of calories you burn in a day?

What factors influence the number of calories a person burns at rest?

What determines the amount of calories you burn?