How Does Weight Loss Work?

Food, exercise, sleep, hydration. So much goes into weight loss.

But how does weight loss work, exactly? In the simplest sense, weight loss happens when you consume fewer calories than your body burns. Your body then turns to stored fat as a source of energy. 

But it’s not quite as straightforward as that. Factors like genetics, metabolism, and set-point weight can affect how weight loss works for you personally. 

Below, we’ll explain the ins and outs of weight loss and how to lose weight in a healthy way.

Weight loss works when you consume fewer calories than your body burns — this is known as a calorie deficit. If your body doesn’t get the calories it needs from food, it’ll start breaking down stored body fat as a source of energy. 

If you stay in a calorie deficit, your body will keep turning to fat for fuel, leading to weight loss. 

What happens to fat during weight loss? Research shows that fat molecules are broken down into water and carbon dioxide. Water leaves your body in bodily fluids — like sweat and urine — and carbon dioxide leaves your body when you exhale.

To consume fewer calories than your body burns, you can: 

• Reduce how many calories you eat by reaching for foods lower in calories or eating healthy portion sizes

• Increase how many calories you burn by doing more exercise and general movement and changing your body composition

These changes can help tip the balance toward being in a calorie deficit to promote weight loss.

You don’t necessarily need to count calories to lose weight. But, if you’re looking for a general guideline, experts recommend consuming 500 fewer calories than you burn each day. This can lead to about one pound of weight loss a week. 

Calories in versus calories out — sounds like a simple math problem, right? But many factors go into weight loss beyond this. 

Your metabolism is all the reactions in your cells that provide your body with energy. This energy is needed for growth, recovery, and other basic functions that keep your body running.

Your rate of energy expenditure at rest is known as your basal metabolic rate (BMR). In simpler terms, this is the number of calories your body needs to just survive and perform basic tasks — like breathing, digesting, and pumping blood around your body.

The higher your BMR, the more calories your body burns while at rest on a daily basis. That’s before you take into account any added physical movement, so having a higher BMR makes it easier to lose and maintain weight. 

BMR is determined by factors like: 

• Age

• Sex

• Genetics

• Body composition — the higher your muscle mass, the higher your BMR 

When you lose weight, you might find your metabolism slows down. This means your body burns fewer calories, making it harder to stay in a calorie deficit.

Weight loss isn’t just about how much you eat and how much you exercise. Genetics play a role in many factors of a person’s weight.

For example, there’s some research suggesting that genetics may affect how much weight you lose over time.

Yet more research shows genetics might impact both the development of obesity to begin with and where your body stores fat — this one may be especially true for women.

So, the genes you inherited from Mom and Dad could affect how much weight you gain and lose and what weight loss looks like for you.

Set-point theory is the idea that your body has a set weight range it wants to stay within.

If you try to lose weight, your body may make changes to fight weight loss to stay near its set weight. Or, if you’ve already lost weight, you might regain it over time and end up back at your previous body weight. 

What kind of changes are we talking about? Well, there’s a lot going on. For instance, when you lose weight, your body might trigger a shift in satiety hormones — hormones that help you feel full. This could increase your appetite. At the same time, your metabolism may slow down. 

These changes mean you might consume more calories and burn fewer calories, leading to weight gain and your body eventually getting back to its desired set-point weight.

On the flip side, if you eat more calories than you burn, your body may make changes to your appetite and metabolism to stop you from gaining too much weight above your set-point range. These changes aren’t as strong as those preventing weight loss, though. 

Don’t let this dishearten you. Bariatric surgery, weight loss medications, and losing weight slowly and steadily may help lower your body’s set-point weight — so you can keep off the weight you lose.

Your body might be sabotaging your weight loss efforts, and you may just need an extra helping hand on your weight loss journey.

Set-point theory is just that: a theory. But it can help partially explain why weight loss is so tricky and why many people regain the weight they’ve lost — and how that’s nothing to be ashamed of.

Many things about weight loss might be out of your control — like genetics or your set-point weight. But the good news is there are many things you can control to achieve healthy weight loss.

Here’s how to start losing weight in a safe and sustainable way. 

1. Eat Nutritious Foods

Eating nutritious foods can help you consume fewer calories than your body burns. It takes a while to burn calories, so reducing your calorie intake is a key step for weight loss.

Opt for: 

• Fruits

• Vegetables 

• Whole grains like oatmeal, brown rice, and whole-wheat bread 

• Lean protein like chicken, fish, eggs, and tofu 

• Legumes like chickpeas, lentils, and beans 

• Healthy fats like avocados, olive oil, nuts, and seeds 

Try incorporating more of these foods into your main meals and snacks. 

How much you eat is also key for weight loss. Check out our guide to healthy portion control to learn more.

2. Do More Movement 

Doing more movement can increase how many calories your body burns each day, helping you stay in a calorie deficit. 

Guidelines from the DHS (U.S. Department of Health and Human Services) say you should aim for: 

• At least two hours and 30 minutes to five hours of moderate-intensity aerobic exercise a week. This could include activities like brisk walking, jogging, cycling, or swimming.

• Or at least 75 minutes to two hours and 30 minutes of vigorous-intensity aerobic activity. You can do this instead of moderate-intensity exercise to save time. This could include sprints, CrossFit, or another kind of high-intensity interval training (HIIT). You can also aim for a combination of the two. 

• At least two strength training sessions a week. These should focus on all major musical groups.

These are the recommendations for all adults. For those looking to lose weight, engaging in physical activity that goes beyond these guidelines can burn more calories.

Beyond structured exercise, think about how much general movement you do each day. Increasing the amount of movement you do can also help you increase how many calories you burn.

You can try: 

• Incorporating a walk into your morning routine  

• Playing catch with your kids or fetch with your pet 

• Standing while taking phone calls or meetings 

• Taking the stairs over the elevator 

• Doing physical household chores like gardening 

• Walking or cycling to work — or part of the way 

Need some inspiration? We created a workout weight loss plan for women.  

3. Drink More Water

Drinking water can help you stay hydrated, which helps keep your skin, digestion, joints, brain, and just about everything else in your body healthy. 

But drinking more water can also help you lose weight. 

A 2022 review of studies found that “preloading water” — when you drink water before meals — can promote weight loss. Specifically, drinking roughly 17 ounces of water before eating a meal can improve weight loss by two to five pounds over three months.

Drinking water before meals can help you feel fuller, meaning you may naturally consume fewer calories. 

On top of this, some research suggests that water may promote lipolysis, the breakdown of fat for fuel. And it can help exercise feel easier, meaning you’re more likely to work out and burn more calories. 

Check out our guide to drinking water for weight loss to learn more. 

4. Get Enough Sleep 

Getting enough sleep can make lots of things in life easier — and weight loss is no exception.

Research suggests that when you don’t get enough shut-eye, the hunger hormones ghrelin and leptin may be thrown out of whack. This can lead to an increased appetite and consuming more calories.

A small study from 2015 found that not getting enough sleep at night led to a decrease in resting metabolic rate. This would reduce how many calories your body burns, making it harder to lose weight or maybe even maintain a healthy weight. 

Plus, when you’re sleep-deprived, you probably won’t have the energy or motivation to hit the gym or make a healthy meal. 

According to the Centers for Disease Control and Prevention (CDC), adults need seven to nine hours of sleep a night.

5. Consider Weight Loss Medication 

Weight loss medications can play a positive role in your weight loss journey, if appropriate for you. They can suppress your appetite, curb food cravings, and give you time to adjust to new diet and exercise routines to support long-term weight management.

Medications come in the form of injections or pills. 

Injections for weight management (which are sometimes prescribed off-label for reasons other than their FDA-approved purpose) include: 

• Semaglutide (Ozempic®, Wegovy®, and compounded semaglutide) 

• Tirzepatide (Mounjaro®, Zepbound®, and compounded tirzepatide) 

• Liraglutide (Saxenda® and Victoza®, and compounded liraglutide) 

Pills that may be taken for weight loss (some of which are also prescribed off-label) include: 

• Semaglutide (Rybelsus®) 

• Metformin 

• Orlistat (Xenical®)  

• Naltrexone-bupropion (Contrave®)

• Phentermine-topiramate (Qsymia®)

• Topiramate (Topamax®)  

Weight loss medications are typically used alongside changes to your eating habits and exercise routine to help you lose weight. 

There are many weight loss medications available. A healthcare provider can talk you through the pros, cons, and side effects of each and which ones could be suitable for you. 

To get you started, we’ve compared Ozempic vs. Wegovy for weight loss. 

6. Reach Out for Support 

If you’re looking to lose weight, you don’t need to go it alone. Losing weight can be tricky, and it can sometimes take a toll on your mental health. 

Reaching out for support can help you reach your goals — and feel your best along the way.

Friends, family, a therapist, a dietitian, or other health professionals can make up your support system. You can also consider joining a dedicated weight loss program. 

Research shows that group interventions — like joining a group weight loss program — can help you lose more weight compared to going solo. And yet more research shows that online health interventions can be more effective than no interventions.

If you’re looking for an online holistic weight loss program, we offer access to personalized plans that include weight loss medication, realistic eating plans, behavioral change tools, and expert guidance.

In its most stripped-down version, weight loss is all about calories in versus calories out. But there are so many more things at play, making losing weight not as straightforward as it seems. 

How does weight loss work? Here are the key facts: 

• To lose weight, you need to eat fewer calories than you burn. This is the simple equation at the core of weight loss. You can reduce your calorie intake by eating foods lower in calories and increase your calorie output by doing more physical activity and changing your body composition.

• Many factors affect weight beyond calories. Genetics, a slowing metabolism, and set-point weight — it can feel like your body is conspiring against you sometimes. All these factors (and more!) might make it harder to lose weight. 

• Weight loss is possible. Despite this, it is possible to make lifestyle changes and move toward your weight loss goals. Eating nutritious foods, doing more movement, drinking more water, and getting enough sleep can help. Weight loss medications and professional support might also be useful. 

If you’re considering weight loss medications or weight loss programs, take our free online assessment to find out more about your options.