How Much Weight Can You Lose in a Week? What Experts Say.

WE’VE ALL BEEN there. You told yourself you were going to get in shape in time for the class reunion, wedding, or some other important event. Now it’s a week away and the scale hasn’t changed. Or maybe it did but in the opposite direction you intended.

So how much weight can you lose in a week? Healthy weight loss is a slow and gradual process, but you might have heard amazing feats of people melting fat in a short amount of time (or read some of our inspiring weight loss transformations). Sometimes that’s done in a healthy manner, and sometimes people take drastic measures to shed those pounds. But surely there’s a way for you to safely lose 10 pounds for your upcoming event, right?

The answer depends on several factors. When you know how your body works, there is a way to maximize your weight loss. And again, we’re talking about healthy non-medicated weight loss. Here’s what experts say.

The Science Behind Short-Term vs. Long-Term Weight Loss

EVERYONE WANTS TO know the amount of weight they can lose quickly—and everyone wants that to be a big number—the answer isn’t always straightforward.

That’s because it’s based largely on the size you already are. The more weight you have on your frame, the more you’ll lose in a short amount of time. That’s especially true when you first start trying to lose weight, says David Creel, PhD, RD, a psychologist and registered dietitian at Cleveland Clinic.

The less you weigh, the harder your body will cling to the weight you do have, making it even harder for you to lose. That’s because your body is fiercely protective over the weight you already have. It’s also the reason why the longer you stay on a weight-reduction plan, the harder it can be to see the number move on the scale.

“Unfortunately, our brain doesn’t have a scale saying, ‘when you get to a healthy weight, we’ll stop all this compensation,’” Dr. Creel says. “It doesn’t work that way.”

As we shed pounds, our metabolism—i.e., our body’s internal fat-burning furnace—also starts to slow down, causing us to burn fewer calories than we used to. “It’s kind of like taking a backpack off,” he adds. “Breathing requires less calories, walking down the street requires less calories, everything requires less energy.”

What if you only have a week to lose weight?

There’s a difference between how much weight you can lose in a week versus how much weight you should lose in a week—and trying to figure out the former can be dangerous.

“Wrestlers, boxers, people who have to make weight for a sport will often dehydrate themselves,” says Dr. Creel. “You can see people who maybe lose 20 pounds in a week intentionally—but it’s very risky.”

Plus, here’s the thing about extreme diets. As much as you might want to lose 10 pounds in the short term, you’re not doing yourself any favors over the long term. Super low-calorie diets can cause dehydration, so any weight you’re losing is probably water weight, says Dr. Creel. Let’s face it, water weight doesn’t exactly count.

Another issue with extreme dieting is that it can cause you to lose muscle, which can further hinder your metabolism. That’s because our muscles play an important role in helping our bodies burn calories throughout the day—the more muscle mass we have, the higher our metabolic rate.

“If someone goes on a pretty restrictive diet, they might lose 20 percent to 25 percent of their weight as muscle,” says Dr. Creel. (Here’s 6 signs to know if you’re losing weight while dieting).

How Much Weight Is Safe to Lose in a Week?

EXTREME EXAMPLES ASIDE, Konstantinos Spaniolas, MD, associate director of Bariatric and Metabolic Weight Loss Center at Stony Brook University, has an answer: one percent of your body weight per week. He does caution that this is still rapid weight loss—but within reason.

Say you start at 300 pounds. A goal of one percent fat loss per week means you’ll shed three pounds a week. That can be reasonable. But if you’re just looking to drop three pounds a week from a relatively lean 160-pound frame, you’ll probably have a harder time losing it without sacrificing some muscle mass.

The more time, the better. Generally, Dr. Creel says people should aim to lose 1 to 2 pounds per week. Even then, those numbers aren’t always consistent from week to week—it can be more of an average.

“A lot of people lose weight kind of like stair steps, not a straight line,” says Dr. Creel. “They might drop four pounds in a week, and then their weight doesn’t change for two weeks, and then they drop two or three pounds.”

How to burn fat, not muscle

If you want to lose fat without losing muscle or lose fat and gain muscle, you’ll want to start strength training. One Columbia University study showed just how much strength training matters for preserving muscle mass.

Scientists had people cut calories and then either do strength training or cardio workouts three times a week. After eight weeks, everyone lost more than 9 percent of their body weight. But in the aerobic group, 20 percent of that came from lean tissue (mostly muscle), while the resistance group limited lean-tissue loss to 8 percent, while still trimming down overall. (Need guidance? Check out MH’s 12-week beginner’s guide to strength training).

To preserve muscle, you’ll also want to make sure you’re eating enough protein since it provides essential amino acids your body uses to make muscle. Dr. Spaniolas recommends eating about .8 to 1 gram of protein for every pound you weigh in order to retain muscle. There are plenty of ways to get that protein, including these 25 delicious, high-protein recipes you can make in 25 minutes or fewer.

What Factors Affect Weight Loss?

BESIDES YOUR STARTING weight, other factors can make it easier or harder for you to lose weight.

Dieting history

Scientists are still working to understand the mechanisms, but research has shown that people who have lost weight burn fewer calories than people who never dieted.

Not only will you burn fewer calories if you’re smaller, says Yoni Freedhoff, MD, author of Why Diets Fail and How to Make Yours Work, but complex hormonal and metabolic shifts are also at work, making it harder to burn fat the longer you’re losing. That doesn’t mean you’re doomed if you tried and regained weight. It just means you tend to lose weight faster at first.

Lack of sleep

Not getting enough shut-eye also throws hunger and metabolism hormones like leptin and ghrelin out of whack. One small study published in Annals of Internal Medicine found volunteers on a reduced-calorie diet slept either 5.5 or 8.5 hours a night. In two weeks, they both lost a little more than 6.5 pounds—but those who slept more lost twice as much of that from fat.

Current diet

Of course, diet also plays a major role in how much weight you lose. Dr. Spaniolas says correctly estimating how many calories your body needs is complicated, but recommends using a body weight chart or calculator from the National Institutes of Health. From there, you can omit about 500 calories per day to lose weight, but shouldn’t go much lower than that to begin with. Even then, Dr. Spaniolas says it may not be easy to sustain this reduction in calories if you’re already lean and need fewer calories to begin with.

Alcohol

Alcohol can easily increase your daily calorie intake if you don’t monitor those calories. Men consume an extra 433 calories on days they consume alcohol when they have a “moderate” amount of drinks, according to one study. With any weight-loss plan, you need to factor in these liquid calories.

Best Way to Track Weight-Loss Progress

IF YOU’RE LOOKING to lose a lot of weight or make bigger changes to your body, you might want to consider investing in a body composition scale, which can measure fat, muscle mass, and more. A tape measure and a mirror can also work.

Just remember—it’s not all about the numbers. Sure, you might want to drop as much weight as possible one week. A better question, however, is what kind of changes to your lifestyle can you make that will improve your health over the long term, says Dr. Creel. “There are other things to focus on other than one-week weight loss.”

Cindy is a freelance health and fitness writer, author, and podcaster who’s contributed regularly to Runner’s World since 2013. She’s the coauthor of both Breakthrough Women’s Running: Dream Big and Train Smart and Rebound: Train Your Mind to Bounce Back Stronger from Sports Injuries, a book about the psychology of sports injury from Bloomsbury Sport. Cindy specializes in covering injury prevention and recovery, everyday athletes accomplishing extraordinary things, and the active community in her beloved Chicago, where winter forges deep bonds between those brave enough to train through it.

Melissa Matthews is the Health Writer at Men’s Health, covering the latest in food, nutrition, and health.

Maria Masters is a contributing editor and writer for Everyday Health and What to Expect, and has held positions at Men’s Health and Family Circle.