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What Happens in Your Body When You Lose 10 Pounds in a Week

Quick weight loss is possible, but it’s not sustainable

A salad, clock and measuring tape on a wooden tabletop.

We’ve all heard that slow and steady wins the race. But when you want to lose weight quickly, patience (and sometimes, even common sense) can fly out the window.

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We know that living at a healthy weight is good for our bodies. And, frankly, losing a few pounds can be a boost to our self-image.

But if you’re looking for a quick-fix diet to lose 10 pounds in a week, you’re probably barking up the wrong tree.

“Sure, it’s going to be possible to lose significant weight quickly, but when you understand what that does to your body, you’ll see that it’s probably not a good idea,” says endocrinologist and obesity specialist Marcio Griebeler, MD. “It’s not going to give you the results you’re actually looking for.”

What does quick weight loss do to your body? Dr. Griebeler breaks it down.

Can you lose 10 pounds in a week?

Yes, it’s entirely possible to lose 10 pounds in a week. But that doesn’t mean it’s a good idea or that it’s going to last.

Say you have a vacation coming up or a big event. Naturally, you want to look your best. Nothing wrong with that.

So, you follow the celebrity advice du jour for rapid weight loss. Maybe you eat only veggies for a week straight. Or you cut out all carbs and sugars. You kick your workout routine into hyper-drive.

Maybe it pans out. Maybe you really did lose those 10 pounds in a week. It’s certainly possible to do. But that weight loss is likely to be very short-lived.

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Dr. Griebeler explains that’s because quick weight loss is often a result of losing not only fat, but also water and muscle mass. For weight loss to be successful and sustainable, you need to burn fat and preserve muscle. And that will take some time and dedication.

The effects of crash diets

Often, our first go-to if we want to shed some pounds quickly is to significantly restrict our caloric intake (aka, crash diet). Cutting way back on calories for a short amount of time can have effects on your weight, sure. But it’s just not something you can do long-term.

“You’re not going to stay on a 500-calorie-a-day diet for very long,” Dr. Griebeler says. “It’s not sustainable. Your body needs fuel, and it will adapt to keep you from keeping that kind of diet up for long.”

Those adaptations are changes in your body’s metabolism that are designed to keep you from losing weight. They’re evolutionarily programmed defenses to protect us from the threat of starvation.

You’ll get a surge of hunger hormones. You’ll have a steep drop in hormones that signal when you feel full. Your body will conserve its energy. And you’ll shed muscle mass.

So, after dieting for seven days and dropping those 10 pounds, what are you left with? An insatiable appetite. Low energy. Weakness. All in all: A perfect storm that will lead to eating more and exercising less.

So, what happens? Those 10 pounds you dropped are now right back where they started.

Cardio for rapid weight loss

Cardio exercises are great for cardiovascular fitness and an important part of a healthy lifestyle. The American Heart Association recommends we get at least 150 minutes of moderate-intensity exercise per week (or 75 minutes per week if you do more vigorous aerobic activity).

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So, yes, your favorite cardio exercises — like running, ellipticals, cycling and so on — are a great way to get your heart pumping and burn off serious calories.

But in order to effectively perform cardio exercise, we have to provide the body with energy.

“You need to replenish those calories that you’re losing from exercise. Your body will be begging for them — incessantly,” Dr. Griebeler states. “If you don’t eat, you’re going to be tired, and, therefore, you’re not going to be able to keep up all that exercise.”

Strength training and weight loss

Strength training is an important component in weight loss. Converting fat into muscle helps to keep your body strong and ward off chronic conditions, like heart disease, diabetes and so on.

Dr. Griebeler says that’s because building muscle helps improve your body composition and improves your metabolic rate. Strengthening exercises increase muscle and decrease fat, which is a very healthy and good thing for your body. More muscle actually helps your body burn more energy at rest. So, no doubt, strengthening is a good thing.

But for quick weight loss? Not so much.

Muscle weighs more than fat. So, if you’re looking to lose weight fast, extra strengthening isn’t going to do it. (Though, as Dr. Griebeler points out, your body composition is a better indication of your health than the number on your bathroom scale.)

What’s more is that building muscle takes time. More than a week. And here’s the rub — in order to build muscle, your body needs energy. It needs you to bring in the calories. That’s why bodybuilders are always pounding those protein shakes. So, you won’t build muscle when you’re also restricting calories.

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Sustained weight loss

It’s not the advice you wanted to hear, but sustainable weight loss takes time. That’s just the plain truth of it. It takes time for your body to adjust to your new routines and get comfortable with the idea of weight loss.

Quick weight loss is a signal to your body that you’re starving. So, it fights back.

Gradual weight loss allows your body to get comfortable with a new normal. It’s a signal that all is well. That you got this handled. So, your body lets you take control.

The U.S. Centers for Disease Control and Prevention (CDC) recommends that you aim for losing one to two pounds per week.

Dr. Griebeler says that’s because gradual weight loss gives your body a chance to adapt. But even with that guidance, everybody will respond to weight loss a little differently, so even if one to two pounds per week is the general goal, your weight loss may look different from that. And that’s OK.

Remember, too, that your weight is only one side of the coin. Losing fat should be the real goal. And that can be done without the number on the scale budging.

“If you’re building muscle, you’ll be burning fat, even though your weight is the same or even if it goes up a bit,” Dr. Griebeler says. “If you have more muscle, I can guarantee you your metabolic rate is up and you’re burning fat. And you’ll be overall healthier, regardless of whether you’ve hit that weight number that you’re looking for.”

He also offers these quick tips for lasting weight loss:

  • Focus on quality foods. Eat more natural foods and fewer processed and packaged ones.
  • Increase your exercise. Aim for a combination of cardio and strengthening exercises. Start slow and gradually increase your activity.
  • Get enough sleep. “Sleep is very important to making sure you’ll be refreshed the next day and have the motivation and energy to keep up a healthy routine,” Dr. Griebeler says.
  • Keep your stress levels manageable. Stress eating is a real thing. Living with stress can raise the hormone levels that activate your appetite. “Stress is just altogether no good for weight loss,” he adds.
  • Keep a food journal. Writing down what you eat (or tracking it with an app) can help you notice any unhealthy eating patterns and make you more aware of what you’re eating and its nutritional value (or lack thereof).

If you’re living with obesity (a BMI of 30 or higher), though, your body may be less likely to respond to these tactics, Dr. Griebeler notes. That’s because obesity is a metabolic disorder that can keep you from losing weight and keeping it off, even when you go gradually. If you’re living with obesity, talk with a provider about options like anti-obesity medication.

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