How to Lose Weight Quickly

Medically Reviewed by Jabeen Begum, MD on April 23, 2024
Written by Marsha Walton, Matthew Hoffman, MD
6 min read

"Lose 10 Pounds in 10 Days!"

"Eat as Much as You Want — and Still Lose Weight!"

"Drop One Dress Size a Day!"

Rapid weight loss can seem easy if you believe these advertising claims.

Fad diets and weight loss supplements promise a slimmer body in no time. In the U.S. alone, consumers spend $33 billion each year on weight loss products.

Do any of these products really lead to rapid weight loss? Are they safe? And what are the risks of rapid weight loss? WebMD took a look at some rapid weight loss claims, as well as the available evidence.

So many marketers promise "fast weight loss" that it's difficult to sort through them all. A rapid weight loss program is a diet where you lose more than 2 pounds a week for several weeks.

Most rapid weight loss pitches fall into these categories:

Starvation diets

This kind of diet is exactly what it sounds like — a plan that promotes fasting and severely limits what foods you can eat. Beyoncé popularized the so-called "master cleanse" diet: water, lemon juice, maple syrup, and cayenne pepper. Variations of these diets have been around since the 1950s. They often also promise "detoxification" through colonics or enemas.

Diet pills and supplements

Dozens of diet supplements promise to speed up weight loss. Generally, they claim to block the absorption of nutrients, increase metabolism, or burn fat.

Very low-calorie diets (VLCDs)

One proven method of rapid weight loss is the medically supervised very low-calorie diet (VLCD). Most of what is known about rapid weight loss comes from studies of people on these diets. VLCDs are often used before weight loss surgery and under the guidance of a doctor. They are usually recommended for 12 weeks or less.

Creams and other devices

There seems to be no end to the questionable ideas promoted in the name of rapid weight loss. Most promise to replace diet or exercise. Some creams promise to aid in weight loss when used on specific body parts. Be cautious if an advertiser claims that you can "lose weight with this patch or cream," as the Federal Trade Commission has made it clear that such claims are false.

When it’s time to lose weight, most of us want it to happen fast.

Your doctor should decide if several prescription medications that cause rapid weight loss are safe for you.

Also, beware of over-the-counter weight loss products. The U.S. FDA does regulate dietary supplements. But it treats them like foods rather than medications.

The FDA also doesn't regulate claims made by over-the-counter weight loss products. Unlike drug manufacturers, the makers of supplements don’t have to show their products are safe or effective before selling them on the market. This means that dietary supplements do not need FDA approval before they are marketed.

In any rapid weight loss program, what really burns fat is not a pill or type of food. It's the substantial reduction of calories, combined with exercise.

Rapid weight loss creates physical demands on the body. Possible serious risks include:

  • Gallstones, which occur in 12%-25% of people losing large amounts of weight over several months
  • Dehydration, which can be avoided by drinking plenty of fluids
  • Malnutrition, which usually results from not eating enough protein for weeks at a time
  • Electrolyte imbalances, which can sometimes be life-threatening

Side effects of rapid weight loss

Other side effects of rapid weight loss include:

The dangers of rapid weight loss increase with the time spent on the diet. Eating a no-protein diet is particularly risky.

Before beginning a rapid weight loss program, check with your doctor. They can provide guidance, often with the help of a dietitian, on a program that works with all of your health conditions.

A very low-calorie diet (VLCD) may be the right choice for some people with obesity who are already facing serious health problems, such as diabetes, high cholesterol, or high blood pressure. These are people with a body mass index (BMI) greater than 30.

Weight loss to attain a healthy body weight can also reduce the risk for some types of cancer, including postmenopausal breast cancer, as well as ovarian, colon, and pancreatic cancer.

But super limiting diets also come with many cautions. They are hard to stick to and can lead to other health problems. A dramatic cutback in calories can cause you to lose muscle mass as well as fat. And it slows down your metabolism — your body’s calorie-burning process.

Some rapid weight loss programs cut out entire food groups. That can lead to:

  • Constipation
  • Fatigue
  • Loss of bone density
  • Lower immunity
  • Hair loss

Rapid weight loss diets can have ill effects, but so does obesity. For this reason, VLCDs are considered a reasonable weight loss option for people with obesity needing rapid weight loss for a specific purpose such as weight loss surgery.

VLCDs are doctor-supervised diets lasting several weeks. The meals are nutritionally balanced but expensive -- people can end up spending thousands of dollars over time. VLCDs can safely result in a loss of 15%-25% of body weight in 12 weeks. That's for those who finish the program: 25%-50% of people don't complete the program. Weight returns rapidly when the diet is stopped; most experts say it's best to take a more sustainable approach to weight loss, similar to that of regular diets.

Most people seeking rapid weight loss usually do it on their own. Often, they do it to achieve a short-term goal, such as fitting into a dress or looking good at the beach.

Starving yourself is certainly not a good idea. But if you're otherwise healthy, a brief period of extreme calorie reduction isn't likely to hurt you. You should tell your doctor what you're doing, and be sure to include protein in your diet (70-100 grams per day). Take a multivitamin, and eat potassium-rich foods (tomatoes, oranges, and bananas).

Also, remember that crash diets rarely help you achieve a sustained, healthy weight. Most people put the pounds right back on.

Rapid weight loss after giving birth may result from the pressures of being a new parent, including sleep deprivation and being too tired to eat. 

Your body burns more calories while you're breastfeeding. If you lose weight too fast, you could start producing less milk. So, it’s recommended you wait until your baby is at least 2 months old before you make a drastic cut in calories to get back to your prepregnancy weight.

About 3% of people who give birth develop postpartum thyroiditis. That’s when your thyroid gland, which controls how your body uses energy, becomes inflamed. Sometimes this leads to an overactive thyroid (hyperthyroidism). That can be accompanied by weight loss. Treatment may include beta-blockers, prednisone, or both.

Several common antidepressants are linked to weight gain. It’s a reason many people give up on their mental health medications. Doctors may choose a prescription, such as topiramate, associated with significant weight loss.

Being overweight or obese can increase your risk of developing certain types of breast cancer. Extra body fat may increase levels of estrogen and other hormones, which can increase breast cancer risks. Losing weight can lower hormone levels, and also the risks of hormone receptor-positive breast cancer.

Beware of fad diets, detox schemes, and magic potions that promise a slimmer you without any effort. Rapid weight loss may be the right choice if obesity is affecting your health. Work closely with your doctor and dietitian for a weight loss plan that may include drugs, healthy foods, and exercise.

What can cause rapid weight loss?

Rapid, unexplained weight loss may be caused by cancer, diabetes, thyroid disease, Crohn’s, Parkinson’s, HIV, drug abuse, or dementia. It may also be the result of mental health conditions, such as depression, anxiety, or obsessive-compulsive disorder (OCD).

When is weight loss concerning?

Check with your health care provider if you lose more than 10 pounds or 5% of your body weight in less than a year without making any changes to your diet or physical activity.

What is considered unhealthy rapid weight loss?

Losing more than 2 pounds a week could be a threat to your health.