Learn more about fad diets.

You may have seen ads online for low-calorie fad diets. These promise easy, rapid weight loss.

Social media influencers and lifestyle gurus often promote these diets. They claim these diets kickstarted their weight loss journey. They often consist of costly pre-packaged foods, pills, and meal plans.

But research shows that crash diets simply don’t work in the long term. They can even damage your health. Here’s what to know about low-calorie diet plans.

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Do Calorie-Restricted Diets Work?

These diets may lead to quick weight loss. But, the results will likely be unsustainable. They can also pose long-term health risks, says Rachel Sproat, RDN, LDN, a registered dietitian at UPMC Western Maryland.

These companies pay online influencers and celebrity doctors to endorse their plans. They may include calorie-restricted meal plans or dietary supplements. But they often make claims not backed by science or health experts, Sproat says.

“They’re selling their products based on personal anecdotes,” Sproat says. “Not the science behind it.”

“You may see rapid weight loss and a short-term drop in cholesterol and blood pressure,” Sproat says. “But research shows people who follow low-calorie diets often gain the weight back.”

Many of these meal plans restrict calories to as low as 1,000 to 1,200 a day. This can be dangerous, Sproat says. Anyone on a low-calorie diet should consult a healthcare provider.

These diet regimens are often unsustainable. They are costly. Long-term food deprivation has physical and mental effects.

Caloric and nutritional needs vary from person to person. This is due to differences in activity level, age, height, metabolism, and other factors. Most adults need between 1,600 and 3,000 calories daily to keep a healthy weight.

Weight loss strategies that work include regular meetings with a registered dietitian nutritionist. They’ll help you create a balanced diet of fruits, vegetables, whole grains, and lean proteins. They can also encourage healthy habits, like regular exercise and proper sleep.

These tactics are more effective. They can also save you from spending hundreds to thousands of dollars on fad diets.

“You have to ask yourself: What is the intent of this program?” Sproat says. “Are they really teaching you how to make food choices, grocery shop, and cook for yourself? Or are they trying to earn money off of you?”

Risks of Calorie-Restricted Diets

Doctors may sometimes suggest short-term low-calorie diets. Often, this is for people who need surgery. In these cases, rapid weight loss can reduce the risks of surgery.

In this case, Sproat notes, “it’s done under medical supervision.”

“Low-calorie diets don’t tell you the risks that may be associated with them,” she says. “If you’re at a very low-calorie intake, you’re at risk of nutrient deficiencies.”

“Your body adapts and prioritizes vital functions,” Sproat says. “You may not notice it in the short term, but you’re going to see long-term issues.”

Potential risks of a very low-calorie diet include:

  • Heart rate and rhythm issues.
  • Dehydration and electrolyte imbalances.
  • Fatigue, brain fog, memory problems, and trouble concentrating.
  • Gallstones.
  • Irritability and mood swings.
  • Lethargy.
  • Loss of muscle mass.
  • Low blood sugar.
  • Metabolism changes.
  • Nutritional deficiency, including nutrients essential for heart health.
  • Poor gut health, diarrhea, constipation, and nausea.
  • Rebound eating, binge eating, and long-term failure associated with food deprivation.
  • Guilt and shame associated with yo-yo dieting.

Dietary supplements are often sold alongside high-profile, low-calorie diet plans. They claim to “manage insulin levels” or “boost metabolism” for weight loss. But, Sproat says, these claims are not evaluated by the U.S. Food and Drug Administration (FDA).

The FDA does not test supplements for safety or to see if they work. There’s also little research that says if they work or not.

Many companies fail to list exactly what’s in their “complex” or “proprietary” supplement blends, Sproat says. This can be dangerous for people on certain medicines. It’s also a problem for people watching their sodium, potassium, or phosphorus intake.

Should I Try a Calorie-Restricted Diet?

It’s important to consult your care team before changing your diet. “In general, low calorie-restricted diets are not recommended without medical supervision,” Sproat says.

Keeping a balanced diet and getting regular exercise is a more effective weight loss strategy. It’s also more sustainable.

About UPMC

Headquartered in Pittsburgh, UPMC is a world-renowned health care provider and insurer. We operate 40 hospitals and 800 doctors’ offices and outpatient centers, with locations throughout Pennsylvania, Maryland, New York, West Virginia, and internationally. We employ 4,900 physicians, and we are leaders in clinical care, groundbreaking research, and treatment breakthroughs. U.S. News & World Report consistently ranks UPMC Presbyterian Shadyside as one of the nation’s best hospitals in many specialties and ranks UPMC Children’s Hospital of Pittsburgh on its Honor Roll of America’s Best Children’s Hospitals. We are dedicated to providing Life Changing Medicine to our communities.