New diets appear each year to tackle the global issue of rising obesity rates. The 500-calorie diet may seem like a recent development, but it has been around in various forms for many years.

In this article, learn why some people use the 500-calorie diet and whether or not it is safe.

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The 500-calorie diet is a type of very-low-calorie diet (VLCD).

People on the 500-calorie diet aim to eat only 500 calories a day, which is about a quarter of the daily recommended intake for adults. The upper limit on the diet is 800 calories per day.

Diets such as the 500-calorie diet are called very-low-calorie diets (VLCD). Although doctors have prescribed VLCDs for many years to treat some conditions, eating so little does come with risks.

Doctors may recommend the 500-calorie diet to help people with obesity who cannot have bariatric surgery.

VLCDs are also useful before bariatric and laparoscopic surgery. Losing fat can reduce operative time, blood loss, and the risk of complications.

There are many things that a person should consider before following a 500-calorie diet without a doctor’s supervision. These include the following:

1. Chance of nutritional deficiencies

Eating 500–800 calories a day may put people at risk of deficiencies. Specific groups of people may be at higher risk. Older adults, in particular, may be at risk as they are more like to have reduced nutrient absorption from the small intestine.

2. Possibility of gallstones

A person may have an increased risk of gallstones while on the 500-calorie diet.

Gallstones form in the gallbladder. They can block the bile duct and cause abdominal pain.

The following factors increase a person’s risk of gallstones:

  • fasting for extended periods
  • obesity
  • quick weight loss
  • pre-existing gallstones
  • repeatedly losing and gaining weight

Previous studies found that VLCDs with a higher fat intake may help prevent the formation of gallstones.

Eating foods high in fiber and reducing consumption of refined carbohydrates and sugar can also help prevent gallstones.

3. Lack of healthful fats

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Avocados are high in calories.

Of the three macronutrients, which are fat, protein, and carbohydrates, fat is the highest in calories.

Because fats contain many calories, it is difficult to eat enough of them while on a 500-calorie diet. Unsaturated fats, such as those in salmon and avocado, are highly beneficial to the body.

A low-fat diet also increases the risk of deficiencies of fat-soluble vitamins, such as vitamin E, and poor absorption of antioxidants.

4. Doctor supervision is necessary

A poor variety of foods and the risk of nutritional deficiencies can make a 500-calorie diet dangerous.

It is essential for people to get supervision from a doctor and a dietitian before embarking on this diet.

5. Meal replacements are not a long-term solution

People sometimes use meal replacements for one or two of their daily meals while on a low-calorie diet. Although these can be useful, consuming them for a prolonged period can be detrimental to a person’s health.

Vitamins, minerals, macronutrients, and phytochemicals all have important interactions in the body when a person is eating whole foods. Artificial foods cannot replace these vital interactions.

6. It can be costly

Even though a person on the 500-calorie diet is eating less, the cost per pound of food is higher than on other diets.

The cost of meal replacement foods, such as Optifast, is often much more than the equivalent amount of whole foods.

Most programs also suggest weekly consultations with the supervising doctor.

7. Lifestyle changes vs. a quick fix

Anyone trying a VLCD should take care to implement other healthy weight loss strategies as well. These may include nutrition counseling and physical activity.

Being on a VLCD does not establish good health behaviors, as the diet is not sustainable over time. It is a much better idea to make small but lasting changes that are easier to maintain.

8. Consider the 5:2 or alternate day diet

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Other diets provide opportunities to eat more vegetables, fruits, and healthful fats.

Other low-calorie diets include the 5:2 diet, time-restricted feeding, or alternate-day fasting (ADF). These diets provide opportunities for consuming higher quantities of vegetables, fruit, and whole grains, as well as healthful fats.

On the 5:2 diet, a person eats a regular amount of healthful calories on 5 days of the week, then limits their calorie intake to 500–600 calories for 2 non-consecutive days.

Time-restricted feeding extends the nighttime fast to between 12 and 16 hours. This means that a person can only eat during certain hours of the day. For example, they may fast during the night and only eat between 9 a.m. and 7 p.m.

When a person does ADF, they alternate their daily calorie intake, eating 500 calories one day and consuming a regular number of healthful calories the next.

A recent meta-analysis and systematic review found that people using ADF achieved slightly higher fat loss than those using VLCD. They also seemed to have a lower risk of muscle loss.

ADF or the 5:2 diet can help a person achieve the same weight loss or health benefits as using a 500-calorie diet, while also being much easier to follow.

9. Muscle loss

Losing weight very quickly could put a person at risk of losing muscle instead of fat.

A decrease in muscle mass can negatively impact a person’s metabolism. This is an undesirable effect as it reduces a person’s ability to burn calories and prevent injury.

Building lean muscle while eating a healthful diet is often a better approach to sustainable weight loss.

10. Missing out on social events

Eating out can be difficult on a 500-calorie diet. Many restaurants do not reveal the total calorie count of their meals.

Being on the 500-calorie diet may also cause anxiety about ordering food or eating with family and friends.

11. Not suitable for people with certain diseases

Doctors do not recommend VLCD and meal replacement products for obese or overweight people with certain medical conditions.

People with the following conditions should not try the 500-calorie diet without a doctor’s approval and supervision:

12. Possible decrease in bone health

The long-term effects of a VLCD on bone health are unknown because people do not use the diet for prolonged periods.

However, a lack of essential minerals and nutrients can weaken bones over time.

A 500-calorie diet may be beneficial in the very short-term for people with obesity, or as a pre-operative measure.

However, people just looking to lose weight should try making sustainable diet and lifestyle changes, such as increasing their vegetable intake in all meals.

They may also consider the 5:2 diet, time-restricted feeding, or ADF instead.

People should not use the 500-calorie diet for longer than a doctor recommends.