The hCG diet has been popular for many years.

Proponents claim that it causes fast weight loss of up to 1–2 pounds (0.5–1 kilogram) per day. What’s more, you’re not supposed to feel hungry in the process.

However, the Food and Drug Administration (FDA) has deemed this diet dangerous, illegal, and fraudulent (1, 2).

This article examines the science behind the hCG diet.

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The hormone hCG, or human chorionic gonadotropin, is present at high levels in early pregnancy.

In fact, this hormone is used as a marker in home pregnancy tests (3).

It’s also been used to help treat fertility issues in both men and women (4, 5).

However, elevated blood levels of hCG may also be a symptom of several types of cancer, including placental, ovarian, and testicular cancer (3, 6, 7).

A British doctor named Albert Simeons first proposed hCG as a weight loss tool in 1954 (8).

His diet consisted of two main components:

  • an ultra-low-calorie diet of around 500 calories per day
  • hCG hormone injections

Today, hCG products are sold in various forms, including oral drops, pellets, and sprays. They’re also available through countless websites and some retail stores.

Summary

The hormone hCG is produced in early pregnancy. The hCG diet uses a combination of hCG and an extremely low calorie intake to achieve dramatic weight loss.

hCG is a protein-based hormone that the body produces during pregnancy.

It helps maintain the production of important hormones such as progesterone to support the healthy growth of the uterus and fetus (9, 10).

After the first 3 three months of pregnancy, blood levels of hCG decrease.

Summary

The hormone hCG is produced in large amounts in the first 3 months of pregnancy. It stimulates the production of other essential pregnancy hormones.

Proponents of the hCG diet claim that it boosts metabolism and helps you lose large amounts of fat — all without you feeling hungry.

Various theories attempt to explain hCG’s weight loss mechanisms.

However, multiple studies throughout the years have concluded that weight loss achieved by the hCG diet is due to ultra-low-calorie intake alone. It has nothing to do with the hCG hormone (8, 11, 12, 13, 14, 15).

Most of these studies compared the effects of hCG and placebo injections given to individuals on a calorie-restricted diet. Weight loss was identical or nearly identical between the two groups.

Furthermore, these studies determined that the hCG hormone didn’t significantly reduce hunger.

Summary

Several studies indicate that weight loss on the hCG diet is due only to drastic calorie restriction. It has nothing to do with hCG — which is also ineffective in reducing hunger.

One common side effect of weight loss is decreased muscle mass (16).

This is especially common in diets that severely restrict calorie intake, such as the hCG diet.

Your body may also think it’s starving and reduce the number of calories it burns in order to conserve energy (17).

Proponents of the hCG diet claim that it only causes fat loss, not muscle loss.

They also claim that hCG elevates other hormones, boosts metabolism, and leads to a growth-promoting, or anabolic, state.

However, there’s no scientific evidence to support these claims (13, 14).

Low calorie diets may promote rapid short-term weight loss, but they’re not effective for long-term weight loss.

When you’re on a very low calorie diet, your body adapts by increasing hunger hormones and slowing energy expenditure, which makes maintaining your weight loss very difficult. This is why nutrition experts recommend small calorie deficits over extreme calorie restriction (17).

Summary

Some people claim that the hCG diet helps prevent muscle loss and metabolic slowdown while severely restricting calories. However, no evidence supports these claims.

The hCG diet is a very low fat, very low calorie diet.

It’s generally divided into three phases:

  1. Loading phase. Start taking hCG and eat plenty of high fat, high calorie foods for 2 days.
  2. Weight loss phase. Continue taking hCG and eat only 500 calories per day for 3 to 6 weeks.
  3. Maintenance phase. Stop taking hCG. Gradually increase your food intake but avoid sugar and starch for 3 weeks.

While people seeking minimal weight loss may spend 3 weeks on the middle phase, those seeking significant weight loss may be advised to follow the diet for 6 weeks — and even repeat all phases of the cycle several times.

During the weight loss phase, you’re only allowed to eat two meals per day — usually lunch and dinner.

hCG meal plans generally suggest that each meal should contain:

  • one portion of lean protein
  • a vegetable
  • a piece of bread
  • a serving of fruit

You may also get a list of approved foods to select from in specific amounts.

Butter, oils, and sugar should be avoided, but you’re encouraged to drink a lot of water. Mineral water, coffee, and tea are allowed as well.

Summary

The hCG diet is usually divided into three phases. During the weight loss phase, you take hCG while eating only 500 calories per day.

Most of the hCG products on the market today are labeled as homeopathic. In general, homeopathy involves the use of potent substances that have been highly diluted.

Homeopathic, over-the-counter (OTC) products don’t contain any actual hCG. Real hCG, in the form of injections, is administered as a fertility drug or hormone treatment. It’s available only through a doctor’s prescription (2).

Only injections can raise blood levels of hCG, not homeopathic products sold online.

Summary

Most of the hCG products available online are labeled as homeopathic and don’t contain any real hCG.

The FDA hasn’t approved hCG as a weight loss aid.

On the contrary, the FDA has questioned the safety of the hCG diet as well as OTC hCG products. These products are unregulated, and they contain unknown ingredients. As a result, they should be avoided (1, 2).

There are also a number of side effects associated with the hCG diet, such as:

These may be largely due to its starvation-level calorie intake, which is almost guaranteed to make people feel miserable.

In one 2014 case study, a 64-year-old woman was on the hCG diet when blood clots developed in her leg and lungs. It was determined that the diet likely caused the clots and other side effects (14).

Summary

Official agencies like the Food and Drug Administration (FDA) have questioned the safety of hCG products, and numerous side effects have been reported.

The hCG diet limits calorie intake to around 500 calories per day for weeks at a time, making it an extreme weight loss diet.

Any diet that’s this low in calories will make you lose weight.

However, numerous studies have found that the hCG hormone has no effect on weight loss and doesn’t reduce your appetite.

If you’re serious about losing weight and keeping it off, there are plenty of effective methods that are much more sensible and safer than the hCG diet.

Speak with a doctor, dietitian, or nutritionist to determine which method might be right for you.