There are no quick fixes for weight loss. Any of these diets might work to lose a few pounds, but for the weight to stay off, the diet must be something you can follow for the rest of your life.

When you hear the term “fasting,” you probably think of going without food for several days. But anymore, “fasting” also might mean restricting only certain foods, drastically reducing calories or restricting when foods are eaten. Different types of fasting diets are popular for weight loss, but do they work? And more importantly, are they safe?

Following are three types of fasting diets, along with pros and cons for each.

1. Ketogenic diet.

This diet severely limits carbs, so grains, dairy, fruit, beans, starchy vegetables and alcohol are avoided. A true ketogenic diet consists of about 75 percent fat, five percent carbs and 20 percent protein and is not the same as a low-carbohydrate diet. The theory is that when carbs are avoided, the body must convert stored fat into energy. In order to convert fat to energy, ketones are produced.


There is an initial fast weight loss, which can be motivating.

Some studies show a decrease in insulin resistance when following a ketogenic diet.

This diet has shown promise in helping control seizures related to epilepsy.


The rapid initial weight loss is due to water loss because carbohydrates tend to hold water.

It is a very restrictive diet, which makes it hard to stick with for long. Eating out and socializing can be difficult when on such a restrictive diet.

The diet must be strictly followed for at least seven days to ensure a state of ketosis, and participants must continually monitor their urine or breath to assure they are in nutritional ketosis.

Brain fog, fatigue and bad breath are common side effects.

The diet is lacking in fiber, which may cause digestive issues and change your gut microbiome.

Long-term adherence to the diet could result in vitamin deficiencies due to lack of major food groups and nutrients.

The diet is very high in fat, which can increase LDL cholesterol and your risk for heart disease.

Persons with diabetes or kidney disease should not follow this type of diet due to potential deadly consequences.

Weight regain once returning to a more balanced diet is likely, and this weight will likely be fat, rather than muscle.

2. Intermittent fasting diet.

There are several variations within this diet. Some require that you do a full 24-hour fast twice a week; some recommend an every-other-day 500-calorie fast; some suggest eating normally for five days a week and restricting calories to around 500 for just two days a week; and some recommend no food for 16 hours and eating all your meals within an eight-hour-period every day. Whatever the specifics, the premise is that going longer periods of time without eating allows your body to access and burn your fat stores.


No food is eliminated or even restricted on off-fast days, thus making compliance easier.

There is minimal muscle loss because the diet is not overly restrictive.

Metabolism is not affected as with some low-calorie diets because the restricted period is short-lived.


You will be hungry on fasting days.

There is a risk of binge-eating on off-fast days.

Some people will rely on caffeinated beverages to get through the fast days.

3. Restricted-calorie diet or longevity diet.

This diet promotes eating 20 to 40 percent fewer calories than your body needs to slow aging, promote weight loss and extend life.


There is some truth in the claim that eating fewer calories can extend your life.

Weight loss will lower blood pressure, improve lipid levels and improve blood glucose levels in most people, which in turn may lengthen life.


Hunger can make this a difficult diet to follow.

Anything less than 1,200 calories is not recommended for the long-term because your body needs about this many calories just to perform basic functions, such as breathing and moving.

This diet makes it difficult to get all the nutrients you need for health; everything you eat needs to be packed with nutrients and have few calories.

There is an increased risk of muscle loss, decreased bone density and anemia with any extended low-calorie diet.

There are no quick fixes for weight loss. Any of these diets might work to lose a few pounds, but for the weight to stay off, the diet must be something you can follow for the rest of your life. Eating a little healthier and a little less, combined with moving more, is a tried-and-true formula for weight loss that can be followed for life.

Before embarking on any weight loss diet, check with your health care provider to be sure it is safe for you.