Protein-sparing Modified Fast

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What exactly is the Protein-Sparing Modified Fast? (PSMF)

The Protein-Sparing Modified Fast is a very effective method for those who wish to lose a large amount of weight in a relatively short amount of time. First created in the 1970s, it was made to help morbidly obese patients (those with a BMI much greater than 30) lose weight that was affecting their health in an immediate way. It has been studied exclusively in the adult population and has been proven to be a safe way to achieve rapid weight loss.

The Protein-Sparing Modified Fast is a diet that consists of very low amounts of calories creating a large deficit that will help you lose a lot of weight fast. It is not an easy diet as it is essentially a prolonged fast and should not be used in the long run as there can be negative side effects to it. It is also often used as a short term diet for people who are looking to kick start their weight loss.

Protein-Sparing and Ketosis

Apart from the very low calories, this diet follows a very important principle that many might be familiar with in our day and time. That little magic trick is called Ketosis and it’s what Protein-Sparing is all about.

Ketosis is a state that occurs when there are not enough carbohydrates available to the body and in order to provide enough energy for its every day functions, the liver starts to oxidize fatty acids. During that state, ketones are produced.

Ketosis has been linked with a suppression of appetite and rapid weight loss. This happens because while regular weight loss is taking place, the body starts to produce some hormones that try to promote weight gain in order to resupply the fat that was lost. In Ketosis though, fatty acid oxidation seems to protect against the production of those hormones and therefore makes it a lot easier to stay on track and continue with the weight loss plan.

Protein-sparing allows the body to lose weight without losing any muscle tissue. That happens because the proteins you consume are not what your body uses as a main source of energy. This way, you make sure that your body uses the protein you eat in order to build and repair tissues and muscles as well as create enzymes and antibodies. Therefore, your body uses bigger amounts of your stored fat in order to have enough energy for its daily activities and you end up losing more fat while maintaining muscle.

Summary: The PSMF diet was created in order to help morbidly obese patients lose a great amount of weight in a short amount of time. It works by putting the body in ketosis, a state which enhances weight loss and preserves muscle.

How long should a PSMF last?

The Protein-Sparing Modified Fast consists of two phases. First comes the Intensive phase, the actual dieting part of the fast where the calories consumed during the day don’t exceed 800 kcal (this value may be higher or lower depending on your lean body mass). This phase is very restrictive and it is not recommended that you follow it for more than six months.

The second part of the diet consists of the Refeeding phase. In this stage, the person can slowly start to add back carbohydrates and fats into their diet. The amounts of protein consumed are finally reduced. This is the stage of the diet that helps a person learn how to manage the weight that they lost so they are able to keep it off for good. For this part, experts encourage those who wish to follow it, to stay on the increased carbohydrate load for a minimum of 12 weeks.

The Protein-Sparing Modified Fast is not recommended for long term use. In fact, most studies have shown that it is safe when it lasts around 12 weeks but it is usually administered for 6-16 weeks depending on the severity of the obesity. For people with class 3 obesity (morbidly obese), the PSMF diet can be continued beyond week 16 as long as that person is closely monitored and the fast is well tolerated.

The PSMF diet is not a lifestyle and should only be used on a short term basis, lasting for a few weeks for initial motivation and rapid weight loss.

Should you exercise during a PSMF diet?

In most studies, exercising is encouraged in order to intensify the effects of the weight loss. In a study conducted by Blackburn, Whatley et al, they found that the group that incorporated walking and resistance training into their diet that was very low in carbohydrates had achieved additional loss of fat mass and at the same time had achieved the preservation of fat free mass.

In any case, exercising while being on a PSMF diet can help you not only see results much faster but it can also help you feel a lot healthier in a short amount of time. It is especially needed when the person moves to the sustainable diet where they will have to maintain their weight.

People who lose weight without exercising are the ones that usually put the weight back on and that is very sad as it makes all their hard work and effort go to waste. However, it is strongly advisable that exercise is mainly limited to just fast walking and resistance training as opposed to vigorous cardiovascular exercise.

Summary: The PSMF should not be considered a lifestyle and whoever decides to follow it should only do so for the time that is deemed safe by the experts. Only walking and some resistance training is advisable on this diet due to the already very large calorie deficit it creates.

Who is it suitable for?

This diet is suitable for those who are very overweight and need to kick start their weight loss. This quick fix, as some might say, can act as a great means of motivation to those who need to lose a great amount of weight and wish to see some immediate results.

People who have a smaller amount of weight to lose and want get their diet off to a good start can also benefit from this fast as long as they don’t follow it for an extended amount of time.

The PSMF diet can also act as a treatment prior to bariatric surgery with the consumption of either foods or liquid meal replacement shakes. This lasts for a period of around two weeks and results in quite considerable weight loss given the short length of time.

Positive effects have also been noted with many people who suffer from type 2 Diabetes. This is a result of the glycemic benefits that a PSMF diet provides. In a study conducted by Bistrian, Blackburn et al, the PSMF diet had helped reduce the insulin and glucose concentration in the participants and had allowed for the withdrawal of exogenous insulin after just 6.5 days.

Along with that, studies have shown that those who sustained the weight loss experienced an improvement in many comorbid diseases associated with obesity. Even 5% weight loss has great health benefits for people suffering from diabetes, hypertension, hyperlipidemia and cardiovascular disease.

The important thing here though is to only use this diet for a very short amount of time and then continue with a weight loss plan that allows for consistent weight loss, as that is the best way to ward off these diseases.

Summary: This diet has been known to have positive effects on many people who are facing different problems. Studies have shown positive effects of the PSMF diet to not only morbidly obese patients but also those with type 2 Diabetes as well as many comorbid diseases that are linked to obesity.

What are the macros for PSMF?

The PSMF diet is all about limiting the amount of carbohydrates a person consumes and at the same time reducing the amount of calories to less than 1000 kcals a day (this amount varies depending on your lean body mass).

The number one thing that this diet plan does differently than a Ketogenic Diet is that the amount of fats that are consumed is also very low. In the first part of the diet, protein intake rounds up to 1.2-1.5 grams per kilogram of the person’s goal body weight. As far as the carbohydrates are concerned, those who follow a PSMF are only allowed 20-50 grams of them a day. Last but not least, fats are limited to what comes with the protein source you choose.

Once the person reaches the refeeding phase, during the first month of it carbs are increased up to 45 grams and during the second up to 90. On the other hand, protein is reduced by about 40 grams per month. This part of the diet is progressively getting higher in calories as more carbohydrates and fats are being added to the person’s every day diet.

What is meant by nitrogen balance?

Nitrogen is an essential component of protein. Its urinary secretion can be measured in a lab. Inadequate nutrition and an unbalanced diet result in the production of a negative nitrogen balance in the body. As a result, the body starts to lose lean body mass. Lean body mass is very important when it comes to weight loss as it plays a very important part to the body’s metabolic rate.

The PSMF diet has shown in clinical trials that it has helped increase the nitrogen balance in the bodies of the participants. As a result, people who follow this diet to the letter will be able to have a higher metabolic rate and therefore lose weight faster.

Summary: The essence of this fast is to keep carbohydrates and fats as low as possible and to increase your protein consumption. Each phase of the stage is different, and once you reach the refeeding stage, you will slowly start reintroducing carbs and fats back into your diet. The PSMF diet helps achieve a nitrogen balance that is essential to retaining lean body mass and maintaining a higher metabolic rate.

Which foods to eat?

In the first phase of the diet, the Intensive phase where the proteins are high, it is essential to consume conventional foods which contain high biological value protein such as:

  • Lean Meats
  • Egg whites
  • Fish and seafood
  • Poultry

During this phase, it is also important to consume some vegetables that are low in carbohydrates such as:

  • Asparagus
  • Broccoli
  • Cauliflower
  • Lettuce
  • Carrots
  • Brussels Sprouts
  • Mushrooms
  • Zucchini

As far as condiments are concerned you can choose to use very small amounts of the following:

  • Butter sprays (sparingly)
  • Mustard (max. 1 tbsp. per day)
  • Tabasco sauce
  • Vinegar
  • Bouillon cubes
  • Fresh garlic, onion, parsley and celery

As far as dairy is concerned, milk, yogurt and fatty cheeses are definitely out of the question. On the other hand though, you can consume some nonfat variations of cheese and cottage cheese but in smaller amounts too.

You can also drink decaffeinated coffee or herbal tea along with your water. You should try staying away from diet sodas or any other drinks that contain caffeine as it can slow down your weight loss process.

In the refeeding phase, it is important to start incorporating more complex carbohydrates, foods rich in fiber including fruits and vegetables and also fats, once the goal weight is achieved.

If you wish to take a closer look at this diet, you can use our Meal Planner to help you automatically create a PSMF weight loss diet plan.

Just remember that this is not a conventional ketogenic diet. This means that fats should also be kept at a low amount along with the carbohydrates.

Summary: As long as the foods you consume are high in protein but low in fats and carbohydrates, you will be able to stay in ketosis and benefit from this fast. You should always try and read labels of the products you buy so you make sure you don’t accidentally consume anything you shouldn’t.

What are the side effects of PSMF?

There have been many reported side effects in subjects who have participated in trials of this diet.

Some of the most common are:

  • Cold intolerance
  • Constipation
  • Dizziness
  • Dry skin
  • Fatigue
  • Brain fog and headaches
  • Hunger

The side-effects that a person will experience during the PSMF are to a great extend the results of your body going into ketosis. This happens because of the lower insulin levels that are achieved due to the low amounts of carbohydrates that are consumed. The lower insulin causes the kidneys to excrete more water which leads to the body losing not only water weight but also important electrolytes.

Along with that though, the fact that this diet is so low in calories will definitely aid to the appearance of these side effects that were mentioned earlier.

When is medical supervision needed?

The Protein-Sparing Modified Fast is one of these diets that definitely need medical supervision if the person following it is carries a lot of extra weight. Not only will that person have to be working with a licensed dietician when deciding to follow this plan, but they should also let their doctor know so they can run the tests that are needed to help see if they are in a good enough condition to follow this plan.

The biggest problem for these people is that this is a very low calorie diet that completely changes a person’s eating habits when followed for a long period of time. Most people are definitely not used to consuming such low amount of carbohydrates and fats and that can become a great issue once they reach the Refeeding stage.

On the other hand, if you wish to find a diet plan that is very efficient and safe and that will help you kick start your weight loss, you can give the PSMF a try yourself and benefit from the amazing results.

This applies to those who are not intending to follow the meal plan for more than two weeks though.

Therefore, if you have some weight to lose but you aren’t very overweight, you should definitely consider giving this a try at the beginning of your dieting journey as it will boost your confidence and make you want to try harder to achieve your goals.

As long as after the two weeks have passed you return to a normal meal plan and proceed with your weight loss in a way that is more sustainable and easy to follow, you will be healthy even if you don’t work with any particular medical practitioner.

Will I need supplements during the PSMF diet?

The answer here is yes. A PSMF diet is not nutritionally complete and is usually low in some essential compounds in a person’s every day diet and therefore supplements are the only way to get them without breaking the Macronutrient plan.

Here are some of the most important ones:

  • Potassium
  • Calcium
  • Multivitamins
  • Magnesium
  • Sodium

Not only will those nutrients help you stay hydrated and healthy, but they can also help ease some of the symptoms of the diet that are naturally occurring when the body is going into ketosis.
How much water should I drink during the PSMF diet?

In most studies, participants were instructed to consume a minimum of 64 ounces (around 2 liters) of fluids on a daily basis, so you will need to be drinking about that much water and liquids too. The liquids you consume will have to be sugarless, so the best options here are either plain water or some enhanced drinks with electrolytes and vitamins. Be very careful of sport drinks though, as they might be hiding added sugar or glucose in the ingredients.

Drinking a lot of water is very important in this diet as the more water you drink the faster you will be able to eliminate ketones from your body. This also plays an important role in preventing renal injuries.

Will this diet help you keep the weight off?

Maintaining weight loss and preventing weight gain can be a very difficult thing to do for many obese people as some habits can be very hard to break and it is simply very easy to go back to our old ways. You will definitely be in need of some tips to help you understand some things that you should be doing after you finish your diet plan.

Many studies that followed the results of a Protein-Sparing Modified Fast have reported that most participants have earned more than 50 percent of the weight they had lost in a time frame of 2-3 years after the diet.

In another study by Chang JJ et al, the subjects that had attended their follow-up visits after the diet was through were the ones who managed to see the most significant weight loss at the end of their PSMF when compared to those who did not seek the follow-up instructions. Even at 12 months post-PSMF, they had managed to maintain greater weight loss too.

In cases that the PSMF diet was used right before a bariatric surgery, the results were much better and helped aid the weight loss even after the surgery had taken place.

The PSMF diet is no magic pill that will allow you to lose weight and keep it off if you do not put in the personal effort. It is essential that you get the proper training you need in order to know how to start adding more carbohydrates and fats into your diet so you manage to increase your calories without piling on weight that you worked so hard to lose.

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