The ultimate guide to the PSMF diet - the most scientific safe crash diet

Let me first clarify the most important thing: The PSMF diet isn't a way of eating for life! It's more like a battle mode for those who need/want to lose a massive chunk of fat for a certain event in the near future, like a wedding.

What is the PSMF diet - protein sparing modified fast?

The PSMF diet, or also known as protein sparing modified fast, is a ketosis-based diet. The main goal is to invoke rapid weight loss in just a few weeks with minimal additional exercise.

Essentially, it is the most scientific and useful crash diet out there. While on this diet, you're able to lose 1.5-3kg/4-7lbs of body fat and 4.5-9kg/10-20lbs of weight in about 2 weeks. This is due a very restricted caloric intake of around 1000 kcal per day.

It is usually used to help people lose a tremendous amount of weight and then transition into a more sustainable way of dieting.

PSMF diet is very useful when it comes to:

  • prevention of muscle loss
  • appetite suppression
  • complete reliance on body fat and ketones to fuel the body

How does the PSMF diet work?

As you can tell by the name, PSMF is a form of fasting. Meaning, consuming food only during a set period of time. But in this special case, you're restricting food and drinks in a very specific way.

Your most important food source is a calculated intake of protein based on your lean body mass. Protein sources include lean meats and milk protein isolate protein powder. Just keep it simple here.

Carbohydrates and fats are mostly removed from your diet. Yes, this makes the diet nutritionally incomplete. You can make up for these deficiencies by taking supplements. But let me come to that later.

Furthermore, it's very important to eat a lot of healthy and low carb veggies, which will keep you satiated.

Your body will reach ketosis, so your body is forced to use body fat for fuel. Thus it's a ketogenic diet.

Basically, your body eats away his own fat for energy and the consumed protein helps spare your lean muscle. From a hormonal standpoint, insulin and glucose will decrease, while glucagon, growth hormone, adrenaline and noradrenaline increase. This is another fact, that will help with the fat breakdown.

Who should PSMF use?

Initially, the PSMF diet was created to help adults with a body mass index of 30 or higher. Meaning people who are qualified as obese.

Nowadays, this diet is also used to treat people who suffer from type 2 diabetes, hypertension, sleep apnea, osteoarthritis, fatty liver disease or Hepatic Steatosis.

Furthermore, anyone who want to lose weight in a pretty short amount of time can try a PSMF diet. All you need is extreme will power and proper background knowledge.

Potential side effects

Being on such a crash diet is very challenging - physically and mentally. It is a very intense diet, which may come with behavioural changes. You might be more bad-tempered and exhausted.

Every time you remove a full segment of food from your diet, your body will react in a dramatic way. This can include:

  • headache
  • fatigue
  • blood pressure drops
  • constipation
  • menstrual changes
  • hair thinning
  • muscle cramps

Keep in mind, that these side effect aren't permanent. Either your body will adjust, or you can adjust your supplementation or fluid intake. If nothing helps, the side effects will subside when you're switching into a healthier diet program.

If you suffer from heavier side effect make sure to consult a doctor.

PSMF diet and fat loss

Normally, our bodies run on carbohydrates as its primary source of energy. When you're limiting your carb intake to nearly 0, the body begins to burn body fat as its primary fuel. Because of the rapid fat breakdown, our livers start to produce ketones, which are excreted through urine. You're now in a state called ketosis. Ketosis itself does not help with fat loss directly, only a caloric deficit does, but it helps with muscle retention and satiety.

How much body fat can I loose during a PSMF diet?

During every 'normal' healthy weight loss diet you aim for a 0.5kg/1lbs loss per week. More is unhealthy and unsustainable.

However, during a PSMF diet fat losses of 0.2g per day in women and 0.3g per day in men and weight loss of around 1.2-2.5kg/3-5lbs per week are not uncommon.

The PMSF is shown to be way more effective for people who are obese. If you are already a lean bean, you simply don't need the PMSF diet.

If someone is obese, his/her body has a lot of alternative fuel. As opposed to someone who is already lean, with very little body fat.

How to calculate your macros on PSMF

This one is pretty easy. You eat as much protein, preferably lean meat from animal sources, as you require in order to don't lose lean muscle mass, but maximise the fat loss.

Furthermore, you add heaps of low-carb fibrous veggies, everything that is green, such as spinach, courgette, kale, broccoli, lettuce, asparagus or chard. You can add anything you want as long as it contains an sensible amount of digestible carbs.

Aim for 2g of protein per kg of lean body mass (or roughly 1g per lean pound). If you feel hungry, add some healthy fats, but don't overdo it here.

If you are obese, you can spare more muscle mass due to having more body fat, while people who are much leaner have an increased nitrogen deficit.

Actually, that's it. As I said before, you're cutting carbs and fats nearly completely out of your diet (except for fibrous vegetables and some healthy fats). Cook with very little fat. Plus, eat no fruits, sugar or starches. Furthermore, drink at least 1.5l of fluids every day and use 5g of salt every day.

Normally, people will maintain this diet for a few weeks, then do a refeed and resume with a more sustainable, healthier diet.

How to calculate your lean body mass

Start by figuring out your bodyweight in pounds - which is pretty simple, just step on the scale. Now figure out your body fat percentage. There are several ways to do so. This guide is the easiest way.

Now that you know your body fat percentage, you are able to calculate your lean body mass, which is crucial for the amount of protein you need while doing the PSMF diet.

For example, I weigh 120 pounds and my body fat percentage is around 15%. Here's the calculation:

120 x 0.15 = 18 pounds of fat

120 - 18 = 102 pounds of lean body mass

In this example the lean body mass is 102 pounds.

I'm training regularly, so I should aim for a protein intake of 1g per lbs lean body mass. My ideal protein intake during the PSMF would be roughly 100g of protein per day.

What about supplementation?

Fish oil

While being on the PSMF diet you'll definitely lack on essential fatty acids. Therefore, a supplement is crucial! If you don't want to take fish oil, you can also use flax seeds.

Protein powder

You don't need to use it, but protein powder can be very useful and adds some nice flavour to your diet.


On a PSMF diet you can't eat fruits and only limited veggies, which will lead to vitamin deficiencies. Take multivitamin supplementation to make sure this doesn't happen.


By lowering your carbs, you will decrease your potassium, sodium and magnesium levels. Add 3g of sodium (you can simply use more salt), up to 1g of potassium and 500mg of magnesium. This will also help you with fatigue.

How to exercise while doing the PSMF diet?

Most people will not exercise at all, while being on this diet. In fact, exercising should be restricted, because calories need to be adjusted upwards to make sure you don't lose any lean muscle mass.

Once you switched to a more sustainable diet, you can slowly begin to introduce workouts back into your routine. But start with moderate exercise.

However, if you decide to do any exercise, make sure to increase your protein intake!

How long should I do the PSMF diet

You can follow this diet until you reach your target weight, but most will only do it a few weeks at a time. Some people are able to follow this plan for several weeks, some just for a few days. Just do whatever you feel comfortable doing.

The more body fat you have, the longer you should be able to stay on the diet, but as said before it's mentally very challenging.

The ultimate goal is always a transition into a healthy diet. The PSMF diet is just an initial strategy to kickstart your weight loss.


Yes, this diet sounds crazy. But think about how many people go on useless very low calorie "magazine - diets" every day, which don't even work and kill muscle mass. I showed you a fast and safe way to get rid of some extra pounds, while covering at least some nutritional bases and reseting your taste buds.

Always keep in mind, that this is a crash diet, not a way of living!

Have you tried the PSMF diet and want to share your experience with us? Awesome, write a comment and let me know how you felt and what your results were!

If you're looking for a more sustained and healthy lifestyle. Check out the video about our nutrition course below.

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