What is a Protein-Sparing Modified Fast?

OK, tell me the basics

The protein sparing modified fast diet (PSMF) is a very low calorie diet, based on a prolonged fast, and is used for rapid weight loss. With a typical calorie allowance below 1,000 per day, its intention is to induce a state called ‘ketosis’, where the body is forced to utilise its fat stores as fuel. Calories would largely be drawn from lean protein sources, with minimal amounts from fats and carbohydrates. The high amount of protein helps reduce muscle loss and wastage.

The PSMF diet is not a lifestyle; it should only be used on a short term basis, lasting a few weeks for initial motivation and rapid weight loss. It is then advisable to make the transition onto a more sustainable healthy and balanced diet for the long-term.

A little more detail..

The types of foods typically eaten on the PSMF diet are chicken breast, extra lean beef, tuna, egg white, and cottage cheese, with small amounts of low carbohydrate vegetables.

In addition to a high protein diet, followers of the PSMF diet are advised to take supplements such as vitamins, minerals and both DHA and EPA rich fatty acids. This is to avoid nutritional deficiencies that could result from a lacking in food variety.

For most people seeking to lose weight, 1-2 weeks would be sufficient to kick off their diet before starting on a far more sustainable weight loss programme. For those with a BMI (body mass index) of 30+ it may be possible to undertake the PSMF diet for a longer duration but it is highly recommended that medical clearance be obtained first.

The benefits

  • Potentially significant and rapid weight loss, giving a real incentive to keep going with the diet.
  • High protein and the process of ketosis both help to suppress appetite, so feelings of hunger are less of a big issue.


  • Although appetite can reduce following this diet, it is likely that some individuals could feel hungry for the first few days.
  • One side effect of the PSMF diet to watch for is dehydration due to loss of electrolytes. This can cause dizziness, headaches and lack of energy.
  • Dieters may experience constipation due to the lack of fibre present in the diet.
  • The diet is not nutritionally complete and does require supplementation.

Is it for me?

Protein Sparing Modified Fasting is an extremely effective way to lose weight to ‘kick off’ a more moderate and longer-term diet, but it does come with its own challenges. The extreme calorie reduction and lack of variation will be hard to stomach at first and could be difficult for some to maintain. The PSMF diet is probably not best suited for people who are highly active or those following vegetarian or vegan diets. A short trial of a week or two might suit some people, possibly followed by consultation with a healthcare professional to ensure your safety.

For anyone with an existing medical condition it is highly recommended to seek advice from a medical practitioner before starting on a PSMF diet.

How can I follow a Protein-Sparing Modified Fast using the Diet Meal Planner?

  1. Go to the “Lose weight” page found under diet plans and select PSMF from the drop down list
  2. Select how many meals and snacks you wish to have on your “normal days”
  3. Enter any personal nutritional requirements, allergies and any foods you don’t like
  4. Click “Create My Meal Plan” and let the Diet Meal Planner do the rest of the work for you!


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