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A Guide to the Protein-Sparing Modified Fast or PSMF Diet

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  Published on August 9th, 2023
  Reading time: 4 minutes
  Last modified July 21st, 2023
Meal during the protein sparing modified fast diet

The topic of protein has become more important these days, especially among people who are conscious of their health. This includes those who exercise regularly, are healing from an illness, want to lose body fat and preserve muscle, and want to age well. 

While protein is a must in any diet, there’s one diet that focuses solely on this macronutrient—it’s called the PSMF diet. PSMF is highly effective for anyone looking to lose weight quickly. However, it’s not for the faint-hearted. 

Let’s take a closer look at the PSMF diet plan, what the research says, and whether you should consider giving it a try.

What Is the PSMF Diet?

PSMF stands for protein-sparing modified fast. In essence, it’s a high-protein and very low-calorie approach that’s considered both effective and safe for rapid weight loss, according to research. [1]

You might be surprised to find out that PSMF was introduced all the way back in the early 1970s and co-developed by Dr. George Blackburn as a way to reduce the risks associated with protein-calorie malnutrition. For those who don’t know, protein-calorie malnutrition results from poor protein and calorie intake due to an illness or low-calorie diets followed by obese patients.

It’s important to remember that PSMF should only be used short term. If you have a medical condition, such as diabetes or high blood pressure, it’s best to consult your healthcare provider before undergoing PSMF. 

How Does the PSMF Diet Work? Plus Foods and Recipes to Try

The protein-sparing modified fast involves two phases: 

1. Phase one is the intensive phase, wherein you eat only 800 calories per day for up to 6 months. As for how much protein you’ll need, aim to consume 0.7 grams per pound of body weight. For example, if you weigh 180 pounds, you’ll require about 126 grams of protein (This provides 504 calories since each gram of protein has 4 calories).

Omelette for a protein-sparing modified fast

It is recommended to stick to protein sources with fewer than 3 grams of fat per ounce, such as chicken breast, egg whites, tilapia, and tuna. Keep your carbs under 20 grams per day. 

Taking a multivitamin supplement and electrolytes while you’re in phase one will greatly help in preventing vitamin, mineral, and electrolyte deficiencies.

2. Phase two is the refeeding phase, which lasts up to 2 months (or 8 weeks). During this period, you slowly incorporate more fat and carbs into your diet. You can now consume up to 45 grams of carbs daily for the first 4 weeks, and up to 90 grams daily thereafter. 

You’re also going to decrease protein by 28-57 grams (or 1-2 ounces) every 4 weeks. 

Below are examples of foods eaten on a PSMF diet: 

  • Skinless chicken breast
  • Top sirloin steak
  • 95% lean ground beef 
  • Egg whites
  • Tofu
  • Tilapia
  • Cod 
  • Catfish
  • Shrimp 
  • Pork tenderloin
  • Non-starchy vegetables, such as spinach, broccoli, cauliflower, and lettuce

Avoid fatty cuts of meat, butter, full-fat dairy, and other high-fat foods during the intensive phase of PSMF. 

Steer clear of anything that’s high in carbs and sugar during both phases, such as grains, honey, baked goods, and desserts. 

Try these PSMF-compliant recipes from Ketogenic:      

Potential Benefits of Following the PSMF Diet

Tuna for psmf diet

The PSMF diet results in rapid weight loss due to a decrease in calorie intake and ketosisPSMF results in the metabolic state of ketosis during the intensive phase since carbs are limited to only 20 grams per day. Eliminating carbohydrates will deplete your stored glycogen, which in turn teaches your body to burn fat for fuel. Being in ketosis can also suppress hunger, leading to weight loss. [2]

Let’s also not ignore the fact that protein plays a huge role in boosting weight loss by increasing your fullness and the number of calories you burn. [3]

A 2020 study found that patients who started the PSMF diet achieved more weight loss by 3% compared to those on the control diet. Weight loss was already obvious during the first year of doing PSMF. It’s also interesting to note that the patients on PSMF experienced a decrease in their systolic and diastolic blood pressure, especially those who lost at least 5% of their weight. [4]

Losing body fat through the PSMF diet can make a positive difference in other areas of your health. It can lower inflammation (which drives chronic diseases) and restore high blood glucose to normal levels in those who have diabetes or are at risk. [5] [6]

Furthermore, it also helps reduce some of the risks of carrying excess weight, such as high triglycerides, sleep apnea, and decreased mobility, according to the CDC. [7]

Possible Drawbacks You Should Know

Like other diets, the PSMF diet isn’t perfect. Because it’s very low in calories, it can lead to nutrient deficiencies. This is the reason why you will likely need to take a supplement. 

Another thing to watch out for is the keto flu. Since protein-sparing modified fasts induce ketosis during the intensive phase, you may feel temporary symptoms like fatigue, headache, brain fog, reduced exercise performance, and insomnia. Here’s a guide to help you understand the keto flu. 

How the PSMF Diet Differs from the Keto Diet 

Although a protein-sparing modified fast limits carbohydrates, which results in ketosis, it differs in that it focuses on protein as your main source of calories. The keto diet, on the contrary, makes dietary fat your main fuel. 

While you can stay on the keto diet for years, PSMF diets are only meant to be followed short-term to minimize the risks of eating too few calories and fat. 

So, have you tried the PSMF diet? How did you find it? Share your thoughts below!

Tiffany is a health writer and registered nurse who believes in low-carb nutrition, exercise, and living simply. She has carefully followed the ketogenic diet (mostly clean keto) since 2019, which helped her lose 44 pounds, heal PCOS, and gain more energy. She hopes to educate and inspire others through her content here at Ketogenic.com and on her personal blog Ketogenic Buddies.



Thomas, D. D., Istfan, N. W., Bistrian, B. R., & Apovian, C. M. (2018). Protein sparing therapies in acute illness and obesity: a review of George Blackburn's contributions to nutrition science. Metabolism: clinical and experimental, 79, 83–96. https://doi.org/10.1016/j.metabol.2017.11.020


Dashti, H. M., Mathew, T. C., Hussein, T., Asfar, S. K., Behbahani, A., Khoursheed, M. A., Al-Sayer, H. M., Bo-Abbas, Y. Y., & Al-Zaid, N. S. (2004). Long-term effects of a ketogenic diet in obese patients. Experimental and clinical cardiology, 9(3), 200–205.


Moon, J., & Koh, G. (2020). Clinical Evidence and Mechanisms of High-Protein Diet-Induced Weight Loss. Journal of obesity & metabolic syndrome, 29(3), 166–173. https://doi.org/10.7570/jomes20028


Pfoh, E.R., Lowenthal, G., Jeffers, L. et al. The Effect of Starting the Protein-Sparing Modified Fast on Weight Change over 5 years. J GEN INTERN MED 35, 704–710 (2020). https://doi.org/10.1007/s11606-019-05535-0


Bianchi V. E. (2018). Weight loss is a critical factor to reduce inflammation. Clinical nutrition ESPEN, 28, 21–35. https://doi.org/10.1016/j.clnesp.2018.08.007


U.S. Department of Health and Human Services. (n.d.). Achieving type 2 diabetes remission through weight loss - blog - NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/professionals/diabetes-discoveries-practice/achieving-type-2-diabetes-remission-through-weight-loss 


Centers for Disease Control and Prevention. (2022, September 24). Health effects of overweight and obesity. Centers for Disease Control and Prevention. https://www.cdc.gov/healthyweight/effects/index.html 

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