Protein Sparing Modified Fast


You’ve heard of Keto and Carnivore, and you’ve heard of Fasting, but what in the world is a Protein Sparing Modified Fast, or PSMF?

Let’s take a look at what it is, how it’s different from a true fast, and who might benefit from it.

What is PSMF?

PSMF is not a true fast. 

It’s become quite popular in the Keto/Carnivore world, mostly due to Maria Emmerich, who teaches it and creates tons of PSMF recipes. 

But Maria did not come up with the term or the plan herself. It goes back a long way. 

The name itself is a little confusing. It almost sounds like it means you’re sparing protein. 

But it’s actually the opposite. 

PSMF ramps up the protein. A more accurate name would be muscle sparing. 

Because that’s the premise behind it. 

PSMF was developed with the idea that fasting can cause muscle loss. 

For the record, if you have enough body fat, fasting does not burn muscle. 

But for the sake of explaining what PSMF is, we’ll let that slide for now. 

So the idea here is that two or three days a week you ramp up the protein, and lower the fat.

And of course carbs still stay way low, as well. Ideally under 10 carbs a day, but up to 20.

Calories are also severely restricted.

Then the other days of the week you continue with your Keto or Carnivore diet as usual. 

How much protein?

There are calculators out there to determine your macros. 

Maria and her husband, Craig, have a great macros calculator on their website which includes the PSMF option. 

But many people don’t bother with trying to hit specific macros. 

Rather, they do a few days a week of higher protein foods, like chicken and other lean meats. 

And then the other days they switch back to higher fat and moderate protein. 

Who is this good for?

Even though it came about as a way to prevent muscle loss during fasting, the real beauty of PSMF is that it can help beat weight loss stalls. 

On the days that you’re doing PSMF, your fat intake is much lower, giving your body a chance to tap into your stored fat more. 

If you’ve been following a Keto or Carnivore lifestyle and it’s not working for you, or maybe your fat loss has slowed down, this could get things moving. 

Another benefit of PSMF is that protein is very satiating.

That could potentially help if you’re someone who struggles with hunger and cravings.

Who should not do PSMF?

If you’re very close to a healthy weight, you should not do PSMF. 

You won’t have enough body fat to sustain it. 

If you have any medical conditions, such as diabetes or kidney disease, or if you are on any medications, you should check in with your doctor before you try PSMF. 

If you are pregnant or breastfeeding, you should not try PSMF. 

And while children can certainly eat high protein foods, they should not do PSMF. 

They still need plenty of healthy fats for their growing bodies. 

PSMF is not a long-term diet!

Unlike fasting, this is not something you can do over and over. 

The very limited calories and the limited fats will catch up to you. 

A few times a week for a couple of weeks at a time is plenty, and then only if you have lots of body fat. 

After that, you should take a break before you do the PSMF again. 

Even with Extended Fasting, we recommend taking a break every once in a while. 

Doing a PSMF too often could crash your metabolism. 

The conundrum … 

Our fasters might be scratching their heads by now. 

We know that, according to Dr. Fung, when insulin is spiked fat burning is shut down. 

Even if you’re only eating 700 calories on a PSMF, you’re still spiking insulin.

Therefore you are not tapping into fat stores. 

And most people who are obese have insulin resistance. PSMF will not fix insulin resistance. 

So does PSMF work because of the calorie restriction? Or does it actually burn fat? 

Worth it? 

Is PSMF all it’s chalked up to be? Maybe. There are lots of success stories out there. 

If you’re someone who is experiencing a weight loss stall, or just looking to switch things up a little, a PSMF might be an option. 

Otherwise, stick to Water Fasting and a Keto or Low Carb diet when you do eat.

Author: Roo Black

Roo Black

Roo is a fasting coach with over 5 years of experience. She leads the admin team of the Official Fasting for Weight Loss Facebook group – one of the largest fasting communities on social media with over 125,000 members. We highly recommend this group for anyone who is looking for fasting advice or coaching.

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