The basics of Protein Sparing Modified Fasting (PSMF): Is it a good fit for you?

6 minute read • December 14, 2021
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PSMF (Protein-Sparing Modified Fast) has gotten a lot of attention lately due to its reputation to help people lose a lot of weight quickly. And indeed, it can be a fantastic way to break through a stall, but it isn’t for everyone and, depending on how you implement it, isn’t typically used for extended periods of time. The PSMF subreddit sums it up this way:

PSMF is a ketogenic diet designed to jump-start a weight loss program (either for rapid fat loss for a body builder or those with some weight to lose) or break a stall. It is a modified fast and as such is not a lifestyle. The idea is basically to only eat [enough] to prevent lean muscle loss (protein).

The Basics of PSMF

shrimp in bowl

With a typical ketogenic diet, you will be getting 20-50g of carbohydrates as an upper limit. You will also be getting anywhere from 90-160g of protein (depending on goals, activity, and other factors), with fat as a variable that can come from the food you consume or from your body’s fat storage.

For the rest of this article, I’m going to be using numbers from Maria Emmerich’s Macro Calculator. I’m setting the calculator to give numbers for a 220 lb., 40-year-old female with 35% body fat that we will call “Jane.” Your numbers will be different so please make sure you pull up the page and enter in your measurements. The calculator says that if Jane wants to lose weight quickly, she should use two different calorie/fat/protein/carb combinations (click to embiggen!):

PSMF Calculator Results for Jane

If Jane had selected regular “Fat Loss” instead of PSMF, it would have told her to do 1659 calories with 118g of fat, 130g protein, and 20 total carbs. There are a few important points that I would like to cover here:

  1. You will notice that we are talking about grams, not percentages for the fat/protein/carbs. Macro percentages are generally only used for treating epilepsy, and even then it’s more properly done with a 4:1 or other ratios of fat calories to other calories instead of percentages. If you’re looking at a macro calculator that uses percentages, I’d recommend finding a different one.
  2. If you have looked at other keto macro calculators, you may notice that the amount of protein recommended is much higher on Maria Emmerich’s calculator. Craig Emmerich covers a lot of the old fear that people used to have about protein and why it’s unfounded in his presentations about PSMF given at Keto Salt Lake 2021 – I highly recommend checking it out.
  3. The text above the figures reminds you that protein is a minimum. You’ll want to get at least that much. You can get more as long as you stay below the calories (by getting less fat).
  4. If you use Maria’s calculator, it explains the basic setup of how to do PSMF. “Add 1-3 days a week of PSMF to speed up fat loss or break stalls. Then Fast Fat Loss macros above on the other days. If doing this two or more weeks in a row, add an overfeeding day each week with 400-600 additional calories of protein and fat.”
  5. Maria recommends you stay under 10g of TOTAL carbs. You will quickly find that 10g of total carbs and 30g of total fat will necessitate a major change in how you eat on your PSMF days (hello, chicken breast!).

How you can use Keto Chow for PSMF

natural strawberry

OK, we’ve covered some of what PSMF is and how to do it. How can you use Keto Chow as a tool to help you be successful with PSMF? First things first: we need to address the total carbs situation.

Most flavors of Keto Chow contain around 7.6g of total carbohydrates. If you wanted to use three meals of Keto Chow on your PSMF days, that would be 22.8g of total carbs before you even add any other food. That’s obviously a lot more than the 10g Maria recommends!

Here’s the thing about the total carbs in Keto Chow: 5.71g of that is acacia and xanthan gum fiber (mostly acacia). Acacia gum is some REALLY cool stuff, especially for a keto diet. There’s a long explanation of the benefits of acacia gum on keto on this page, but the short version is: your body can’t digest acacia gum, but your gut bacteria DOES and it turns the former carbohydrate into short-chain fats. Carbs in -> turned into fats = happy gut biome with energy for your intestinal cells.

All of this is why I, personally, do not count acacia gum (or xanthan gum) towards my total carbohydrate limit. With that acacia and xanthan gum quantity removed, the result is 1.8g of fiber and lactose carbohydrates. Let’s make the math easier and call it 2g just for fun. 6g of carbs from 3 meals of Keto Chow still leaves me with 4g and that’ll be taken up by the incidental carbs in anything else I’m eating to cover the rest of my protein goal after three Keto Chow meals made with 10g of butter each.

Enough about me, let’s go back to Jane and her goals! Jane needs to get 159g of protein, and stay under 30g of fat. For Jane, that means 78.6g of protein from three meals of Keto Chow (or 52.4g if she uses two meals of Keto Chow – the number of meals of Keto Chow is entirely up to you!).

Jane will be 80g of protein short doing three Keto Chows, even though she knows that she got a full 100% of her vitamins and minerals from them. How can Jane get that additional 80g?

It’s time for Cron-o-meter!

group of people smiling

We love Cronometer around here! More info here about using Cronometer to track your net carbs.

The key difference between Cronometer and most other tracking programs like MyFitnessPal and Carb Manager is that Cronometer uses a curated database. That means every entry you find has been verified to be correct. I switched from MyFitnessPal after I tried entering butter into my tracking and there were 7 different entries that were wrong.

Anyhow, the intricacies of Cronometer are beyond this particular blog post, but let’s say Jane took the numbers from Maria’s calculator and put them into Cronometer as custom targets:

keto chow cronometer - chocolate toffee

Jane has entered the food she’s planning to eat. In this case, it’s three different flavors of Keto Chow, along with the 10g of butter that she’s having in each meal to make sure that she will be able to absorb the fat-soluble vitamins.

Food and Targets 1-Cronometer

But wait a minute…the fat is a little high when she uses 10g of butter in each shake! That would be 8.1g of fat, plus 6.1g for each of the skinless chicken breasts that she wants to include in her meal plan for the day. Let’s lower the amount of butter in each Keto Chow to 7g. That will make for 21g of butter in total. Jane still wants to get around 10g of fat per meal so she can either have a chicken breast in two of her meals, or actually split up the two pieces of meat into three portions and have 2/3 of a breast with each meal.

Now here’s how her targets are looking:

cronometer texas roadhouse

That looks really good! Jane is half a gram over on fat and 3g over on protein, but both are exceptionally close to her targets.

Now for a non-PSMF day, Jane could have two Keto Chows, along with some beef for her third meal. Let’s say she decides to have two of the same 7g of butter Keto Chow shakes she had the previous day and then she’s going to go to Texas Roadhouse and get a 12oz Prime Rib along with a side salad.

Food and Targets 3

Honestly, that’s phenomenal. Jane has a good plan in place!

Additional recommended PSMF resources:

Make PSMF Meal Prep Easy

uncooked chicken

If you’re unsure how to get started on meal prepping for the PSMF diet, you can check out our free PSMF e-book. It’s full of delicious and easy recipes created by influencer Maria Emmerich. Sign up to get it here!

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