Protein Sparing Modified Fast Diet

protein-sparing-modified-fastThe PSMF (Protein Sparing Modified Fast) is a temporary ketogenic style diet that can be used to start weight loss or break a stall in weight loss. As the name says, it’s a modified type of fast and not intended to be a complete diet. The intent behind PSMF is to reduce calories to the lowest level possible while still eating enough protein to preserve muscle mass.

PSMF was created in the late 1970s as a diet for a rapid weight loss for the morbidly obese. As a very low calorie diet, dehydration can be a problem, so there has to be a focus on getting proper hydration, as well as vitamins and minerals such as potassium, magnesium, sodium, and calcium.

A PSMF is an alternative to a complete fast designed to help preserve lean body mass by consuming the amount of protein necessary to prevent muscle-wasting. During the PSMF, you eat 1.2x your lean body mass in grams of protein.

As an example, if you weigh 180 pounds and are at 15 percent body fat, you have 27 pounds of fat; 180 – 27 = 153 pounds of lean body mass, so you would eat 184 grams of protein per day (153 x 1.2).

And that’s it. While you are allowed some carbs and fat as possible, your goal should be to limit calories from these sources to as little as possible (no more than 50 calories from carbs and 90 from fat daily).

Stick to foods like fat free cheese, fat free yogurt, grilled chicken breast, and some cruciferous vegetables for fiber.


  • Extra lean hamburger
  • Chicken or turkey
  • Beef – chuck, flank, tenderloin, rump, and round
  • Pork – well-trimmed tenderloin or lean ham
  • Lean cuts of lamb
  • Low-fat cheese
  • Eggs


  • Fish: salmon, bluefish, porgies, swordfish, halibut, tuna
  • Skinless white meat chicken or turkey
  • Organ meats like liver and kidney
  • No-fat cheese
  • Egg substitutes (like egg beaters)


  • White fish like haddock, sole, flounder, cod, etc….
  • Shellfish – shrimp, lobster, clams, crab, scallops
  • No-fat cottage cheese
  • Egg whites

At a minimum, drink eight 8-ounce glasses (2 quarts) of no-calorie liquid every day.


  • Unlimited
    • Water (includes tap, spring, mineral, seltzer or soda water)
    • Decaffeinated drinks like black coffee, green or black tea, herbal teas
  • Limited
    • Diet soda (no more than 24 ounces a day)
    • Caffeinated coffee or tea (12 ounces per day due to caffeine)

Guidelines for Running the PSMF

  • If you’re under 15% body fat, limit your PSMF to 2 weeks, using 1 re-feed day per week.
  • If you’re between 15 to 25% body fat, you can run this diet for up to 6 weeks max with 1 cheat meal and 1 re-feed day per week.
  • If you are above 25% body fat, you can run this meal until you get down to 15%, however long that takes

Break your eating up into 4 meals per day, evenly spaced, with each meal containing 25% of you protein goal.

Does it Work?

For these 668 obese patients, PSMF worked very well. Participants on average consumed less than 800 calories a day along with:

  • Vitamin and mineral supplements providing the RDA of all essential vitamins and nutrients
  • Minimum of 50 ounces of fluids daily
  • Minimum 5 grams of table salt daily

The patients in this study lost an average 46.2 pounds. They improved their blood pressure, blood sugar control, and blood lipid numbers. Other studies have also found PSMF is helpful for diabetes and effective in diabetic patients.


PSMF is a short-term tool, not a diet you’ll be on for extended periods. It can be a difficult regimen to stick to, but if you can, the results will be fast and dramatic.


Leave a Reply