Protein Sparing Modified Fast: The Hydrogen Bomb Of Safe Crash Dieting

I was 20 years old the first time I went on a diet. After years of being the skinny kid and taking up weight training, I bulked up to my highest weight and largest waist ever. 12 weeks after starting my diet I was 20lbs lighter and 5 inches slimmer; thus began my black box dieting adventures. Two weeks ago, I embarked on what is widely considered the extreme smart bomb of the diet world: the protein sparing modified fast.

A protein sparing modified fast (psmf) is essentially the most scientific “crash diet” available, allowing the loss of 4 to 7 pounds of fat and 10 to 20 lbs of weight in 2 weeks time. For me, I wanted to try this before I visited my girlfriend in Ecuador as a means of being extra impressive. I also had a couple pounds of fat to lose coming out of 6 week cyclic gaining phase, so I was mentally, physically, and hormonally ready to go. This is how I planned to do it.

1. Eat Good Protein

Duh. Eat 1.25 grams of protein per pound of lean body mass (lbm) on non-workout days. Consume 2 grams of protein per pound of lbm on workout days. Protein sources include lean meats and milk protein isolate protein powder. Keep it simple.

2. Eat unlimited green veggies

They’re mostly fiber to begin with, which will increase satiety and keep you regular. I was mixing spinach into my protein shakes, which worked quite well. You’ll also gain a taste for veggies, which is part of the reprogramming aspect of the diet.

3. Take a multi-vitamin and 6 grams of fish oil each day

Essential fatty acids found in fish oil are, well, essential. Your body can’t make them so you must obtain them from diet. The multi just covers nutritional bases.

4. Constantly remind the over-concerned that you’re not going to die

All of the food you’re taking in is nutrient dense and/or biologically active, as opposed to the collagen protein used in the Last Chance Diet. This combined with the vitamins and minerals from supplementation will keep you right as rain.

5. Do this as long as you can stand

The max should be 2 weeks before embarking on a short refeed, but leaner individuals might find themselves returning to modified eating habits sooner.

This meant that on a normal day, I was taking in between 950 and 1400 kcal. While this might sound crazy, think about how many people have given their body less calories and nutrients when embarking on really dangerous shit like the master cleanse. This PSMF covers all of the nutritional bases while also attempting to reset your taste preferences. When starting any sort of effort to get lean, seeing results up front goes a long way toward compliance and motivation.

What were my results? I managed the stay on the diet 6 days before needing a 5 hour refeed. After which, I spent 3 more days on the diet before another 5 hour refeed. After a few days of my regular paleo-ish eating habits, I weighed in 5lbs lighter than when I started. While I was up to 9lbs lighter during the diet, the weight regained was water and glycogen. I’ve since returned to a cyclic, paleo-based style of eating, using some of the methods discussed in my post-workout nutrition post.

For more information, I’d suggest purchasing Lyle McDonald’s “Rapid Fatloss Handbook.” It’s worth every penny.

Also: I recently wrote a post of tips for making the fast tolerable. Read all about that here.


33 thoughts on “Protein Sparing Modified Fast: The Hydrogen Bomb Of Safe Crash Dieting

  1. I’ve just started a similar diet but less protein and no exercise. I’m just wondering if you should weight train on such a low calorie diet. Wouldn’t this eat up the protein (and muscle) you are trying to spare in the first place?



    Muscle is “use it or lose it” due to the metabolic expensive of actually building it. Strength training during the diet is meant as means to keep muscle tissue but should be of a lower intensity than you would normal have during normal circumstances.

    I would encourage an increase in protein, as that’s what is helping your body to spare muscle and use fat.


  2. I’m strongly considering this diet but I wondering about the suggested protein intake. According to the calcs, my lbm is around 190 lbs and my overall weight is 265. That would mean that my protein intake for this diet would be 237 grams and 380 grams for the days on / off. Is this accurate? It seems like a lot of protein…then again, as I wouldn’t be eating anything else I suppose it isn’t that much.

    Anyway, just wondering. Don’t want to screw it up if I commit.

    Thanks for any help you can offer.


    1. Ben,

      Those numbers are correct. I linked it in the article, but you might want to check into Lyle McDonald’s book if you haven’t already; it’s really the purist “how-to” guide there is. It also has a ton of recipes.

      1. Fantastic. Thanks a bunch. I’m starting it on Monday so wish me luck! I’m trying to get down to 185 as a final result so this is the first step.

  3. For anyone considering this, it would be wise to check with your doctor first. In some cases, as where I live, your local hospital may have a monitored program employing this type of diet available.

    My wife is about to embark on the PSMF program at the Cleveland Clinic. She did this many years ago and lost over 50 pounds.

    1. Ed,

      Thanks for the reminder; it’s something that should be supervised if you’ve not previously been on a diet before or had health issues. As I noted, thanks to improved supplementation, the quality of the nutrients for the person embarking on such a plan is much greater than the original “Last Chance” diet.

  4. Hi there. I’m wanting to start this diet and am just reading up on it. I’m worries though, that once I drop the weight and go back to to a healthy but more normal way of eating, that it will just all come right back on. Had that been you experience? Also, I’m unfamiliar with the idea of “re-feeding.” Can you explain that to me better? What should you eat during a refeed?



    1. Krystal,

      Many apologies for not getting back to your sooner. Your fear is founded but in my experience the rapid regaining of the weight doesn’t happen. This is mostly, I think, because I’m typically working with clients during the diet. You’ll lose a lot of fat, but you’ll also (if you’re paying attention) have a psychological shift. Suddenly, the idea of eating mostly paleo (for instance) seems like it would be really, really tasty compared to the PSMF. So that’s how I look at the diet: it jump-starts long term gains and it resets your idea of what YOUR “normal” diet can be.

      Now, the refeed is a time period, anywhere from 3 hours to 2 days, when a person would intentionally overeat (in a controlled, measured manner) carbohydrates to raise fat burning hormones and take a mental break from their diet. For most people looking to lose a lot of weight, this isn’t really needed. Refeeds generally apply to leaner folk looking to get really lean. I hope I answered your questions!


  5. I started the PSMF diet 121 days ago. My beginning weight was 313 pounds. My current weight is 240 pounds. Total weight loss thus far is 73 pounds. I go on a brake for three weeks and hope to be down to 200 (actually 195) by the New Year. My doctor is amazed and my Endocrinologist is very happy. I encourage anyone to give it a try. I am not hungry and if I say so myself, I look and feel great. By the way I am 48 years old and my wife is very happy as well.

  6. I need to drop some weight. A lot of weight. After looking into “The Rush Limbaugh diet” and scoffing at the Quick Weight Loss Center’s $450.00 every 6 week price tag, I recalled a very short section from a book I read years ago titled “The Ketogenic Diet”.

    The PSMF is desribed, but in much less detail than the TKD and CKD, and in fact I recall Lyle cautioning against it. At that time (over 10 years ago) I was lifting daily and stayed away from it, but my age, my family and my career have all conspired to keep me out of the gym and put an extra 6 inches on my waistline. Along with it, pre-diabetes, sleep apnea and even asthma.

    It’s time. Googling PSMF lead me here.

    Thanks for the post and the inspiration, Skyler.



  7. I have been on “Dukan diet”, and am totally bored. Went to dietician at Cleveland Clinic and she said I am basically following their PSMF diet plan, but am eating too many carbs. Their carb portion in 20g a day. Not much. I started on 8/1/10 at 210# and am down to 170. I have cheated a bit the last 2 weeks…this winter weather makes me hungry. The holidays are a nightmare for trying to stay on a program. I go to gym 3x a week and do mostly cardio. I feel stuck right now.

    I am a diabetic, type II, off of insulin and just on Byetta (an injection before breakfast and dinner).

    Right now I crave bananas and chocolate. Help! Blood work is normal. All I take is a general vit tab, MegaRed krill oil, and a combo pill HCTZ/enanapril for water retention and BP, which is normal.

    Constipation is a nightmare. I don’t eat red meat, just have: chicken, tofu (no carb tofu), fish, seafood, turkey. My cholestoral went up 30 points, but still under 200, so that is why I take the MegaRed.

    What can I do to kill the cravings and stay on tract? I still have 20# more to go.

    1. Lisa,

      First, I must add the usual “I am not a medical doctor” disclaimer and don’t follow my advice without your doctor’s holy water blessing. 😉

      Now, are you doing any sort of counting on this diet? Are you upping calories on training days and lowering them on non-training days? Do you have any planned free meals?

  8. Hi,
    I’m a 5’3″ female, currently 125 lbs looking to be 120-121 lbs at the end of this fast. I began 3 days ago and plan on doing for ten days, and then decide to go on if I like what I see.
    I have been eating egg whites, protein shakes, lettuce, tuna, cod, turkey slices, diet coke and occasional broccoli/cauliflower. drinking lots. I always stay under 600 cals.
    I do HIIT (10 int) four times a week and one long distance run of 4-5 miles a week.
    two questions:
    -should I do a refeed if all im looking for is fat loss, mainly in the abdominal area?
    -is my 5lb goal reasonable for the 10 days? if not, how can I increase the efficiency of the diet?
    please point out any mistakes I’m making.
    xx, steff

    1. Cut the cardio to steady state twice a week and 2 short intense (but not gut busting) weight workouts. You’ll sabotage your progress if you work too hard; you don’t have enough calories to recover from the workload you’re proposing.

  9. HOw do you train on this. I have all my supplies but I wanted to know, do I do depleation workouts? strengh? Power? Please let me know. I am in a major dilema,



  10. I dont know if my other message was recieved here. Can some one let me know if it did. I so not computer savvy!

  11. I am on my first day of the PSMF. I’m getting married in 3 months and hope to be down 60 lbs. I am 48 years old and currently weigh 228 lbs. I will update in 30 days.

  12. Hi Skyler,
    I am seriously considering giving this plan a try. I am currently pretty strict paleo, and while I feel great on it, I am not seeing the weight loss that I would like to. I am considering purchasing Lyle’s book to follow.
    But, I am TERRIFIED of post diet weight gain. I am a former amateur bodybuilder, and tend towards an endomorph/mesomorph body type. I gain muscle and fat very well, and retain both VERY WELL! In a nutshell, in a 20 week contest prep, my trainers had to practically torture me into contest shape with low carbs/calories and insane amounts of cardio, multiple times daily. I never was able to get my abs out, however, nor would my body release the water at the end, even with diuretics… 😦
    However, the post contest weight gain was unbelievable!!!

    It seems like every gram of carbs I ate went straight into fat storage. While I no longer compete, I do want my bod back!! Since my competing days (my last show was ~5 years ago), I have done nothing but struggle with body fat.

    What do you think, should someone like me give Lyle’s “Rapid Fat Loss” a go or a miss?

    Any advice would be so appreciated!

    1. Lyle’s book is worth the cash. Tips and tricks for transitioning off the diet are there and are heavily emphasized.

  13. I want to do Insanity on the day I have free meal or 5 hours refeed.
    Do you think it’s OK or that’s still too much cardio?
    The rest of the week, I just do light exercise.

  14. Hi,

    thanks a lot of the info, this is the 1st time i’ve learned about this diet. While i intend to purchase the book soon, i have quick question regarding muscle mass, do you end up loosing some of it while on this dies?

    thanks again for all the info

  15. I dont think your protein calculations are correct – it was most likely per KILO which would be 2.2 pounds of bodyweight per gram or protein.

    1. Actually Mike I mean pounds and the calculations are correct. The point of the PSMF is to provide enough protein to spare muscle tissue for amino acid requirements, and the absolute minimal glucose requirements, while taking advantage of the increased metabolic rate that comes with a large amount of protein.

  16. Skylar’s right, it’s protein per pound.
    If I was any of you guys, I really wouldn’t try to Google how to do this diet, I’d buy the Lyle McDonald Rapid Fat Loss handbook. It explains exactly what you should do and explains why, including the physiological and psychological reasons.
    You can get it on torrent for free but that’s an old version, which has since been updated, plus this is a niche area, and you’re depriving a person of their right to be paid for their work.
    I came across this blog after doing a YouTube search for RFL. I’m a low Category 2, Skylar, also in the UK. Do you have any tips or advice that you haven’t already put down? I’m looking to lose about 10-15lbs over about 4 weeks before moving to maintenance then a recomposition period.
    After spending most of my life 25+% bodyfat I’ve recently lost nearly 5 stone and want to get pretty lean before increasing the calories and putting some muscle on.
    Any advice would be gratefully received.
    Thanks, Terry.

  17. That’s odd, most people that actually follow that diet lose 30-35 lbs in 6 weeks. You barely averaged 1.5 lbs/wk, which is pretty ordinary for a 2000 calorie/day diet WITH carbs. You must have cheated.

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