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Protein-Sparing Modified Fast While on BDW


Hi Chris,

Next week I will start a fat loss phase during which I want to use an approach Lyle Mcdonald discussed in one of his book, which is a Protein-Sparing Modified Fast (PSMF).

I’m sure you are familiar with it but for anyone else reading: a PSMF consists of only eating protein with an omega 3 supplement along with unlimited fibrous veggies.
I’m also going to consume 30 g of cyclic dextrins during my workouts along with 15 g of hydrolyzed casein.

My questions are:

  1. Is BDW a good choice for training during such a diet? In his book, McDonald recommends cutting down on training volume AND frequency, but I figured maybe this advice doesn’t necessarily apply to BDW since the parameters are already laid down in such a way to help recovery.

  2. If it is, are there any suggestions as to how this program could be optimized during an extreme dietary regime like PSMF? I can’t see volume being cut further but maybe there’s something else it can be improved on.

  3. Do you have any suggestions as far as ab work? I’m referring to an article in which you said that doing abdominal work paired with cardio and a deficit can help to burn the fat in the abs preferentially. However, I’m not sure doing cardio would be smart while on a very low calorie diet like this. What are your thoughts?

Thank you


I ran such an experiment last month using the principles behind McDonald’s version of PSMF (Category 1) and in conjunction with BDW2. I found they fitted very well together and I had no real fatigue whatsoever. That said, that was for one cycle (12 days) only.

You may also want to consider that McDonald has since revised his views on refeeds which, in summary, boils down to 5 days of aggressive dieting following by 2 days off (at maintenance or thereabouts) in order to accommodate hormonal adaptations. This is closer to what I am doing currently, again with no fatigue issues using BDW2.

Finally, IMO, if you are going rock bottom then you don’t need 30g CHO to fuel BDW sessions; 5-15 CHO is ample. Just my own views, although they may be biased from my usual practice of targeted ketogenic dieting.


Thank you for the insight, this is exactly what I was looking for.

I am thinking of trying to run a 14-day cycle, followed by 2 refeed days (the first one at around 820 g of cho, the second at half that amount as suggested by him in the book) and then a one-week break at maintenance. I am thinking this mainly because it’d fit my schedule better and because I’m kind of an in between cat 1 and 2 as far as body fat percentage. Do you think that could work or is 2 weeks too much?

You are probably referring to his UD2, which I know about. However, it believe it would be more effective if it were accompanied by a specific workout protocol, as he does, which thus wouldn’t allow me to train with BDW.

Thanks for the input. I might try with the low end first and possibly ramp up if needed.


As mentioned, he very recently revised his views based on the research around leptin. This applies to RFL as well as UD2. The upshot is your leptin levels start to take a hit around day 4 or 5. It then takes at least 2 days of energy increase (mainly carb increase) to offset this. Therefore, the original idea that ‘free meals’ through the week and ‘refeeds’ can offset a drop in leptin has been superseded.

I personally think your plan is ok but I am a ketogenic dieter so do not buy into the need for carb refeeds, particularly the numbers McDonald comes up with. I also believe there is some evidence showing switching between keto-based diets and high carb diets leads to quite dramatic fat regain based on the premise your body never truly fat adapts during the short keto phases.


Is there any public article he posted about this change of mind and new research or did he talk about it in a later print of the book? I read edition 1 print 1.

Anyway, I’m not really keen on changing my plan at this point—not because I don’t think the new discoveries you mentioned are important, but rather because I truly believe that even disrupting hormone balances a little more than I was expecting, but for only a small time frame like 2 weeks, isn’t going to be a big deal.

You mentioned running a 12 day cycle and I’m assuming you didn’t have any bonus carbs during. Did you lose any visible muscle?

Yeah the numbers mentioned by him look a bit high to me but I think McDonald is extremely knowledgeable and I trust his methods. And I would rather gain a bit of fat back than risk losing muscle, plus I can still run a second cycle if I need to lose more fat. It’s about risks vs rewards I believe.


I picked it up via a few podcasts he did last year.

I aimed for around 25g CHO per day, which included 5-10g cluster dextrin pre-workout. I lost just under 14lbs, a large portion of which was water/glycogen. I certainly never felt as though I lost muscle but did not have any accurate measurements to verify one way or another.


I’m actually shooting for slightly less than that.
I’ll take 5 g of cyclic dextrin pre workout along with whey, and 10 g during together with hydrolyzed casein, as per recommendation. Nothing else aside, as I already planned my nutrition which will consist of tuna, shrimp, chicken breast, egg whites, protein powder, egg whites, and basically nothing else. I’m not counting green veggies which add virtually no digestible carbs.

Anyway, since we’re here I’ll ask for a personal opinion.
This is what I currently look like

And I weight about 80 kg (179 cm tall).
My goal is to get as lean as possible (abs very visible) while retaining my muscle mass, and then start adding lean mass again.

Realistically, how close to my goal will a 2 week cycle of this diet bring me?


Difficult to determine based on what you have shared. Realistically, your energy deficit should yield 4 maybe 5 lbs of fat loss in 14 days. Any other scale weight is water. However, after 14 days the mirror may convince you you’re not as fat as you thought. This is deceptive. Getting abs is a true 12-14% body fat level. Check my last training thread ‘James Brawn’s Training Log’ and you’ll see me post-PSMF. I have abs but a week later I looked substantially different after regaining water. PSMF is a kick start to longer term dieting. That’s your challenge, having the mental discipline to do the 14 days then not binge afterwards. If you can keep that going then I’d estimate you could see real changes in 6 weeks or so.


I’ll take a look

I’m confident enough that I’ll stick to the plan and to keep myself accountable I will be opening a whole new daily log so that if something doesn’t go as expected, I’ll easily find the cause.

Anyway, what do you suggest after finishing that first cycle? You mentioned good results in 6 weeks which, if I use the "14 day PSMF -> 7 day break (2 days to refeed + 5 days at maintenance) -> repeat "layout would mean doing 2 full cycles. Right?

Or should I go with a smaller deficit after the first?


That’s up to you, see how you get on. If you’re the type that does well on a fixed program then you could follow McDonald’s Cat 2 recommendations and do RFL for 6-8 weeks.