AUTHOR'S NOTE: The author is engaging in a four week trial of the PMSF as research for this writeup
When people say they want to "lose weight", what they actually want to lose is "fat". There's very, very few people who ever say "I'd really like to waste away my muscle tissue and end up with the same amount of fat but less muscle". For the record, we've even got an expression for this, "skinnyfat", which describes someone who did way too much cardio and ended up with muscle wastage and fat retaining.
But losing fat is tricky. The body likes to hang on to it. It really does. Especially those "last ten pounds" which strongly resist being lost. There's an evolutionary reason for this, of course - the human body has adapted to store excess energy and hold on to it for survival purposes.
It sucks if you want to look good at the beach, though.
Various protocols have been suggested for weight loss: calorie counting, eating only certain types of foods (Atkins, keto), and so forth. But the biggest problem with diets is compliance. People like to eat. A lot. They don't like to be hungry. And when you suggest to someone that they need to eat less, the brain responds by saying "hey! I'm using more energy than I'm consuming! Go find food!"
It then does a lot of other things like slowing metabolism and sparking hunger, but another major problem here is that you lose AT MOST a pound, at the extreme end of things TWO pounds of fat per week. If you're fifty pounds overweight, that means almost a year of undereating. If you've ever been near a running track or gym around New Year's when people resolve to "finally get in shape" you'll note that they tend to stop showing up after week two: and given that people's motivation to eat right tends to evaporate after a while, especially after stepping on the scale after all that running which hurts and nibbling on carrot sticks for a week staring at hamburger ads like a teenage boy looks at hardcore pornography and seeing that they're a half a pound lighter, a lot of people simply say "fuck it" and go grab a pizza. You can't lose weight. It's my glands. I have a thyroid. I have a "condishun".
The protein muscle sparing fast is used in a variety of venues: specifically bariatrics when they're prepping someone for lap band surgery and need them to lose a lot of weight in a hurry. It's also a fad that's come and gone over the years, the latest of which is being pushed by various newsletters as "the Velocity Diet". With the advent of protein, fat and carb supplements, you can technically dial up an exact calorie matrix - need to consume 1300 calories with a VERY specific breakdown of fats, carbohydrates and protein? Enter a bunch of powders and liquids, and you can dial it in to the calorie.
So the gist of the PMSF is to drastically reduce calories, but maintain a high amount of protein and enough fat to keep the hormone systems humming. It's usually a liquid diet, because it's easier to weigh out a scoop of protein powder than to put all your chicken breast on a scale, and protein powder free of carbohydrates is nutrient dense for its caloric load. The Velocity Diet basically tells you to take four meals a day that consist of 220 calories/40g of whey and casein (think fast acting/slow acting proteins), blended with a mix of dried fruits and vegetable powder that provide the vitamins and minerals. The latest iteration says to also eat a SENSIBLE meal of 500 calories or less: basically chicken breast and green vegetables, that sort of thing. This helps mitigate two of the largest problems with the PMSF - compliance with the human need to eat solid food, and... well, the problem of elimination: either it being nonexistent, or explosively liquid.
1300 calories a day for an athletic human male expending a significant amount of energy lifting heavy things and doing steady-state cardio is a starvation diet. With high protein and demands on the muscles telling the body to hang on to muscle, and a steady caloric need requiring fuel, and enough calories being consumed so the body doesn't go into "starvation" mode - the idea is to lose as much fat as possible in a four week period.
These kinds of diets got a bad rap in the 1970s. People have died from them, most notably the comedian John Candy. But these folks were using poor quality protein supplements, cheaply made with collagen. Given that they weren't usable as food, the caloric intake dropped below levels that were safe and their bodies literally cannibalized heart muscle and other critical resources. Modern takes on the PMSF are nowhere near as drastic in terms of caloric restriction and demand the use of whey and casein, or extremely lean meats.
Like any other keto diet, there is a RAPID initial weight loss due to diarrhea, water loss and carb loss. The body loses its "fullness" and anyone who trains for muscle will see their physiques looking "flat". It's also extremely difficult to maintain the same energy output as the body fights very hard in terms of resisting switching from "burn carbohydrates for fuel" to "burn ketones for fuel". But when the body switches to ketones, the ketones come from fats. Stored body fat.
If you want to track your progress day to day you can look at a scale, but you can also purchase "ketone" test strips from the diabetic section of the pharmacy. Urinating on one of these and then looking at the color scale printed on the side lets you know whether you are burning fats for fuel or not.
If you stick with it for the four weeks, there are some benefits that arise from doing one:
- Initial rapid weight loss presents a psychological boost: stepping on a scale and seeing a loss of six or more pounds in the first week is encouraging, even if you know intellectually that you're throwing off water and/or carbohydrates. If you're down 20+ lb by the end of four weeks, you're far more likely to not want to revert to practices that will add that amount back on.
- The microbiome changes: there are bacteria inside your digestive tract that we're now starting to think are the cause of what you choose to eat. With such a drastic change in diet - "bad" bacteria die off and the "good" bacteria stay - meaning that you're far less likely to have the kinds of cravings you had before for junky, carbohydrate-laden food. Compliance with healthy eating is more likely when people are less motivated to seek out the foods they were literally craving before.
- Dieting seems like a luxury. If your consumption was nothing but water, black coffee and four protein shakes a day along with a small meal, the ability to eat four or five three hundred calorie meals is not so much a deprivation, but MORE FOOD.
- The body is primed to keep using ketones for fuel: so if you choose to stick to some other kind of low carb or ketogenic diet, you've already had the flulike symptoms and haunting cravings for carbs that you'd otherwise have to endure during the induction phase of these eating strategies. There's even a way to reintroduce carbs back into your diet if you really MUST have that Pop-Tart or occasional slice of cherry pie: if you eat these carbs immediately after a brutally taxing weight-bearing exercise, your muscles suck the carbs into your musculature as glycogen, and starve the fat cells of their own fuel.