Protein sparing modified fasting is a medical diet that was created in the 1970s to help morbidly obese patients who absolutely had to lose weight.
It is a very extreme diet and it isn’t for everyone. As a matter of fact, for many people, there are more appropriate strategies. There is no mystery or magic to fat loss. Our bodies require a certain amount of energy to survive. If we do not have access to that energy when we need it, we will die. In order to avoid this situation, we will start cannibalizing our own body tissue for energy if need be. In preparation for such an event, our body will store energy as fat – a calorie dense reserve for times of starvation.
In addition to our fat stores, we can also break down muscle and organ tissue for energy, and for amino acids that are required for metabolic processes. If you are trying to lose weight, you need to consume less energy than you burn. The larger the energy deficit, the more fat, and muscle tissue you will need for energy, and the faster you will lose weight. So, if you need to lose weight fast, the larger the caloric deficit you can create, the better.
In order to accomplish this, you could undertake massive amounts of exercise to burn calories – but most people severely overestimate how many calories they burn exercising, and very few people can consistently exercise at levels that will create 1500, 2000, 2500 or more calorie per day deficits; especially if they are carrying a lot of extra weight. The other way to create a large caloric deficit is to stop eating (a true fast).
This may work for an extremely short period, but health consequences and even death are very real concerns with a complete fast. During a fast, your body can use fat for energy, but a major concern is the underlying functions and metabolic processes that require other nutrients – amino acids, vitamins, minerals. Your body will quickly run through the vitamins and minerals that it has stored and the amino acids it requires will be obtained through the breakdown of lean tissue (muscle and organs).
Muscles will be metabolized and lost at a high rate, not just for energy as many people assume – but also for many processes essential to life itself. Organ tissue will be broken down and the potential for serious damage will be present. So how do we create a large deficit and minimize the risk of muscle loss and organ damage?
Of course, with a modification to the true fast – the protein sparing modified fast.
By providing the body with an adequate supply of dietary protein, we can spare the protein in our body (muscle and organ tissue) from breakdown. By having this supply of protein and keeping fat and carbohydrate intake to extremely small, “trace”, levels we can create a large deficit that is guaranteed to cause weight loss, often rapid weight loss, while reducing the potential for the loss of lean tissue and health consequences.
Is this strategy for everyone?
If you have 40+ pounds to lose though, and the idea of 20-40 weeks of dieting at 1-2 pounds of weight loss a week isn’t something that you find motivation (who would?) …then this diet may be the strategy you need to get your life going in the right direction again.
There are also times when someone may have a significant amount of weight to lose and a deadline by which to lose it – a wedding, graduation, etc. – this diet is certainly better than outright starvation.
Critics of this diet will often point out that it is not a viable long-term strategy or solution to obesity. The thing about critics is that they wouldn’t be there if they weren’t right, at least in some way.
This is not a viable solution and this diet cannot be followed forever. But that doesn’t mean it can’t be an appropriate and highly effective tool when used in the right situation, for the right reasons, and with the correct application.
I would first suggest your read the Psmf guide table of contents. If you have decided to consider following a Protein Sparing Modified Fast diet, you will need to know some very basic parameters. There are also many questions you will have.
The good news is, the diet is actually rather simple. The first thing you need to do is to figure out your body fat statistics. We have a Calculator Tool to assist you in quickly figuring out everything.
Figuring out your bodyweight is simple enough – step on a scale.
The second step is to figure out your body fat %. There are a number of ways to do this.
There are scales that use else electrical impedance to estimate body fat. I have a body fat calculator located on the bottom of the page here.
There are skin fold calipers which pinch your skin and measure fat in different areas of your body and there are highly accurate DEXA scans. There are even visual charts online that show photos of different people at different bodyfat percentages that you can compare yourself to. I would suggest using a couple of different measuring tools and come up with an estimate of your body fat that you think is reasonably accurate.
Once you know your body fat percentage, you can calculate your lean body mass. Your lean body mass will determine the amount of protein you should eat each day.
As an example, if you weigh 250 pounds and have 45% body fat you can calculate:
250 x 0.45 = 112.5 pounds of fat.
250 – 112.5 = 137.5 pounds of lean tissue.
To keep things simple, you will want to eat approximately 1 gram of protein per pound of bodyweight. 1 gram per pound of lean mass is a good estimate for most. So this person will need 137.5 grams of protein per day. Of course, you can round this to 140.
So, what makes this diet so extreme?
Well, the goal ultimately is to eat ONLY that 140 grams of protein.
If it were possible you would eat no fat and no carbs. This isn’t exactly possible in reality and you will have trace amounts of fat and carbs. You will also be allowed to eat a reasonable amount of cruciferous vegetables.
While the vegetables will provide a few additional calories, they will also keep you healthy by providing vitamins and minerals (especially electrolytes) and fiber that will keep you more full and regular. Don’t go overboard on these veggies, but don’t skimp.
In the exams above, 140 grams of protein will provide 560 calories. 4-8 servings of broccoli will provide 120-240 additional calories for a total of 680-800 calories for the day.
Add in incidental fat and carbs and maybe this 250-pound person is eating just 900 calories per day.
A woman that weighs 140 pounds and has 85 pounds of lean mass will be eating around 500 calories per day maybe (85 g protein = 340 cals).
You should also supplement with a few items to ensure proper vitamin, minerals, electrolyte supplies, etc.
There is so much more that can be found in the PSMF Diet guide if you feel you still need any additional questions answered.