The Protein Sparing Modified Fast (PSMF) is regarded by many to be the most effective way to lose body fat while preventing loss of lean muscle and rebound binge eating due to nutrient deficiencies.
First developed in the 1970s, the PSMF has seen various permutations in weight loss clinics and the bodybuilding community.
While the details vary depending on context, a PSMF generally defined as an energy restricted diet with adequate protein while simultaneously limiting carbohydrates and fat.
Technically, the PSMF will be ketogenic because a significant amount of body fat will be burned due to a restricted energy intake.
Adequate protein is provided to prevent loss of lean muscle mass. Supplements are often used to prevent nutrient deficiencies.
This article outlines the key principles of the PSMF that can be applied to weight loss or maintenance over the long-term.
Optimal nutrient dense foods are identified for someone looking for an aggressive weight cut (e.g. a bodybuilder leading up to a competition) as well as hybrid low carb – PSMF approach for someone who is insulin resistant wanting to lose a significant amount of weight over a longer period.
Medical applications of the PSMF
In the medical application of the PSMF patients obtain the majority of their energy from protein while keeping energy from carbohydrates and fat low.
- Protein levels are set at 1.2 to 1.5 g/kg of ideal body weight per day. (For someone with 30% body fat wanting to get to 10% body fat this would be equivalent to 1.5 to 1.9g protein per kilogram of lean body mass or LBM.)
- Carbohydrate intake is typically restricted to less than 20 to 50 g/day.
- Additional dietary fat beyond what comes with lean protein sources is minimised.
- Patients in the weight loss clinic setting are restricted to less than 800 kcal/day.
- patients are encouraged by the initial period of rapid weight loss which leads to a lower dropout rate;
- meal replacements in the form of commercial shakes or bars can be used, however learning to make meals from whole foods critical to developing habits that lay the foundation for long-term success;
- the PSMF is effective for people with normal glycemic control as well as pre-diabetes or type 2 diabetes;
- people on a whole food-based PSMF are significantly less hungry and preoccupied with eating compared to those on a liquid-formula based version of the PSMF; and
- most of the weight lost during a PSMF is from fat tissue rather than muscle.
Adherence to a very-low-calorie, ketogenic PSMF program results in major short-term health benefits for obese patients with type 2 diabetes. These benefits include significant weight loss, often more than 18kg, within 6 months.
In addition, significant improvements in fasting glucose and haemoglobin A1c levels are linked to the caloric and carbohydrate restriction of the PSMF.
Body building applications
Lyle McDonald reinvented the PSMF in body building community with his 2005 Rapid Fat Loss Handbook.
McDonald details how someone can individualise the PSMF based on their goals and context.
- Someone who is already very lean and undertaking heavy weight training will need higher levels of protein.
- Someone who isn’t yet lean may do better with a less aggressive approach over a longer period.
- McDonald’s recommended protein intake ranges from 2.2g/kg LBM to 4.4g/kg LBM!
- Unlimited green leafy fibrous veggies are strongly encouraged as they are filling and provide the vitamins and minerals with minimal calories.
- McDonald also recommends to supplement with a good multivitamin, sodium potassium, magnesium, taurine, calcium and fish oil.
- A PSMF is typically not a long-term proposition due to nutrient deficiencies.
KetoGains’ Luis Villasenor added:
McDonald’s recommendations seem “massive” to most people due to the book being geared toward strength athletes who DO require more protein as they are effectively breaking it down when strength training.
Bodybuilders who diet down to 4 – 5% bodyfat need an increased protein intake when preparing for a contest as their aim is to maintain as much as lean mass as possible; and for that, one needs protein and resistance exercise.
With my clients, to avoid nutrient deficiencies, we use a “Ketogains PSMF” which adds 3-4 whole eggs a day, at least 150g spinach, plus other green veggies, and some avocado. The rest is lean sources of protein and more veggies, plus electrolytes. This effectively puts the person in between 35 to 50g fats and 20g net carbs. The rest of their energy comes from lean protein.
Protein drives satiety
The body strongly defends loss of muscle mass by increasing appetite after periods of fasting or low protein consumption to ensure that muscle mass is retained.
If we eat lower protein foods we may end up consuming more energy to obtain our adequate protein. Conversely, we can ‘hack’ our appetite by prioritising adequate protein while minimising energy from carbohydrate and fat.
- Minimum carbohydrate requirement: While there is a need for the vitamins and minerals that are often packaged with carbohydrate containing foods (i.e. vegetables), there is indeed no such thing as an essential nutrient.
- Minimum fat requirement: Most people have plenty of body fat stores that they can draw on and hence do not have an immediate need for dietary fat other than the essential Omega 3 fatty acids.
So, theoretically, if we get adequate protein as well as vitamins, minerals, the essential fatty acids can go a long way to providing everything that we need for long-term survival with less energy which is really the holy grail of weight loss and long-term maintenance.
Thermic effect of food
The other advantage of consuming a higher protein diet is increased thermogenesis (i.e. the energy lost in the process of converting food into energy). The thermic effect (or specific dynamic action) is 5 to 15% for carbohydrates and fat and 20 to 35% for protein.
While we can convert protein to glucose (i.e. gluconeogenesis), it is really hard and our body doesn’t like to do unless it has to.
Satiety typically kicks in quickly once we have had adequate protein and we go in search of fat or carbs which are easier to convert to energy. Just think, you can only eat so much steak, but you always have a ‘dessert stomach’, even after a big meal.
While there is much debate over the “metabolic advantage” of fat vs carbohydrates with claims that we can eat more calories of fat than carbs there is actually an advantage’ when it comes to how many calories of protein we eat versus how much we can convert to energy.
Should you just eat the highest protein foods?
So, the obvious question is:
What should I eat on a PSMF?
The table below lists the foods with the highest protein content as a percentage of energy. These foods may be useful if you are looking to boost your protein intake.
|orange roughy (fish)||92%|
|mozzarella cheese (non-fat)||90%|
|protein powder (whey)||89%|
|turkey breast (fat free)||88%|
|whey protein concentrate (WPC)||78%|
|ham (lean only)||73%|
|top round steak (fat trimmed)||72%|
I have summarised these in this image for easy reference.
The problem with a very high protein diet
While you may be getting plenty of essential amino acids if you focus purely on high protein foods, there is a good chance that you may not be getting all the vitamins and minerals you need.
As shown in the chart below, there is a strong relationship between protein and nutrient density. However, if we just focus on high protein foods we may still end up missing out on the harder to find vitamins and minerals.
The chart below shows the micronutrients provided by the top 10% of the foods in the USDA database when sorted for maximum protein content.
Now imagine, that rather than getting 2000 calories, we are getting only 800 or 400 calories during long-term fasting or extreme dieting. We have a higher chance of becoming deficient in many key nutrients which may in turn increase appetite and drive us to eat more than we would like to.
Ensuring you are getting adequate micronutrients is a key component to long-term success in weight loss and maintenance.
In the Rapid Fat Loss Handbook McDonald mentions ‘The Last Chance Diet’ which was popular in the 1970s and 80s. It was essentially a PSMF centred around liquid nutrition which led to the death of a number of devotees due to a number of fatal flaws. 
First, they picked the cheapest protein source available, collagen; a protein that provides essentially zero nutrition to the body. Second, they provided zero supplemental vitamins and minerals (some of which would have been obtained if the dieters had been eating whole foods in the first place). This caused a couple of problems including cardiac heart loss (from the total lack of protein) and arrhythmias from the lack of minerals.
Basically, the problem wasn’t with the approach so much as with the food choices.
PSMF’s based around whole foods (which provide high quality proteins as well as vitamins and minerals) and with adequate mineral supplementation have shown no such problems.
Bruce Ames’ Triage Theory
Nutrient density becomes even more important when we consciously try to limit our energy intake.
Attaining adequate micronutrients can help to mitigate metabolic / mitochondrial slow down and adaption to the severe calorie deficit. If we are getting the range of micronutrients we need the body is more likely to keep on feasting on our own excess fat stores without reacting like there is an famine and holding onto our excess fat stores.
Similar to the protein leverage hypothesis, it seems if we provide the body with low nutrient density food it is driven to consume more energy to ensure that it gets the nutrients it needs.
I get a number of comments in response to the Nutrient Optimiser analysis suggesting that the Daily Recommended Intakes (DRI) for various micronutrients are excessive because a certain person has done fine on a diet per for a period of time with a less than optimal nutrient profile.
While we can argue that the some of the DRIs for various nutrients are overly conservative you also don’t have to look too far to find people that argue that we need multiple times the DRI for another specific nutrient to optimise our health and longevity.
I don’t think we need to worry about precisely meeting the daily recommended intake for every single micronutrient every single day. There is no diet that meets the daily recommended intake for every nutrient without overdoing others. I think a healthy well-balanced diet will achieve the DRI for the majority of the essential micronutrients most of the time.
More research is required to understand whether our requirements for different nutrients change depending on our diet (e.g. how much less vitamin C do we require if we are not consuming as much glucose) and how much more bioavailable nutrients are from plants versus animals.
However, if you are an order of magnitude under the DRI for a handful of nutrients perhaps you should consider focussing on foods that contain that contain higher levels of that cluster of nutrients. If you are an order of magnitude over the DRI for a certain group of nutrients you don’t need to prioritise foods that contain those nutrients.
Bruce Ames’ sobering Triage Theory suggests that if we are low in critical nutrients the body will prioritise those nutrients for functions critical to short term survival rather than longevity and preventing the diseases of aging (e.g. cancer, heart disease, Parkinson’s, Alzheimer’s etc).
“The triage theory posits that some functions of micronutrients (the approximately 40 essential vitamins, minerals, fatty acids, and amino acids) are restricted during shortage and that functions required for short-term survival take precedence over those that are less essential. Insidious changes accumulate as a consequence of restriction, which increases the risk of diseases of ageing.” 
So, while we might do OK with poor nutrition for a period of time, we will probably do better if we obtain a solid amount of all the essential nutrients. Ideally we would obtain these nutrients from whole foods which are more likely to contain all the non-essential but also beneficial vitamins and minerals that we don’t track.
Low energy density
Another way to maximise nutrient density and prioritise protein at the same time is to reduce the energy density of the food we eat.
As shown in the chart below there is a relationship between the harder to find nutrients and energy density. While fat is a great fuel source and should not be feared or avoided, refined high fat foods do not typically contain high levels of the harder to find vitamins and minerals that we need to thrive. Foods with more fibre and water are also more filling and are harder to overeat and will lead to increased short term satiety.
If we prioritise adequate protein while minimising fat and carbohydrates we make up the deficit from our own body fat stores, hence there is no need to prioritise dietary fat.
The nutrient dense adequate protein diet
So, to recap:
- getting adequate protein is important, especially if we are fasting or restricting energy intake, and
- not getting adequate nutrients is potentially dangerous and possibly the fatal flaw of the PSMF.
We can use the Nutrient Optimiser to prioritise foods with the nutrients we want to obtain more of. Listed below are the 20 nutrients that have been prioritised in the following list of prioritised foods.
- Alpha-linolenic acid
- EPA + DHA
- Vitamin E
- Vitamin D
- Pantothenic acid
Prioritising amino acids is usually unnecessary because a maximising vitamins and minerals generally leads to more than adequate protein. However, in a PSMF where we are severely limiting energy we want to increase protein as well (hence valine, leucine and tyrosine have been included). As well as nutrient density, we have also prioritised low energy density foods in the multicriteria analysis.
The chart below shows the resultant micronutrient profile achieved if we ate 2000 calories per day of these foods. In the chart above we saw that if we just focus on protein we will not be meeting the DRI for eleven nutrients. However, when we focus on nutrient density we get adequate quantities of all nutrients other than the Omega 3 fatty acid alpha-linolenic acid.
The chart below shows the same foods if we only ate 600 calories per day rather than 2000. Even with these highly nutrient dense foods we miss the DRI for eight of the essential nutrients. Hence, we may still benefit by supplementing with Omega 3, vitamin D, calcium, magnesium and potassium. The nutrients provided by an energy restricted diet without also prioritising nutrient density would be much worse.
It’s not hard to imagine that our ability to maintain a low energy intake and achieve sustained weight loss is likely related to getting adequate levels of the various essential micronutrients without having to overconsume energy. Conversely, a nutrient poor diet will likely drive us to consume excess energy which will lead to obesity.
Best foods for a PSMF
The tables below summarise highest ranking 10% of foods in the USDA database when we prioritise for high nutrient density and low energy density.
Also included in the tables are:
- the nutrient density score (based on the 20 nutrients listed above),
- energy density, and
- the MCA which is the overall ranking from the multi criteria analysis.
Compared to the highest protein food listed above which are 80% protein, these foods work out to be 59% protein, 20% fat, 13% net carbs and 8% fibre. While this may seem high, as we will see in the ‘calorie math’ section below, it becomes more reasonable once we account for the energy from body fat.
It would be hard to imagine getting fat by overeating the vegetables listed below.
Maximising your intake of these vegetables will ensure you are getting adequate vitamins and minerals and hence maximise your chance of long-term success.
While these vegetables have a very high nutrient density score (ND) in terms of nutrients per calorie, they also have a low energy density which means you need to eat a lot of them to get the nutrients you need.
The downside of vegetables is that they can be expensive and take time to prepare fresh.
|yeast extract spread||52%||12||185||1.5|
These animal products are both nutrient dense and have a low energy density compared to fattier cuts of meat. While the nutrient density scores are not as high as for the vegetables, the energy density is higher so you will be able to get more nutrients in using these foods.
|ham (lean only)||73%||16||113||1.9|
|chicken liver pate||27%||9||201||1.1|
Omega 3 fats (EPA, DHA and ALA) are essential and harder to get so you should prioritise fish in your nutrient dense PSMF.
Egg and dairy
Eggs are nutritious. Only a couple of low fat dairy products make the list. Higher fat foods such as butter and cream need to be minimised on a PSMF to allow your body to use the fat from your butt and your belly.
|cream cheese (low fat)||61%||11||105||1.5|
|cottage cheese (low fat)||51%||7||81||1.1|
These nutrient dense PSMF foods are summarised in this image for easy reference.
To make this a little more practical let’s look at some calorie math using a hypothetical scenario.
Let’s say Super Ted is looking to get shredded for the Ketogains conference in two weeks where he wants to pose for shirtless but also wants to stay strong and to win the arm wrestle and beat the reigning champion, Mighty Mouse.
Super Ted currently weighs 160 lbs or 73kg and has 10% body fat. His maintenance energy intake is 2336 cal/per day.
While getting the majority of your energy intake from protein might seem excessive…
… it’s not so dramatic when you also take into account the body fat being burned.
Between the 8% dietary fat (8%) his body fat stores (60%) Super Ted will be getting a ketogenic level of 68% of his energy from fat while also adequate protein to maintain his muscles and enough carb containing vegetables to get the vitamins and minerals that are also critical to his long-term success.
The details of the calorie math are shown below. Once you take the energy deficit into account Super Ted is consuming 2.2g/kg LBM.
|body weight (kg)||73|
|body weight (lbs)||160|
|body fat (%)||10%|
|lean body mass (kg)||62|
|protein (% diet)||59%|
|fat (% diet)||20%|
|net carbs (% diet)||13%|
|diet protein (g)||138|
|dietary fat (g)||21|
|body fat (g)||156|
|body fat (kg/week)||1.1|
|net carbs (g)||30|
|protein (% energy burned)||24%|
|dietary fat (% energy burned)||8%|
|carbohydrate (% energy burned)||5%|
|protein (g/kg LBM)||2.2|
These calculations assume that Super Ted’s insulin levels are going to be low enough to allow him to yield a significant amount of energy from his body fat stores. Similar to fasting, it may take a few days before glycogen stores to be depleted enough for his insulin levels to drop which will allow his fat stores to more easily flow out of storage.
These calculations also do not account for the metabolic slowdown that you will get during long term energy restriction. This is the same with any way of eating that consciously restricts energy intake. However, I think if we can minimise nutrient deficiencies we will have a better chance of avoiding an increase in which could drive our body to seek out the missing nutrients that it is not getting enough of.
When you look at his Nutrient Optimiser analysis you see that Ted Naiman (aka Super Ted) is actually consuming 2.4g/kg LBM.
Meanwhile Luis Villasenor (aka Mighty Mouse) is also consuming protein at 2.4g/kg LBM during his PSMF. Luis says his normal protein intake is around 140g increases this up to 180g during a strict PSMF.
Insulin resistant long-term fat loss scenario
For most of us such an aggressive fat loss approach might be hard to maintain long-term. So, let’s consider another scenario with another hypothetical character.
Introducing… Big Ted.
As you can see, Big Ted doesn’t post shirtless for photos on the internet.
At 110kg and 30% body fat Big Ted is far from shredded.
Big Ted is also prediabetic.
His doctor has warned him that if he doesn’t lose a significant amount of weight he will need to take Metformin and then insulin before too long.
Big Ted is motivated to drop a significant amount of weight with perhaps a calorie deficit of 30% which will take him about 30 weeks to get to his goal weight of 90kg.
We can refine Big Ted’s PSMF approach given that his circumstances and goals are different from Super Ted’s.
Nutrients to prioritise
Given Big Ted is not looking to be as dramatically calorie restricted we only need to prioritise the following nutrients.
- Alpha-linolenic acid
- EPA + DHA
- Vitamin D
- Vitamin E
Although amino acids are not prioritised the resultant list of foods is still 36% protein, 30% fat and 20% net carbs.
Rather than simply prioritising nutrient density and energy density, this scenario also prioritise a lower insulin load in view of Big Ted’s looming prediabetes situation.
This is basically a hybrid between a PSMF and a low carb diet.
The chart below shows the nutrient profile of these foods once we take a 30% energy deficit into account. Big Ted will be meeting the DRI for all his nutrient other than Omega 3s which he may need to supplement.
The charts below show the energy consumed and energy burned.
There is a significant amount of fibre which will not be metabolised for energy but rather feed his gut bacteria. There is still a solid amount of net carbs from veggies, however there is no sugars or processed grains to be seen so they’re not about to boost his insulin or send him on a blood sugar roller coaster.
Once his body fat loss is accounted for, half of Big Ted’s energy expenditure is still coming from fat.
Although we didn’t prioritise amino acids we still get a solid 2.2g protein per kilogram LBM.
|body weight (kg)||110|
|body weight (lbs)||242|
|body fat (%)||30%|
|lean body mass (kg)||77|
|protein (% diet)||36%|
|fat (% diet)||30%|
|net carbs (% diet)||20%|
|diet protein (g)||169|
|dietary fat (g)||63|
|body fat (g)||100|
|body fat (kg/week)||0.7|
|net carbs (g)||94|
|protein (g/kg LBM)||2.2|
Optimal foods for Big Ted are listed below.
|turkey drumstick (with skin)||50%||1||221||0.8|
Nut sand seeds
This image below summarises these foods for easy reference.
The nutrient profile for these foods is also excellent. These foods will help Big Ted to minimise his chance of developing nutrient deficiencies which may lead to rebound binge eating and derail his long term weight loss efforts.
How often should I eat on a PSMF?
Big Ted is fond of intermittent fasting. He finds it easier to not eat for a day or two and then eat to satiety rather than trying to count calories or restrict energy.
Meanwhile Super Ted likes to eat two meals per day which saves him time and helps him not overeat.
Personally, I don’t think it matters exactly when you eat as long as you stick to the foods that align best with your goals. Recent research suggests that in the fasted state we can use up to 3.5 g/kg/day and digest up to 4.3 g/kg/day. This makes sense in an evolutionary context when there wouldn’t have been a regular supply of food but we would have needed to be able to use the food when we came across a big hunt after a long famine.
Either Super Ted or Big Ted could still utilise their required protein intake if they followed an alternate day fasting or 5:2 plan or really any other permutation of fasting. What is important though is that they ensure that they stick to their nutrient dense diet when they break their fast rather than reaching for the more energy dense foods when they eat again.
How low can you go?
Hopefully this article has given you some actionable principles:
- During weight loss, you should ensure that you get adequate protein while fat and carbs can be limited to achieve the energy deficit required to suit your target rate of loss.
- As well as protein intake, we should aim to maximise all micronutrients (vitamins, minerals, essential fatty acids and amino acids) ideally using whole foods.
- You will find it hard to obtain adequate vitamins, minerals and essential fatty acids at one extreme or the other of protein intake.
As discussed in the ‘How Much Protein is Too Much’ article I noted that the minimum intake of protein and minimum essential fats tallies up to around 314 calories as shown in the table below.
If we could stick to this approach we would have a massive and highly ketogenic 85% of our energy coming from our body fat. However, you would be at an increased risk of inadequate vitamins, mineral and fatty acids with such a low energy intake.
|macro||DRI (g)||DRI (calories)||% energy|
If you’re starving to death and only have lean protein available you might call it “rabbit starvation”. However, if you still have plenty of body fat to burn it’s a PSMF.
Lyle McDonald suggests that people following a PSMF for aggressive weight loss over a short period (e.g. cutting in the lead up to a bodybuilding show) might be eating between 400 and 800 calories per day.
Each person needs to find the ideal approach that they can live with in the long-term.
How to do a nutrient dense PSMF
- Eat mostly foods from the lists below.
- The nutrient dense PSMF diet foods are ideal for aggressive short term weight loss (i.e. leading up to a bodybuilding comp).
- The nutrient dense weight loss foods for insulin insulin resistance may be more appropriate if you have more weight to lose over a longer period.
- Minimum protein intake in a weight loss clinic setting is 1.2g/kg total body weight.
- Appetite will likely drive you to eat more protein if you are working out. 2.4g/kg lean body mass is typical for someone lifting heavy.
- The highest protein foods can be used to increase protein intake if required.
- Focusing on these foods will ensure you still get adequate protein as well as vitamins and minerals while minimising energy intake.
- Limit carbs to what comes with non-starch veggies (i.e. no processed grains or sugars).
- Limit fat to what comes with the lean protein foods.
- Don’t eat too much
- It will be hard to overeat these high nutrient density low energy density foods.
- You may not have to consciously limit your food intake if you can focus only eat these foods.
- It may be beneficial to track or plan your energy intake to achieve your goals.
- Ratchet down your energy intake until you achieve your desired rate of weight loss.
- Lift heavy / exercise (optional)
- Working out will help you to use the protein to build lean muscle and keep your metabolic rate up.
- The protein sparing modified fast (PSMF) provides adequate levels of protein to support lean muscle mass while restricting energy from carbohydrates and fat.
- Protein intakes vary widely depending on the goals and the level of energy restriction between.
- Providing adequate nutrients, ideally from whole foods, is critical to long term weight loss and maintenance.
- Simply maximising protein may not provide optimal levels of vitamins and minerals. Therefore, it’s important to prioritise nutrient dense foods to improve your chances of long-term success.
- While the PSMF is commonly used in weight loss clinics and in the bodybuilding community, the principle can also be applied in other situations.