Skip to content

Primer 52: The program An advanced strategy for muscle growth and fat loss

Primer 52: Das Programm Eine fortgeschrittene Strategie für Muskelwachstum und Fettabbau

Improving your body is full of dilemmas:

  • To build muscle you need to eat a lot, but that also means you're likely to gain some fat.
  • To lose a lot of fat you need to maintain a calorie deficit, which often interferes with your training and can even lead to a loss of strength and muscle.
  • Heavy training will make you stronger and more muscular, but it can also (over)strain your joints and tendons.
  • You can build muscle by doing lighter workouts that are easier on your nervous system and joints, but you may lose strength in the process.

It's hard to combine the different ways of exercising that you like. And it's even harder to try to eat for the type of workout you're doing or have done.

All of this has led to the development of a nutrition and training approach known as "Primer 52". This approach is similar to the 5/2 fat loss diet for strength athletes, which combines two days of aggressive calorie restriction with 5 days of eating at maintenance calorie levels or with a calorie surplus.

However, Primer 52 goes one step further and focuses on advanced biochemistry principles and a specific combination of training and nutrition. The program is revolutionary in that it allows you to do whatever you want when it comes to reshaping your body - be it gaining muscle mass, losing body fat or both. You eliminate all the dilemmas mentioned above.

Before I get into the specifics of Primer 52, I need to first list the three muscle growth factors that are essential for muscle growth and also explain the value of a calorie deficit and how we can manipulate mTOR and AMPK with ease.

Muscle Growth Factor 1 - You don't need a calorie surplus to build muscle

Yes, you read that right. The "evidence-based" trainers will tell you otherwise, but I have scientific research to back up my statement when I say that you don't need extra calories to build muscle. In fact, a caloric surplus is not one of the main variables when it comes to building muscle. It is only indirectly involved.

A few years ago, Dr. Stuart Phillips and a group of scientists at McMaster University recruited two groups of 20 men. Both groups were put on a diet that prescribed a 40% calorie deficit over a 4 week period. (All meals were provided to closely monitor this deficit).

One group had a daily protein intake of 1.2 grams per kilogram of body weight and the other group received approximately double that at 2.4 grams per kilogram of body weight.

Both groups trained with weights 4 days per week and performed sprint training 2 days per week. After 4 weeks, both groups had lost a significant amount of fat (about 3.5 kilograms). The group with the lower protein intake had lost a small amount of muscle, while the group with the high protein intake had actually gained muscle (1).

This clearly shows that protein is the nutritional key to muscle growth and not a calorie surplus.

Muscle growth factor 2 - You need sufficient energy to build muscle

This factor may at first glance sound like it contradicts what I just wrote about not needing a calorie surplus to build muscle, but this is not the case as I will show you in a moment.

To build muscle you need energy. You need 3 kcal to synthesize 1 gram of protein, to be exact. One kilo of muscle contains 220 grams of protein, which means you need at least 660 kcal to produce enough protein for one kilo of muscle.

In reality, this value is much higher due to the daily protein turnover (you are continuously breaking down and building muscle tissue). And the more you train, the higher this turnover will be. Even if the exact figure is not important, it is safe to say that you need at least 1000 kcal to provide energy to build up one kilo of muscle mass.

Again, that sounds like I'm saying you need a calorie surplus to build muscle, but that's not the case. If you need more energy than you have consumed, your body will simply draw on its reserves (stored fat or glycogen). The same applies to muscle building. If you need energy for this process but are in a calorie deficit, your body will use stored energy to accomplish this task.

This is also the reason why the leaner you are, the harder it is to build muscle during a calorie deficit. Fatter people have a lot more reserves and it is not a threat to their survival if this stored energy is used to build muscle.

Muscle growth factor 3 - you need to stimulate protein synthesis

It is sufficient to have enough protein available to build muscle and to have enough energy for this process. If you don't stimulate an increase in the rate of protein synthesis, you won't build muscle.

And this is where the calorie surplus plays a role - even if only indirectly through an increase in insulin levels (which happens when you eat more carbohydrates and protein) and IGF-1 levels (the liver needs insulin and growth hormone to release IGF-1). Increasing insulin levels is important because it both reduces protein breakdown and stimulates protein synthesis by increasing mTOR.

At this point it should be noted that resistance training itself also increases mTOR and can also increase local IGF-1 levels if muscle fatigue/lactate release is high enough, which is why frequency of training can be important if you are trying to build muscle.

If you can release IGF-1 and increase mTOR at the right times, and you have enough protein available, then you can build muscle even when you are not in a calorie surplus. Primer 52 uses mTOR maximization days to stimulate muscle growth, while there are also days when mTOR is kept low in favor of health, fat loss and anti-aging.

The role of calorie deficit in fat loss

There is one thing about fat loss that is 100% correct: you need to be in a state of calorie deficit. This isn't the only thing that matters, but if you're not in a deficit, the other things won't matter.

Yes, insulin sensitivity does matter. The lower your insulin sensitivity, the less likely you are to reduce stored energy (fat) in the hours after a meal.

To lose a kilo of fat you will need a deficit of just over 7000 kcal (2). The typical way to do this is to generate a small/moderate calorie deficit - perhaps 500 to 750 kcal per day - for 7 days.

However, if you generate the same total deficit over fewer days - e.g. two days - then the fat loss will be the same. In the long run, this method could even result in greater fat loss as you will be less likely to reduce the body weight regulating hormone leptin as you are not in a continuous calorie deficit.

This is what Primer 52 does: you generate a high calorie deficit two days per week, you have two days per week where you are in a state of calorie surplus, you have two days where you eat your maintenance calories or where you are in a slight deficit (depending on your goal) and you have one day with a moderate/low deficit. You plan your training accordingly so that it fits in with the way you eat that day.

This is much more elegant than simply reducing your calorie intake. Rather, we manipulate two of the body's key enzymes.


Both mTOR and AMPK are enzymes that play key physiological roles. They are normally considered antagonists, as AMPK can inhibit the actions of mTOR.

Even though mTOR is normally seen as a positive enzyme when it comes to building muscle, it's not all sunshine and roses. Accelerating cellular growth is great for muscle mass, but excessive mTOR activity can also have negative effects such as accelerated cancer cell growth and premature aging.

AMPK, on the other hand, increases glucose and fatty acid uptake and oxidation when you're in a calorie deficit (and can help you lose fat). It reduces the formation of new fat cells and increases fat loss.

Even more interesting is that a lot of recent research has established a strong link between AMPK and aging. As we get older, we become less responsive to AMPK, which results in the following:

  1. Less orderly cell recycling (autophagy)
  2. Increased oxidative stress
  3. Increased subliminal inflammation
  4. Increased fat storage
  5. Higher blood sugar levels
  6. More frequent occurrence of metabolic syndrome (3)

So we need to manipulate these two enzymes carefully. As for mTOR, we favor its expression when:

  • Caloric intake is higher (caloric surplus)
  • Carbohydrate intake/insulin levels are higher
  • Protein/amino acid intake (especially leucine, valine, isoleucine and glycine) is high - We perform resistance training

In turn, we favor AMPK expression when the circumstances under which we favor mTOR expression are more or less reversed:

  • Calorie intake is lower (calorie deficit)
  • Energy expenditure is higher
  • Carbohydrate/insulin levels are kept lower
  • Amino acid intake is kept lower
  • You complete a cardio workout

This is very simplified, but precise enough for our purposes. But how do you reconcile muscle building (favoring the mTOR system) with extending lifespan and improving health (favoring the AMPK system)? That's where the Primer 52 system comes in.

Primer 52 Overview

The Primer 52 system includes 3 (or 4) different types of days, each using a different strategy to utilize the enzyme system to your advantage. The type of training you choose is entirely up to you and the same goes for food choices, but there are a few recommendations.

1 - AMPK/fasting days

On these days, the goal is to achieve the highest possible AMPK activity. This will help slow down aging, increase fat oxidation, reduce systemic inflammation and maintain insulin sensitivity.

Diet: This part is quite simple. You fast for at least 24 hours on these days.

For example, you can stop eating at 6pm the day before and have a small protein/fat meal at 8pm on the fasting day itself. While some prefer a 24-hour fast, I prefer to fast until the next morning, which corresponds to a fast of 34 to 36 hours.

On these days, avoid any liquids that contain calories (black coffee is fine). And don't take any protein or amino acid supplements. You can fast until the next morning or have a small protein/fat meal (something like 120 to 180 grams of beef and some green vegetables) in the evening.

Training: No training with weights on these days.

There is no point in exercising if you don't have the amino acids to repair the damage. However, you can do cardio, HIIT, sprints, walking, yoga, flexibility training, etc. Any low intensity activity is fine.

2 - Hypertrophy/mTOR days

On these days, the goal is to maximize hypertrophy and protein synthesis via an increase in mTOR - especially around your training sessions.

Nutrition: These are days with a calorie surplus with high carbohydrate and protein intake (but low fat)

You should maintain a calorie surplus of 15 to 20% on these days (a good starting point would be 40 to 42 kcal per kilogram of body weight), with your protein intake at 2.7 to 3.2 grams per kilogram of body weight and you should consume 80% of your non-protein calories in the form of carbohydrates and 20% in the form of fat.

I recommend that you eat about 50% of your daily carbohydrates around your training sessions, 25% in the evening and the rest spread over the other 2 to 3 meals.

Training: These are typical bodybuilding days

Your repetitions should be between 8 and 15 per set and the number of exercises per training session should be 6 to 8 with 3 to 5 sets per exercise. You can use typical hypertrophy methods such as supersets, descending sets, mechanical descending sets, rest/pause, myo reps, etc.

3 - Strength days

These are the days when we focus on neurological training - i.e. heavier weights. We don't need to activate as much mTOR on these days as we do on hypertrophy days.

Nutrition: Depending on your primary goal, your calorie intake can be somewhere between a small deficit and a small calorie surplus

A good starting point is 33 to 35 kcal per kilogram of body weight with 2.2 to 2.7 grams of protein per kilogram of body weight and 80% of your non-protein calories in the form of carbohydrates and 20% in the form of fat. The carbohydrates should be consumed in the time window around your workout.

Training: Your training should resemble a powerlifting workout - perhaps 5/3/1 or a conjugate/westside max strength setup

The key is fewer exercises (3 to 5), heavy multi-joint exercises, heavier weights (sets of 1 to 6 reps) and longer rest intervals.

You can use supramaximal methods such as heavy partial repetitions or isometric training. You can also perform heavy loaded carries (farmers walk, zercher carries, weight sled training).

4 - Customizable days

This is not really a fourth type but more like a day where you can choose the type of workout and diet based on your goal:

  • If fat loss is your primary goal, then eat a low-carb, high-protein diet with moderate fat intake and perform sprint training.
  • If muscle growth is your primary goal, make this day a third mTOR day with hypertrophy training for your weaker muscle groups.
  • If strength building is your primary goal, make this a third strength day with low carbohydrate, moderate fat and high protein intake.
  • If longevity/health is your primary goal, then perform an energy system combo (sprints, strongman training, cardio, HIIT, etc.) at a calorie deficit with low carbohydrate intake and low to moderate protein intake.

In terms of calories, 27 to 30 kcal per kilogram of body weight with 2 to 2.2 grams of protein per kilogram of body weight and 80% of your remaining calorie intake in the form of fat and 20% in the form of carbohydrates is a good starting point. (The carbohydrates should be consumed during the window around your training). You can adjust your calorie intake depending on your goals.

However, if you make this customizable day a third hypertrophy day, then your diet should be the same as the other hypertrophy days.

Note: You do not have to treat this day as either another strength day or hypertrophy day. Alternatively, you can dedicate this day to what I would call "athletic training", i.e. things like sprints, jumps, throws, Olympic weightlifting drills, etc.

Primer 52: The weekly setup

The days are structured so that each day prepares the body for the next day. For example, the fasting day increases the anabolic response to the high protein, high carbohydrate day that follows the next day. The high-carbohydrate days recharge you and make you stronger for the strength days. And the low-carb/high-fat days make the fasting days more effective in terms of AMPK activation.

A typical week looks like this:

  • Sunday: Fasting/cardio (AMPK activation day)
  • Monday: Upper body hypertrophy day with high carbohydrate and protein intake and low fat intake (mTOR activation day)
  • Tuesday: Lower body strength day with low carbohydrate intake, high protein intake and moderate fat intake
  • Wednesday: Fasting/cardio (AMPK activation day)
  • Thursday: Lower body hypertrophy day with high carbohydrate and protein intake and low fat intake (mTOR activation day)
  • Friday: Upper body strength day with low carbohydrate intake, high protein intake and moderate fat intake
  • Saturday: Sprint or Strongman training with low carbohydrate intake and moderate protein and fat intake.

Note: You can also fast on other days (e.g. Tuesday and Saturday), but you should always schedule the hypertrophy days on the following days.

What Primer 52 will do for you

Primer 52 is the easiest way to simultaneously build muscle and lose fat while improving various health markers. What's more, this system also easily forgives you the occasional cheat day (which hopefully falls on a hypertrophy day). Once you get into the rhythm, you'll see that this is the easiest way to get everything you want in terms of body development.


  1. Thomas M Longland, Sara Y Oikawa, Cameron J Mitchell, Michaela C Devries, and Stuart M Phillips. "Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial." American Journal of Clinical Nutrition, January 2016.
  2. Kevin D. Hall, Steven B. Heymsfield, Joseph W. Kemnitz, Samuel Klein, Dale A. Schoeller, and John R. Speakman, "Energy balance and its components: implications for body weight regulation," Am J Clin Nutr. 2012 Apr; 95(4): 989-994.
  3. Antero Salminen Kai Kaarniranta. "AMP-activated protein kinase (AMPK) controls the aging process via an integrated signaling network. Ageing Research Reviews Volume 11, Issue 2, April 2012, Pages 230-241.


by Christian Thibaudeau

Previous article The definitive guide to preventing muscle loss