Do you want to be leaner, rapidly?

You’re not alone. In fact, I’d say that the vast majority of trainees, particularly those new to the gym – have this goal in mind.

Let’s face it, 9/10 people start training because they hope to look better and the last 1/10 is lying.
If it’s not the biggest reason to start eating well and lifting weights or getting more active, then it’s definitely the #2 or #3 reason.

I’ve picked up a couple of nutrition clients this week who have some things in common:

In their best efforts to improve their body composition they dropped both their fats and carbs right down, and kept their protein intake high.
Of course this resulted in a very low overall calorie intake, particularly with both clients doing at least 5 sessions in the gym per week (one doing 10!).

Because of the amount of activity these guys are doing, it reminds me somewhat of a protein sparing modified fasting approach, wherein protein is heightened but both carbs and fats are significantly reduced.

So what is a protein sparing modified fast (PSMF) and why am I cautioning you AGAINST going down the path of very high protein but hardly any carbs or fats?

Or at least, doing it for longer than a few weeks at a time, or combining it with a high intensity and frequency of training?

Let’s find out!

A PSMF is a period where you aim to drop significant bodyfat and weight.

It’s an approach used by clinicians typically where people are severely obese, type 2 diabetic or in need of extreme lifestyle interventions and must drop bodyfat and bodyweight at a very quick pace. The approach is used for a pre-determined amount of time (articles tended towards 6 months) after which carbohydrates and calories are re-introduced. It is intended to be done only with medical supervision.

Because your total calorie intake is incredibly low (a clinicial PSMF is typically 800 calories per day or less), you’re effectively asking your body to spare protein whilst burning fat as fuel. Which is perfectly feasible if you have a very large amount of stored bodyfat.

But in my research for this blog I reviewed a number of scholarly articles about PSMF’s and found that the vast majority of subjects regained weight following the refeed period, and concerns about the long term efficacy of the plan are well-founded, with “nearly all of the patients regaining most of their weight after 5 years.

FACT: Drastic diets don’t work long term.

And whilst we cannot truly compare a clinical PSMF with what my clients were doing (given that calories were still very low, but much higher than 800 per day!), we can still eek out some insights from what happens when we starve our bodies of protein sparing nutrients;

Carbohydrate (glycogen) and liver glycogen stores are depleted
This lack of available glucose will initially enhance fat loss by ensuring that triglycerides and amino acids are utilised as a fuel source.
Fasting glucose levels are lowered
Low glucose levels will result in a very low insulin output, in which case insulin sensitivity rises.
Ketones are used as a substitute for glucose
With no carbohydrates available either in storage or in the diet, ketones are produced to create ATP (energy).

The overall result is that fat loss is achieved because of the dramatic loss of available energy.

However, what happens when you are consuming a high protein diet, with low fats and carbs – and then you throw intense exercise into the mix?

Exercise increases the utilisation of fats and carbs as fuel.

The process by which we create ATP (energy) for the mitochondria of the cell, is reliant upon the presence of both fats and carbohydrates. At higher intensities, more carbs are used and at lower intensities, fat is used. Individual amino acids are intended to play only a minor role in this creation of energy, and are instead utilized to replenish bodily tissues such as muscle, skin, hair and nail cells.

Protein is not intended to be a fuel.

When protein is used as a fuel, it is converted to glucose by a process called gluconeogenesis. If you have ever heard of someone “going catabolic,” this is an intrinsic part of this. In order to find energy and create ATP, in the absence of protein sparing fuels the body can do three things;

– Remove all carbohydrates from storage
– Create ATP from fat stores, and/or
– Create ATP from proteins.

If you’re not eating carbohydrates or at least, not eating enough carbohydrates to refuel glycogen, then fats, proteins and ketones can be used to create ATP. If your energy intake is insufficient, if you are training frequently and intensely but not providing your body with protein sparing nutrients like carbohydrates and fats – then it’s very likely that a large amount of your weight loss is not just coming from your fat cells, but from your muscle.

Obese people have less concerns when it comes to losing muscle, because fat stores are abundant. But if you’re generally fit, healthy and of an average to lean frame – then it’s not the best approach because your fat stores aren’t overflowing and…

Rapid/ongoing weight loss = muscle loss

Long periods without sufficient calories, particularly energy from fat or carbohydrates, means that muscle tissue will be compromised!
If you are not obese or morbidly obese to begin with and have reduced your total bodyweight by a significant amount in only a month or a couple of months, it’s highly likely that you’ve also lost a significant amount of muscle.

This will

– prevent you from lifting heavier or getting stronger in the gym
– prevent you from rebuilding muscle whilst your calorie intake is still so low
– reduce the intensity levels which you are capable of reaching, and
– reduce the total amount of calories burnt from activity by way of adaptive thermogenesis and loss of intensity.

Our calorie expenditure goes down as we get lighter, this is an inescapable fact.
However, you are only reducing your calorie expenditure unnecessarily by dramatically reducing your bodyweight, and removing the same tissue that contributes to your shape, strength, quality of life, insulin sensitivity and metabolic rate.

Typically on a very rapid weight loss, very low calorie diet, particularly where weight training isn’t prioritised means we end up looking like a smaller version of ourselves when we begun.
Not really leaner or more muscular, as we had hoped – but smaller and softer.

A better way…

Might be for someone who is not significantly overweight or obese to utilise a PSMF approach for very short periods of time, or for a maximum of 1-2 weeks at the beginning of a fat loss phase.
If you are significantly overweight or obese, and largely sedentary – this could be something you utilise for few months before beginning a refeed period.

What if you’re already quite lean and training very hard? Then this approach has a higher risk to reward ratio. You can still use it, but depending upon your circumstances (stress levels, physical activity, sleeping patterns, inflammation, digestive health etc) it would not be something I would recommend for more than 1 or 2 weeks at a time because lean individuals do not have the same amount of protein sparing capacity.

There are actual benefits to periods of low calorie intake!
Improved digestion, reduced inflammation, improved insulin sensitivity, better glucose tolerance, fat loss.
So it’s not all bad. There are still some merits for the average trainee with average bodyfat levels!

One way for a leaner, more active individual to include a PSMF approach would be to adopt a protein only, very low calorie day only on 2-3 of your rest days, and keep protein sparing macronutrients (particularly carbohydrates) higher around your workout periods for better recovery and lean muscle retention. When used in conjunction with alternate day fasting, this may provide significant health benefits, provided stress is managed.

Please note however, that your training intensity, strength and stamina on the days following your fast will probably go down, but you will still need to train hard and heavy with weights to stimulate the muscle protein synthesis that helps to retain lean tissue. I have found that for any significant bodyfat loss to occur, we need at least 3, high volume resistance training sessions per week, hitting each muscle at least twice over a 7 day period.

If you want better fat loss but are not currently making resistance training the focal point of your physical activity, well…. I’d suggest lowering your calorie intake a little and then starting a periodised, well written weight training program that aims to build strength and lean muscle tissue. Cardio can be included but in a manner and frequency which does not deter from your ability to train hard. (I know a very experienced coach who specialises in this area… *hint*)

Long term consistency beats short term whim every time

Over a short period of time you could still drop quite dramatic levels of bodyfat, however you can prevent both the long term loss of muscle tissue and also the quite realistic chance of going AWOL and eating everything in sight because you’re so hungry. Protein sparing macronutrients are essential to the longevity of any approach, and would be a far more logical way of approaching a solution to your problem.

If you are already relatively lean or of a healthy bodyfat percentage and have an event which you want to look good for in 1-4 weeks – you could look to starting a PSMF approach, however consider this;

The weight which you lose over those 1-4 weeks will not be pure bodyfat, and whatever weight or bodyfat you lose over this time, is highly likely to be regained.

A more moderate nutrition approach, in which you diet with higher calories and support your training in the gym is far better long term. So if you can wait, be patient and work hard all year round – I’d implore you to do that instead!


Further reading

If you are seeking further reading on rapid fat loss, you really can’t go past Lyle McDonald’s Rapid Fat Loss eBook, available at

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