Episode 41 – Choosing the Right Sized Calorie Deficit and Rate of Weight Loss

Key Topics Covered

How a calorie deficit works 

  • Energy balance – is the balance of the calories coming in through food and the calories being burnt through the metabolism and daily activities  
  • Calorie deficit – is specifically when you are burning more calories than what is coming in through food
    • When this deficit occurs, your body makes up for it by taking the energy required from your internal stores such as body fat  
    • The size of that deficit is directly correlated to how much and how fast you lose weight  
  • 7000kcal deficit per week = ~1kg of fat loss
    • Although this is influenced by so many variables etc 

Is it possible to be so low-calorie that it prevents weight loss? 

  • Many people will say that “Calories in vs Calories out” is outdated.
    • Suggesting that it doesn’t take into consideration hormones etc.
  • The amount of calories that you require is a moving target.
  • Hormones do affect your calorie requirements.
    • Ie. Low thyroid hormones reduce calorie requirement, lower grelin makes you hungrier.
  • However, if you’re eating less calories then you require the energy must come from somewhere, so you will burn through these calories. Could come from fat or muscle, but it will result in weight loss.

The only way that someone wouldn’t lose weight on extremely low calories is if metabolic adaptations have occurred. They can still lose weight if they reduce their calories, however, this isn’t necessarily healthy. This is probably something that should be discussed with a medical professional to understand why your calorie requirements have reduced so much.

Medical Conditions that can Decrease energy requirements include hypothyroidism and PCOS.

Pros and cons of larger vs smaller calorie deficits 

Cons of large deficits (<75% of maintenance)  

  • Hunger 
  • Restriction 
  • Fatigue 
  • Muscle Loss  
  • Poor training 
  • Potential sleep disruption 
  • Increase risk of injury/illness 
  • potential issues with relationship with food  


  • It is quicker  
  • Less time in a deficit means less time spent experiencing the downsides of a deficit 

With my clients, I am more inclined to use mild to moderate calorie deficits – but I think there is a time and a place for being more aggressive  

Woman weight loss before and after front view in linen, fat loss vector illustration in pop art retro comics style

For example: 

  • You have left your weight cut to the last minute and just need to be pretty aggressive to make weight 
  • You have a long weight loss journey ahead of you and are motivated by quick changes – I sometimes use periods of aggressive dieting with some clients  
  • Because you like getting in and getting it done quickly – generally I am a more aggressive dieter because I’d rather be very restricted for a short period of time than moderately restricted for a prolonged period of time  

Interesting Research on the topic 

Study 1 – “Effect of Two Different Weight-Loss rates on Body Composition and Strength and Power-Related Performance in Elite Athletes” 

  • 0.7% weight loss per week predicted weight loss (slow – 20% calorie deficit) vs 1.4% predicted weight loss (fast – 30% calorie deficit) were compared. 24 total athletes split over the 2 groups. 4x lifting sessions per week.  
  • Similar total weight loss of 5.5kg, the fast group just got there in ~5 weeks vs ~8.5 weeks for the other group.  
  • The slower group GAINED 2.1% lean mass. The fast group had their lean mass remain unchanged.  
  • The conclusion was that if you want to gain strength and muscle in a deficit, slower is the way to go. Arguably though, an interesting conclusion is that the other group cut pretty quickly and retained all their lean mass, which is also a win.  

Study 2 – “Moderate energy restriction with high protein diet results in healthier outcome in women” 

  • 15 women who were non-elite athletes who lifted weights regularly 
  • 0.5kg vs 1kg per week weight loss for 4 weeks 
  • 1.4g/kg+ protein per day 
  • At the end of the study there was no change in lean mass for either group 
  • The quicker group had their testosterone drop 30% more.  
  • But the results in performance were interesting. The 0.5kg group had no change in any performance metrics. The 1kg group had their bench press decrease slightly, but their ability to squat 50% of their body weight to failure improved, whereas it didn’t in the 0.5kg group. So once again, not as bad as you would expect from a quicker rate of weight loss. 

Study 3 – “Evidence-based recommendations for natural bodybuilding contest preparation” 

  • This study summarised a lot of research on the topic.  
  • One thing that is obvious, but was covered well in this, is that people with more body fat can lose a lot of weight with minimal coming from lean mass.  
  • As people get leaner, the more it is likely to come from lean mass.  
  • This is one argument as to why slower rates could be more beneficial if particularly lean.  
  • Even in the first study that Aidan mentioned, if you look at the leanest individuals, the ones in the fast weight loss group lost lean mass, whereas the less lean individuals did not. 
  • This study proposed 0.5-1% weight loss throughout a bodybuilding prep, with the higher end being utilised at the start and the lower end nearer to the competition.  
  • Going faster than this risks more lean mass loss. Slower means you cut into your offseason and miss out on more time spent growing. 

Practical conclusion  

  • Individual choice – personal preference 
  • I personally like the 0.5-1% weight loss per week approach – but keep an open mind to different options being relevant for different situations 
  • As you can tell from the pros and cons list, there are a lot of downsides to quicker rates of weight loss. For some people, the upside of the it being quicker could outweigh that though. 

Useful Links/ Resources

Studies Mentioned:

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