Is Quick Weight Loss Safe? • Common Purpose

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Is Quick Weight Loss Safe?


Words by Common Purpose Team

Published 28th January 2020

Approximately 10 Minutes Reading Time


Brief Article Overview


  • There are certain scenarios where a quick weight-loss intervention may be beneficial if approached strategically. These scenarios include;


  1. To kick start a fat loss journey.
  2. To break an extended plateau.
  3. To experience periods of fasting and gain the potential health benefits of fasting.
  4. To act as a learning opportunity to build individual skills and strategies.
  5. In preparation for a specific competition (sports involving weight classes) or event (wedding, holiday, reunion etc.).


  • Our evidence-based approach to quick weight loss goes as follows:


  1. Enter a significant calorie deficit (60-70% of maintenance).
  2. Use a Protein modified fasting protocol, which requires adequate levels of protein intake (1.5-2g per kilo of lean mass or 40% of calorie intake).
  3. The maintenance of essential nutrients through food choice and suggested supplementation.


Short term, quick weight loss interventions and crash diets conjure images of late-night television adverts selling juice detoxes, fat burners and strong laxatives! Which are unhealthy, unrealistic and unsustainable.


As health and fitness professionals, we take your physical and mental health seriously, so we often avoid extremes. We prefer a gradual long-term approach, based on lifestyle change formed by repeated healthy habitual behaviour. 


Although this remains central to our ethos, we do think that there are scenarios in which temporary periods of heightened discipline are worthwhile. Benefits include quick progress, a sense of achievement, increased self-confidence and an opportunity to learn useful skills and strategies.


There are times in life where you are ready for a challenge and want to expand your comfort zone. Harnessing these temporary bouts of high motivation to achieve significant results could do wonders for long term success. 


Extended plateaus in progress (although perfectly normal and often just require some patience) can become demotivating and frustrating. Short aggressive interventions are sometimes necessary to act as a “jump-start” both physically and mentally.


The idea is to we can maximise your fat loss potential in an evidence-based, strategic manner. 




This is essentially an adaptation of Lyle MacDonald’s highly regarded Rapid Fat Loss Handbook, which we recommend reading if you’re interested in the science behind the plan. For now, think of this article as a rationale, summarising the main themes and answering the most popular FAQs.


Don’t take this diet lightly or enter on a whimThis plan will test your resolve and we’re not going to start on the premise that the process will be a walk in the park. As a rule of thumb the more aggressive the diet, the smaller the margin for error when it comes to sticking to the plan. So read this thoroughly. If you have any further questions after reading this article, get in contact with us.


The Premise

This approach is what’s known as a “protein modified fasting protocol”. You decrease your calories to 65% of your estimated maintenance (putting you in a 35% deficit). This calorie deficit is taken from “non-essential” carbohydrates and fats, whilst maintaining relatively high protein levels (30-40% of intake).


When is Quick Weight Loss Appropriate?


As previously mentioned there are a few scenarios where a short, aggressive diet can be appropriate;


1. Kickstarting your fat loss journey – Using this plan can initiate specific physiological (glycogen depletion and increased fat utilisation) and psychological (self-efficacy and buy-in) processes that have been proven to help in the long run. 


Ethan and Rossner (1) list the magnitude of initial weight loss as a key predictor for sustained weight loss success.


2. Breaking a plateau – Plateau is perfectly normal and takes some patience to get over. Remember, every day you don’t regress, is progress. However, if your plateau is getting you down to the point of utter demotivation, this approach may be needed. 


3. Gaining multiple health benefits – there are a few well-proven benefits to a period of caloric restriction: improved insulin sensitivity, reduced risk factors (lower blood pressure and lower cholesterol) for age-related diseases such as diabetes, heart disease, and stroke. Decreases in some inflammatory factors and thyroid hormones, cellular clearing and renewing. 


4. Taking back control – Ever think that you’re always “giving in” to your cravings? As if food controls your behaviour, as opposed to the other way around? These short diets can be a simple, effective way of experiencing real physical hunger which, if approached correctly, can put you back in control of your relationship with food. 


4. Preparing for a Competition or Event – Certain sports require athletes to be in specified weight classes (most combative sports and powerlifting for example). A few weeks before a competition, a well thought out, quick weight loss strategy may be necessary to reach the desired weight as safely as possible.


In less extreme cases, events such as weddings, reunions and holidays may act as a deadline to reach the desired physique. Quick weight loss may act as a final “tighten up” to help you feel in your very best shape!


Weight Loss vs Fat Loss

Although a seemingly arbitrary distinction, weight loss and fat loss are two different things, and important to remember when tracking progress. The weight you lose over a short period (2-3 weeks) won’t all come from fat. Don’t get us wrong, the plan is always to maximise fat loss, but some of the weight loss will inevitably include some lean body mass e.g. water, glycogen, even stomach contents! 


As a note, this is why people often feel like they regain weight when coming off a strict diet. Very low carbohydrate diets, for example, will gradually deplete muscle glycogen, which also means water content. Upon the re-introduction of carbohydrates, these stores will be replenished, hence the appearance of weight gain.


Having said this, losing weight does indicate you’re heading in the right direction (in a calorie deficit), and there will be some significant fat loss, it is then down to a well-structured exit strategy to ensure you carry on utilising fat for fuel and retaining as much lean mass as possible. 


How Much and How Fast?


How much weight you lose and how quickly will depend on how much you weigh in the first place. A nice rule of thumb is that 1lb of fat costs about 3,500kcal. If you start at high body weight (and body fat %), your maintenance calories will be high, thus giving you more room to create a calorie deficit. 




If a 200lb man expends 3,000kcal/day and starts eating 1,250kcal/day, his daily deficit would be 1,750kcal (3000-1250). So technically he could shift 1lb of fat every 2 days. 


If a 140lb man expends 2000kcal a day and goes on the same 1,250kcal/day diet, his deficit would be 750kcal a day (2000 – 1,250). So it would take 4-5 days to lose the same 1lb of fat. 


To even the scales (pardon the pun) we can look at weight loss as a % of starting body weight. So, if a 200lb person loses 10lb, that’s a 5% loss of body weight. A 100lb person will need to lose half the actual weight (5lb) for the equivalent percentage loss (5%).


A weight loss of 3-5% of body weight over 2 weeks is realistic if you stick to the plan. 


Down to the Bare Essentials 


Some nutrients from the food you eat are “essential”. Essential nutrients are those which your body cannot produce/make itself, so need to derive from food and drink. 


To stop the body from eating into its lean mass to much, we will ensure that you maintain the required intake of essential nutrients.  This is done by prioritising certain food choices and taking specific supplements. 


The Essential Nutrients are:


  • Essential Fatty Acids (EFAs) – Omega 3 and 6.
  • Essential Amino Acids – histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. 
  • Most Vitamins and Minerals.


Prioritising Protein 


When it comes to prioritising macronutrients (carbohydrates, fats and proteins) for body composition and fat loss, protein wins! The word protein is translated from the Greek word “proteios”, meaning “primary”, or “holding first place”. 


When in a relatively large calorie deficit, the body will use amino acids (the building blocks of protein) to form glucose. Glucose your bodies main energy source, and without it, you would die (ask a diabetic). When glycogen is depleted and adequate protein is not present, it will take these amino acids by breaking down muscle tissue. This is not ideal. 


This is why we recommend a relatively high protein intake (1.5-2g/kg of lean body mass (3)). Supplements may be required if you’re struggling to meet the required protein targets. 


What about “Starvation Mode” and “Metabolic Damage”?

This is a contentious one, on which many books and research articles have been written, but we’ll try our best to summarise the top line take-homes, without getting too bogged down in the details.


It is fairly well established that the body is reluctant to lose weight, and unfortunately less reluctant to gain it (unless you’re one of the lucky ones!). One theory is that your Hypothalamus acts as a thermostat and works around a “set point” which is established post-puberty.


This bodyweight “set point” is fairly easy to increase, but difficult to decrease. If the hypothalamus detects fluctuations in energy intake (via hormonal, autonomic nervous system mechanisms), it will respond by decreasing metabolic rate, not necessarily enough to make up for energy loss, but enough to be a nuisance and slow the process down a bit. 


One fairly simple explanation for this drop in metabolic rate is that if you lose weight, you require fewer calories to function and therefore your metabolic rate slows down. There is, however, an adaptive component, where the metabolic rate has been seen to slightly “overshoot”, reducing metabolic rate more than is required for the loss of weight. 


This phenomenon is still up for debate and there are multiple theories; setpoint, settling point and dual intervention point, none of which are fully understood or proven (2). Nutrition science is a messy business and has to contend with a myriad of biological, psychological and social (biopsychosocial for short), so it’s very difficult to draw clear cut conclusions.


There are a few reasons, however, this plan shouldn’t negatively affect your ongoing progress:


  1. The higher your starting weight and body fat %, the less of an effect this will have on your ability to lose weight. This is partly why it’s harder to lose those last 5lbs compared to the first 20! 
  2. The shorter (<1 month) and less extreme (think near starvation) the diet intervention, the less of a lasting detrimental effect on your metabolic rate.
  3. The main driver for this initial drop in metabolic rate is due to reduced sympathetic nervous system (SNS) output. For this reason, it may be prudent to supplement with caffeine and get adequate sleep to keep your waking SNS high. 
  4. A well-planned exit strategy that aims to maintain the weight loss over a longer period should enable your body to settle at your new weight.


Suggested Supplementation

Here is a list of supplements we would suggest, to keep the body healthy whilst carrying out this diet;


  • A good multivitamin
  • Any other GP recommended vitamins and minerals (taking bloods and consulting your GP before dieting is always recommended). 
  • Creatine – 5-10g per day, depending on gender and size. 
  • Omega 3 fish oil – 1g+ of combined DHA and EPA at a ratio of 1:1.5 respectively, e.g. 400mg+ DHA / 600mg+ EPA.
  • Low-Calorie Whey / Vegan /  – dosage depends on protein needs.
  • Essential Amino Acids – 9-10g/day around during workouts.
  • Caffeine – 100-300mg daily (a double espresso before your workout will do the trick).




Although short term weight-loss interventions have gained a bad reputation, we believe that there are times they can be greatly beneficial. As long as they are not taken lightly, expectations are realistic and evidence-based strategies are followed. In our years of experience, these types of protocols work in conjunction with temporary bouts of high motivation. They provide us with a lot of information and learning opportunities, which equip us with life-long weight-management skills.


If you’re interested in starting your health and fitness journey with us…


Disclosure: This article is not to be used as medical advice. If you are currently experiencing physical or mental health issues, please seek professional advice from a fully qualified Nutritionist, GP or Physiotherapist.



  1. Who succeeds in maintaining weight loss? A conceptual review of factors associated with weight loss maintenance and weight regain. (2005) Elfhag K, Rössner S. Obesity Reviews (1):67-85.

  2. Recent advances in understanding body weight homeostasis in humans. (2018) Müller MJ, Geisler C, Heymsfield SB, Bosy-Westphal A. F1000Res. Faculty Rev-1025.

  3. International society of sports nutrition position stand: diets and body composition. (2017) Alan A. Aragon, Brad J. Schoenfeld, Robert Wildman, Susan Kleiner, Trisha VanDusseldorp, Lem Taylor, Conrad P. Earnest, Paul J. Arciero, Colin Wilborn, Douglas S. Kalman, Jeffrey R. Stout, Darryn S. Willoughby, Bill Campbell, Shawn M. Arent, Laurent Bannock, Abbie E. Smith-Ryan & Jose Antonio Journal of the International Society of Sports Nutrition vol 14 .