A Losing Battle: Why calorie deficit alone doesn't guarantee weight-loss

"For those looking to lose weight and shape up, the first step in their transformation journey is reducing their calorie intake and increasing their daily activity levels to burn more calories than they consume.

The general aim of an effective and sustainable weight-loss plan entails creating a 500-calorie daily deficit through the combination of exercise and calorie restriction.

As burn one pound (0.45kg) of body fat contains approximately 3,500 calories, reaching this daily target can theoretically help you shed the equivalent amount of fat in a week."


 A more intricate process 


While the calculations seem to pan out at first, the the process does not continue in a linear fashion the longer you diet and exercise.

The reality is that our body is a dynamic organism comprised of multiple systems and a change in one part of this integrated system changes others.


In addition, individual genetic, metabolic and environmental differences determine how we each respond differently to diet and exercise.

Factors such as your weight, body composition (muscle versus fat mass), hormonal balance, enzyme function, your gut microbiome, the volume and intensity of your daily activity, and your diet also affect your metabolism and influence your ability to lose weight and keep it off.


 Metabolic slowdown 


While you will definitely lose weight when you initially create a 500-calorie-a-day deficit, this process will only continue until a certain point.

This point is different for everyone, but following an initial period of weight loss, your body will start to adapt to the sustained energy deficit.


These adaptions include a shift in various hormonally-driven biological and physiological processes that effectively lower your daily metabolic rate through a process known as metabolic adaptation or adaptive thermogenesis.


These metabolic changes mean the body starts burning fewer calories to meet your daily energy requirements. You will also experience a rise in hormones that promote hunger while levels of hormones that promote tissue growth (anabolism), energy expenditure and satiety will fall.


 Stalling weight loss 


The end result is that a daily deficit of 500 calories produces slightly less of an effect on each subsequent day of your diet.

While the impact of this effect is negligible at first, the more weight we lose, the greater this response becomes as long as you remain in an energy deficit. It's the reason why many people lose a significant amount of weight initially, especially overweight individuals, but then progress stalls and they plateau.


Calculations using the Body Weight Planner show that the impact of this metabolic adaptation is so profound that over a 12-month period, you can only expect to lose 50% of the weight that the 3,500-calorie rule estimates.


As such, you need to keep creating ever bigger calorie deficits the longer you diet to keep seeing the same  results, which quickly becomes extreme, unsustainable and unhealthy.


 Trigger a new response 


Ultimately, this means that no single weight-loss approach works indefinitely. Thankfully, there are various ways to shift your metabolism back into gear to continue losing fat in a healthy and sustainable manner until you reach your goal.


The best option is changing your diet to add variables beyond just calorie restriction to trigger a response. The concept is known as diet periodisation, which entails periodically changing your macronutrient (carbohydrate, fat, and protein) ratios and/or calorie intakes.


For example, if you followed a low-carb diet for more than six months and your weight loss plateaus, introduce carb cycling – alternating between days of low carb intakes and higher carb days – for a period to potentially trigger the desired response.


When that approach stops working or fails to yield results, try varying your meal timing and frequency with an approach like intermittent fasting, or calorie shifting, which adds in a few high-calorie days (generally called re-feeds) to potentially trigger beneficial hormonal, physiological and metabolic changes that could reignite your progress.



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  2. Egan, A., & Collins, A. (2022). Dynamic changes in energy expenditure in response to underfeeding: A review. Proceedings of the Nutrition Society, 81(2), 199-212. doi:10.1017/S0029665121003669
  3. Martins, C., Roekenes, J., Gower, B.A. et al. Metabolic adaptation is associated with less weight and fat mass loss in response to low-energy diets. Nutr Metab (Lond) 18, 60 (2021). https://doi.org/10.1186/s12986-021-00587-8
  4. Martins C, Roekenes J, Salamati S, Gower BA, Hunter GR. Metabolic adaptation is an illusion, only present when participants are in negative energy balance. Am J Clin Nutr. 2020 Nov 11;112(5):1212-1218. doi: 10.1093/ajcn/nqaa220. PMID: 32844188; PMCID: PMC7657334.
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