What You’ll Takeaway –
1. A diet that creates a calorie deficit causes someone’s metabolism to drop and slow.
2. A further drop in metabolism is observed above and beyond that which is explained simply by a drop in their body weight (12-15.)
3. Dieting on the same calories week on week, losing the same amount of weight each week just doesn’t happen, the leaner you get the hard it becomes to lose weight.
4. Look to only create a calorie deficit of 10-20%, with weight training being your primary type of training to preserve muscle and improve health. (4)
There is no way to lose weight without a calorie deficit, but creating too much of a deficit through endless cardio and over dieting is not healthy or beneficial.
There are more ‘optimal’ and enjoyable ways!
If all else remains equal, you will lose more weight by adding cardio on top of your lifestyle, but how much should you do?
Research into the impact of exercise and diet restriction on daily energy expenditure, concluded –
‘The optimal combination of diet and exercise, however, remains elusive. It appears that the combination of a large quantity of aerobic exercise with a very low calorie diet resulting in substantial loss of bodyweight may actually accelerate the decline in resting metabolic rate. These findings may cause us to re-examine the quantity of exercise and diet needed to achieve optimal fat loss and preservation of resting metabolic rate.’ (1)
You very often hear of individuals trying to lose weight with excess calorie restriction and lots of cardio struggling to lose weight, ‘claiming their metabolism is damaged or stopped.’ This seems odd due to the calorie deficit they are in apparently. They may of course be lying or highly underestimating their calorie consumption, but what we need to remember is a diet that creates a calorie deficit can cause someone’s metabolism to drop and slow. When you lose weight your new lower body weight will not require the same number of calories, for maintenance that your previous weight did. For example an individual who requires 2000cal to maintain 90kg bodyweight will not require 2000cal to maintain weight when they have lost 5kg. However, a further drop in metabolism is observed above and beyond that which is explained simply by a drop in their body weight (12-15.)
Doucet E et al. managed to show this in both men and women; ‘When changes in rested energy expenditure (REE) are extrapolated over a 24 h period, the observed changes in Fat Free Mass and Fat Mass observed after 2 weeks in men should have caused a 57 kJ/d decrease in REE, based on the reference regression, whereas the actual decrease was 526 kJ/d.’ (13)
Your REE is part of your total daily expenditure (TDEE.) Resting energy expenditure represents the amount of calories required for a 24-hour period by the body, made up of your basal metabolic rate (BMR,) activity levels, non-exercise activity thermogenesis (NEAT, movements such as fidgeting,) and thermic effect of food (TEF, the energy burnt in digesting food.)
So why is there an extra drop in REE?
During a dieting phase an individual will experience a decrease in NEAT and and TEF due to less food being consumed. Both of these will lower their REE. However, metabolic adaptions, called ‘adaptive thermogenesis,’ occur causing a further drop in REE. Arone et al. manage to show that during prolonged dieting caused a decrease in the activity of our sympathetic nervous system, the part of our system that activates what our fight or flight response. (16) Decreases in hormones occur; thyroid (9,) leptin (6,) androgens (7,) and increases in cortisol (8) causing hormonal fluctuations that will cause a further drop in metabolism above and beyond which is expected. (2) This makes dieting harder and harder to sustain as lower and lower calories are needed to maintain your new weight, and have even been shown to occur post dieting at weight maintenance. (13)
How many of you have dieted, and lost the same amount of weight week on week eating the same deficit each week?
This just doesn’t happen, the leaner you get the hard it becomes to lose weight.
These effects are simply a protective mechanism your body uses to stop extreme weight loss occurring and assist the regulation of bodyweight. It has been found that adaptive thermogenesis can cause a decrease in metabolism of approximately 15% during a calorie restricted diet. (10,11) Research has been conducted (5) to measure the changes in metabolism and spontaneous activity levels of dieters on either a diet or diet and training. They found ‘calorie restriction results in a metabolic adaptation and a behavioural adaptation with decreased physical activity levels. This data suggests a large calorie restriction causes large inter-individual variability in the rates of weight loss and how exercise may influence weight loss and weight loss maintenance.’
Your metabolism is important, not just from a health aspect but also for making your weight loss as easy as possible, allowing you to eat more while losing weight. Your metabolism will slow throughout any diet, that is unavoidable as you become lighter, but too much of a calorie deficit from either diet and/or cardio can cause severe adaptive thermogenesis to occur. A daily intake of less than 1000 calories has been shown to have the biggest implication on adaptive thermogenesis. (3)
So when looking to lose weight you should always want to try and ensure the majority of weight loss is from FAT by maintaining as much muscle as possible, and make it enjoyable. Conducting lots of cardio with a severe calorie restriction causes a significant decrease in weight from fat and muscle.
Muscle not only looks good, but is slightly more metabolically active than fat contributing to your metabolism. Therefore you do not want to be running yourself into the ground carrying out endless amounts of cardio on hardly any calories. This will lead to a loss in muscle, a decrease in metabolism and a disturbance in your hormonal profile.
Potentially, this could lead to rapid weight regain if when you have reached your desired weight you revert back to eating how you did not monitoring your calories. Your new maintenance calorie requirement would be disproportionately lower than what can be determined by body weight alone.
Rosenbaum M and Leibel RL manage to show this concluding; ‘This ‘adaptive thermogenesis’ creates the ideal situation for weight regain and is operant in both lean and obese individuals attempting to sustain reduced body weights.’ (12)
So how do I lose weight and mainly fat?
Look to only create a calorie deficit of 10-20%, with weight training being your primary type of training to preserve muscle and improve health. (4) While cardio will aid in creating a calorie deficit by burning calories, it can’t change the shape of your body the way weight training can. Slow weight loss in a step by step approach is the easiest way to reduce adaptive thermogenesis. It is a lot easier to manipulate and control the ‘calories in’ via diet than the ‘calories out’ through cardio, this is why your diet should be your first port of call for losing weight. To create a daily deficit of 500 calories for example could equate to cutting dinner by half, but creating the same deficit through cardio alone could take up to an hour’s worth of sitting on the bike, which can be boring and not achievable within an individual’s lifestyle. Cardio is an additional tool that can be used to aid in fat loss and boost your caloric deficit, and should only be added, from a fat loss perspective, once calories become too low for performance/enjoyment/health or when weight loss has plateaued
*Having said this though, if cardio is going to be the only type of exercise you will/can conduct due to lifestyle or preferences. Then by all means go for a run as any form of exercise is better than none.
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