Active Fat Man: Adaptation to Physical Activity

The first half marathon (Airtel Delhi Half Marathon) which I ran was in the year 2008, and at that time my diet was bad and my weekly mileage was lower than what it has been over the next decade.

Now, after a decade of running more and more every year, I am at the same body weight but I am no longer as lean and cut, as I was during the initial years of running. Granted that age related metabolic decline is responsible to an extent, but that does not explain the pudginess I’ve been accumulating over the years even with increased exercise and less vices in my diet.

Very recently, I came across this paper titled, “Constrained Total Energy Expenditure and Metabolic Adaptation to Physical Activity in Adult Humans” (link to which is https://www.cell.com/current-biology/fulltext/S0960-9822(15)01577-8). 

This is a cross sectional study which only used accelerometers to measure physical activity, so the results can be questioned to an extent but overall it provides answers to what I’ve been usually bewildered with when I see the following high activity individuals with pudginess/high body fat/paunches: 

1. Indian (pedal) rickshaw operators. 

2. Some ultra-runners or runners with high weekly mileage. 

3. High mileage cyclists.
4. Triathletes 

5. Construction site workers. 

6. Rag pickers. 

7. Me. 

8. You (if you’re highly active). 

The aforesaid ‘study’ explains the long-term effect of physical activity on total daily energy requirements using two energy expenditure models: 

a. Additive Total Energy Expenditure Model – This model supports the traditional public health strategy to combat obesity, whereby increased physical activity is recommended to increase total energy expenditure to maintain body weight i.e. exercise more to burn more calories with no upper limit as to where this will model will stop working. So, as per this model, during a night out with friends, you can eat a 1000 calorie pizza accompanied by 3 pints of light beer (450 calories) and then burn these calories off next morning by running 20 kms. This is the model which I have used till now (unsuccessfully, which is I why I’m writing this) since it works on a very logical presumption of ‘plus’ and ‘minus’, as if the human body works on a debit credit banking system. However, as per the study – the human body adapts to physical activity and the total energy expenditure therefrom, as explained by the Constrained Total Energy Expenditure Model below. 

b. Constrained Total Energy Expenditure Model – This model states that “rather than increasing total energy expenditure linearly in response to physical activity, individuals tend to adapt metabolically to increased physical activity, muting the expected increase in daily energy throughput”. Simply put – you cannot outrun a bad diet by exercising more since your body will adapt to the physical activity. You can’t out-exercise a bad diet after a certain basic daily energy expenditure level.

As per the study, for CPM/d above approximately 230 (explained in next para), the total energy expenditure among individuals was negated by compensatory changes in energy expenditure on other activities. These other activities are explained as behavioural changes such as sitting instead of standing and resting more overall, and changes at the biological level. 

CPM/d means ‘counts per minute per day’ which was measured by accelerometers in the study and CPM/d of 230 equates to about 6000 steps per day which furthers equates to about 5 kms per day. The study makes immense sense if you recall the adage, “the last 5 pounds are the hardest to lose”, or when you can recall a friend saying I’m exercising so much but this stubborn belly fat is not coming off. 

The key takeaways from the study are the following: 

1. For sedentary individuals, this study will not apply since they’ve been in sloth mode for a long time and therefore the chances of metabolic adaptation at low levels of physical activity cannot happen. So for sedentary individuals who just discovered or were (vehemently) recommended exercise, there is no need for concern since your only concern should be to reach 6000 steps per day and then start researching more. 

2. More than exercising, a cleaner diet is more helpful in the long term to maintain health and body weight since overreaching in exercise has constrained potential to burn calories and also definitely leads to injuries and illnesses. 

3. The study was cross sectional (not longitudinal) and it only used accelerometers to arrive at its main hypothesis and therefore, if you’re stuck in a weight loss/fitness rut, it would be better to sprinkle more weight training or other exercises/sports every few months to perhaps not allow the metabolic adaptation which comes when CPM/d is above 230 (6000 steps per day). There are other research which show that increasing muscle mass can increase metabolism, even resting metabolism, so maybe lift more weights. 

- Aman Yadav