Author: Shanu Shashank , INFS alumni
I would be flying high if my body could become a machine that converts everything I eat into muscles, whether its carbs or protein or any of the unhealthy food items. While each time I shred, I would lose on those fats and no muscles, literally. Now, this is quite a hypothetical goal to achieve as we do not live in such ideal conditions where every calorie we eat would fill up the muscle glycogen, whereas, every time we lose, it would be through those glucose inside the fat stores. In a nutshell, nutrient partitioning means where the calories go (muscle or fat tissues) when you overeat them, while where does it come from (muscle or fat tissue) when you eat lesser.
So, there must be something controlling this calorie partitioning, right?
There is a very small percentage under our scope, as the amount of muscle mass we gain or lose is largely defined by our genetics. Apart from the exercises, the hormonal levels play an important role in this complex process. While a high testosterone level would act positively, that is more muscles while less fats, on contrast, the high cortisol levels would do the reverse (Ref1). Our genetics play a major role in maintaining an optimal level for these hormones including thyroid hormones as well as the nervous system. (Apart from external injection of stimulating drugs). Having said that, there are two more essential correlated factors controlling energy storage, the insulin and the body fat %.
Individuals with high amount of skeletal insulin sensitivity will tend to store a large amount of calories in glycogen stores inside muscle cells, while the ones with poor sensitivity will tend to store more in fat cells. (Remember, insulin is a storage hormone that helps transport the nutrients to liver, muscle and fat cells). Similarly, the higher body fat % you carry, the more fats you tend to lose while dieting (shredding) and leaner you are, the less fat you tend to lose more muscle (this is also the reason why it’s important to maintain a certain amount of protein while shredding). (Ref 2, 3). However, this is just reverse in case of the individuals who are naturally lean, as they simply gain more muscle even when overfed, while the fatter individuals tend to gain more fat than muscle mass while overfeeding. (Ref 2, 3) (I know you might be able to relate the different body types here).
Here comes the role of leptins (released primarily by fat cells). It denotes the amount of fat in our body, the more fats we have, higher the levels of leptins. Every time you go on a fat loss diet, the leptin levels drop to a certain level. In contrast, it tends to rise up every time we refeed. Leptin is an indicator of the glucose levels in the fat stores. Now, when the body fat % keeps on rising regularly – leptin levels also keep on increasing, the signal that indicates the leptin levels to the brain gets impaired leading to leptin resistance. So now your brain thinks you are starving as it is not getting the correct measure of leptin while your body’s fat levels continue to rise. With time, this leads to the impaired glucose uptake to the cells.
To simplify it: the fatter you are (higher body fat %), the more body fat is available as a fuel source but also your body has a tendency to store the extra energy in your fat cells. The risk of developing insulin resistance and leptin resistance are both high. This is not a good condition for fat loss regardless of your genetics.
Similarly, the leaner you are (less body fat %), the lesser body fat is available as a fuel source (it’s always good to keep having an adequate/minimal protein while dieting). Additionally, your body tends to move extra calories into your muscle glycogen. Finally, the leaner you are, the more insulin sensitive you become.
The final question- how do we improve this partitioning?
It’s not always good to blame our genetics, although a major part is controlled by them. However, the small percentage available to work around with is still good enough to get things under control. Our activity levels and the exercises, especially strength training is helpful in improving the insulin sensitivity. In other words, it improves the glucose uptake into your muscle cells, leading to better nutrition partitioning.
In summary, when we define an individual as endomorph, ectomorph or mesomorph, apart from the genes, it’s resultant of current body fat percentage and the insulin doing their job, which can be improved with constant effort and time.
Ref 1: A Kamba, et al. Association between Higher Serum Cortisol Levels and Decreased Insulin Secretion in a General Population. PLoS One. 2016; 11(11): e0166077
Ref 2: H Sagayama, et al. Measurement of body composition in response to a short period of overfeeding. J Physiol Anthropol. 2014; 33(1): 29
Ref 3: A Leaf, J Antonio. The Effects of Overfeeding on Body Composition: The Role of Macronutrient Composition – A Narrative Review. Int J Exerc Sci. 2017; 10(8): 1275–1296.
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