By Dr Wong Chung Chek
The benefits of fasting are manifold, going beyond just weight loss. One of the effects of intermittent fasting, is overall reduced calories intake, and hence reduction of body weight. Intermittent fasting also leads to improved metabolic health, increased energy and cognitive performance, and autophagy (a natural body rejuvenation process).
Weight loss can be attributed to reduction in adipose deposit, and/or reduction in muscle mass. Reduction of fat tissue is always beneficial for our body, but not so for muscle loss, as low muscle mass is associated with poorer metabolic health (especially blood glucose regulation) and lowered physical performance or even frailty.
Fasting may even increase the rate of age-related sarcopenia. Our muscles also release various myokines that modulate the functions of other organs notably the brain.
Muscle cells physiology
But how do we fast without losing muscle mass? This would require an understanding of our muscle cells physiology.
Net muscle mass is balanced between anabolism and catabolism. Anabolism means building, whereas catabolism refers to breaking down. Our brain cells prefer glucose over fat as a source of energy. Therefore, in a fasting state, the liver triggers a process called gluconeogenesis, to generate glucose from mainly proteins in order for the brain to use.
Hence, with prolonged fast (five days or more), we see a decline in muscle mass, as muscle is the most readily available source of protein (to be converted to glucose via liver gluconeogenesis) in our body. On the other hand, muscle anabolism takes place via mTOR activation.
mTOR activation in muscle leads to muscle protein synthesis, increasing muscle mass and strength. This can be activated by physical exertion of muscles (resistance training) and protein (especially the amino acid leucine).
Both exercise and protein intake activate the mTOR and hence muscle anabolism for about six hours, and in a dose dependent manner, up till a certain limit.
Intake of protein
The first point to reduce muscle loss during fasting is to have adequate intake of protein in our diet. Animal source of protein is the best quality in terms of mTOR activation. In general, the optimal amount of daily protein intake tends to be somewhere between 1.0-1.5g/kg of lean body weight. Therefore, for a person with a 60kg lean body mass, the daily protein intake is between 60-90g.
There is also a limit of protein absorption per meal, as proteins have to be digested, and absorbed as amino acids into our intestinal lining cells through specific transporters, and moved out of intestinal lining cells on the other side into circulation in the blood stream. It is estimated we can only absorb a maximum of 30g of protein in one sitting.
To further reduce muscle catabolism during fasting, we can activate mTOR (the anabolic switch of our cells, including the muscle cells) via physical activities like resistance exercises. Body weight resistance exercise is convenient, easy to follow and safe.
Squats, lounges and push up can be performed with various degrees of difficulty and intensity, with more focus on our torso and lower limbs as those are categorised as larger muscle groups. Be sure to also time your exercises around meal times to further activate the mTOR switch in order to build muscle mass.
There is a myriad of benefits with fasting. With a little more understanding of our body physiology, we can reap these benefits with fasting without the potential issue of muscle mass loss.
Take note of your daily protein intake, be aware of the limit of protein absorption per meal, and engage in some forms of resistance exercise around your meal time in order to reduce muscle mass reduction during your intermittent fasting period.
Dr Wong Chung Chek is Consultant Orthopaedic & Spine Surgeon at ALTY Orthopaedic Hospital.