There is a form of diet that is not related to weight loss primarily. Even some bodybuilders appear to try it. It is a diet primarily designed for utilizing autophagy called intermittent fasting.

What they try to do is to limit the intake of calories by 4 to 8 hours a day. So the rest of the time there will be fasting to tap into this mode of healing. However, there will not cut on the calories they will be just consuming them in a restricted period.

Some studies show that this too can have beneficial effects. There is truth in the statement that meal frequency is not nearly as important as the quantity and quality of food consumed. Thus logically if we still eat all of our calories in the period of 4 hours and are active the rest of the time, it is still unlikely that we will burn all of our glycogen stores because we replenish them every day.

In that sense, intermitting fasting would not be able to tap into the same healing mechanism at the level of calorie restriction. If we eat less and go into calorie restriction, it does not matter because we will be in deficit no matter when we eat. It will be a good idea to put exercise on a regimen of intermittent fasting just before the end of the fast, to deplete the glycogen stores, or we can combine all three methods. Calorie restriction with intermittent fasting with physical activity.

To go around this, there is Alternate day fasting (ADF). It involves a 24-hour fast followed by a 24-hour non-fasting period. Then there are whole-day fasting cycles that specify various ratios of fasting to non-fasting days, such as the 5:2 diet. You eat for five days, then fast on water or vegetable juices for two. So far studies done on animal models have shown that fasting improves indicators of health like blood pressure, insulin sensitivity, and inflammation.

Intermittent fasting in my personal view started as a convenient way to do a calorie restriction diet. To do a full-calorie restriction diet is a hard choice. Most of the population will not do it. The intermittent fasting line is to go and fast 1 or 2 days a week and clean our cells, reset our metabolism to take control of our hunger cravings, and so on. That will help our body to go into autophagy and high HGH levels and will start healing mechanism.

However, there is another essential benefit of calorie restriction, and that is lowering the basal metabolic rate. If we have a car with a million horsepower, it will burn a gallon of fuel in a millisecond, but if we have a car that runs on one horsepower, it will go much longer. It is called efficiency. When you force yourself to become more efficient in burning energy you go longer.

Calorie restriction is not calorie restriction our entire life. It is the only restriction in the beginning period. Our physiology will adapt to hunger to some extent by becoming more efficient with the calories that it has. Basal metabolic rate has the ability to slow down, but only to some extent. Our body will enter the starvation response and will go through the physiological changes that reduce metabolism in response to a lacking of food. The human body has some level of ability to adapt and structure itself known as deprivation response (i.e., metabolic adaptation).

There was a study done on eight individuals living in isolation in Biosphere 2. Biosphere 2 is an Earth Systems science research facility located in Oracle, Arizona. It was initially designed to determine the viability of closed ecological systems to support human life in outer space. The first experiment was conducted on eight individuals for two years. After the experiment was finished, the metabolic rate of these eight isolated individuals was measured and compared with a control group that initially had similar physical characteristics. The starvation response managed to reduce the metabolic rate for 180 kcal on average in daily total energy expenditure.

If you eat regularly 2000 calories and you start to restrict the calories your metabolism slows down to 1800 calories on average. Then when you came back to eat these 1800 calories, it is not restriction anymore. It is in a sense because you are at an artificially lowered metabolic rate so if you start overeating again your basal metabolic rate will go up, but if you stay at this level you will not starve and die. You can live in this new state. People have this kind of idea about the calorie restriction diet that you are restricted continuously. In a sense, you are because you operate at a lower metabolic rate, but you are not in the physical sense or you will eventually die. And that is the reason why calorie restriction prolongs life.

Slowing down metabolism meaning prolonging life through efficiency. Burning fuel means stress in the form of oxidative damage to the DNA that needs to be repaired.

Can you gain muscle on caloric restriction? Probably just some level of body recomposition. If you have some kilograms to lose then lowering by 400 calories can increase muscle and lower fat deposits at the same time if you do resistance training. But if you are already calorie-restricted at the optimal level then no, your body has already lowered your metabolism as much as it can. There is a calorie in calorie out equation based on the first law of thermodynamics. It might be possible on intermittent fasting cycles. Five days of resistance training than two days of aerobic training plus fasting.

One other thing. When we start building muscle our metabolism can slow down if we do not increase calories, it will adapt to some extent. We do not need to start overeating excessively just because we go to the gym. That will give you dirty bulk. One hundred grams of flesh have around 25 grams of protein and 150 calories, and you cannot grow at the rate of 100 grams of muscle mass a day. In my opinion, when we start resistance training, it would be wise to raise calorie consumption at the level of what is burned during the exercise plus a little more, at the top 200 calories more than that. Raising it higher is excess that goes into adipose tissue, basically the waste of energy that has to be burned at some point. Overeating with the excuse:” I go to the gym”, is not a good idea.

Related Posts

1. 
   Calorie restriction, Autophagy, Longevity, and Muscle loss
2. 
   Longevity- The rate of living theory

Sources:

Passages selected from a book: “Go Vegan? Review of Science: Part 1” [Milos Pokimica]

1. Impact of intermittent fasting on health and disease processes. doi: 10.1016/j.arr.2016.10.005
2. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. doi: 10.1016/j.trsl.2014.05.013
3. Intermittent fasting: What questions should we be asking? doi: 10.1016/j.physbeh.2020.112827
4. The alternate-day fasting diet is a more effective approach than a calorie restriction diet on weight loss and hs-CRP levels. doi: 10.1024/0300-9831/a000623