When people talk about fasting, they usually doubt that this is really healthy and sustainable and I was no different back then. When I started intermittent fasting, I had three major concerns:
1. First, I thought I will probably starve until lunch since I’ve learned that breakfast is supposed to be the most important meal of the day, right?
2. Second, I thought I will lose all my hard earned muscles because many "experts" suggest you to eat every two hours to provide the muscles with constant energy.
3. And lastly, I feared that IF will decrease my productivity as the brain doesn’t get the energy it needs.
In this blog, we will to go through these three points and see why these were empty concerns in the end!
In my first week of IF, I was indeed hungry in the morning at the same time I usually would be. Nevertheless, the hunger disappeared without me eating something.
This phenomenon was actually nicely demonstrated in a study from 2005. Researchers out volunteers on a fast for 84 hours and were checking for the concentrations of the hunger hormone ghrelin during the fast. They found two interesting things:
Even though the ghrelin levels were rising around breakfast, lunch and dinner time, the levels went down again even without any food intake.
Throughout the fast, the average ghrelin spikes became actually smaller, as if the body gets used to it.
It looks like, the ghrelin levels simply rise at the times when your body would be expecting food but over some time your body is able to adapt to the new eating style.
This is probably what happened to me. After the first couple of days on intermittent fasting, I stopped being hungry in the morning, as I “trained” my body to not be hungry before lunch.
When I started intermittent fasting, one of my main fears was that I will lose my muscles. After all, a dogma in the fitness industry is to eat about every two hours to give your muscles what they need. However, if we look at the science we see that this is simply wrong for normal people.
A study from 2014 found that when combining resistance training with intermittent fasting, the participants of the study showed more fat loss compared to the group that only did resistance training and that the intermittent fasting group could maintain the same lean mass as the control group. 
Another study went even a step further: In an 8-week trial, researchers split 34 men who were very experienced with weight training into two groups. Both groups were assigned the same amount of calories and protein per day the only thing that differed was the timing of the meals. One group performed intermittent fasting with an 8 hours eating window while the second group followed a normal diet.
By the end of the study, neither group had lost lean mass or strength. However, the time-restricted group lost 1.6 kg of fat, while there was no weight change in the normal diet group. I really like this study as it controls for calories, showing one more time that other factos matter more than calories.
There are two possibilities, why intermittent fasting actually helps to maintain muscles:
During fasting, and especially if you are on a diet, it is likely to enter a state of mild ketosis. Ketone bodies have been shown to be very powerful regarding muscle preservation. 
Fasting increases the human growth hormone. The human growth hormone has many functions in our bodies including cell reproduction and regeneration, it stimulates muscle growth, and improves cognitive functions. A study found that a one day fast already increases the concentration of the human growth hormone fourfold! 
For me personally, I really felt that intermittent fasting help me to preserve my strength in the gym.
My last major concern when doing intermittent fasting was that my productivity might go down. When I first tried intermittent fasting, I just started in a new lab and was working a lot in a biosafety level 3 lab, which really requires you to be conscious of everything you do. However, I was totally fine. In fact, I think I was more focused when skipping breakfast. Especially, if the breakfast would have been a carb-dense meal.
The fear of feeling weak and unfocused when skipping breakfast originate by big parts from commercials that try to make us believe that our brain needs a constant flow of glucose to function properly. However, in a starvation mode, our brain can swtich to ketone bodies as a source of energy. 
Our brains can use up to 70% of their needed energy from ketone bodies and the other 30% are coming from glucose, which our produces itself through a process called gluconeogenesis.
There are several studies that show how intermittent fasting can increase the growth of new nerve cells and increase the levels of an important protein called brain hormone brain-derived neurotrophic factor (BDNF), which is essential for the survival of existing neurons, and encourage the growth and differentiation of new neurons and synapses. 
Skipping breakfast or not eating for an extended period of time can be very beneficial for us. Humans have done it for millennia and only during the last 100 years, we stopped doing it. By now there are many studies showing how intermittent fasting helps to lose weight, decreases the risk of heart diseases, and prevents diabetes and last but not least, benefits your microbiome.
The last thing I want to mention here is that of course IF is not suitable for everyone. My girlfriend tried it after she saw how much I liked it but she doesn't really have any fat to burn and she has trouble to eat a lot at ones, which makes it hard to meet her calorie-needs during a restricted eating window.
However, if you are planning on losing some extra fat you might want to give it a shot. I guess Plato figured it out for himself when he said:
"I fast for greater physical and mental efficiency"
Espelund et al., Fasting Unmasks a Strong Inverse Association between Ghrelin and Cortisol in Serum: Studies in Obese and Normal-Weight Subjects, Journal of Clinical Endocrinology and Metabolism, 2005
Hayward et al., Effects of intermittent fasting on markers of body composition and mood state, Journal of the International Society of Sports Nutrition, 2014
Moro et al., Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males, J Transl Med, 2016
Nair et al., Effect of beta-hydroxybutyrate on whole-body leucine kinetics and fractional mixed skeletal muscle protein synthesis in humans., J Clin Invest, 1988
Ho et al., Fasting Enhances Growth Hormone Secretion and Amplifies the Complex Rhythms of Growth Hormone Secretion in Man, J. Clin. Invest. 1988
Cahill, Fuel Metabolism in Starvation, Annu. Rev. Nutr. 2006
Lee et al., Dietary Restriction Increases the Number of Newly Generated Neural Cells, and Induces BDNF Expression, in the Dentate Gyrus of Rats, Journal of Molecular Neuroscience, 2001