Intermittent fasting. This includes many diets. Most popular these days is the 16:8 diet, where you restrict eating to an 8 hour window each day. The other 16 hours you have just water and other zero calorie drinks.
Why? Most people follow these diets for a weight loss goal, or a perceived health benefit of giving the gut a rest from digestion.
So is there a benefit for such diets? In particular in recreational or competitive athletes.
In people who do no exercise, calorie for calorie there appears to be no difference in weight loss between those who intermittently fast and those who eat whenever they want through the day. So it may be a case of personal preference, at least in young adults.
In people who resistance train - such as powerlifting, weightlifting, and CrossFit - it is a little more complicated! Whilst bodyweight might not differ, when losing weight, research indicates body composition is better in those who eat regularly compared to those who intermittent fast. By this I mean that those who eat regularly have a lower body fat percentage, i.e. they have more muscle and less fat. It is likely this is because the body tends to break down muscle when starved, and regular protein intake can help prevent this. If you are fasting intermittently you have extended periods where you are not taking in energy or protein … so the body may break down more muscle.
Athletic performance and recovery
If you do intensive or long duration (more than 1 hour) of training 5-6 days a week, you have little time to recover between successive days of training. Recovery includes adequately refueling with food for the energy to train and also to repair the muscles of the body and adapt to training. If you fast, you need to think very carefully about the timing of your training in relation to the fast to ensure you can adequately refuel and recover between training sessions. It is not impossible, but it is hard and requires significant attention to detail. For many of us leading busy lives, this might prove a challenge!
Giving the gut a rest
Unless you have one of a limited number of gut diseases (that you would most definitely know about) there is no evidence that it is especially beneficial for the gut to have an extended rest from digestion each day. Sorry guys! Or not sorry, as you can eat up!
This one links to all the elements above. There is some evidence that eating super late at night may disrupt certain body rhythms that can have an impact on how your body works, including metabolism. But more research is needed!! And genetics may play a role. As might lifestyle, including when you train. But this does not necessarily mean intermittent fasting per se is the way forward. It is an interesting area, and more research is needed!!
So, in summary, typically I would not recommend intermittent fasting for those training at high intensity or long duration regularly, in most sports. Simply because it makes maintaining body composition, performance and recovery so much more challenging.