I read lots of nutrition studies as a certified health and nutrition consoler, professional fencing coach, and avid cyclist. I also go to monthly seminars on nutrition to keep me up to date. Rather then cherry picking some study to "prove" my point
(you can find studies to "prove" anything) I will just pass this on.
In nutrition we thrive on a varied diet. Both for health and performance. Your system will adapt to any eating strategy. If we eat simple carbs while training we adapt. If we eat complex carbs we adapt. If we train with depleted glycogen stores we adapt. As in exercising muscles groups it is my opinion that there is merit in mixing things up. You see you can only ingest so much nutrition while doing heavy exercise. It is my opinion that all these energy systems need to be tapped to performs best. It is also important to consider the effects of a diet high in simple carbs (sugar). If your doing 5 or 6 hour rides living off of gels your eating a large portion of your calories with food that is nutritionally empty. In fact multiple studies over many years have found that a diet high in sugar leads to systemic inflammation, may I suggest you look up that term if your unfamiliar as it is the precursor for all sorts of diseases. My advise is that you seek a trained professional if your really serious about optimizing your performance and health with diet. I have seen far to much misinformation on this forum (training) and other online sources. It is almost impossible for the casual observer to tell what is sound advise and what is not without expert help. Also vital is to remember that we are all different and nutritional strategies are different for individuals and should be forever evolving.
I am often asked for specific "tips" on nutrition. To give sound advise one needs a full health history, a detailed record of diet and exercise and an understanding of the subjects history regarding eating issues. So don't ask me for tips in the elevator