You have to be careful when looking at the research for intermittent fasting. Most people I have had contact with, who have been following the diet, try very hard to eat healthily. In fact, you soon learn that if you eat things which are high in calories on a fasting day, you will end up very hungry. Most people will eat a lot of vegetables on a fasting day, because these fill you up - and properly cooked, can be delicious.
The diet I am following is two non-consecutive days on 500 calories a week. I am eating normally the rest of the time. I generally eat no breakfast on fasting days, and either no lunch and all my calories at "dinner" in late afternoon, or a light snack at lunch and the majority of my calories in late afternoon.
I have been attempting to eat in no more than an eight hour window, and trying not to eat after 6pm in the evening. But those are my restrictions, based on things I have read, and not an intrinsic part of the diet.
If you look at the research which has been done into intermittent fasting, especially the rodent studies, you need to consider certain things. Some studies have fed their rats a rubbish diet of high fructose corn syrup and refined carbohydrate. Some haven't allowed the rats free access to food on non fasting days. Some have followed other patterns of eating like alternate day fasting, or have fasted the rats entirely on fasting days.
Some researchers, when talking about intermittent fasting, won't be talking about the 5/2 scheme of dieting, but about the idea that you should restrict your eating hours to eight hours in the day, and fast for 16 hours a day. This Dr Mercola article is addressing that type of eating.
If you are a layperson, getting access to the research papers may be iniquitously expensive, as many papers are published on gated sites which expect to be paid for access to the full papers. For this reason you may find it easier to buy the books which have been published on the subject, which tend to aggregate the research - but you have to trust the author to interpret it correctly, and to give you all the details. If you join some of the online support groups for intermittent fasting or alternate day fasting, many of them give access to research papers.
That having been said, I plan to collect the research I have found on this page, and will add more as it becomes available or I stumble over it.
There's quite a lot of research listed on the wikipedia page for intermittent fasting here. You generally have to look at the references at the bottom of the page to track back to the original research, if links in the article do not take you to it. Annoyingly they often take you to definitions of the terms used in the article instead of the research they are referring to.
While we're looking at websites, there is one for alternate day fasting here. Surprisingly I found this less effective for weight loss, but it was a good introduction to the 5/2 diet, because it made it seem easy by comparison. Although you are still able to take the alternate day fasting diet one day at a time and always tell yourself that although you may not be able to eat X today, you can tomorrow. I found that the attraction of X had often worn off by the following day!
Dr James Johnson pioneered the up day/down day fasting diet, but he includes some extra elements that I haven't adopted. His diet is an alternate day fasting diet. He has published a number of books about the subject. Many people following the 5/2 diet I am on, will talk about "updays" and "downdays" as shorthand for normal eating days and fasting days.