The words "dietary regime" refer to a set of rules for food intake. Most of these rules are based on tradition, some come from medical grounds, but there are almost no rules derived from actual experience.
From the standpoint of modern medicine, food should contain a sufficient amount of proteins, fats and carbohydrates, as well as micro- and macronutrients and vitamins. Moreover, the caloric intake should satisfy human needs for energy." This information can be trusted because it is a medical fact.
Food should be consumed at a certain time and at certain intervals. That guarantees the best general condition and health." And here's an unsubstantiated assertion.
Experience shows that the best dietary regime, for a particular person in a particular situation, is the one that allows not only to obtain the necessary energy, but also to achieve the goal at hand. For example, to cure an allergy. a week-long food pause should be held. To cure hypertension, a series of week-long pauses, once a month. To cure hormonal infertility, a five-day-long pause, right after an ovulation. In the treatment of coxarthrosis, this diet was proven effective: the patient eats during a week, then holds a week-long food pause. In contrast, with daily nutrition you wouldn't achieve the desired effect, even if you take medication.
So what kind of diet to choose?
Usually, excess weight requires changing the diet. This is a problem on the lines of "abnormal body composition", and the dietary regime successfully solves it. Today, regimes also attract interest among athletes and bodybuilders. It turns out that body shaping by training only has its limits.
Let's consider the dietary regimes they practice.
Fasting every other day. Eating as usual during one day, eating nothing during the night and the next day (36 hours). Proponents of the technique advise choosing healthy food, but basically allow eating anything.
Freedom from any regime (random diet). Some believe that we should eat and train like our ancestors, randomly. It means skipping meals and training not according to the schedule, but whenever you want. You also have to eat "evolutionarily correct" food and alternate the caloric intake. The diet is very flexible, there are no rules in a strict sense: you eat when you want to, then fast for two days, then have a snack and go without food again.
Eating-pause-eating (a day without food, 1-2 times a week). You have to fast for 24 hours 1-2 times a week and eat mostly unprocessed, healthy food that is high in protein. The technique is flexible, you may choose when to fast and from what exact moment, e.g. from breakfast to breakfast or from lunch to lunch. John Berardi, a doctor and a sport nutrition specialist, tested it on himself and found it very promising.
Martin Berkhan's system (16 hours of fasting / 8 hours of satiety). The system recommends eating only during a certain time interval. The rest of the time, you should refrain from eating. For example, you may eat only from 1 to 9 in the afternoon every day. However, that is not the only rule. Your diet should include high-protein food, alternating carbohydrate meals, hungry workouts, and proper timing (you should consume most of your daily diet immediately after a workout).
Military diet (20 hours of fasting / 4 hours of satiety). According to this technique, you may eat only during a certain period of time. For example, from 6 to 10 in the afternoon every day, training on an empty stomach. For this regime, a carefully chosen diet is recommended. As a rule, the 4 hours of satiety fall on the evening.
Those are the most popular dietary regimes at the moment.
Each regime has its own specific features, but the main thing is that various regimes are finally being discussed, and not just different diets within the only correct regime. In medicine, there is still only one regime for everyone with different diets.