WARNING 1: Look around this site, find the "FAQs" and read. Condensed there is a huge amount of valuable information that most people want. Failure to read these FAQs can lead to unnecessary worry, confusion and general uneasiness.
WARNING 2: 5:2 is not a quick weight loss diet (in fact, it was not designed as a weight loss diet at all). So if you are here to lose enough weight to fit into that (fill in clothing blank) by next month, or expect to lose the weight you have put on over several years as soon as possible, you are probably in the wrong place.
Looking around, you will see that the average weight loss with 5:2 is about one pound a week. As that is an average, it means quite a few people are losing less than one pound a week. It is sad but true that if you are a short woman with only a few pounds to lose, your weight loss may be somewhat less than a pound a week. I guess it is also sad but true that if you are as fat a man as I am, you will lose weight somewhat more quickly. But the fact all of these slowly losing weight people are still here should give you a clue that 5:2 has something going for it that makes it more than your average 'weight loss diet'.
WARNING 3: Combining WARNING 2 with the fact the body retains water to varying degrees in various amounts at various times, your scales may give you a false reading on how 5:2 is working for you. You can do everything 'right', get on your scales, and see you have gained one or two pounds. On the other side, you might see you have lost three pounds (joy), but then go for two or three weeks without further weight loss (depression). If you like to weigh yourself often (more than every other week or so), get used to the weight swings (but don't give up).
WARNING 4: Failure to focus on doing your two diet days correctly may lead to failure. 5:2 works because it causes a calorie reduction in your weekly diet by limiting your caloric intake to 5/600 calories per day for two days a week. If you ‘fudge’, you reduce your calorie reduction and reduce your weight loss. More likely than fudging, however, is the probability that you really don’t know what 5/600 calories of food really is. And, even if you have an idea, you probably will forget to count the calories in the milk in your tea, the cream in your coffee, the tastes you take while cooking or the sugar in your gum or breath mints. Calorie counting for a couple of days at the start won’t hurt, and may really help, your progress on 5:2. And for those of you coming from WW, there are no ‘free’ foods -you have to count all calories (even those in celery ).
WARNING 5: Don’t get distracted from your focus on 5:2. This site covers lots of intermittent fasting programs. Bouncing from one to another, or tacking one on to 5:2, probably won’t help and may hurt your initial attempts to adopt IF as a way of eating. Before you jump off the high dive, you first need to learn how to swim. Successfully do 5:2 for at least two or three months before trying to decide if the grass is greener in another IF pasture.
WARNING 6: 5:2 allows you to eat the foods you love, and does not require you to eat foods you do not like. If having the freedom to decide what foods you would actually like to eat today is too difficult to do on an ongoing basis, 5:2 may not be for you. On your diet days, you can eat 5/600 calories of whatever foods you want in any number of 'meals' at any time(s). However, many find a single high fat/protein meal in the evening works best for them.
WARNING 7: You will get hungry on your fast days, but you will not die from that hunger. (The not dying part is a good thing.)
Many people that want/need to lose weight rarely get hungry, and it is a new experience when they do. Be advised that learning what hunger really is has certain long term benefits. On your non-diet days, you will come to recognize if you are eating because you are hungry, or for some other reason. Over time, you may slow down your eating for 'other reasons', and lose weight a little faster than you otherwise would have.
Lest you think only eating 600 cal. or less for a day is somehow 'dangerous' or 'bad for your health', note that one documented case follows a guy who did not eat a calorie from food or drink for 54 weeks, 3 days (medically supervised, of course), and was alive, kicking and 276 pounds lighter at the end. If that can be done, surely eating only a few hundred calories for only one day at a time is a piece of cake!
WARNING 8: You might get cold. About 10% of your body energy is used to digest food. Digesting food creates heat. If you don't eat because it is one of your diet days, you are not digesting food and heat is not created. Some, but not all, report they feel cold. I put on socks and add a blanket at night.
WARNING 9: You might get a headache. Your body gets up to 40% of its daily water needs from food you eat. If you don't eat, you are shorting your body of water. Most headaches can be prevented by drinking additional water on your diet days. If that does not work, a shortage of salt is a secondary cause. Drinking some bouillon, which is mostly salt, or putting some salt on the food you are eating will usually do the trick.
If I have not scared you away with all of these warnings, please enjoy slowly losing as much weight as you want, all the while knowing that when you reach your goal, you will know how to keep it off forever.
One of my favorite lines picked up on this site is "A year from now, you will wish you started today." Enjoy the ride!