In an up/down day intermittent fasting approach, every day is either a regular eating (“up”) day, or a fasting (“down”) day.  There are many patterns of fasting/eating days to choose from, and you can vary approaches to see what works for you. In most of these up/down day approaches, you aren’t required to do full fasts on your down days. Instead, you are allowed up to 500 calories on those days.  These plans (as written by the original authors) aren’t true fasts.  You still reap many of the benefits of fasting, and the up/down pattern of eating works well to prevent the metabolic adaptation you find in a typical low calorie diet (remember the Biggest Loser study, which you read about in the chapter about calories.) Even though you are allowed to have 500 calories, think back to the lessons we have learned in the chapter on insulin.  You don’t want to have frequent insulin release on your fasting days, so structure your intake for maximum fat burning potential.  See the chapter on what you can have while fasting for specific tips to avoid insulin release during the fasting period. While these plans “allow” you to have up to 500 calories on the down days, I prefer to reap as many benefits from the fasting period as possible.  For that reason, when I have a down day, I do an actual fast with 0 calories (other than the negligible calorie content from black coffee).  I have found that, for me, it is easier to abstain from food completely for 36 hours than it is to limit myself to 500 calories.  You are free to experiment to see what works best for you—the way that is “best” is the one that you will stick to with the least amount of discomfort on fasting days. The way I work a down day is this:  I wake up, and stick to black coffee/water/sparkling water all day, until bedtime.  I go to bed without having eaten anything all day.  The next day when I wake up, it’s an up day and I am free to break the fast whenever I want.  If I break the fast with breakfast, I have fasted for approximately 36 hours.  If I wait until lunch to break the fast, I have fasted for about 42 hours. There are several specific plans that you can choose from if considering an up/down day approach to intermittent fasting.  The most extreme version of up/down day fasting is called “Alternate Day Fasting”, or ADF.  ADF is exactly how it sounds:  one day you fast, and the next day you eat according to whatever schedule you want.  It continues indefinitely in the alternate day pattern.  ADF is heavily researched by Dr. Krista Varady, and she explains her findings in the book The Every Other Day Diet.  The Alternate-Day Diet, by Dr. Johnson, is another book that recommends an alternate day approach.  Both Dr. Varady and Dr. Johnson recommend that you count calories on your fasting days.  Dr. Johnson also suggests calorie counting on your regular eating days. Dr. Varady claims that according to her research, people rarely overdo it on the up days, and weight loss occurs at a consistent pace without calorie counting.  You can decide which approach appeals to you most.  Personally, I don’t want to count calories, EVER.  Maybe that is one additional reason that I choose to do a full fast on my version of the down days:  it’s easy to count to 0. At the other end of the up/down day spectrum is a plan generally referred to as 5:2.  The numbers 5 and 2 stand for the number of days of the week that you do it.  The first number is how many regular eating days you have per week (5), and the second number is how many fasting days you have per week (2).  In 5:2, you can choose any 2 days to have as your fasting days, and you eat “normally” for
the other 5 days of the week.  Remember—just like with ADF, you are allowed to have up to 500 calories on the fasting days, though I always stick to 0 calories. 5:2 is a great plan for many reasons, and one of the main attractions is the fact that you are only restricting the foods you eat for 2 days per week, and the rest of the time you eat normally.  For me, one of the main drawbacks to 5:2 is also the fact that you are only restricting the foods you eat for 2 days per week, and the rest of the time you eat normally.  5 days of eating normally per week is just too much food for me.  I don’t lose weight on 5:2, but it is a great maintenance plan for me.  I maintained my weight throughout the summer of 2015 by following 5:2 from April – August.  For specifics on how to use 5:2, you can read more about the plan in The 5:2 Diet, by Kate Harrison or The Fast Diet, by Michael Mosley and Mimi Spencer. If ADF sounds like too much fasting, and 5:2 doesn’t sound like enough, I suggest you try a plan called 4:3.  As with 5:2, the first number stands for the number of days where you eat normally (4), and the second number stands for the number of fasting days each week (3).  I lose weight (though slowly) when following 4:3, so it works better for me as a weight loss plan than 5:2, which strictly works for me as a maintenance plan. When you use ADF, 4:3, or 5:2, you need to consider how you want to schedule your week.  One problem I always had with true ADF was timing.  There are 7 days per week, and so that means that one week you fast on Monday, Wednesday, Friday, and Sunday, and the next week you fast on Tuesday, Thursday, and Saturday.  I don’t want to do a full fast on a Friday or a Saturday—ever—and I prefer to have more of a predictable routine to my fasting.  Therefore, for weight loss, rather than true ADF, I would use a 4:3 routine that looked like this:  I would fast on Sunday, Tuesday, and Thursday, leaving me with Friday and Saturday as up days for weekend social events.  If I had an event scheduled for Sunday, Tuesday, or Thursday, I would either fast through it or rearrange my fasting schedule to suit.  (Fasting through an event is always an option.  Nobody really notices whether you eat or not—plus, I have found that I am less willing to eat something just because it is there, and the food has to be worth it.)  When I used 5:2 for maintenance, I would fast on Monday and Thursday each week.  I was always ready for a good fast on Monday after the weekend, and then Thursday I fasted in preparation for the upcoming weekend.  This routine worked very well for me. As with 4:3, I could always rearrange my fasting days if I had a special event. Up/down day intermittent fasting plans such as ADF, 5:2, and 4:3 are very popular, because many people really like the idea of having some days where you don’t have to think about “dieting”, and you can eat like everyone else.  That was one of the attractions for me, as well.  I found that over time, however, I had some problems with both 5:2 and 4:3.  I started to dread the fasting days, and one reason for that is that I don’t sleep well after fasting all day.  I also didn’t enjoy the up days nearly as much as I thought I would.  I spent all day thinking about what I should eat next, or deciding if it was time to eat, or calculating how much time until I could eat.  I had SO MANY THOUGHTS ABOUT FOOD that it wore me out.  Plus, I fell victim to the afternoon slump on the eating days.  I’m not saying I will never use ADF, 5:2, or 4:3 again, but for now, I prefer the one meal a day (OMAD) approach, which I will describe in the next chapter.