It’s one thing to lose 43.3 pounds. It’s another thing entirely to lose 43.3 pounds while having your fill of cheeseburgers, pepperoni pizza, and beer.

There are precious few situations where you literally get to have your cake and eat it, too, but the 5-2 Diet is such a case.

You can read about the specifics at http://thefastdiet.co.uk. Better yet, read the authors’ book on the subject. But for the sake of brevity, I will cut to the quick. The rules are simple:

1. Five days per week, eat your normal diet. Don’t go crazy, but there are no calorie restrictions or particular foods to eat or avoid.
2. Two days per week, restrict yourself to 600 calories divided over just two meals. (Similarly, on these days there are no particular foods to eat or avoid.)

That’s it.

Two Steps Forward. One Step Back.

I tend to lose two to four pounds on fast days. That’s not a typo. Two to four pounds. Of course, I also tend to gain back a good slug of that the next day. But not all.

In the chart above, you can see the drastic weight loss following Monday and Thursday. I weigh in daily, first thing in the morning, so my Tuesday morning result reflects the weight lost Monday.

On the balance, I lost precisely two pounds that week, which made it a better-than-average week. It took 41 weeks to lose 43.3 pounds, so we are looking at an average of about one pound per week.

Such is my experience with the 5-2 Diet: Two steps forward and one step back. For weeks that don’t involve any extraordinary events like weddings or barbecues (or insane workloads paired with intense stress and lost sleep), you lose a couple pounds, padding your numbers in advance of these heavier weeks.

Life on a Fast Day: Taking Those Two Steps Forward

Working out: I try to work out every fast day to maximize the impact those days have (see “Moving the Needle” below!). I do this first thing in the morning so that I am working out on an empty stomach.

Breakfast: After my workout, I typically have a natural protein shake, yogurt/granola, or eggs. I avoid those miserable “meal replacement” products and high-glycemic foods like breads and cereals. 250-300 calories. Check.

During the day: I drink of ton of water on fast days. Black coffee is allowed, but I stick with iced green tea — by the bucket.

Dinner: By 6:30 I am hungry. There are lots of options, but my personal favorite is a can of Progresso Soup. Even the decadent 18.5 oz Italian Style Wedding (chock full of meatballs) weighs in at a svelte 240 calories. Yes, it’s a sodium nightmare, but let’s not get bogged down. One bridge at a time.

Alternatively, if you steer clear of starch and cheese, a fairly hefty plate full of sautéed or grilled vegetables (broccoli, brussel sprouts, asparagus, etc.) and a modest cut of lean meat sails in under 300 calories. Even on a fast day you can get your grill on.

Pro tip: Mustards, hot sauces, and vinegars are your friend on a fast day. Zero calories but they pack a punch from flavorville.

Sleep: Stay up late, and you’re sunk. If I am cranking away until 11pm, I get hungry again and binge out, so on fast days I get the kids down, get some work done, and get to bed. Plenty of sleep helps the fasting process along, and I avoid pounding a pint of Talenti’s heavenly Mediterranean Mint.(“Tomorrow, Adam-san. Tomorrow.”)

The Psychology of Moving the Needle

Scroll back up. Take another look at that chart. It’s ridiculous. Imagine how different that week must feel emotionally as compared with the grueling process of simply containing calories every day for months on end. In such a meager existence, you put in the work all week and hardly move the needle at all. Results are so gradual that you hardly experience the win.

From a behavioral standpoint it is tough to associate your actions with the result. There just isn’t a visceral feeling of cause and effect.

Just the opposite with intermittent fasting. You see and feel the result immediately, even if you give up ground the next day. You can rally because you know beyond any doubt that your eating and exercise habits have an immediate, palpable impact.

The Psychology: Month 1

During the first month, don’t sweat it if you feel like pounding a large triple pepperoni and a six-pack on an off day. Having those cheat meals fuels the will power for the fast days.

More importantly, even in the first month you start to feel the dramatic differences in how you feel the day after both types of days. You experience a visceral difference, and that’s the point.

The Psychology: Month 5

Before long you hate seeing the weight pile back on the day after a fast day, so you naturally start taking it easy on your normal days. I found myself eating more vegetables and leaner meats all week. Raspberries and almonds rather than a sandwich. I also found myself cutting back on mindless snacking and grazing.

The Psychology: Month 9

Eight or nine months in, I started craving my fast days. I still don’t like doing two in a row, but I love having a couple days per week where I don’t have to figure out what to do for lunch. I have more focus on those days, and I feel so much lighter the next day (indeed I am).

I drink a ton of water every day now. I love feeling hydrated and hate feeling hungover, so the binge eating and drinking has largely subsided, as well.

Ultimately, it has become the most sustainable diet ever, because in under a year it has become a lifestyle unbefitting of the term “diet.” I don’t have any crazy restrictions that prevent me from enjoying fresh pasta or a giant cheeseburger with bacon and a slutty fried egg on it, but the majority of my week’s calories are coming from healthier foods without any effort.

Boom.

Intermittent Fasting is No Fad

You probably noticed that I avoided discussing the science behind the diet. Mosley and Spencer, the diet’s proponents, do a much better job of explaining the human body’s response to intermittent fasting (a response that is tens of thousands of years in the evolutionary making).

I also avoided discussing how, for all of recorded history, humans have been fasting in a wide variety of capacities for health and religious reasons. This isn’t something we just thought up.

For me these two factors were encouraging only as a means to mitigate the guilty feeling of attempting yet another fad diet. Put another way, for me the science and the heritage of fasting are only useful in addressing other people’s objections. Ultimately the proof of the pudding, as they say, is in the tasting.