human behavior

How to Lose Weight: The 5:2 Fasting Experiment

Posted in Health & Medicine by humanb on March 6, 2013

The secret to losing weight is eating less. We all know that.

But humans love to eat.

So we turn to the math:

calories burnt > calories consumed = weight loss

So we head to the gym! For some reason, we consider the prospect of eating less food decidedly more painful than:

1) Spending money: gym membership + gym wear + sneakers + gas money to the gym + bottles of water and Gatorade + energy bars to fuel workouts


2) Spending time: gym prep + commute to gym + spin class (or whatever) + weight training (or whatever) + cool down + trip from gym + shower


3) Actual pain: Psychological dread before gym + extreme exertion during workout + post-workout exhaustion + next day muscle ache and immobility

I think that’s interesting.

Don’t misunderstand me: I’m a doctor. The single most important thing I can teach my patients is the importance of exercise. It’s absolutely the most powerful lifestyle factor in your arsenal in the pursuit of health and prevention of disease. It is the single best prescription for pretty much everything. It’s TRANSFORMATIVE. It will enhance your life, change your life, and prolong it.

I’m such a strong supporter of exercise, that I suspect fitness instructors and personal trainers save more lives and prevent more disease than most doctors.


But we’re talking about weight loss now. The formula is true: if you burn more calories than you take in, you will lose weight. But I reckon it’d be a lot easier to lose weight, if we focused on adjusting the intake side of that formula. By all means, exercise. Take the stairs. Walk – don’t drive. Play a sport. Actually swim at the beach – don’t sunbathe. Strengthen your muscles by whatever means you prefer. And sure, join a gym, if that’s your thing. Get 30 minutes of moderate-intensity exercise most days if you can.

But if you really want to lose weight, cut the calories.

So a few days ago, I happened upon an article in the New York Times about the new fad diet out of the UK:

England Develops a Voracious Appetite for a New Diet

It’s called The Fast Diet and the principle is simple. In a 7 day week, pick 2 non-consecutive days (say Mondays and Thursdays) to restrict your calories, and continue to eat as you normally do for the remaining 5 days.

If you’re a man, eat only 600 calories on your two ‘fasting’ days. If you’re a woman, eat only 500 calories.

However you normally eat on the remaining five days, keep that up. Don’t eat more than normal or less than normal. Just your usual.

The result? if you normally eat 2,500 calories a day, that amounts to 17,500 calories a week. If you calorie-restrict on two days however, you drop your weekly total to 13,500 if you’re a woman. That’s 4,000 fewer calories a week.

That’s 208,000 fewer calories a year.

And that’s the thing. Calorie restriction doesn’t have to be on an arbitrary 24-hour-cycle. Most diets involve restricting yourself every day – i.e., all the bloody time. But the end goal is the same as in The Fast Diet: calorie restriction.

So now I’m intrigued.

I know that scientific studies in mice have shown that calorie restriction (within reason) can prolong life. And I see no medical problem with restricting calories over a 24 hour period, as opposed to say, over our usual 3 hour period between meals, or 8 hour period during sleep – assuming you don’t have a medical contraindication. The recommended calorie intake per day is not a fast and fixed rule for a set number of calories over a defined time frame. It’s the average daily intake that matters. So why not average it over a week?

So I propose a study of one – the flimsiest, least powerful, most unreliable study there is.

Starting today, I’m going on The Fast Diet, and I’ll let you know how I go, how I feel, and what (if anything) I lose. If you want to consider calorie restriction yourself, talk to your doctor.

This is only a study of one!


DAY ONE (Thursday, 7 March 2013)

Weight: 128 lbs (58 kg)

Height: 5’3″ (160 cm)

Ideal Body Weight: 115 lbs (52 kg)

BMI: 22.6 (normal)

Weight loss goal: 13 lbs (6 kg)


I’ve chosen Mondays and Thursdays for my fast days, and since I’m a woman, that means 500 calories total on these days. I have no idea how to accurately calculate the caloric count of a piece of food, so I’m using an iPhone app called Lose It! that offers guestimates. The Fast Diet also offers a guide. I’ll use both.

For the rest of the week, I intend to eat as I normally do, which means I’ll be eating two meals a day plus snacks – including potato chips and chocolate if I feel like it. I’ll also be enjoying the empty calories in a tall glass (or two) of Shiraz on my normal days. 😉


FYI: I had 200 calories this morning for breakfast. Black, sugarless coffee = 0 calories.


Wish me luck!

Full Disclosure: I have absolutely no pecuniary interests in The Fast Diet whatsoever. I can’t even remember the name of the guy who developed it.

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7 Responses

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  1. Bunny Eats Design said, on March 6, 2013 at 8:16 pm

    I’m curious. For this to work, do you have to still eat 3 meals a day on those days? Or is skipping meals ok? I’m one of those people who have never been to the gym, but also don’t want to eat differently. Portion sizes I can alter, but eating different foods, I’d prefer not. I do walk every day though including 2-3 trips to and from the grocery store. This includes carrying my bounty home. Of course, if I ate less, there would be less to carry.

    • humanb said, on March 6, 2013 at 8:32 pm

      So I haven’t read the book all the way through. I just bought the Kindle version, read the beginning, got the gist, then skipped to meal examples. I’ll take my time reading the filler. But weight loss ‘works’ if you reduce your calories. It’s that simple. The 5:2 Diet suggests a breakfast and a dinner, so I’m doing a morning meal and an evening meal, and no mid-day meal. Well, it will depend when I wake up, but I’m looking at having two meals, 12 hours apart. As for the other five days, this particular diet suggests you eat as you normally do. I work in Emergency. I’m not a dietician or a general practitioner, so the perfect diet is not my area of expertise. I don’t know if 3 meals daily or five meals daily is better. As a doctor, I know what foods are good for you, and what foods you should only eat in moderation. If you don’t want to change what you eat, then just change how much you eat. This diet doesn’t tell you what to eat, it just tells you to restrict your calories, so you need to know how many calories are in your preferred foods. Also, the diet suggests that you opt for your preferred protein-rich foods on your ‘fast’ days as these are more filling. That means stay away from your sugar and starches on the ‘fast’ days. I’m only eating things I normally do. I would normally eat boiled eggs and bananas for breakfast, but I might normally eat three boiled eggs + 2 pieces of buttered toast + a banana with yoghurt. See? I’m just paring things down. For dinner, I might normally eat a piece of meat with vegetables and potatoes. I plan on shrinking the size and cutting out the potatoes and butter. If you eat processed foods or dishes like lasagna or something, it might get trickier calculating the calories. Walking 2-3 times daily is excellent. If you can find ways to introduce more ‘incidental’ exercise (in contrast to intentional exercise) like taking the stairs, housework, garden work, etc. then great. It’s the sitting for prolonged periods and inactivity that are not good for us. We can’t all be gym rats, but we can all be more active. Hope this helps. 🙂

      • Anonymous said, on March 7, 2013 at 8:26 am

        I went on a weight watchers a couple of years ago and dropped weight without exercise using the formula above – calories burnt > calories consumed = weight loss. I have returned to my previous habits and have started to gain. I like this method of just focusing on 500 calories 2 days a week and plan to also give it a try. Thanks for posting about it.

  2. Angela said, on March 6, 2013 at 9:19 pm

    This is a diet I might actually be able to stick to! I’m interested in seeing how it goes for you!

    • humanb said, on March 6, 2013 at 9:25 pm

      Yeah, sacrifice is good for the soul, and doing it only twice a week is pretty doable! The beauty is that you’re not actually fasting. I am eating those days. Just, you know, not so much! I think after the first few fast days, I’ll get used to not grazing all day. Fingers crossed…

  3. Leticia said, on March 14, 2013 at 10:28 am

    Hello! I’m at work surfing around your blog from my new iphone 4! Just wanted to say I love reading through your blog and look forward to all your posts! Keep up the superb work!

    • humanb said, on March 14, 2013 at 10:36 am

      Wow. Thanks! It’s great to know someone is reading. I just write because I have to, you know? Cheers. 🙂

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