May 22, 2013 § 8 Comments
On 2 January Jessica Irvine launched a very public weight loss challenge. Her aim: to lose 10 kilograms by Budget night in May, using an economist’s approach to calories and exercise she named Dietonomics. Specifically, she set out to create a cumulative deficit of 75,000 calories based on the formula that 1kg of body fat is equal to 7,500 calories.
As summer shifted into autumn Irvine set to work, sharing occasional triumphs (in the gym) and disasters (in the deep fryer) via her Twitter account.
Now Budget night has come and gone and the results are in.
She says ‘this time I wanted to lose the weight AND keep it off’. I think it’s fair to say that whether she keeps it off will be determined at some future point. (For reference, in 2011 Irvine lost 20 kilograms courtesy of Michelle Bridges 12 Week Body Transformation and then regained 8 of them courtesy of other stuff.)
So, results. She lost 4.8 kilograms instead of 10. A score of 48%, almost a pass mark.
Irvine is undeterred by this. Actually, she is triumphant. ‘Calories in minus calories out works’ and so too does ‘the magic number’ of 7,500. She concludes that ‘all you need to do to lose one kilogram of fat is create a calorie deficit of that size and bingo.’
Bingo is right because, just like bingo, Dietonomics is a game of chance.
In fact, weight loss by numbers involves very large servings of…guesswork. The three critical inputs—basal metabolic rate, calories out and calories in—are all pretty flawed.
Basal Metabolic what
The starting point for Dietonomics is knowing your Basal Metabolic Rate—the calories you use up just by being alive. There is a highly scientific way to do this involving a laboratory and a space suit. But no one can afford that so instead there are online calculators that do a vague approximation. You might end up a bit out though. There’s a looooong list of factors that kick it up or drag it down. Researchers have found variations of more than 700 calories per day for people of the same body weight (equivalent to a daily 10k run) and were left scratching their heads over large (27%) variations that were unexplainable by any of the usual suspects.
But hey, if you’re an average man you’ll probably use up a dozen calories just reading this article. ‘Awesome!’ you say, ‘I’m an average man.’ Assuming you are not eating your lunch at the same time, there’s a calorie deficit right there.
Out, damn calories
The measurement of calories ‘burned’ (calories are tortured mercilessly by keen dieters) by machines and monitors is based on a theoretical person who (assuming you enter your data correctly) approximates your age, gender, height and weight. This theoretical person was probably based on a clinical trial involving either elite athletes or the morbidly obese. People just like us, in other words.
Counting calories burned (smashed, stabbed, strangled) based on what a poorly-informed computer estimates is imperfect at best and dead wrong often. For example, if you hold on to the rails on the treadmill you burn many fewer calories. But boy is every calorie sacred when it’s one that is coming off the balance sheet. Liquid crystal displays are like liquid gold when you’re huffing away on the stair master. (Don’t hang on.)
Calories in, theory
Calorie values on food labels are based on 100-year-old experiments using primitive methodologies like burning food and can be woefully inaccurate. And tallying up calories on self-prepared food is subject to the powerful urge to come out of any test looking half-decent. People, especially fat people, routinely underestimate portion size and quantity.
Also, it’s increasingly clear that all calories are not equal. There are, Irvine tells us somewhat ruefully, 1448 calories in a peperoni pizza. You could eat one per day, OR you could eat a variety of other stuff. It’s all the same to Dietonomics, where the balance sheet is the only thing that matters.
Even if these errors were somehow eliminated, calories in and calories out are affected by food processing, cooking, metabolism, physical conditioning and other stuff we are only just beginning to appreciate. It is very, very far from being an exact science.
I could have, I just didn’t
Economists are very good at explaining things with the benefit of hindsight. They were always correct in their theory, except some unforeseen event happened, which outweighed the effect of the forecast.
But how many times can we say that the theory is perfect and the results varied because they didn’t quite follow the experiment before the method itself is a crock? If a thousand people fail to reach their goal but only because they ate more and exercised less than they meant to, the method doesn’t produce the expected results and the interesting bit is WHY.
Irvine, who had powerful reasons to succeed and all means at her disposal, missed her target by a long shot. Why did she fall so short in the face of such mathematical rigor and grim determination? Isn’t this an interesting question? Isn’t this the question?
Jessica Irvine should take her heart rate monitor off and watch the episode of Seinfeld where Kramer announces he is stripping his apartment of all its contents and installing cushioned ‘levels’. Jerry says it’s not gonna happen and a bet is duly made. When Jerry claims victory Kramer argues that he COULD have done it, he just decided NOT to.
Wide error margin ahead
In the end there is a 0.6 kilogram difference between Jessica’s weight loss and the formula’s prediction based on what she actually did. ‘I’m calling that even,’ she says, declaring Dietonomics a success. But that’s 15% out, not ideal when you’re spruiking a model of mathematical purity. Most people would consider that an unacceptable margin for error.
There’s an old joke about three economists deer hunting. They see a deer and the first one shoots and misses by 15 metres to the right. The second takes a shot and misses by 15 metres to the left. The third then jumps up and down excitedly shouting ‘We got it! We got it!’
The loss of 4.8kg proves that that a person who determinedly restricts calories and hits the gym will lose a few kilograms, at least temporarily. This is not in dispute. It does not prove that we can chuck out everything except the numbers written on pizzas and spat out by treadmills.
Why are we even having this conversation?
At 1.79m tall and 74.7 kilograms, Irvine had a BMI of 23.3 which is at the higher end of the healthy range for adults. At 65 kilograms (her target) her BMI would be 20.3, at the lower end of the healthy range. I’ve seen her Budget week videos and she looks pretty great.
Maybe, instead of Dietonomics, Irvine could apply herself to why it is that so many people don’t succeed at weight loss by numbers and also why my Waterlilies didn’t turn out like Monet’s. Or better yet look at the actual and serious economics of fat: the fact that a person’s socio-economic status is a far better predictor of their future weight than any formula.
But if you must be guided by numbers in the fight against fat, at least use results-based ones that mean something. What do you weigh now compared with a year (note: not a week) ago? Are you wearing bigger pants or smaller ones? Can you cover that distance faster than before, or go further, or last longer? Those are pretty good numbers.
Losing weight because you suffer for a few months doesn’t really prove anything.
The following day, in my hungover state, I consumed the following: A Big Mac (493 calories), Large fries (454), Chicken burger (315), 2 slices pizza (432), a packet of Twisties (265), a box of Smarties (230) and a banana paddle pop (110). My daily calorie intake was 2330, above my weight maintenance intake of 1800. Not good.
Yeah, not good.