## The Hacker’s Diet

I’ve struggled a bit with my weight over the years. I try to keep my BMI around 25, but if I don’t watch what I eat it tends to creep upwards towards 27 and even 28 before I even notice. Hence I’m always looking for new techniques to control my diet. This morning I came across an on-line book called The Hacker’s Diet. Written by John Walker, the founder of Autodesk, Inc., it’s a geeky, data-driven approach to maintaining your weight.

I liked this book right away, because Walker seems to have come to some of the same conclusions I’ve reached over the years. First of all, what you eat makes little difference to your body. Whole wheat, organic, natural, vegetarian, high carb, low carb, raw, Paleolithic or Neolithic, it doesn’t matter. Human beings are omnivores, and we can thrive on almost anything. Weight control is all about calories, and to lose weight you have to eat fewer of them. As an aside, take look at this article about a guy who lost 27 pounds on a diet of Twinkies and Doritos.

I’ve also come to the conclusion that while exercise is great for maintaining health, it has little effect on your weight. The book makes this clear: there just aren’t enough hours in the day to perform enough exercise for it to have a significant effect on your weight. Walking for an hour burns as many calories as there are in a single donut. So why not just skip the donut?

Not long ago (see this post), I came to the conclusion that dieting is a matter of weight, not calories. I still think there’s something to this idea — after all, there’s nothing relativistic happening in our bodies, so the principle of conservation of mass has to hold — but The Hacker’s Diet, and this figure showed me that the situation is a bit more complicated. The intake and excretion of water has too great an effect on the mass balance. As Walker writes:

On a day to day basis, the water you consume, whether directly in beverages or as part of the foods you eat, and the water you excrete in your various excursions to the hydraulic accommodations, dwarfs the weight of the food you eat and the solid waste you dispose of … Most of the changes in weight you see have nothing to do with how many calories you’re eating or burning. Instead, all you’re seeing is how many pounds of water happen to be inside (your body) at the moment.

In addition, foods vary greatly in the amount of water they contain, so you can’t focus strictly on the mass of what you’re eating.

As far as I can tell — and I haven’t read all the way through yet — the diet depends on calorie counting and daily tracking of weight, coupled with exponential smoothing to even out the daily variations. It looks very promising.

## The mathematics of weight loss

There’s something about the following that doesn’t seem quite right:

The mathematics of weight loss is, in fact, quite simple, involving only subtraction. “Take in fewer calories than you burn, put yourself in negative energy balance, lose weight,” says Braun, who has been studying exercise and weight loss for years. (from this recent article)

I’ve read variations of that statement for years, and always assumed it to be a basic truth. However, after reading that article it occurred to me that there’s nothing relativistic happening at the macro scale in the human body: energy is not converted into mass, and mass is not converted into energy. So why the focus on calories? Dieters are trying to lose body mass, not energy.

Which weighs more: a ton of feathers or a ton of bricks? I’ll bet you fell for that one the first time you heard it (probably back in elementary school if you’re like me). The dieting analogy would be as follows: which will cause you to gain more weight: eating a pound of spinach or a pound of steak? You’ll be one pound heavier after consuming either one of course.

Which is not to say that eating steak is the same as eating spinach. The spinach contains more water, which your body will eventually excrete (unless you happen to be dehydrated). But why not think in terms of a mass balance instead of an energy balance? A simple mass balance for the human body would look something like this:

$\Delta m = \Delta m_i - \Delta m_o$

where m is your body mass, mi is what you drink and eat, and mo is what you excrete. What this says in words is that the change in body mass over a given period of time equals what you consume, minus what you excrete.

That is the basic equation of weight loss, and it’s not a simple subtraction problem because there are two unknowns. If I eat a pound of steak, nobody can tell me precisely how much of that pound I will eventually excrete and how much my body will retain. It all depends, certainly, on how much exercise I do. But it also depends on my rate of metabolism — that is, how many calories my body consumes during its resting state. It also depends, I’m sure, on what my body happens to need at the moment. If I’m already full, my body doesn’t need the steak, so most of the mass will be excreted. But if I’m hungry and haven’t eaten in a while, my body will retain as much of that mass as it can and convert it into nutrients for my cells.

## Calorie labels don’t work

Many public health professionals believe that if people only knew how many calories were in their Big Macs, they’d order fewer of them. This has led to laws requiring restaurants to post caloric and other information about their menu items. But a study of New York City’s law shows that while people are aware of the information, it doesn’t cause them to eat less. In fact, according to an article in today’s New York Times, the study showed that:

..people had, in fact, ordered slightly more calories than the typical customer had before the labeling law went into effect, in July 2008.

What the article doesn’t speculate on is why this might be the case. I think people are less likely to purchase that extra Whopper when they don’t know how many calories are in it. When they find out how many calories the sandwich really has, they probably figure, “ah well, that isn’t too many, and besides I can make up for it by ordering a diet Coke.”

So what will the health police try next?

## Another study shows it’s better to be a bit overweight

In 1993-1994, demographic data were collected on a sample of 11,326 Canadians over the age of 25. The Cox proportional hazards model was used to determine the effect of BMI on mortality over a twelve year period. It was found that people who were overweight but not obese — BMI from 25 to 29.9 — had lower mortality than people of so-called normal weight (B.M.I. of 18.5 to 24.9).

According to an article in the New York Times:

“Overweight may not be the problem we thought it was,” said Dr. David H. Feeny, a senior investigator at Kaiser Permanente Center for Health Research in Portland, Ore., and one of the authors of the study. “Overweight was protective.”

The abstract is available on-line.

## Rethinking Thin

There is no doubt that Americans have become heavier in recent decades. As a result, we are spending upwards of \$40 billion a year on books, products, and programs designed to help us lose weight. But is this money well-spent? Rethinking Thin, by New York Times Health and Fitness reporter Gina Kolata, is an eye-opening examination of the obesity epidemic in the United States. Kolata follows a group of subjects in a University of Pennsylvania study comparing the Atkins diet with a traditional low-calorie, low-fat one. Along the way, she explores the conventional wisdom about dieting, obesity and health, and finds that much of it is contradicted by the evidence. For example:

Overweight individuals have slower metabolisms. False. There is little association between body weight and the rate of metabolism.

Low fat diets promote weight loss. False. It’s all about the number of calories you consume in a day, and the composition of those calories has little effect.

Being overweight is hazardous to your health. Not true. A study by Flegal et al. found that while obesity (BMI>30) and underweight (BMI<18.5) are both associated with higher mortality, the range classified as overweight (25 < BMI < 30) is actually associated with lower mortality than the so-called normal BMI range from 18.5 to 25.

The measures usually advocated to prevent children from becoming overweight are effective. False. Two large studies examined the effects of integrated programs that taught school children about nutrition, provided healthy breakfasts and lunches, promoted regular in-class exercise, and even involved the parents, to try to improve the type of food the children ate at home. The result? Children in schools that received the interventions did reduce their fat intake, but there was virtually no change in weight as compared with children in control schools that had not received the interventions.

I must admit that after reading this book I am more confused than ever about what is a healthy weight and how to maintain it. But I prefer the confusion to the pseudo-science that passes for diet advice these days.