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- Alex Hutchinson (@sweatscience)
Weight loss is a pretty controversial topic, so I always expect to take some flack when I write about it, from people who are convinced they know “the truth.” (The fact that I hear from so many different people with so many different versions of “the truth” is a good reminder that it’s impossible to make everyone happy.)
I certainly don’t know the full truth about weight loss, but I did my best in Monday’s Globe article to summarize my understanding of the current literature. The most common complaint I’ve heard so far relates to my treatment of Gary Taubes’s ideas. Early in the piece, I referred to his latest book as an “anti-carb polemic.” Later in the piece, I wrote “Mr. Taubes’ core idea, that refined carbs cause a damaging spike of glucose that can affect insulin function (and thus fat storage) is backed by quite a bit of science.” To me, that seems like a fairly even-handed treatment — if anything, I’m coming down on his side. Nonetheless, I’ve heard from several people who say I’ve careless misinterpreted or misunderstood Taubes’s point.
For the record, I think Taubes’s critiques of existing nutritional orthodoxy are enormously important, and I made significant changes to my diet after reading Good Calories, Bad Calories. However, I also think he does exactly what he accuses his opponents of: drawing conclusions from epidemiological and mechanistic studies without confirmation from intervention trials. Or to put it another way, just because everyone else is wrong doesn’t mean Taubes is right and his orthodoxy can’t be questioned.
I had a very long and very interesting interview with Taubes a few years ago. In case anyone’s interested, here’s a transcript of one of the last questions I asked him. This question — and his response — is one of the reasons I don’t believe he has the “final solution” to understanding weight loss, diet and health.
AH: The last thing that I was trying to reconcile is the role of exercise. If you were to take a sample of 100 serious marathon runners, you’d have a fairly emaciated group who, traditionally, have been instructed to eat as many carbs as they can.
GT: Here’s the way I see it, and I’ll give you my bias. Growing up, I had an older brother who was always lean. He used to be famous, at least in our family, for saying he never got full, he just got bored of eating after a couple of hours. But he would run 10 miles a day, and he was a rower. I played football, and even when I was running a lot, the most I could do was 8 miles before my body broke down. I’ve always been thicker than my brother. In high school, he was 6’5”, maybe 180, and I was 6’2”, 210.
The question is, was my brother leaner because he ran more, or did he run more because he was leaner? I think the answer is the latter, because of a concept called fuel partitioning. You imagine two people eating 1,000 calories per day. One of them is predisposed to store those calories as fat, so he stores maybe 700 calories as fat tissue, and has 300 calories left for energy to run his body on. The other one—call him Lance Armstrong—his fat tissue that doesn’t want to store energy, so he only stores say 200, and has 800 calories left for fuel. Which one’s going to be more energetic? Now Lance has 800 calories in his blood stream impinging on his muscle cells, like somebody’s putting their foot down on the accelerator and he’s a car. So he’s gonna go.
The Lance Armstrong type eats a 1,000-calorie meal and then goes for a three-hour bike ride, because he’s now got 800 calories floating around that he’d like to get rid of. The Gary Taubes character, meanwhile, eats a 1,000 calorie meal, but there’s only 300 calories left for fuel and he’s storing 700, so he wants to conserve his fuel, and he goes and takes a nap.
The pre-World War II clinicians used to talk about the “impulse to physical activity.” So the question is, does someone who’s a runner have that impulse because their body doesn’t want to store calories as fat? The more carbs they eat, the more energy they get from it. But if your body does want to store calories as fat, the more carbs you eat, the more calories you store. And this is what fuel partitioning determines, and that’s driven by the body’s response to insulin.
What you can’t tell, by looking at somebody or at a group of people, is where the causality lies. Are runners lean because they run marathons, or do lean people run marathons because they’re constitutionally lean. The only way to find is to find out is to do these clinical trials where you, say, take 100 people and randomize 50 of them to exercising daily and 50 of them to being sedentary, and try to maintain some kind of stable diet, and see whether the people who exercise lose weight or not.
I just don’t buy that. I know plenty of people who’ve discovered running or other forms of exercise partway through life, after being sedentary and overweight. Did they undergo some genetic change that suddenly created the “impulse to exercise”? As Matt Fitzgerald said to me an interview on a completely different topic, “It’s like Freud saying, ‘It’s all sex.’ Sure, sex explains a lot — but not everything.” Until I encounter further evidence, that’s my attitude to carbs: they explain a lot, but not everything.