science of us

Diets Only Work If You Believe They Will

Photo: Maximilian Stock Ltd./Getty Images

In an interesting conversation on the podcast EconTalk, host Russ Roberts interviewed health journalist Julia Belluz about diet, alcohol, epidemiology, exercise, and Belluz’s own recent experience of having spent 23 hours in a metabolic chamber (which she wrote about for Vox, and which changed her assumptions about her own metabolism). The whole thing was great — it got especially interesting toward the end — but I particularly enjoyed their discussion of her time in the metabolic chamber:

Roberts: What did you find out about yourself?

Belluz: I found out I’m a very boring research subject. My metabolic rate was exactly what they’d have predicted for someone my height, size, age, and sex. And I was surprised by this. I really thought — like, I definitely exercise, and I’m careful about my diet and all these things. I don’t just blame my metabolism […] when I gain weight. But I did think it was a contributor — I really thought I had this sluggish metabolism, and that it explained, like, why it’s a little bit harder for me. And so, I debunked that. And, yeah, it caused me to think about where we get these narratives from, and this messaging. And how much […] they affect how we think about ourselves, and how sometimes I can be completely wrong.

Roberts: So, you’ve lost this crutch. Are you less happy now?

Belluz: [Laughs.] Am I less happy? Um, I would say I’m happier. I think there’s some liberty in knowing the truth, right?

Roberts later made a comment about how diets and lifestyles are only useful if we believe in them, which resonated with me. Regarding friends of his who’ve maintained weight loss by following a diet he thinks is based on bad science, he said: “One of my theories is: If you believe [in] the diet, it might work. But otherwise, for the average person, it doesn’t.”

Belluz picked up on this, sort of, agreeing that it all depends on the person and the diet, and that everyone should try out a lot of things before settling on a routine that works for them (ultimately, though, she said that “the bottom line” for weight loss is to consume fewer calories). I think there’s more to be teased out regarding the importance of belief, though. In my experience, believing in something is an inner shift that can make a thousand outer shifts effortless. It’s believing in an entire system rather than examining its many small parts that can count. There’s no question of adherence: something you believe in becomes automatic. And believing in an entire way of eating is often a lot easier than piecing together a general/moderate approach. But then, what is truth, and is it good to be disabused of a belief if it’s personally beneficial but not necessarily true? Beliefs are wild. You heard it here first.

Diets Only Work If You Believe They Will