Essentials: The Science of Eating for Health, Fat Loss & Lean Muscle | Dr. Layne Norton

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health and performance.
I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now for my discussion with Dr. Layne Norton. Dr. Norton, thank you so much for being here. This is a long time coming, and I have to say, as a fellow PhD scientist, I feel a great kinship with you. I know you have tremendous experience in fitness and nutrition in a number of areas. I'd like to start with something that's rather basic and yet can be pretty complex. And that's this issue of energy balance and energy utilization. What happens when we eat food of any kind? And how is that actually converted into energy as a way of framing up the discussion around weight loss, weight maintenance, weight gain, and body composition?

**Layne Norton** (0:55)
It's a great question. And like you said, this is one of those things where people use the term calories in, calories out. And they say, well, that's way too simplistic. And I'm like, if you look at what actually makes up calories in, calories out, it's actually very complicated. So a calorie just refers to a unit of energy, of heat specifically. Really what you're talking about is the potential chemical energy that is in the bonds of the macronutrients of food. Right? And by digesting, assimilating, and metabolizing those nutrients, we're able to create energy. The end product of that mostly is ATP, adenosine triphosphate, which is your body's energy currency. So a lot of metabolism is simply creating ATP. Protein's a little bit different because protein gets converted to amino acids, which can be used for muscle protein synthesis or protein synthesis in other tissues.
But it also can be converted through glycogenesis to glucose. And there also are some ketogenic amino acids as well. Then you have fatty acids, which are able to create energy through what's called beta oxidation, where essentially you're taking these fatty acids and you're lopping them off two carbons at a time to produce acetyl-CoA, which again can go into the Krebs cycle, produce those hydrogen ions that can then power the production of ATP.
So that's kind of like at the cellular level of how this stuff works. But stepping back and taking it back out, like what does that have to do with weight loss or weight gain, right? When you think about the balance of energy in versus energy out, sounds very simple. But let's look at what actually makes up energy in versus energy out.
First of all, you've got to realize that the energy inside of the equation is more difficult to track than people think. So one, food labels, which we like to think is being, you know, like from upon high, can have up to a 20% error in them.

**Andrew Huberman** (2:53)
Really?

**Layne Norton** (2:54)
Oh yeah. The second aspect is there's what's called your energy, but then there's also metabolizable energy.

**Andrew Huberman** (2:59)
Right?

**Layne Norton** (2:59)
So if you have food stuff with say, a lot of insoluble fiber, typically insoluble fiber is not really digestible. And so you could have, you know, quite a bit of carbohydrate, but if you can't extract the energy from it, and typically this is because insoluble fiber from like plant material, the carbohydrate or even some of the protein is bound up in the plant structure, which makes it inaccessible to digestive enzymes. And so this is what like adds bulk to your school stool and whatnot. But again, reduces the metabolizable energy in there. And there's some evidence that based on people's individual gut microbiome, that some people may actually be better at extracting energy out of fiber compared to other people. So just starting off right there, okay, there's quite a bit of play in the energy inside of things. Now one of the things people will say is, well, see, that's why you shouldn't worry about tracking calories, because if the food labels can be 20% off. And what I'll say is, okay, I understand where you're coming from. But typically, if it's off, it's going to be consistently off. And if you're consistent with how you track it, eventually you'll be able to know kind of what you're taking in. So now let's look at the energy outside of the equation, which is actually way more complicated, right? So your energy out is a few different buckets.
The first one and the biggest one is your resting metabolic rate, so your RMR. That for most people is anywhere from 50 to 70% of your total daily energy expenditure. Sedentary people will be on the higher end of that, so it'll be a bigger proportion, whereas people who are more active, it'll be a little bit lower, not because their metabolic rate is lower, but because they're expending a greater percentage of their calories from physical activity. Then you have something called the thermic effect of food, which is a relatively small percentage of your total daily energy expenditure. It's about 5 to 10%.