Okay, I need to talk about something that's been bugging me for months. I am always hungry. Like, genuinely always. I'll finish a full dinner and an hour later I'm back in the kitchen, staring into the fridge like something new might have appeared since last time. My dad keeps joking that I eat more than he does now, and honestly, he's probably right.
It hit me during squash practice one day. I'd eaten what I thought was a solid lunch, but halfway through our session I just crashed. My legs felt heavy, my reaction time was off, and my coach asked if I was feeling okay. I was fine, I just hadn't eaten enough. And that got me thinking about why my body suddenly needs so much more fuel than it did a couple years ago. Turns out, growing up is one of the most metabolically expensive things your body will ever do.
The Growth Tax: Why Puberty Is So Expensive
Here's a number that shocked me: about 50% of your adult body weight is gained during adolescence. Half. That means every single organ, every bone, every muscle is expanding, and your blood volume is literally increasing to keep up. The growth rate during puberty is second only to when you were an infant, but it lasts way longer. So the total nutritional demand during this period might actually be greater than at any other point in your entire life.
To put this in perspective, teenage girls generally need 1,400 to 2,200 calories per day, and boys need 2,000 to 3,200. But if you're athletic (like me with squash), you could need up to 5,000 calories a day. Five thousand! That's not being greedy, that's your body literally building itself while also powering through intense physical activity on top of it.
Your body doesn't just need more calories though. It needs more of everything. More protein for tissue growth, more calcium and iron for bones and blood, more zinc for immune function, more folate for cell division. It's like your body is running a construction project while simultaneously being the construction workers AND the building materials.
Your Body's Weird Growth Hack: Insulin Resistance
This was probably the most surprising thing I learned. During puberty, your insulin sensitivity drops by about 50%. If you heard that out of context you'd think something was wrong, but it's actually totally normal and on purpose.
See, insulin normally tells your cells to absorb glucose from the blood and store it. But during puberty, your body deliberately makes cells a little more resistant to insulin. Why? Because it wants that glucose floating around in the blood, available for growth rather than just getting tucked away into storage. Your body compensates by doubling its insulin production to keep things in balance. It's essentially your biology prioritizing building over storing.
What makes this even wilder is that growth hormone is behind a lot of this. GH levels spike during puberty, and one of its effects is reducing insulin sensitivity while ramping up fat oxidation. So your body is burning more fat for everyday energy while redirecting glucose toward growing taller and building muscle. It's actually kind of genius when you think about it.
Here's a fun detail: researchers found that insulin resistance actually starts rising around age 7, a full three to four years before any visible signs of puberty show up. Your body starts preparing for the growth spurt way before you even notice anything is changing. Girls also tend to show higher insulin resistance than boys at every age, which partly explains why girls' bodies store more fat during puberty while boys tend to gain more muscle.
The Traffic Lights Inside Your Cells
At the cellular level, your body uses two main sensors to decide whether to grow or conserve energy. Think of them like traffic lights.
mTOR is the green light. When it detects that there are plenty of nutrients, amino acids, and growth signals available, it flips on and tells cells: grow, divide, build protein, get bigger. During puberty, mTOR is basically stuck on green as long as you're eating enough.
AMPK is the red light. When energy is low, when your cells are running out of fuel, AMPK activates and slows everything down. It's your body's way of saying "we don't have the resources for growth right now, let's focus on survival."
These two sensors are constantly talking to each other, and the balance between them affects everything from how fast you grow to when puberty even starts. There's a pathway involving a molecule called kisspeptin that basically reads your body's energy status and decides whether conditions are good enough to trigger puberty. This is why severe malnutrition can delay puberty by up to three years. If your body doesn't sense enough fuel, it holds off on growing because it literally can't afford to.
This also means that crash dieting or chronically undereating as a teenager isn't just bad for your energy levels. It's actively fighting against your body's developmental programming.
What This Means for Me (and Probably You Too)
Understanding all of this changed how I think about food and training. I used to feel guilty about how much I eat compared to my friends. But now I know that my body is running two major operations at once: growing into an adult AND fueling competitive squash. That's a massive metabolic demand, and undereating isn't being "disciplined," it's sabotaging my own development.
I noticed that weeks when I eat well, when I actually get enough protein and don't skip meals, my performance at squash is noticeably better and I don't feel as wiped out after school. A friend on the team went through a phase of eating barely anything trying to "lean out" for a tournament, and she ended up exhausted, getting sick constantly, and playing terribly. Her body was screaming for fuel and she was ignoring it.
Conclusion
The constant hunger, the growth spurts, the endless need for food, it's all part of a carefully orchestrated metabolic process that's been fine-tuned over millions of years of evolution. Your body isn't being difficult. It's building an entire adult human from the inside out, and it needs resources to do it.
So the next time someone gives you a look for going back for seconds (or thirds), just tell them your mTOR is on green and your cells are building. They probably won't know what that means, but you will. And maybe cut yourself some slack. This is one of the most resource-intensive things your body will ever do, and the best thing you can do is show up with the fuel it needs.
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