Feeding Your Growing Teenager

A 16-year-old boy training ten hours a week needs just under 4,000 calories a day.

That is roughly 60% more than his father.

A 15-year-old girl doing six hours of sport needs around 2,400, which is more than most grown women eat. A 13-year-old girl needs about the same as her mother, from a body that is considerably smaller and still building itself.

If you have ever found yourself saying “you’ve only just had lunch”, this is the guide that lets you stop.

He is not greedy. He is hungry. Those are different things, and the difference decides how tall he gets, how strong he gets, and what his skeleton looks like at thirty.

Why underfeeding a teenager does not make them slimmer

It makes them shorter, later and more tired.

A growing body given too little energy has an order of priorities, and growth is not at the top of it. It protects the brain, the heart and body temperature first. What gets downgraded is everything that can be postponed: growth slows, puberty is delayed, periods become irregular or stop, immune function drops, and bone accrual slows at exactly the point it should be fastest.

None of that shows up on a scale, which is why almost nobody notices.

The bank account you can only pay into once

Around 90% of adult bone mass is laid down before the age of 20, and roughly a quarter of it arrives in the two years around the growth spurt. The bone built in those two years is comparable to what most adults lose across their entire later life.

That window does not reopen. What they finish with at twenty is broadly what they are working from for the next sixty years.

What is inside

38 pages. Twelve chapters. Summary box at the top of each one, the reasoning underneath.

1. What growing actually costs. The numbers by age, sex and activity, and why your instinct about portions is calibrated to an adult.
2. The bank account you can only pay into once. Peak bone mass, and why calcium alone is not the answer.
3. Why 5-a-day was never the science. A 1991 marketing campaign. The research says benefit keeps going to ten.
4. Variety, and what it is actually feeding. Thirty different plants a week, and the gut mechanism behind it.
5. Protein and the growth spurt. How much, why breakfast is where it goes missing, and why it will not make them bulky.
6. The nutrients that matter most right now. Iron, calcium, vitamin D, zinc, iodine and omega-3.
7. Why they are ravenous, and why that is not naughtiness. Including the body-clock shift that explains breakfast.
8. Fuelling sport and school. Before, during and after training, the lunchbox, and exam season.
9. Water. How much, why they are almost certainly short, and what that does to concentration.
10. What under-fuelling actually looks like. The signs worth noticing, and the ones worth a doctor.
11. Cooking, properly. Six techniques that beat a hundred recipes, plus recipes from the Carbon IV library.
12. The fussy eater. Why pressure backfires, and what works instead.

And the toolkit

Every number the calculator produces is also printed as a lookup table, so it works in full on paper.

Who wrote this

I’m Eloy Rodriguez. I run Carbon IV, a performance nutrition and strength coaching practice in Dubai.

I wrote this because the same teenagers kept arriving in front of me: training four or five times a week, eating like a ten-year-old, tired, getting slower over a season, and getting injured. Their parents were doing everything asked of them. Nobody had told them the numbers.

So this guide gives you the numbers, and then explains the biology underneath them, because being told what to do without being told why is how families end up here in the first place.

Questions

Is this a diet plan for my teenager?

No, and it is the opposite of one. There is no weight management content, and the only body measurements are height and weight. Chapter 10 explains at length why there is no waist measurement anywhere in it.

My child does not do much sport. Is it still relevant?

Yes. The calculator has a band for under two hours a week, and the chapters on bone, protein, nutrients and fussy eating apply regardless of how much they train.

What format is it?

Two PDFs and a web-based calculator. Download the PDFs to any device. The calculator opens in a browser on any phone, with nothing to install and no account.

Is there a training programme in it?

No. This one is about food. The guide covers fuelling sport rather than prescribing it.

My teenager is vegetarian.

The protein and iron chapters both cover it directly, including why plant iron is absorbed less well and what to serve alongside it to fix that.

Feed them properly while the window is open.

Adolescence is the second-fastest growth phase of human life, and it lasts about five years. This is the guide that tells you what it costs.

For general education. Does not replace individual medical advice. If you have any concern about your child’s growth, eating, development or health, please see a doctor.