I want to explain this a bit more since 'health' and 'biology' are loosely speaking, special interests of mine and also what I went to school for.
People SAY that your health 'suddenly' starts to decline in your 30s but that's not really a good way to put it A) bc that's not really accurate and B) bc it frames this decline as something inherent and unavoidable, which does nothing to convince you that you have some agency about this.
So I'm going to explain this in LOOSE NON-SCIENTIFIC language:
When you are an infant or child, you are actively growing. Nature is throwing tons of new cells into you bc your body needs to BUILD BUILD BUILD. What you're able to do, eat and heal from is all largely dictated by this-- for example little kids often LOVE sweet foods or dairy-like foods and are relatively less interested in anything else. This is bc their body is running on HIGH all the time since building body parts is very energetically intensive. They can eat a fistful of sugarcubes and burn them off in an hour. Ask me how I know.
When you are a YOUNG ADULT you are actually still developing to a secondary extent, but your bones and such are fused and now that development goes into solidifying the structure and also finetuning its reproductive capabilities and features-- these, too, are HIGHLY energy consumptive when they first come online. Nature is STILL, thus, throwing tons of energy and new cells your way hoping you'll do something cool with them. You regenerate very quickly, and recover from harm rapidly-- But please note: swift recovery from harm is not absence of harm. This most relates to the consumption of 'junk food' and alcohol-- many people say they could 'eat whatever they wanted and nothing would happen' when they're in their 20s or that they could go out drinking and 'not be affected'. You were affected. You didn't notice.
Once everything has come online you go into maintenance mode. Nature stops throwing excess cells and energy your way bc you don't need that-- your body is yours and you are not responsible for maintaining it...hopefully with what you learned by experience in your 20s. IF YOU WERE NOT PAYING ATTENTION, you did not learn this, and are in for a surprise in your 30s bc your 'free recovery' subscription has ended. Recovery and maintenance- processes that are constant in the human body- now cost MINERALS & ELECTRICITY. You can go into DEBT now, and that debt will come in the form of joints that pop, inability to recover well, lowered immune function, and feeling like shit.
This debt accrues interest RAPIDLY once you hit 36-- the age of around 36 to 46 or so is a kind of reckoning stage where Nature assesses how well you've managed your body and you will be SWIFTLY downgraded if the result is you were just winging it.
So how do you build this account? 2 main things ( LOOSELY SPEAKING this is so not 100% scientific but I have to be general here): MINERALS -- you get these from eating well, mostly. You might want to take supplements based on your unique needs. But you need Minerals & Vitamins (i'm lumping these two together) bc they are the chemical building blocks (currency) your body uses to rebuild and fix up cells. ELECTRICITY is- again loosely speaking- having the proper chemical voltage throughout your body. This 'voltage' drops when you don't move enough, or when you're dehydrated. The building and repairing process your body wants to do may have the materials (minerals and vitamins) but there's not enough power in the factory, or the AC isn't working and the workers are overheating and can't work well. To fix this, drink lots of water and MOVE AND STRETCH your body. The action within your muscles and bones GENERATES ENERGY and it keeps your cells happy.
So the thing is, it's not that you suddenly find yourself taking damage after 30+. You were taking damage the whole time. You're just kept from really feeling it bc you're young and full of extra juice and given time to figure things out.
But at some point Nature expects you to do that, and you will pay if you don't.
Best to start out giving a shit, even if none of your friends think you're cool, even if you get called a 'health nut' bc you will still be able to frolick at 45, 50, probably so on while everyone who said it was dumb to have 'balanced meals' shares memes about how they wake up feeling like shit every day.
Sidenote don't let our shitty fatphobic society obscure the fact that it's okay to care about what you eat. Counting calories or being preoccupied with physical perfection is a sad way to relate to your body BUT that doesn't mean that paying attention to your diet AT ALL is bad. Baby, bath water, etc.
