Roughly eighteen months ago I graduated from college with a fancy degree in mathematics. I'm still not "on my feet" financially, and the last thing I think about doing with my paychecks is investing. My focus lies on paying rent, paying friends back who helped cover my rent in the past, paying various other bills, and buying good, clean groceries.
I know people my age who put away a bunch of money for retirement each month, but they eat cheap, crappy processed foods. They're going to have much more money than me upon retirement, but how will their health look? I may get myself in trouble for saying some of these things, but I'm convinced that investing in long term health via nutrition and exercise is the most important temporal investment that we can make. What good is a bunch of money if you've neglected your body for decades and aren't able to enjoy activity with loved ones?
At this point in time I find the idea of being able to run around and play with my (great)grandchildren much more attractive than being able to send them a $100 bill in their birthday cards.
Do I think that my diet makes me invincible? Not for a second. I understand that I could end up in a nasty car accident on my way home from the coffee shop that I'm sitting in right now. I do believe that by controlling the things that I can control - in this case, diet and activity - I give myself a much better chance of having a healthy body for much longer.
There certainly is a need for balance here. If one becomes too consumed in their health it becomes an issue of selfishness, and that's not a good place to be. On the other side of the coin is the wonderful experience for your loved ones to have the able-bodied and able-minded you around longer than they would have had you not made the investment. This is anything but selfish.
Is eating a plant-based diet the best diet out there to achieve this long term health? Is running trails the best type of exercise? I don't know. Probably not. There are tons of different diets and exercise routines that encourage long term health. I choose to eat a vegan diet and run trails because it's a diet that promotes long term health and a form of activity that does the same. On top of that, it's fun, interesting, and it aligns with my values. I'd encourage you to find a diet and activity that does the same for you.
I'm not an expert in this stuff (I studied math, remember?), but I have enough of a background with these things to feel comfortable sharing a few ideas to help get the ball rolling towards this investment.
First, start eating whole foods, and stop eating processed garbage. The way I look at this may be too simplistic, but I know what I'm getting with whole foods (it's good), and I don't know what I'm getting with those chemicals we can't pronounce on the side of a box of Cheez-Its. They could be good, they could be bad - I go with the sure thing here.
Don't feel bad about spending money on good, clean food; it's an investment. It's true that sometimes real food costs more than the stuff scientists develop for us to eat - and that's okay. Put your money where your mouth is. Get it? If I can make this work on my budget, then I imagine that you can too.
Second, find something fun and active to do with other people, then make a habit of going and doing it.
Ultimately this is a quality of life issue. If you're not enjoying doing these things, then maybe reevaluate your activities and/or diet. This long term investment affects the here and now as well, and I believe it should be a positive experience throughout once you find the right fit for you.