An article regarding advice that spinach is best eaten raw.
https://coach.nine.com.au/2018/12/28/09/29/spinach-smoothie-lutein
My wife always uses baby spinach in her breakfast smoothies that she makes in her Nutri Bullet and we now use it instead of lettuce on BLT’s and hamburgers.
It tastes better, has a crispier texture, and stays fresh for longer than lettuce does.
Raw Spinach: contains nutrients, some of which are more available to our bodies when we consume them raw (eg folate, vitamin C, niacin, riboflavin, and potassium).
Cooked Spinach: contains nutrients. When you eat spinach that has been heated, you will absorb higher levels of vitamins A and E, protein, fibre, zinc, thiamin, calcium, and iron. Important carotenoids, such as beta-carotene, lutein, and zeaxanthin, also become more absorbable.
With respect to lutein (the stuff that is in dark green leafy vegetables, and is good for eye health) while raw spinach might contain more lutein, microwaved spinach has it in a more absorbable form (and microwaved spinach contains more lutein than boiled or fried spinach).
https://www.vegetariantimes.com/health-and-nutrition/nutrition-face-off-raw-vs-cooked-spinach
I prefer my spinach uneaten, to be honest.
It depends what you mean by ‘spinach’. In some circles silverbeet (swiss chard) is called spinach and there are another half dozen leafy greens that have been called the same name at various times and places.
If sticking to spinacia oleracea then age and freshness matter. If you like it cooked for heaven’s sake don’t cook it into a green sludge, aside from destroying some nutrients the look and feel will be horrid.
Turns out Popeye was onto something 
