Sauteed Spinach is healthy.
In fact studies have shown that when you cook or Saute Spinach or other vegetables it becomes more nutritious.
Also Sauteing the Spinach in Vinegar makes it more healthy because the vinegar has vitamins and it helps make the nutrients in the spinach more easily absorbed by your body.
Cooking or sauteing Spinach and other vegetables also releases antioxidants by breaking down cell walls which in turn results in much higher blood levels of beta-carotene which is an antioxidant thought to guard against heart disease and lung cancer.
Not only that but adding vinegar to Spinach makes the Spinach taste better.
Also adding vinegar to spinach makes the nutrients in the Spinach easier to digest because of the Vitamin C in Spinach.
Another thing is that when adding vinegar to spinach the vinegar helps to break down or concentrate the digestible iron in spinach.
That makes it more nutritious for your health.
I like to pour a little bit of vinegar onto my spinach so it makes it taste a bit better.
My mom has always put vinegar in with her spinach and it made me eat it better as a kid and I still love vinegar on spinach.
Just don't drink vinegar by itself though as it can cause health issues.