Leaves are the solar panels of plants. This means that they are as full of defense chemicals (oxalates etc...) as they are of "useful" nutrients.
Most actual lettuce (Lactuca spp) seems to be bred for minimal defense chemicals and maximal structured water, so that's not too bad.
This was our salad mix though: 
Consisting of 90% leaves of the cabbage family (Brassica spp). A family of vegetables that was traditionally only eaten when fermented. For good reason!
A quick Internet search shows that the human body produces oxalic acid when required, but considering the insane amount of lying in medical research...
The late Dr Max Gerson, his late daughter Charlotte and their Gerson clinic in Mexico (fled there due to gov and pharma attacks) have 90 years of verifiable results with salads and vegetable juices, even curing cancer at those with 1 foot in their grave, being brought in on a stretcher.
Closing down a good company does not happen on a whim. I suspect you did considerable research. Can you share that? I'm always eager to challenge deep rooted beliefs (in Gerson and vegetables).
Exclusion diets often have an effect because they exclude certain things, not necessarily because of the thing you do eat.
Most diet research is total rubbish so I prefer to look at actual groups of people that have been thriving for generations on various diets. An approach that Weston A. Price pioneered. None of the tribes he visited ate salads, raw cabbage or similar. Herbivores need 4 stomachs of bacteria at work to turn it into saturated fat they can actually use.
PS: We only closed down those activities and had others to fall back on.
Hey Niels, I took some time to formulate a good reply.
1st, agree on the exclusion. It starts in the supermarket, don't buy poison. But once in the fridge, then getting sick and unable to access the fridge also helps. Healing from degenerative disease is usually a detoxing process while fixing deficiencies.
W.A. Price indeed proved that meat is not bad. But that was 120 years ago. The people Price visited ate meat from free roaming animals.
The 4-stomach argument is weak because not all grass is the same. Some are as tough as nails, others as soft as jelly. Even cows only eat certain grass and avoid others.
The best qualifier is Your own body. If you have great skin, a clear mind, sleep well, regular easy stool, never feel tired, never head aches etc. Then your diet is perfect. Be it meat, fish, greens, cabbage juice or chocolate chip cookies etc. If not, then changes are required. Especially the stool is a good indicator, if you're struggling there, then changes are definitely needed.
