Whether it definitely has to be cooked or not, I don't know, butI will say this: I did a thorough web search of technical papers examining how canning affects phytochemicals, and of asparagus specifically. As you probablt know, heat not only renders some nutrients more bioavailable, it also converts some phytochemicals into a more potent form. Canned foods are some cases higher in nutrients than their fresh counterparts. It is not the canning itself that is particularly destructive (except for heat labile nutrients such as vitamin C, for example) it is the REHEATING after we take them out of the can that affects their potency. The largest amount of nutrient degradation took place after microwaving canned produce. So, at this point, if I eat a canned vegetable, I eat it straight from the can.
I did try the canned asparagus. I have a lot of trouble in recent years of feeling that my energy levels must be parceled out with a teaspoon. Even so I will hit a wall fairly frequently. The canned asparagus, pureed and drunk, seems pretty fantastic. I am impressed. I do feel better, and my body greets the asparagus drink with pleasure. Even my cat goes wild for it--she will not let me finish a cup without tithing a few tablespoons to her!
On another post I noticed someone said that they did not know what part of the asparagus was the most potent--stalks, leaves, roots, or what--while on another post providing a link to pubmed (ncbi) the writer said it was shown that the roots were the most potent. The NCBI post was referring to asparagus RACEMOSUS, which is the ayurvedic remedy called Shatavari. Racemosus means "wild". This root has traditionally been used in Ayurvedic medicine; whether the leaves and stalks are equally potent I am not sure. It is possible they are: with regard to ginseng, for example, the leaves (much much cheaper) are just as potent as the highly prized root. The leaves of the pau d'arco tree are also apparently as potent as the bark. But back to the question of what part of the ordinary asparagus plant that we eat is the most potent. What we grow and eat in the US is called asparagus OFICINALIS (NOT RACEMOSUS, although they are both types of asparagus). Of the part that we commonly eat, the stalk, the greatest amount of phytonutrients are concentrated toward the apical end, that is, toward the little pointy end that is covered with the flat leaves adhering to the stalk. (the part we dip into butter or mayonnaise). Of course, it is possible that the roots of asparagus oficinalis are also rich in these same phytochemicals. In fact, I'd be surprised if they weren't. It doesn't matter: there really seems to be something to this canned asparagus remedy. It is simple, relatively inexpensive, and it really makes you feel strong. I personally think it is well worth a try. I have bought a whole bunch of cans of the stuff and am enjoying a glass 2-3 times a day. I juice up the canned asparagus with the water in the can, so as not to lose anything. It just takes a second, and then I ladle out 4 tablespoons into a glass, mix with water, and drink. Very nice.