pbear - Texture is an excellent reference however the OP was (and still is, in my mind) very unclear about exactly what he wants to do and why. And it looks as though he isn't coming back again to explain himself further at this point. We are probably talking amongst ourselves (a fun thing but not helping the OP much I think) right now.
Making spaghetti strands out of vegetable juice may work fine as an interesting technique and 'surprise' element for the diner but if the idea is to completely fool an adult eater to ensure that person actually happily consumes whatever food product on the plate thinking they are eating 'junk food' while unknowingly eating vegetables they don't like, I am not sure that agar agar noodles will do the trick, unless they are smothered in gravy or ketchup perhaps (whatever the diner DOES like) so you can't tell what they contain as the flavouring ingredient - but then why bother? Vegetable juice tastes a lot like tomatoes - so if they don't like tomatoes for instance, ketchup or tomato sauce would not be appealing methinks.
According to what I understand from the OP, he wants to HIDE the taste of vegetables and fruit from adult diners (so even that suggestion of his that he make these noodles out of agar agar and vegetable juice is not going to achieve that objective). The noodles will still taste of vegetables - nothing he suggested will disguise that part and agar agar has no taste of its own - so the question still is will they eat much of it if they hate vegetables that much? The only way to disguise vegetables and fruit tastes/textures, etc. from adults is probably by looking at how mommies do it for their kids (by including small amounts in casseroles, breads, soups, smoothies and the like) and hoping that the adults he is feeding are no brighter or more observant than a child might be.
One also needs to better define what is meant by 'junk food' in this case. If one is primarily referring to single or few ingredient items ... like French fries or popcorn or potato chips or gum or chocolate bars .. I don't know how one might conceivably add a large amount of real fruit or vegetable nutrition (if nutritional advantage is the aim - not even sure that is the case though) to those items while also retaining their original taste (that of the standard unadulterated junk food item) in order to (ostensibly) get more nutrition into someone who will not eat those fruits or vegetables otherwise.
