Over the course of the Forever Knight series, Dr. Lambert makes numerous attempts to persuade Nick Knight to give up drinking blood, even cow's blood, and instead substitute some sort of artificial alternative. To this end, she has devised a variety of formulae, none of which Nick has found even remotely palatable.
In much fan fiction, Nick regularly subsists on blood substitutes (also known as protein shakes), with only occasional backsliding into the consumption of blood. Canon suggests otherwise. In the actual television series, Nick only drinks Natalie's concoctions when she personally presents him with a new version; he invariably protests vigorously before trying it; and he drinks no more than a mouthful or two, often spitting out even that.
The following are the various blood substitutes that Natalie tries to get Nick to drink over the course of the series:
"Eye of newt, grasshopper buns, what do you care?" responded Natalie when Nick asked her what was in it. The first blood substitute seen on the show (in the series premiere, "Dark Knight") was an improbable looking transparent green that looked like nothing so much as liquid lime jelly. Natalie stirred it up in her office in a glass mug labelled "Natalie Lambert only".
Under protest, Nick took one sip. He promptly dashed for the sink and spat it out.
Dying to Know YouEdit
Although the colour of the glass in which Natalie proffers it somewhat obscures the colour of the blood substitute in "Dying to Know You", it appears to be white—or at least a pale opaque liquid resembling milk.
While Nick was sitting in his living room, Natalie brought the glass of blood substitute over from the kitchen. He shied a bit when he saw it; but then took it from her. After one dutiful sip, though, he simply remained holding it untouched for the rest of the scene.
At the end of the episode, Nick is in Stonetree's office with Natalie and Schanke. They are all about to have some food; and Schanke is the first one to tuck in. There is a container intended for Nick in the box; and Schanke assumes it is a milk shake and takes a drink. Clearly it tastes horrible. He quickly hands it over to Nick, who hands it off to Natalie, who is thoroughly amused by the incident.
In "Dead Issue", Nick and Natalie are talking in the loft. As he has a flashback to the Renaissance, she is getting him one of her drinks. As usual, he looks at it in dismay, takes a sip, and then grimaces with disgust. He then hands the drink back to Natalie.
The blood substitute in this scene may possibly be the same formula that Natalie concocted in "Dying to Know You". Certainly both are pale opaque liquids. However, in the earlier episode, it was given to Nick in a greenish coloured glass, making the exact shade of the liquid hard to discern. In "Dead Issue", on the other hand, Natalie gives it to him in a clear glass, making it obvious that the drink is a wholly unnatural looking shade of pale turquoise or aquamarine.
In "Blind Faith", Natalie was once again whipping up one of her concoctions in her office. This time she used a blender, whizzing up an opaque red liquid that resembled tomato juice. The result was not poured into a glass. Nick was presented with the whole blender-ful of protein shake. It was, she informed Nick, full of iron. "Nostrovya!"
Once again, Nick made a face as he was presented with his dinner. Once again, he no more than sipped it. Then, duty done, he set it aside with a look of relief.
In the following works of fan fiction, blood substitutes play a significant role in the story: