How interesting: ‘Nicotine is named after the tobacco plant Nicotiana tabacum, which in turn is named after the French ambassador in Portugal, Jean Nicot de Villemain, who sent tobacco and seeds to Paris in 1560, and who promoted their medicinal use.’
[Extract above from ‘Nicotine – From Wikipedia, the free encyclopedia’: http://en.wikipedia.org/wiki/Nicotine ]

Hi, Anneli – Thanks for the excuse to research a totally new subject area to me – Snuff, Snus (Swedish, pronounced as in ‘goose’) and nicotine. Make what you will of the following extracts:

‘Nicotine changes how your brain and your body function….[It] initially causes a rapid release of adrenaline, the “fight-or-flight” hormone. If you’ve ever jumped in fright at a scary movie or rushed around the office trying to finish a project by your deadline, you may be familiar with adrenaline’s effects: Rapid heartbeat / Increased blood pressure / Rapid, shallow breathing.
Adrenaline also tells your body to dump some of its glucose stores into your blood….
Nicotine itself may also block the release of the hormone insulin. Insulin tells your cells to take up excess glucose from your blood. This means that nicotine makes people somewhat hyperglycemic, having more sugar than usual in their blood….
Over the long haul, nicotine can increase the level of the “bad” cholesterol, LDL, that damages your arteries. This makes it more likely that you could have a heart attack or a stroke….’
[Above extracts taken from How Stuff Works Website: ‘How Nicotine Works’ by Ann Meeker-O’Connell http://science.howstuffworks.com/nicotine3.htm ]

‘In smaller doses (an average cigarette yields about 1 mg of absorbed nicotine), the substance acts as a stimulant in mammals, while high amounts (30–60 mg) can be fatal….For chewing tobacco, dipping tobacco, snus and snuff, which are held in the mouth between the lip and gum, or taken in the nose, the amount released into the body tends to be much greater than smoked tobacco….
Nicotine is the natural product of tobacco, having a half-life of 1 to 2 hours. Cotinine is an active metabolite of nicotine that remains in the blood for 18 to 20 hours….’
[Extracts above taken from ‘Nicotine – From Wikipedia, the free encyclopedia’: http://en.wikipedia.org/wiki/Nicotine ]

‘Snus (/ˈsnuːs/; Swedish pronunciation: [snʉːs]), is a moist powder tobacco product originating from a variant of dry snuff in the early 19th century in Sweden. It is consumed by placing it under the upper lip for extended periods of time….
The nicotine content of snus varies between brands, with the most common strength being 8 mg of nicotine per gram of tobacco. In recent years, snus manufacturers have released stark (strong or sterk) and extra stark (extra strong or extra sterk) varieties with greater nicotine content. Stark varieties contain, on average, 11 mg of nicotine per gram of tobacco, while extra stark varieties may contain up to 22 mg of nicotine per gram of tobacco.
A large study of almost 10,000 Swedish men published in the International Journal of Cancer in 2008 was unable to statistically confirm a risk elevation for the combined category of oral and pharyngeal cancer. Other studies and opinion pieces in renowned journals such as the British Medical Journal and the Lancet suggest a probable increased risk of pancreatic cancer as a result of snus use.
Many cardiologists believe nicotine products (oral)….may aggravate hypertension due to the effects of nicotine on cholinergic and dopaminergic neurotransmission. At higher doses, tachycardia and reflex bradycardia can also occur, triggering serious arrhythmias or even cardiac arrest in sensitive individuals. Further studies are needed in this regard.’
[Extracts above taken from ‘Snus – From Wikipedia, the free encyclopedia’: http://en.wikipedia.org/wiki/Snus ]

You ask ‘will nicotine mess up the good things you benefit from fasting’ and I assume you’re particularly interested in acheiving the potential health benefits. To my mind, messing with one’s insulin levels and raising one’s blood-sugar levels is bad news at any time, let alone when deliberately adding stress to the body by using Intermittent Fasting. The general medical concensus seems be that snuff and snus cause less harm than the smoking of cigarettes but that’s not saying much, by the sound of it. Best wishes to you.