Does dietary fiber knock me out of ketosis?

I have read people clocking blood sugar spikes from quest bars and other things using sugar alcohol and similar "fibers". Any bar in particular ?

Great What about this one? http://www.questproteinbar.com/protein-bars/cookies-and-cream-box-of-12.html there's written Isomalto-Oligosaccharides (Prebiotic Fiber)

I'm a Type I diabetic who controls my blood glucose with a ketogenic diet, and I've tried several of the quest bars - all with the same result.

After eating a Quest bar I get the equivalent spike in glucose I'd get from ~20g of carbohydrate.

Can it "knock" you out of ketosis? Any excess carbohydrate can. For me I've found it best to ignore any "net carb" claims on what is supposed to be a low-carb processed food item. The only 'fiber' amounts I deduct are the well-known and trusted dietary fiber amounts in fresh vegetables and fruits.

Mmmmm... love Quest bars and I eat them pretty much daily. They have never knocked me out of ketosis... only tasted delicious and given me good numbers for my fiber column.

Possibly a stupid question, but how can you tell if something has knocked you out of ketosis? Is it just based on lbs lost that week or something more immediate?

The only way to know for sure is to measure ketones. A blood ketone meter is the most-accurate method, and what I personally use every day.