But people do say that having one a day slows weight loss down. In part, I suspect that this is because people start having them in week 3 when weight loss slows down anyway.
It could also have something to do with tolerance to carbs, as someone's already said. But being in ketosis doesn't speed up the rate of weight loss. If you slip out of ketosis, you might retain water, I s'pose - but you'd shed that in time.
The other thing I've noticed is that if you are one of the unlucky individuals who is very sensitive to carbs you might be more likely to go off plan and have things you shouldn't be eating (because you get hungry if you slip out of ketosis). It's usually that slipping off plan thing that makes the difference to weight loss, not eating the bars themselves....