I haven't used the tablets BB - I use the powder but the amount needed differs from person to person. The only way to discover your ideal 'dose' is to experiment a bit.
Remember, the dosage they are suggesting is for someone they think is having additional fibre in the form of veggies etc and we're not having that on a VLCD so the dose probably isn't as high as you think.
I have 6 teaspoons of the powder a day (I have 2 teaspoons in my shake and 4 in my soup) so that's probably even more than the six tabs! Even that amount doesn't have me running to the loo so I doubt if 6 little tablets will have that effect on you.
Even so, if you're a bit nervous about taking them, why not try just one each meal and see if that does the trick (remember to drink an additinal glass of water each time). If that doesn't seem to have much of an effect then increase the dose until you're happy with it.