Being on the higher side of BMI does cause problems on a trek.
But, this does not mean that you are not eligible for the trek. We ask for the BMI just to alert ourselves. But we care more about fitness than your BMI.
Even if you are on the higher side of BMI and clear the fitness criteria mentioned for the trek, you are eligible to do the trek.
Our fitness team does give special attention to those trekkers who are above the 26 BMI limit.
If the BMI is above 28, you are not eligible to go on the trek. Here is an article which tells you how you can assess your BMI before you go to a trek.