From the Kay Erdwinn’s Post Teaching Yoga for Round Bodies
Unless there are knee problems, most fat people are comfortable with the first phase of this asana. The second phase is harder for everyone, of course. The fat person performing this asana must be sure of his/her leg strength and knee health, since s/he must carry more weight. The most troublesome part is keeping the knees pointed forward as s/he completes the squat, due yet again to abdominal and thigh fat. I have found that I and other fat people unconsciously lean back in order to breathe better, which places stress on the lower back as well as hinders an already precarious balance. I teach fat students to go down as far as possible, maintaining alignment, then to come out of the asana.
Alternatively, they can start the asana from a slightly duckfooted and externally rotated leg position. We’re talking a couple of inches, no more. This allows the necessary room for the thighs and belly as they squat. This changes the lower back stretch and which aspect of the quadriceps is working the hardest, but I believe that as long as the legs are opened from the hips, and the knees stay in alignment with the feet, there is no extra danger.
As with any student, if it’s too hard to come straight up out of the second phase of Utkatasana, a fat student can bring his or her hands forward onto the floor, resulting in an all-fours position. Then s/he can simply straighten up to “standing” on the knees and step up to Tadasana.