For purposes of discussion, the abdominal (tummy) region may be thought of as being comprised of five physically distinct layers. From the most superficial layer to the deepest layer, they are: skin, fat, muscle, the lining of the abdominal cavity, and, lastly, the abdominal cavity itself.
Anatomically, the fat in the abdominal region is located in two distinct areas and is referred to as being either extra-abdominal or being intra-abdominal.
Extra-abdominal fat is the fat that is located just below the tummy skin and it sits on top of the abdominal muscles; this is the fat that is physically removed during a tummy tuck procedure. Fat found in the hip/waist/flank, and back areas that is located at this same level (below the surface skin but above the muscle) is removed during liposuction procedures.
Intra-abdominal fat is the fat that is found inside the abdominal cavity (remember this cavity anatomically exists far below and is deeper to the tummy muscles, being physically separated from them by the lining of the abdominal cavity), along with the intra-abdominal organs such as the gall bladder, uterus, intestines, spleen, and kidneys, etc. This fat is intimately associated with the arteries, veins, and lymphatic channels associated with these intra-abdominal structures and the critical maintenance of their functions and, therefore, is never involved in the tummy tuck procedure. Furthermore, this intra-abdominal fat responds favorably only to the increased caloric expenditure and decreased caloric intake associated with weight loss.
In my opinion, a critical component to the result of a tummy tuck involves the tightening or repositioning of the tummy muscles back to their most optimal anatomic location with the use of sutures. However, the presence of excessive intra-abdominal fat may place too much pressure on the back side of the abdominal musculature and may physically impede the adequacy of any attempted muscle tightening/repositioning; the end result could be a suboptimal visual appearance of abdomen (persistent convex or protuberant shape). In combination with the removal of pre-existing flank fat by liposuction, this undesirable effect may be even more dramatic.
Additionally, muscle tightening in the presence of too much intra-abdominal fat can even result in difficulty with breathing after surgery as the tightened muscles may put pressure on the intra-abdominal fat itself (same amount of intra-abdominal fat now in a smaller space brought about by tightened tummy muscles) which then interferes with the dynamics of breathing.
Routinely, a well-trained and experienced tummy tuck surgeon will determine the physical contribution of both the extra-abdominal and intra-abdominal fat layers to the visual appearance of the tummy area before surgery such that he/she will, ultimately, be able to deduce the likelihood that the presence of excessive intra-abdominal fat will limit the results following surgery.