Basically, diazoxide is a compound that has been used to treat hypoglycemia and reduces insulin secretion. Two groups of 12 obese hyperinsulinemic adults were treated with diazoxide or placebo for 8 weeks while each consuming the same Optifast diet.
Changes in abdominal subcutaneous fat water content with rapid weight loss and long-term weight maintenance in abdominally obese men and women
Water content of abdominal subcutaneous adipose tissue increases with weight loss in obese persons with the metabolic syndrome, and may reflect increased subcutaneous fat tissue nutritive blood flow. The increase in water content correlates with the increase in insulin sensitivity, suggesting that weight loss and consequent improved insulin sensitivity could mediate the increase in abdominal subcutaneous fat hydration.
So increased insulin sensitivity -- which increases insulin action on adipose tissue -- can cause greater hydration of fat tissue - e.g. increase fat mass. If the work of Sims cited in GCBC is correct, and carbs increase insulin sensitivity in adipocytes this could perhaps explain why in the short term (the time frame of the above study was 9 weeks weight loss followed by 1 year maintenance) we often see differences in weight loss exceeding the glycogen depletion differential. I've posted before how low carb in effect mimics adipocyte IR (excessive NEFA release) so maybe this is also at play.
In the DZ study the authors discuss that DZ can directly impact adipocytes as well as to reduce insulin levels which would mimic decreased insulin sensitivity if sensitivity of the adipocytes is not improved. If this is the case, the placebo group conceivably had increased water content in the fat = greater "fat mass" while the DZ group had the same or even further decreased water content in the fat = lesser "fat mass". Interestingly several of the DZ group experienced edema. That might seem to counter this hypothesis except that perhaps some of the water liberated from the fat tissue in the DZ group collected in other tissues, but still some may well have been excreted. As I said, this kind of thinking off the top of my head, but it is a plausible explanation for that which MUST be explained!
OK so let's couple this with Disparate Hydration in Adipose and Lean Tissue Require a New Model for Body Water Distribution in Man.
Adipose tissue contribution to total body water has been generally disregarded be cause its water content per unit weight is less than one-fifth that of the traditional "lean body mass." Indeed Pace's formula defines the "lean body" as containing all body water (16). Such a formulation was useful when adipose tissue formed a minor percentage of body weight, and when body composition measurements in vivo were limited to indirect estimates, such as skin fold thickness and body density. The advent of fatter populations, and of more varied and to some extent more direct measurement techniques have disclosed significant water, primarily extracellular, as sociated with adipose tissue. Widespread interest in obesity as a disease state, and in body composition measurements in obese patients, as well as a gradually fatter "normal" population, have motivated a new experimental look at the water phase of adipose tissue, and based on these measurements, a new model for adipose tissue in man.
Some acronyms used: TBW = total body water, AFM = adipose free mass, AT = adipose tissue, ECW = extracellular (between cells) water, ICW = intracellular (inside cell) water. The water content of AT is ~14% of which ECW is ~11% and ICW is ~3% for an ECW:ICW ratio of ~3.5:1 . The water content of AFM is ~79% in on average for all, but the distribution of ECW:ICW differs considerably in obese v. lean: ECW ~33% vs. ~24% in obese v. lean for a ratio of 0.76 for obese v. 0.42 for lean. The ratios and distribution varied widely with ECW related to degree of obesity and ICW varying inversely.
What all this says to me is that, especially short term, a lot of body composition analyses are really to be taken with somewhat of a grain of salt. Any general "diuretic effect" that would impact extracellular water content would disproportionately influence both fat mass (FM) and fat free mass (FFM/LBM). Given the differences in the ratios, greater losses of ECW would skew FM losses more, especially when FM is considerable.
Again, I've not done an awful lot of mental math gymnastics here, but I think water weight has been both under and over estimated. On the one hand, to some extent, weight is weight and volume is volume. If I can shrink my fat by decreasing ECW, I'm all for it!!! If moving FA's from fat cells to, say, muscle cells influences my water distribution in an aesthetically pleasing manner, I'm all for it with a few reservations on the whole lipotoxicity thing. But, especially in the obese when we're talking tens of if not hundreds of pounds of excess weight, water sure does make up enough of the equation to explain just about any anomaly we see in any short term study or even longer term one where relatively minimal losses are involved. Water is ~14% of fat tissue and ~79% of fat free tissue. When the former is relatively low, that's one thing, when it's high, it can be a different story. I'm sure in addition to gains and losses, there are shifts that are included in the measurements of fat tissue and lean mass.