The studies he cites are these:
They appear to be for smaller, non-mixed meals. Also, there are some differences in the definition of T_lag (2% vs 10% of contents emptied). Nonetheless, this level of variation is somewhat larger than I would have expected (though it's all on the short end rather than the long end).
Also, if you have any links for other 80-90 minute studies besides the one I've been citing, I would be interested.
I think I have a preliminary answer to this question. And I think it involves a phenomenon which has only recently been discovered.
When the stomach is processing food, one of its main jobs is to break solid food chunks down into a fine-particle "soup" (which, when mixed with liquid, acid and various enzymes secreted by the stomach is called chyme). Much of this breaking-down action is performed by muscular contractions of the stomach wall, which "churns" and squeezes the food to break it into smaller pieces. But the stomach alone is not capable of reducing solid food into the fine particles necessary for optimum digestion further down in the intestines.
And this is where the recently-discovered phenomenon comes in. It is now known that the pylorus (the last part of the stomach, which connects to the duodenum) and the duodenum "collaborate" to squeeze and filter solid food matter. The way it happens is this: the food matter is squeezed from the pylorus into the duodenum, through the pyloric sphincter (the valve consisting of a ring of muscle at the division between the pylorus and the duodenum). The duodenum then passes the food matter
back through the pyloric sphincter and back into the pylorus. This process goes on for a number of repetitions, with the pyloric sphincter becoming narrower and narrower during each transition. In this way, the solid food particles are squeezed through an increasingly-small opening in the sphincter, and are thus "sieved" into finer and finer pieces.
Once this process has taken place, the pylorus spends time manipulating the sieved matter, and its sensitive nerves can determine whether there are still any pieces of food among the chyme that are too large for efficient digestion. Only when the pylorus determines that the chyme is incapable of being broken down any further* does the main transition of food from the stomach into the duodenum start.
The studies you've referenced above are looking for the first appearance of labelled food matter in the duodenum.
But this timing is almost certainly related to the commencement of the back-and-forth "sieving" operation carried out by the duodenum and the stomach. I'm not sure if this phenomenon was even known at the time these studies were published (1991 and 1996), but it was certainly known by the time the Hellmig et al study was published in 2006 (this is the study giving the 82-minute median T(lag)).
The time that is relevant to establishing the ToD for Meredith is the time when the food starts to leave the stomach
for the last time - i.e. after the "sieving" operation has taken place. This is the time after which one would necessarily find chyme matter in the duodenum and the jejunum. If no chyme is found in the duodenum or jejunum, it means either that a) the food has not left the stomach at all, or b) the food has been processed by the stomach, has been "sieved" between the pylorus and duodenum, and has returned to the pylorus (part of the stomach, remember) to be analysed again. In Meredith's case, it's highly likely that her pizza meal had undergone this back-and-forth "sieving" operation, but had fully returned to the stomach by the time she was attacked.
I will try to get decent cites for the "sieving" phenomenon, together with some indication when it was first discovered. But I think it's a highly reasonable suggestion that what the earlier studies were measuring was the commencement of this "sieving" process, rather than the ultimate transition of food from the stomach to the duodenum (and beyond)
* Some foodstuffs remain incapable of being ground down - which is why, for example, tomato seeds pass out whole in faeces.
). It's worth remembering that Greater London (i.e. not even including the outer suburbs) is around 600 square miles in area, with around 8 million inhabitants. The trouble has taken place in probably around 20 square miles (maximum) of those 600, and probably only around 1,000 people maximum (out of 8 million) have been actively committing criminal acts. Context is everything......
