I agree with the previous post that no one would have simply opted to reduce headroom in your kitchen for the sake of fashionable or stylish architecture alone. There was obviously a necessity to lower the ceiling, and the most obvious reason I can think of is that the room above that kitchen is a bathroom that's been renovated. If so, I suspect that what's happened is that someone decided to relocate the toilet as part of their renovation plans.
The drain pipe from a toilet is 3 inches in diameter, and you don't want to cut a hole in a floor joist that big, or you'll severely weaken the joist. So, probably someone decided to lower the ceiling of the room below so that the toilet drain pipe could then run under the floor joists from it's new location and connect to the vent stack at a slightly lower elevation. But, if that was the best option they could think of at the time, it probably still is, and cutting a hole in that ceiling is likely going to just create work in requiring you to then repair that hole.
PS: (you don't need to know the rest, but I thought I'd toss it in)
A toilet is nothing more than a glorified siphon hose. The difference is that with a siphon hose you suck on the discharge end of the hose to fill it with water to get the siphon hose to start flowing. The laws of physics dictate that as long as the siphon hose is full of liquid, and the downstream end is lower in elevation than the upstream end, it will keep flowing. With a toilet bowl, water flows from the tank into the bowl and then into the toilet bowl's discharge channel opening at the bottom of the bowl faster than it can flow through that tortuous discharge channel. That results in the discharge channel filling up with water. Once the discharge channel is full of water, exactly the same laws of physics take over and the discharge channel of the toilet suddenly becomes a great big siphon hose that siphons the water (and everything in that water) out of the bowl. Simple as mud, really.
Newbie DIY'ers often presume that the curvatious and undulating shape of the discharge channel somehow acts like the p-trap under a sink to prevent sewer gasses from getting into the house, but any explanation of it's shape or how that shape results in the better trapping of gas than a straight channel is beyond the capacity of mere mortals to undersand. But, they claim, that has to be the reason because there doesn't seem to be a better one at hand. It's just not that complicated or mysterious. The curves are there to reduce the rate at which water can flow through that channel to ensure that it fills up with water and becomes a siphon. Once that toilet discharge channel becomes a siphon hose, then barring anything else from interfering with the process, you have Sir Isaac Newton's personal guarantee of a successful flush.
And, you can use that understanding to help diagnose toilet flushing problems. If your toilet isn't flushing properly, pour a 5 gallon pail of water into a toilet bowl as fast as you can without causing the bowl to overflow so that you end up spilling water all over the floor. If the bowl THEN flushes properly, then the problem is in the bowl or upstream of it. The issue is that there's not enough water flowing into the bowl (and hence the discharge channel) fast enough to cause the discharge channel to fill with water. That could be that the jet hole at the bottom of the bowl or the holes under the rim of the bowl are clogged up, or that the toilet flapper isn't opening wide, or there simply isn't enough water in the tank.
However, if the toilet still doesn't flush properly after doing the 5 gallon pail trick, then the problem is in the bowl's discharge channel or downstream of it. It could be that there's something stuck in the discharge channel and toilet paper is accumulating on that obstruction and preventing flow through the channel. Or, it could be that the drain pipe from the toilet is already full of water, so there's no place for the newly added water to go.