I can definitely tell when I eat more fat my BMs do tend to float more.  Yes I have to flush more then once somedays. 

I'm guessing you have a newer "low flush" toilet, that uses less water for flushing.  Large volume of loose stool, with minimal water to flush is likely why "it won't go down in one flush".  My house is over 30 years old, and had the standard flush toilets. When the newer low flush ones came out, I bought one to put into the main bathroom in the house. The kids primarily used this bathroom, as well as anyone who visited my home. Almost immediately, I noted the low water flush caused issues.  Many times, a double flush was needed.  This was an earlier design, with a smaller tank next to the wall. The manufacturer had placed a plastic resevoir inside to hold less water.  I took out the plastic resevoir. The toilet still uses less water than before, due to smaller tank. 

Newer low flush toilets are designed better.  But this tip may help.  Most toilets use a "flapper valve" to le****er out of the bowl. Their design does not always allow them to remain elevated long enough to drain mos****er out of the bowl.  Some hardward stores have flapper valves with "foam disk floaters" attached to the flapper. Idea is to keep flapper up longer to allow more water to flush.  If you can't find this type of flapper--suggestion number 2.  Get a fishing bobber, and attach to chain.  Don't use the biggest one available, but either a couple of small size or a mid range. The fishing bobbers will hold the flap up longer to help your situation. You can likely discharge the bowl in 2 flushes (if you issue continues) instead of 4.

I have 2 Koehler toilets I put into the 2 other baths about 10 years later. These are higher than standard toilets, with rims a few inches higher than standard toilets. It's easier to sit down and get up from this elevated toilet compared to the standard one.  But, with the low flush, these still have some minor issues. They flush well most of the time.  BUT CONSTIPATED HARD STOOL my wife has had has created either clogs, or would not flush at all.  I keep an old wooden spatula behind the toilet to "break up" the toilet logs.  I got tired of plunging toilets daily or mopping up floors from a clogged toilet a few times.  Hope this helps. DAVE

Thanks for the suggestions. I actually don't have one of those newer toilets - I live in an 30 year old apartment building with a standard toilet.  I always had problems with my stools floating but they always flushed - maybe one little piece would stay behind but this past week, I find that with the large amounts of loose stool, I have to flush multiple times every time I go.  This doesn't only happen in my apartment, I find it happens if I go to a restaurant or a store also.  So, it has to have something to do with my stools and not MY TOILET>

Well, that's a relief.

(hehehe--I crack myself up sometimes)

1. You can always start flushing while you are still sitting on the commode.
2. Make sure the holes under the rim are clear. You might not be getting enough water power to flush. To check this, you can try flushing with a bucket. If it goes down faster, it is the holes in the rim that are clogged. Hard water does this.
3. Don't use the toilet bowl cleaner that goes in the tank. It clogs the rim and also eats up certain components.
4.Try holding the handle down a bit longer when you flush. The flapper may be closing too soon and if you don't know how to adjust the chain this might help.
If you frequent the landlord bulletin boards you will find that toilets that don't clog is second only to pet urine in popularity and number of posts. Or maybe its carpets and laminate right now.
If you ever get your own place, the current favorite is the Japanese brand Toto.
If you are close enough to the border, you can buy a 3.5 gal per flush commode in Canada. (Made in the US, by the way--can make up, just can't sell them here.) Tourist info places at the border have maps and/or lists to the plumbing supply houses. I got my Gerber that way. You will never see the good ones sold in a big box store.
I put American Standard in my rentals. They had a commode with a wider opening which was guaranteed to flush like 34 golf balls in one flush. The landlords had a contest with live video feed online. We got it to flush a lot more than that. Have not had a problem with them. The only thing that worked better was a commode made in 1910.

 Well My daughter had problems with her bowels when she was little.  She was tested and ultrasounded and everything else and everything was fine.  The longest she held it once was 8 weeks.  Yep.  After awhile your body will stop giving you signals that it has to go if you don't.  She is 17 now and resolved that as she got older.
I have IBS.  I have loose stools constantly.  I have a friend who has Krohns.  We both did the same thing.  Eat and go to the bathroom and lose it all.  I had a colonoscopy done and i was fine.  That might be something you should think about doing.  You might have ulceritive colitis or Krohns.   
My doc told me most people have problems with constipation after the surgery so maybe i will be one of the lucky ones and not have the problems.  I even get sick from the magnesium citrate so he told me i didn't need to use it if i didn't want to the day before my surgery.  Hope all your issues are resolved and try the magnesium oxide.  Sounds like it works like a charm.