Did a little experiment of my own...take the results with a grain of salt....
I thought I would put this out there. I have been breeding rats since 2011. They make wonderful pets. I do not breed them for snake food! I know a lot of people find them gross, that is fine, but I decided to switch up their diets to see if LE and HE diets effect them at all. Take this all with a grain of salt...obviously rats and humans are quite different.
Since their cycles are every 5 days or so I decided to put them on each diet for 15 days (the equivalent of 3 months for us). They average 8 babies each time. I only breed a female once at 3 months old. I only breed once every three months.
I started this little experiment 10 months ago. I decided to do the LE diet first since I started the LE diet around that time as well. Just the female got a low fat low protein diet- I gave her a set limit of food each morning and night. She didn't necessarily get a lower calorie diet, but she got a set amount in the morning and didn't get more until the evening. I didn't worry much about vitamins since I was concerned about the babies health. None of my rats get a supplement, they all get vitamins from their diets, so I didn't mess with it.
Her litter was only 5 pups, which is a bit less than what I am used to (once in awhile we get 7 or 9, but never 5). She had 4 females and 1 male...which got me a little excited since it seemed the diet had worked. Most of the time my rats have 5 males and 3 female pups, sometimes we get lucky and get four females and four males. So my conclusion was that diet does play a pretty important role.
Three months later I did another experiment with a female. I did the HE diet this time. The female got a high protein and high fat diet. I gave her the food in a dispenser so she had unlimited food and could eat all day and night. Once again vitamins didn't really get messed with since they were all food based (but I guess she did get more, since she ate more).
Her litter was 13 pups! That rarely happens, and I had to supplement some of the babies since she couldn't feed them all like she should have. She had 10 boys and 3 girls. I think the HE diet worked for her...since she got 75% boys instead of the usual 60%. So once again I really think diet is quite important.
I did another "experiment" in February using the LE diet again, just to see if it was just a fluke, or if there was something to it (I'll be doing another HE diet soon). Did everything the same, diet for 15 days, low fat, low protein and set times for eating.
The female had 4 babies this time and this time she had all girls (I was very pleasantly surprised!). She had half the usual amount of babies, so I'm concluding she was less fertile/didn't produce as many good eggs?
So currently in my little experiment the LE diet has been successful 89% and the HE diet has been successful 75%. I'm sure that number will go up with the next breeding. I'm impressed with how well this little experiment of mine has worked. Maybe it was just luck, but this has really opened my eyes to how important diet is! I also didn't realize how important fat and protein was for fertility...I still can't believe how diverse the number of pups were!