IIFYM ... I love it ...I live it ...However it is confusing to some and could possibly hinder results for you for one simple fact. Somehow Lyle McDonald , Layne Norten, Martin Berkhan basically all of them agree it works ...and it does. However I have something for you to think about before you go FULL IIFYM.
As we all Know Meat = Muscle Right
Right well I happen to be in the Feed industry and have been my entire life .... We feed the Meat you eat. This gives me an interesting perspective because our Business is ALL ABOUT THE GAINS!!!! We sell feed for many species and formulate rations for Swine Cattle, Goats, sheep, Chickens turkeys ...hell we even have a customer that feeds RATS!! yes rats ...for snakes ....so technically we feed snakes too LOL!
However,
Our biggest business is Swine ; also the animal with the closest Anatomy to Humans. Cattle Goats sheep Etc all have very different digestive systems than us but swine are particularly similar to humans in how they digest and utilize food. So we will focus on the swine feed only.
First Off to get efficient Gains in swine the Feed is "processed"........ Corn is ground fine
...beans are ground into Beanmeal
...Amino acids are added as well (lysine threonine and Dl methionine etc) and also extra vitamins packs and minerals to help the animals stay healthy and grow as efficient and lean as possible basically everything is taken to a small particle size for absorption ...and this can make a big difference in efficiency because digestive enzymes can be much more effective. And remember this is a business ....efficiency counts big time.
If you don't believe me that the particle size matters here is proof http://www.swinefeedefficiency.com/factsheets/IPIC25d%20SFE%20Influence%20of%20Particle%20Size.pdf
HOW THIS RELATES TO BODYBUILDING
Now this would be equal to us eating "processed" foods when practicing IIFYM . The food is taken down to smaller meal type food stuffs and then re-packaged into chips , pop-tarts , cereal etc. Hence the Idea of whole grains being better for you. They really aren't ...they just aren't absorbed quite as well.
So in summary IIFYM works for sure ...calories and macros in/out ...but you want the opposite as a hog ...if you are like me you want to eat more food ...you don't want an efficient metabolism ...However if you are on a cut if practicing i would overestimate calories by 3-5% depending on how much processed goods you are eating. If bulking eat maintenance with more processed goods and this should give you an efficient fuel source to gain muscle.
EXTRAS
When doing rations in animals Protein being too high can cause "HEAT LOSS" which is similar to TEF and can also make feed conversions very inefficient. Remember efficiency is the opposite of what we want ...Personally i would like to eat more food and stay lean. Efficiency sucks ....so more protein the better.
Also certain Beta Agonists are used in livestock ...this is similar to the stuff in your inhaler for your asthma. The opposite of Yohimbe HCL.... if you don't understand then research it. One that is super effective in swine and makes them much leaner and increases muscle mass by up to 10% is known as PAYLEAN or in cattle OPTI-FLEX ...same exact compound that is actually known as RACTOPAMINE...."I would never take personally because i have a family and am all natural but i could understand why someone would ....It was originally tested on humans but caused irregular heartbeats so was scrapped but is widely used and safe in aimals and i am suprised the bodybuilding community hasent latched on to it yet .... http://en.wikipedia.org/wiki/Ractopamine Now don't pay attention to the countries that banned it like China and Russia as it wasn't actually saftey concerns it was a backhanded trade strategy to try and lower the price of imports ...china and Russia are well known for pulling these backhanded antics.
Thanks for reading and hope this puts some more perspective on your diet and helps someone.