Getting lean is the hard part. Staying lean is easy as pie IF you follow a few guidelines. In fact, once you are lean it's near impossible to get fat, no matter what you eat, if you follow these guidelines.
1) Never, ever snack – Forget about snacks forever. Snacks are for fatties who can't control themselves. Since you got yourself lean (sub 10% body fat) we know you can control yourself. Snacks exist only to make you fat, they have no other purpose. They aren't filling. They aren't full of proteins, vitamins and minerals. They are full of fatness for you. Take a look around your office, watch all the fatties snack throughout the day, and then count how many times they say “I don't know why I can't lose weight, I don't even eat meals, I just snack!” If you have a sweet tooth have some dessert after your meal, just don't do it between meals. Give your stomach a rest and give your body a chance to digest all that food and a chance to keep burning that unwanted fat.
2) Eat 2 big meals per day on average – Eating 2 big meals per day will keep you lean forever. It's damn near impossible to gain any weight eating twice per day (so eat more when you want to bulk up) no matter what you eat. Obviously you will still want to eat well most of the time (steaks, eggs, fish, chicken, duck etc..) but it's no problem to go and grab some McDonalds and ice cream sometimes. Sometimes you will eat 3 or 4 meals per day, but if you average two meals per day you will be fine. For the doubters, it is not hard to eat two meals per day, it is quite easy. Skip breakfast and have lunch and dinner. Skip dinner and have lunch and breakfast. Have brunch and supper. Doesn't matter. Eat big, eat until you're full and it's a piece of cake.
3) Don't drink calories – Drinks like soda, sweet tea and Gatorade are quite deceiving. They are chock full of sugar and calories, they usually don't quench your thirst so you end up drinking more and just getting fatter. Stay away from these and watch the fat stay off. Quench your thirst with water, black coffee, and unsweetened tea. If you are lean it's easy enough to have a beer or two with dinner or a soda with dinner and not see any unwanted fat, but only with meals. The one exception is that sometimes you just need to drink a six-pack of beer or a pint of Jack Daniels with a Coca Cola chaser. It isn't going to harm you if you follow the other rules.
4) Don't forget to hit the gym – Don't forget what sculpted your guns in the first place. Once you get down to a respectable body fat it's easy enough to coast and maintain. Hit the gym every week (even 3 days per week will help you maintain), follow the rules above, and watch yourself never get fat.
Once you get lean and wish to only maintain your leanness it's really very easy. No need to count calories, to count macronutrients, to do cardio, to drink 2 gallons of water per day, to eat 6 meals per day of dry chicken and brown rice. Eat twice, hit the gym, and live your life with your hard-as-a-rock abs.
Easy Peasy Japanesey.