I'm a strong advocate of not counting calories, because your body has a built in mechanism for maintaining a specific fat level: leptin.
The hormone leptin wasn't discovered until 1994--just 18 years ago--so there's plenty of conventional diet wisdom that doesn't take leptin into account. That's why, imho, conventional diet wisdom (including counting calories) doesn't work.
Leptin is a hormone produced by your fat cells. The more fat your body carries, the more leptin in your blood stream. The less fat your body carries, the less leptin in your blood stream.
Your brain has the ability to detect the amount of leptin in your blood stream, and reacts to the amount.
- High leptin levels result in increased metabolism and reduced hunger.
- Low leptin levels result in decreased metabolism and increased hunger.
The practical result is your body regulates your body fat based on your leptin level.
There are a number of things that can interfere with this fat regulation system.
1) High triglyceride levels have been shown to prevent leptin from crossing the blood/brain barrier. This fools the brain into thinking there isn't any leptin in the blood stream. The result: the brain thinks you need to add fat, so it decreases your metabolism and increases your appetite (to a screaming intensity).
2) It's one thing for you to eat fewer calories because your brain has reduced your appetite due to high leptin levels. It's another thing to eat fewer calories when your body isn't telling you to do so. When you reduce your calories your body thinks there is a famine, and it goes into survival mode. It doesn't matter if you carry 100 pounds of extra fat, your body is going to try and hold onto as much as possible so it can survive the famine. And, how does it doe that? By reducing your metabolism and increasing your appetite--the exact opposite thing you want when you are trying t lose weight.
3) Overeating will still cause you to gain weight. When your body is trying to lower your fat level, there will be days when it reduces your appetite to very low levels. If you track your calories you won't be able to believe that you can get by on so few calories (even though you are not hungry). The result: you're going to eat something (even if you aren't hungry), because the analytic part of your brain just knows you need to eat more calories.
Problems #2 & #3 are a direct result of counting calories. Sure, you can lose weight by counting calories (a lot of people have), but to me counting calories is part of the "just be disciplined and will it to happen" mindset. You can "twist your body's arm" and force it into shape--for a while. But, in the end, your body is in control and will have its way. It's better in the long run to work with it rather than against it.
As far as #1 goes, any good paleohacker knows that eating lots of carbohydrates results in high triglyceride levels. Which prevents leptin from crossing the blood/brain barrier, which causes your brain to think you don't have any body fat, which results in a lowered metabolism and increased appetite (is it any wonder that the typical overweight person is sluggish and always hungry, even though they are carrying tons of extra fat?)
If you've followed the government's food pyramid and eaten high levels of carbs all your life, your body's letpin/weight-regulation mechanism has probably never worked as intended. This is why paleo allows people to lose weight effortlessly. It creates the circumstances that allows your body to regulate your fat level naturally--the way it is supposed to be regulated.
That's the long term answer to keeping your weight in line, not counting calories, discipline, will power, or trying to bend your body to your will.