How to eat to stay fit? That sounds like a billion dollar question:).
I am not a scientist nor an expert on this, yet I’d love to share with you my thoughts and years of personal experience on it. Hopefully that might generate some good thinking, reading, and discussion.
First and foremost, there is no set caloric intake that is right for everyone. If you are following a diet that is telling you to eat a certain level of calories without taking into account your personal stats, 99 out of 100 times it is a bogus diet IMO.
So how many calories should you consume on a daily basis?
A general rule of thumb for determining your break-even (maintenance) caloric intake is 14-16 calories per pound of your body weight (lbs). Note: These numbers are skewed, however, for very lean people or very big people *_^.
Also, to invoke weight loss, a good general rule of thumb shoot for 12 calories/lb or thereabouts, get at least 1g/lb of protein, good healthy fats (75g or so is a good number to start with) and fill in the rest with carbs.
Monitor your progress through measurements. If things are heading in the right direction, modify your approach. Maybe drop your caloric intake to 11 or 10 calories per pound.
Here is an example, my current body weight is 105lbs and I need 1600 calories to maintain it. I’d allocate my protein, fats, and carbs intakes like this:
I like to have 1 – 1.5 gm of protein for each pound that I weigh. Right now let’s say that would be 131.25gms. There are 4 calories in each gram of protein, which equals out to be 525 calories (using 1.25 grams/lb). If I am not weight training, these protein requirements would be lower.
Then I worry about my fats. I like to have somewhere in the neighborhood of 50-100 grams as a minimum. Of this, I keep it to the healthy side of things with monounsaturated (olive oil), certain polyunsaturated (omega-6/9s, flax oil, etc), and a source of omega-3s (fish oil caps, or a serving of omega-3 rich fish like salmon). Let’s say from this, I take in 50 grams of fat. There are 9 calories per gram of fat, leaving us with 450 calories here.
That gives me a total of 975 calories, while I am shooting for 1600! I need 625 more. This is where I add my carbs and I toy around with the other macro-nutrients too. As an average, I would say 200 grams of carbs is a good number for an active individual. I have gone much higher myself though.
At any rate, once I calculate my proteins and fats, I fill the deficit needed to reach my caloric goal with carbs. It tends to be very personal and goal dependent from this point forward. If I am going to do a lot of running, HIITs, I would load up on carbs, especially close to my workouts. Carbohydrates are a common source of energy in living organisms and active people can benefit from carbs. Nutritionists often refer to carbohydrates as either simple or complex. However, the exact delineation of these categories can be ambiguous and there are lots of heated debates on no/low/normal carb diet among experts and even amateurs.
If you are truly interested in and would love to learn more about this subject, there is a good book to read: Good Calories, Bad Calories: Fats, Carbs, and the Controversial Science of Diet and Health by Gary Taubes.
Hope this helps and please feel free to share your own knowledge/experience on this with us~~!