An effective calorie intake is based on your GOAL.
That means the amount you are consuming is effectively getting you bigger or smaller, whichever is your immediate goal.
This is an intake that maintains your current weight. Once you know what intake will keep your weight the same, you can effectively increase or decrease your intake depending on whether you would like to gain or lose weight.
To get a fair idea of what is considered to be maintenance, you need to be consistent with your calorie intake over 1-2 weeks, and track your total body weight.
Initial Calorie Intake
If you have no idea what your maintenance calories are, or just want to start on a specific intake and assess results, you should start with something as reasonably high as possible. If you are trying to find maintenance, it would make no sense to start with an intake of 1400 calories if you weigh 80kg.
If that doesn’t make sense to you, basically… if you weighed 80kg and were eating 1400 calories, you would not be 80kg for much longer (unless you like binge eating on top of that intake).
Generally, a good assumption of maintenance calories (as a starting point) would be 30-33 calories per KG of body weight, assuming you are weight training. Individual adjustments or considerations are made based on lifestyle and activity levels. This is also based on how much lean body mass you have. If your body fat percentage is quite high, consider 30-33 calories per KG of your GOAL body weight as a potential healthy maintenance. Obviously, if you are seriously overweight you aren’t trying to maintain that anyways.
When you are eating in a calorie deficit (less than maintenance) with a goal to drop body fat, your body will start to adapt to your lower intake. Due to this, it is an effective strategy to include refeed days to your diet. A refeed is basically an increase in calories 1-2 days per week that puts you back (or close to) maintenance calories on those days.
An alternative or additional option is to include a diet break. This basically means after a period of eating in a calorie deficit (4-8 weeks), you move back up to your maintenance intake for 1-2 weeks. If you are not satisfied with your overall results, you can move back into a calorie deficit for further fat loss.
An effective calorie deficit is anywhere between 10-30%, however most noticeable & maintainable results are around the 15-20% mark. That means a calorie intake that is 15-20% lower than your maintenance intake.
Reverse Dieting is basically moving your calorie intake back up to maintenance in a progressive fashion so you don’t have to deal with water weight gains, or obvious visual deterioration (oh no, my abs are fading away).
If you maintain weight at 3000 calories and have been in a calorie deficit of 2400 calories, reverse dieting is basically moving up to 2600 calories, then 2800 calories…then 3000 calories, over a couple of weeks.
It can be done faster or slower based on how vain you are, basically. Or how low your calories got to in the deficit, or how long you stayed in a deficit, or how soon you want to start building muscle (moving to a calorie surplus).
None of this means anything if you aren’t consistent or don’t track your food intake. In which case, refer to “clean eating guidelines” which will put you in a calorie deficit by default (generally lower calories but higher volume foods).