One of the first things you need to do if one of your health goals is to lose weight, gain weight or maintain your weight is to calculate the number of calories you need to be eating on a daily basis.
The reason this is so important is because if you have no idea how many calories your body needs to maintain itself, nor have any idea how many calories you are consuming, you could very easily gain or lose weight over a short period of time. If your goal is to maintain your weight you are going to want to eat about the same amount of calories that your body burns each day so as to stay at a homeostasis level.
If your goal is to lose weight on the other hand, then after you have figured out how many calories your body requires, you will want to eat less than this in order to get your body using up its fat stores for energy. This miss-match in energy levels can either come from more exercise added to your day in order to increase the amount of calories you are burning or else by a reduced food intake. Most people choose to use a combination of both to make things a little easier. This is better also because generally it's not a good idea to reduce calories too low otherwise you risk not getting enough nutrients, plus adding exercise into your diet while dieting will help ensure that you maintain as much lean muscle tissue as possible.
When trying to lose weight, the safest decreases in calories are 250 to 500 calories. This will yield a weight loss of ½ pound to one pound per week, which is nice and slow so the weight should stay off. The more overweight an individual is normally the more calories they can reduce without risking the loss of muscle mass since they have more body fat stores they can call upon. The most a person should ever aim to lose though is 2 pounds a week. Anything more, unless they are extremely obese, is not going to be a safe.
If your plan is to gain weight, then you will be basically doing the opposite of those trying to lose weight, adding more calories than your body burns so you can create new muscle tissue. You must accept the fact though that there is a good chance that your body may gain some fat mass along with the new muscle, this is natural and is expected. As long as you don't go eating a ton of junk food, consuming hundreds of calories over your needs than it shouldn't be too big of an issue for you. You will want to stay within the same guidelines as for weight loss, eating about 250-500 calories more than your body needs. Make sure you are including strength training exercise along with this extra food as well, as this will provide your body with the stimulus it needs in order to develop the muscle tissue.
Figuring Out Your Numbers
Now, for figuring out the actual raw number of calories you need you must keep in mind that all equations are guidelines only. Everyone will be slightly individual and will likely have to adjust the number based on real world results, however using them will provide a rough estimate where to start from.
The most popular way to estimate is a formula called the Harris-Benedict equation and is shown below.
Males: 66 + (13.7 x W) + (5 x H) - (6.8 x A)
Females: 655 + (9.6 x W) + (1.7 x H) - (4.7 x A)
where W = actual weight in kg (weight in lb/2.2 lb/ kg)
H = height in cm (height in inches x 2.54 cm/in)
A = age in years
By putting your numbers into this equation you will have a rough idea of how many calories your body would need if you were to lie in bed all day and do nothing else. Basically this is what you need to eat in order to keep your body alive. Obviously no one is going to just lie in bed all day and breathe so next you need to add activity factors.
Activity factors are a rough representation of how many additional calories you need to consume on top of what it takes for your body to function. This is highly variable, both within individuals and on a day-to-day basis as you may be very sedentary one day and highly active the next. The common energy multipliers are:
1.2 if you are sedentary (work a desk job)
1.35 if you are lightly active (light exercise 1-3 days per week)
1.5 if you are moderately active (exercise 3-5 days per week)
1.65 if you are very active (exercise 5-7 days per week)
1.8 if you are very active plus have a labour intensive job.
So taking the number you came up with above, you would then multiple this by your activity factor to get your new number. Note that the true best way to approximate this number would be to actually break down the activities you do and find out how many calories you burn during each of them and then add them up, however this would be quite time consuming in nature and is likely not something most people would be willing to do.
Lastly you will have the thermodynamic effect of food. This represents how many calories it takes for your body to break down the food you are consuming. A good average to use here is 10% of the total number of calories you consume.
It should be stated though, that those who are consuming a high protein diet will likely burn more than this 10% number while those on a high fat diet will consume less. The body often requires up to as much as 30% of the total energy consumed when breaking down protein while it only needs 2-3% of the energy consumed to break down fat. This means that if you ate 100 calories of protein, you will only consume a net of about 70 calories. If you consume 100 calories of fat though, that will leave you with a net intake of about 97 calories. So as you can see, this is one significant advantage to those who are eating high protein diets. Furthermore, carbohydrates lie somewhere in the middle, with about 10-15% of the energy being used to break them down.
So after you have figured out all three of these numbers, add them together to get your total calorie intake. This is the number that you should now manipulate, depending on what your specific goal is. If you want to maintain, try and eat exactly that number of calories per day. If you want to lose, eat less and if you want to gain, eat more.
Remember once again though that these numbers are approximations and you may need to adjust further as you go along based on the results you see. BMR can vary with individuals depending on their current life circumstances. For example, younger individuals tend to have higher BMR's because their body is still growing and requires more calories for this process. Taller, thin people also have higher BMR's as do those who carry a great deal of muscle mass and are very lean.
If you get sick with a cold, your BMR is going to go up slightly as your body will require extra energy to help fight off the infection or virus and if you have been on a reduced calorie diet for a period of time you will find that your BMR may be slightly sluggish for a short period of time as the body has slowed down its metabolism in order to adapt to the fact it is being given less food (tries to accommodate to this so that it can prolong starvation).
So before you start your next diet, take the time to figure out your calorie needs. While it may be slightly time consuming to do this and track your food, when it comes to getting results, you run a much higher chance of seeing positive results if you do expend this extra effort.