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For example, if I use one of these calculators that tells me how many calories to eat, if I put in that I am sedentary it tells me to eat (for example) 2000 calories. If I put in that I'm moderately active and work out 3 times a week it tells me to eat (f. ex.) 2300 calories.

For example, this calculator from the Health Weight Forum recommends almost twice as many calories for someone working out heavily than someone who is sedentary. And it recommends this for losing weight.

This doesn't make sense to me, if I go from being sedentary to becoming very active, surely I would want to eat around the same amount of calories so as to lose weight? Why do calorie recommendation calculators advise me to eat more calories when working out even if my intention is to lose weight? Why would I want to eat more?

And it seems to imply that it makes sense to exercise less and eat less.

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I for one stopped eating more and it seems to work pretty well for me ;-) –  Ivo Flipse Mar 30 '11 at 12:08
1  
You can try it and if you feel low on energy, just eat more. –  rmx Apr 5 '11 at 12:22

4 Answers 4

up vote 15 down vote accepted

Calorie calculators calculate how many calories you need to consume to remain the same weight. If you are active it means you burn more calories during the day, thus you need to consume more calories to remain the same weight. If you'd like to lose weight you should eat less calories then what is recommended (not substantially though).

The key point here is 'you need to consume more Calories to remain the same weight.' To lose weight you need to eat less than that number. The technical term for this is called your 'caloric expenditure' or 'energy expenditure'. What it means is, to lose weight you need to be eating fewer Calories than your 'energy expenditure'.

Generally, one pound of stored fat is equal to about 3500 kcal (or 1kg is ~7000kcal).

As an example. Lets say your 'energy expenditure' is 2000 kcal and you consume exactly 2000 kcal a day (Ie, you neither gain/lose weight). Then you start doing a moderate workout that increases your caloric expenditure to 3000 kcal a day but maintain the same diet. How much body fat mass should you expect to lose in a week?

Well, since you're burning 1000 kcal more than your eating:

(days * (caloric intake - energy expenditure)) / 3500 = lbs of fat burned/week 

or...

(7 * (2000 - 3000)) / 3500 = 2 lbs of fat/week

This is an over-simplification because as you gain more muscle mass your caloric expenditure will go up even if you aren't working out and not all exercises are equal but, that's the gist.

For more specifics on setting goals to lose weight without negatively impacting health be sure to take a look at 'What is a Reasonable Rate of Weight Loss to Work Towards'.

Here are some links about what exactly 'caloric expenditure' and 'energy expenditure' define.

Here's a table that shows the caloric expenditures for different types of activities.

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+1 Good answer. –  Evan Plaice Mar 30 '11 at 15:50
    
@BuffaloBuffalo Could you edit "Lets say your BMI" to "Lets say your BMR"? I missed that typo before I submitted the edit... –  Evan Plaice Mar 30 '11 at 16:54
    
Very detailed answer. The definition of BMR is off though. I think for the most part you just mean energy expenditure, which is the sum of BMR, thermic effect of food, and physical activity level (PAL). BMR only refers to the very base level of energy expended at rest. Aerobic exercise does cause a short-term increase in BMR and, as you mentioned, strength training causes a long-term increase in BMR, but when you're talking about burning calories during exercise, you're usually talking about PAL, not BMR. –  Barbie Mar 30 '11 at 17:22
    
I think you meant BMR instead of BMI above. –  edgester Mar 30 '11 at 17:25
    
@edgester Yea... I know, look at the comments. Unfortunately, I don't own the answer and 1 character edits aren't allowed. Damn typos... –  Evan Plaice Mar 30 '11 at 17:36

The issue is nutrients. Simply reducing calories for an inactive person may reduce weight, but an active person is burning more calories through different processes and will require more nutrients. So if you remain active but don't ingest enough calories, the weight you lose will not be safe. In fact, your body will start breaking down muscle tissue to get the nutrients that you're not eating. So would you rather be lighter and flabby or lighter and more energetic with nice healthy muscles? Simply put.

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Old school thought is that you want to reduce eating and increase exercising to reduce fat - this is true in the short term. HOWEVER to gain long term advantage, you need to ensure that your metabolism is in high gear and burning fat. The problem with fad diets, fasting, etc. is that your metabolism will slow down if you continue to reduce calories - aka starvation mode.

My recommendation is to use the number of calories as a guide and the key to long term weight loss is proper dieting (good sound eating habits and good food) and an exercise program that you can do long term (you got your entire life ahead of you and it should include a regular exercise program).

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I've found that if you eat the same amount of calories (or close to the recommended amount if you're working out) but change the combination of what you eat, you will lose weight. I've had great success with that - swapping out much of the empty carbs I was eating for protein and complex carbs in the form of vegetables and high-fiber carbs. Futhermore, I'm rarely ever hungry (except after a really good workout).

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