The Science behind weightloss

I know that BMR, or Basal Metabolic Rate, is the starting point. BMR is the number of calories necessary to maintain weight with zero activity. This is relatively standard, though never exact, among people with the same height and "build". I'm not sure if there is a difference noted between men and women or old and young. After that, a few hundred to seveal hundred calories are added to include normal activity levels, but this varies considerably between people as some are sedentary and some are nearly hyperactive. This sum represents the number of calories an average person of given height, etc. needs to sustain his/her weight. Then one chooses a weight loss goal, Using 1 pound loss per week as an example: -3500 calories divided by 7 days per week means a daily calorie deficit of -500 is required, either through reduction in intake or increased exercise, although estimating the former is much more reliable than the latter. Hope this helps.

Basic Terminology
1/ BMR (Basal Metabolic Rate): This is the amount of calories you need to consume to maintain your body if you were comatose (base level).
2/ NEAT (Non-Exercise Associated Thermogenesis): The calorie of daily activity that is NOT exercise (eg: washing, walking, talking, shopping, working). ie: INCIDENTAL EXERCISE! It is something that everyone has a good amount of control over & it is the MOST important factor in your energy expenditure. It is what helps keep 'constitutionally lean' people LEAN (they fidget)!
3/ EAT (Exercise Associated Thermogenesis): The calorie requirements associated with planned exercise. Unless someone is doing a whole heap of exercise (eg: two or more hrs training a day) it usually doesn't add a stack of calories to your requirements (30 minutes of 'elliptical training isn't going to do it')
4/ TEF (Thermic effect of feeding): The calorie expenditure associated with eating. REGARDLESS of what myths you have been told - this is NOT dependent on MEAL FREQUENCY. It is a % of TOTAL CALORIES CONSUMED (and 15% of 3 x 600 cal meals is the same as 15% of 6 x 300 cal meals). It varies according to MACRONUTRIENT content and FIBER content. For most mixed diets, it is something around 15%. Protein is higher (up to 25%), carbs are variable (between 5-25%), and fats are low (usually less than 5%). So -> More protein and more carbs and more fiber = HIGHER TEF. More FAT = LOWER TEF.
5/ TEE (Total Energy Expenditure): The total calories you require - and the sum of the above (BMR + NEAT + EAT + TEF).

How much do you need?
There is therefore a multitude of things that impact a persons MAINTENANCE calorie requirements
- Age & sex (males generally need > females for any given age)
- Total weight & lean mass (more lean mass = more needed)
- Physiological status (eg: sick or injured, pregnant, growth and 'enhancement')
- Hormones (eg: thyroid hormone levels, growth hormone levels)
- Exercise level (more activity = more needed)
- Daily activity level (more activity = more needed)
- Diet (that is - macronutrient intake)

In order to calculate your requirements the most accurate measure is via Calorimetry [the measure of 'chemical reactions' in your body & the heat produced by these reactions], either directly (via placing a calorimeter where the heat you produce is measured) or indirectly (eg: HOOD studies where they monitor how much oxygen you use/ carbon dioxide and nitrogen you excrete over a given time). But although accurate they are completely impractical for most people & we mostly rely on pre-set formula t0 calculate our needs.

Estimating Requirements
The simplest method of estimating needs is to base your intake on a standard 'calories per unit of weight (usually kilograms)'. Typically:
- 26 to 30 kcals/kg/day for normal, healthy individuals with sedentary lifestyles doing little physical activity [12.0-14 kcal/pound]
- 31 to 37 kcal/kg/day for those involved in light to moderate activity 3-5 x a week with moderately active lifestyles [14-16 kcal/ pound]
- 38 to 40 kcals/kg/day for those involved in vigorous activity and highly active jobs [16-18 kcal/ pound].

For those involved in HEAVY training (eg: athletes) - the demand is even greater:
- 41 to 50 kcals/kg/day for those involved in moderate to heavy training (for example: 15-20 hrs/ week training) [18.5-22 kcal/ pound]
- 50 or above kcals/kg/day for those involved in heavy to extreme training [> 22 kcal/ pound]

There are then a number of other formula which calculate BMR.
1/ Harris-Benedict formula: Very inaccurate. It was derived from studies on LEAN, YOUNG, ACTIVE males MANY YEARS AGO (1919). Notorious for OVERESTIMATING requirements, especially in the overweight. IF YOU CAN AVOID IT, DON'T USE IT!
MEN: BMR = 66 + [13.7 x weight (kg)] + [5 x height (cm)] - [6.76 x age (years)]
WOMEN: BMR = 655 + [9.6 x weight (kg)] + [1.8 x height (cm)] - [4.7 x age (years)]

2/Mifflin-St Jeor: Developed in the 1990s and more realistic in todays settings. It still doesn't take into consideration the differences as a consequence of high BF%. Thus, once again, it OVERESTIMATES NEEDS, ESPECIALLY IN THE OVERWEIGHT.
MEN: BMR = [9.99 x weight (kg)] + [6.25 x height (cm)] - [4.92 x age (years)] + 5
WOMEN: BMR = [9.99 x weight (kg)] + [6.25 x height (cm)] - [4.92 x age (years)] -161

3/Katch-McArdle:Considered the most accurate formula for those who are relatively lean. Use ONLY if you have a good estimate of your bodyfat %.
BMR = 370 + (21.6 x LBM)Where LBM = [total weight (kg) x (100 - bodyfat %)]/100

You then multiply these by an 'activity variable' to give TEE. This Activity Factor[/u] is the cost of living and it is BASED ON MORE THAN JUST YOUR TRAINING. It also includes work/lifestyle, sport & a TEF of ~15% (an average mixed diet). Average activity variables are:
1.2 = Sedentary (Little or no exercise + desk job)
1.3-1.4 = Lightly Active (Little daily activity & light exercise 1-3 days a week)
1.5-1.6 = Moderately Active (Moderately active daily life & Moderate exercise 3-5 days a week)
1.7-1.8 = Very Active (Physically demanding lifestyle & Hard exercise or sports 6-7 days a week)
1.9-2.0 = Extremely Active (Hard daily exercise or sports and physical job)

So to convert BMR to a TOTAL requirement: multiply the result of your BMR by the variable you fall into!
How Accurate are they?: Well, although they give rough ball-park figures, they are still 'guesstimations' and most people still OVERESTIMATE activity, UNDERESTIMATE bodyfat & end up eating TOO MUCH. So the aim is to use these as 'rough figures', monitor your weight/ measurements for 2-4 weeks, & IF your weight is stable/ measurements are stable, you have likely found maintenance.

no confusion necessary.

so you have a base metabolic rate for your body (called Basal Metabolic Rate or BMR), this rate is how much energy your body burns to run it's basic life functions, I.E. organ function, thermogenesis, digestion, circulatory system, CNS...etc. all the things you need just to stay alive. The you add to it all the energy needed to be alive and ACTIVE, like muscle function, though processing, problem solving (believe it or not, the active brain uses a lot of energy)... Things like walking around, chewing, talking, turning your head, driving a car are all part of daily activity. Depending on how active you are daily that extra energy can be anywhere from 1.2 to 1.8 times your BMR, so someone who is sedentary at work, and doesn't do much around the house is closer to 1.2 and someone who has an active job and exercises or is very active around the house would be near around 1.6 or so, then you have your elite athletes who would be closer to 1.8 some call this AMR, others call it TDEE (Total Daily Energy Expendature, or BMR + daily activity).

MFP calculates your TDEE from what you give it in when you sign up. Then it subtracts the amount of energy from it that you request to lose (I.E. if you say you want to lose 1 lb per week, then it would subtract 500 calories per day from TDEE). Please note, how much you choose to try to lose doesn't mean you WILL lose that much, that depends on how much fat you have, how your nutrition is, how active you are, your sex, your age, genetics...etc. So there's some trial and error usually needed. But the rule of thumb is the more fat you have, the bigger the deficit you can usually have. I.E. someone looking to lose 30 lbs of fat can't have the same maximum daily loss as someone looking to lose 100 lbs (usually).

I wrote a post a while ago so you can figure out a VERY generic weight loss strategy. it's below:

http://www.myfitnesspal.com/topics/show/61706-guide-to-calorie-deficits

hope this helps,

PM me if you have questions.

-Banks

Here try this. Record what you eat for a few to 4 weeks before you start dieting and see how the scale reacts and when your weight is fairly constant that is what you require to maintain (TDEE).......eat less and you'll lose weight.

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