BMR and Weight

                           Role of BMR in maintaining your weight

BMR refers to the number of calories his or her body burns while at rest. Typically, a person's BMR is the largest portion of energy use, representing two-thirds to three-quarters of the calories used each day. The higher a person's BMR, the more calories that individual burns off without engaging in any physical activity.

Ø  Hormone like thyroxin has also impact a person’s basal metabolic rate. If a person does not produce a sufficient quantity of thyroxin, his or her BMR will slow. If too much thyroxin is produced, these rates can increase by as much as 100 percent.

Ø  Genetics- Some people are born with faster metabolisms; some with slower metabolisms.

Ø  Gender- the more lean body mass a person has, the higher his or her basal metabolic rate can be. Conversely, as body fat percentage increases, basal metabolic rate decreases. 

Ø  Age-After the age of 20, basal metabolic rate tends to decrease by about two percent each year. If calorie consumption remains constant but exercise levels do not increase, weight gain will occur as basal metabolic rate declines with age.

Ø  Height and Weight-The bigger you are, the more calories your body needs to keep on breathing

Ø  Muscle tone-Muscle does burn more calories at rest than fat. Thus, regular strength-building exercise makes it a lot easier to maintain the weight loss one can achieve through cutting calories.

Ø  Diet- Starvation or serious abrupt calorie-reduction can dramatically reduce BMR by up to 30 percent. 

Ø  Body Temperature/Health- For every increase of 0.5C in internal temperature of the body, the BMR increases by about 7 percent.

Ø  External temperature- Temperature outside the body also affects basal metabolic rate. Exposure to cold temperature causes an increase in the BMR, so as to create the extra heat needed to maintain the body's internal temperature.

Ø  Exercise- Physical exercise not only influences body weight by burning calories, it also helps raise your BMR by building extra lean tissue.

             How to Calculate Basal Metabolic Rate (BMR) 

        The first step in designing a personal nutrition plan is to calculate

ü  how many calories you burn in a day;

ü   Your total daily energy expenditure (TDEE). TDEE is the total number of calories that your body expends in 24 hours, including all activities.

ü  Adjust your calorie  intake now-To lose weight, you need to create a calorie deficit by reducing your calories slightly below your maintenance level (or keeping your calories the same and increasing your activity above your current level)

ü  Example 1:
Your weight is 120 lbs.(54.43kg)
Your TDEE is 2033 calories
Your calorie deficit to lose weight is 500 calories
Your optimal caloric intake for weight loss is 2033 - 500 = 1533 calories

ü  Example 2: 
Your calorie deficit to lose weight is 20% of TDEE (.20% X 2033 = 406 calories)
Your optimal caloric intake for weight loss = 1627 calories

ü  Selection of food for calorie balance: Some foods do get stored as fat more easily than others, but always bear in mind that too much of anything, even "healthy food," will get stored as fat. You cannot override the laws of thermodynamics and energy balance. You must be in a calorie deficit to burn fat. This will force your body to use stored body fat to make up for the energy deficit.

ü  Important to know How low is too low

Reducing calories by 15-20% below TDEE is a good place to start. A larger deficit may be necessary in some cases, but the best approach would be to keep the calorie deficit through diet small while increasing activity level.

                     Some formulae to calculate BMR:

The Harris-Benedict Formula

Men: BMR = 66 + (13.7 X wt in kg) + (5 X ht in cm) - (6.8 X age in years)

Women: BMR = 655 + (9.6 X wt in kg) + (1.8 X ht in cm) - (4.7 X age in years)

Note: 1 inch = 2.54 cm.
1 kilogram = 2.2 lbs.

Example: 
You are female
You are 30 years old
You are 5' 6 " tall (167.6 cm)
You weigh 120 lbs. (54.5 kilos)
Your BMR = 655 + 523 + 302 - 141 = 1339 calories/day

Now that you know your BMR, you can calculate TDEE by multiplying your BMR by your activity multiplier from the chart below:

Activity Multiplier
Sedentary = BMR X 1.2 (little or no exercise, desk job)
Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
Extr. Active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e marathon, contest etc.)

Example:
Your BMR is 1339 calories per day
Your activity level is moderately active (work out 3-4 times per week)
Your activity factor is 1.55
Your TDEE = 1.55 X 1339 = 2075 calories/day

Katch-McArdle formula (BMR based on lean body weight)
If you have had your body composition tested and you know your lean body mass, then you can get the most accurate BMR estimate of all. This formula from Katch & McArdle takes into account lean mass and therefore is more accurate than a formula based on total body weight. The Harris Benedict equation has separate formulas for men and women because men generally have a higher LBM and this is factored into the men's formula. Since the Katch-McArdle formula accounts for LBM, this single formula applies equally to both men and women.

BMR (men and women) = 370 + (21.6 X lean mass in kg)

Example:
You are female
You weigh 120 lbs. (54.5 kilos)
Your body fat percentage is 20% (24 lbs. fat, 96 lbs. lean)
Your lean mass is 96 lbs. (43.6 kilos)
Your BMR = 370 + (21.6 X 43.6) = 1312 calories

To determine TDEE from BMR, you simply multiply BMR by the activity multiplier:

Example:
Your BMR is 1312
Your activity level is moderately active (work out 3-4 times per week)
Your activity factor is 1.55
Your TDEE = 1.55 X 1312 = 2033 calories

Best wishes:

Smriti Mishra

Registered Dietitian

www.smritimishra.com