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General

Didn't Oprah take this test recently on The Oprah Winfrey Show?

Yep, she did. Sweet Science uses the exact same equipment: the REEVUE indirect calorimeter, developed by Korr Medical Technologies. Incidentally, Oprah's test indicated she should consume around 1600 calories a day to lose a pound of body fat per week.

How does the test work?

The human body consumes a fixed amount of oxygen for each calorie burned. Our metabolic instrument measures this amount, recording it as you exhale into a tube. Based on your oxygen-consumption rate, it then calculates the Resting Metabolic Rate (RMR), the exact amount of calories you burn each day. This technique is called indirect calorimetry.

Once measured, your metabolic rate will be used to calculate your Target Caloric Zones. These zones identify the maximum amount of food you can eat and still lose weight.

I've just taken the test. How soon can I re-test my metabolism?

Once you've started to make lifestyle changes, your metabolic rate may improve in as little as 4-6 weeks. We recommend that you re-check it during the early stages of your weight-loss effort to ensure your regimen is aligned with your body's changing needs.

What exactly IS metabolism?

Metabolic rate, or metabolism, is the rate at which the body expends energy - it's the chemical processes that make it possible for cells to continue living. Knowing your metabolic rate is vital for weight loss, as the body gains or loses fat based on energy balance. It can make the difference between success and failure as you strive to reach your weight goal.

Our bodies burn calories for different things:

Resting Calories: Calories burned while the body is at rest. These calories are needed to maintain life, and they constitute the majority of all calories burned (roughly 70-80%). Metabolic testing measures your resting calories, or RMR (Resting Metabolic Rate).

Activity Calories: Calories burned during normal daily activities. These include walking, eating (digestion), typing etc. The amount of calories burned to digest food is called TEF (Thermic Effect of Food), and accounts for approximately 10% of your total metabolic rate.

Exercise Calories: These calories are burned during exercise.

The sum of all of these calorie groups is your total metabolic rate.

How is metabolism measured?

There are currently only two ways to measure your metabolism:

  1. Direct Calorimetry: Monitoring the amount of heat produced by a subject placed inside a room large enough to allow moderate activity. This method measures the energy expended in the form of heat. It's typically expensive and requires special facilities.

  2. Indirect Calorimetry: Measures the amount of oxygen consumed over a period of time. Traditionally used in hospital and research facilities due to the cost of the machine and the need for trained technicians, this method has recently been simplified to be offered in a medical office setting.

How does Sweet Science Nutrition measure metabolic rate?

Our metabolic-rate measurements are performed using the REEVUE indirect calorimeter. The REEVUE is a simplified version of the machine used in hospitals. It has been validated against the standard metabolic cart and has demonstrated equivalent accuracy in measuring both oxygen consumption and resting energy expenditure.

What about calculating metabolic rate by plugging my height, weight, gender and age into a formula?

Several equations have been developed to calculate how many calories we need in a day. The most common is the Harris-Benedict equation, introduced almost a century ago, in 1919. Unfortunately, it can overestimate the RMR by as much as 24%.

More recent equations correct this overestimation, but they still result in an unexplained variability of up to 30% among individuals, owing to individual differences in metabolic efficiency.

Furthermore, applying any of the estimative equations to people who are 25% or more over their ideal body weight will overestimate their RMR. The bottom line is, estimative equations are nothing more than an educated guess.

What factors affect metabolic rate?

The following factors can increase RMR:

  • Higher amount of muscle mass
  • Habitual exercise
  • Hyperactive thyroid (This can result in as much as twice the RMR.)
  • Epinephrine hormone, released during periods of emotional or physical stress
  • Fever
  • Extreme environmental temperature (In tropical areas, RMR is 20% higher than in temperate climates. In cold areas, RMR depends on the body's ability to insulate from the cold.)
  • Pregnancy (due to fetal and tissue growth and the mother's increased cardiac work)
  • Periods of growth (infancy through adolescence)
  • Higher protein intake slightly increases the thermic effect of food (TEF)
  • Eating followed by exercise doubles the TEF
  • Caffeine and nicotine (although the effect is temporary and neither substance is recommended for use due to their addictive properties)

Other factors affecting metabolic rate are:

  • Body composition (Higher body fat = slower metabolism).
  • Hypoactive thyroid (Low thryroxine level can slow down RMR as much as 30-50%.)
  • The menstrual cycle can make as much as a 359-calorie difference (The low point is 1 week before ovulation, and the high point just before the onset of menstruation).
  • The presence of cortisol, growth hormone and insulin, depending on their interactions in the body.

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