Wednesday, May 30, 2012

Calories in = Calories out? Factor Affecting the Energy Balance Equation

Calories in = Calories out? Factor Affecting the Energy Balance Equation
Jennifer Koslo, PhD, RD, CSSD, CPT
FT Faculty: Health & Wellness & Nutrition Dept

When I first started my career as a cardiac dietitian, I memorized the Harris Benedict equation, which is a long mathematical equation for calculating the resting energy expenditure for men and for women.  Resting energy expenditure (RMR) is the number of calories that a person needs to stay alive while resting. RMR accounts for about 60-75% of total daily energy expenditure so it is important that the equation used to estimate this number is pretty accurate. While Harris Benedict has been around since 1919 and is generally considered to be the gold standard, The Mifflin-St. Jeor Equation created in 1990 has a smaller overall margin of error and is consider most accurate for the average US population. If you have ever calculated your energy needs using an online tracking system like, MyFitness or the government tool, then you most likely entered your height, weight, gender and age and a number was spit out stating that you need XXXX calories per day. This number was most likely calculated using one of these formulas. However, similar to how the calculation for BMI (Body Mass Index) does not account for lean and fat mass, neither do either of these RMR equations. There is another formula you can use if you have these numbers, the Katch-McArdle formula, but accuracy still depends on a correct measurement of body fat percentage.

So why am I telling you all of this math mumbo jumbo? Because energy balance is so much more than calories in = calories out. On top of the calories needed to sustain life, we burn calories in our day to day activities, through food digestion and in physical activity. A couple of important points here: The American College of Sports Medicine recommends 2000 calories of exercise per week for weight loss and 1000 per week to improve health. When people start a weight loss and exercise program they often have that 1000 calorie number on their minds which might mean about 2-3 hard spin classes a week not realizing that they need double that for weight loss.

In light of all of these challenges, why not shift your initial focus away from calorie goals and number of calories burned in structured physical activity to your NEAT (nonexercise activity thermogenesis) activities throughout the day. NEAT calories can vary drastically from one individual to another and can add up quickly. Think things like fidgeting, walking to the bathroom at the very end of the hall, taking several walk breaks throughout the day, chopping vegetables and cooking instead of going through the drive-thru, etc. Simply list your typical Monday-Friday schedule on a log similar to this:

Midnight-06:30 am
06:30-07:30 am
Preparing for work
Continue with your schedule

Use this information to identify the problematic areas of your day, i.e. times when you are sedentary for long periods of time, and challenge yourself to get moving more.  You might be surprised how increasing your NEAT is just the boost your metabolism needs to jump start your weight loss or break out of that plateau. Hopefully you will find that the more you move the more you will want to move!


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