Estimating Energy Needs for Weight Loss

Components of Energy Out

Energy expenditure refers to the use of calories after they have been consumed. There are four components of energy expenditure:

1. Resting Metabolic Rate (RMR)
2. The Thermic Effect of Feeding (TEF)
3. The Thermic Effect of Activity (TEA)
4. Non-Exercising Activity Thermogenesis (NEAT) 

RMR

The Resting metabolic rate (RMR) is the total number of calories burned when the body is completely at rest. RMR is proportional to lean body mass and decreases approximately 0.01 kcal\min for each 1% increase in body fatness. RMR also declines with age: 2% and 3% per decade for men and women, respectively, due to a loss in lean body mass.

RMR represents as much as 75% of total energy needs, making RMR the majority of daily energy expenditure, over the other contributions from thermic effect of feeding (TEF) and thermic effect of physical activity (TEPA) around 10% and 15 – 30% respectively.

TEF

TEF refers to the energy it takes to digest, absorb, transport, metabolize, and store nutrients. Since TEF is estimated at 10% it is rarely calculated into energy estimation equations.

The most common methods for estimating Resting Energy Expenditure (REE) come in a variety of equations with a good range of predictions.

There is also many handy REE calculators online (REE and RMR are interchangeable).

TEA

The thermic effect of activity (TEA) accounts for the most variability of daily energy expenditure. TEA includes energy expenditure due to physical work, muscular activity, as well as planned and structured exercise. Regular and sustained physical activity, both acute and chronic, helps to maintain a healthy body weight and raise RMR.

NEAT

A more specific component of TEA is referred to as NEAT, or non-exercise activity thermogenesis. NEAT is the energy expended for everything we do that is not sleeping, eating or exercising. It is the energy we consume during daily activities, including walking at work, typing, walking to and from meetings and fidgeting. Daily NEAT is any physical activities that may increase metabolic rate, even for a brief period of time, that are not part of structured exercise. 

Those with more active lifestyles tend to have a better energy balance. Research seems indicate that NEAT can be a critical component in how an individual can either maintain body weight, develop obesity, or lose weight. Combine an active NEAT lifestyle with spontaneous and planned activities, like biking instead of driving or taking the stairs can really make an impact on caloric expenditure.

TEPA

The thermic effect of physical activity (TEPA) is the energy a person uses for physical work outside of BMR. Once REE is estimated we can begin to approximate TEPA. We can calculate based on specific activity, or use the Activity Factor both shown below.

To calculate:

1. Multiply weight by “cal/min/pound”
2. Multiply the number from step 1 with the number of minutes spent doing the activity.

Take the REE numbers and multiply it by the Activity factor (AF) to calculate total energy needs. For example, if 1,463 – 1,536 represents my REE range and I identify as a “Low Active” woman, the equation would look like this:

1. 1,463 (REE) x 1.12 (AF) = 1,639 cal/day
2. 1,536 (REE) x 1.12 (AF) = 1,720 cal/day