By Tom Johnson

It is common knowledge that this country is in the midst of an obesity epidemic.  In fact, the weight of the average person in the United States has risen by about 25 pounds since the 1970s.  Because obesity has tremendous health and economic costs, much effort has been given to understanding why we are gaining weight and what we can do to counteract the obesity epidemic.  This effort has led to the mantra that we need to eat healthier diets that have fewer calories and increase our levels of physical activity.  However, while physical activity is an important facet of a healthy life style,  it is not obvious what type of physical activity is the most effective  for managing body weight.

In order to understand the role of physical activity in weight management, it is important to understand some basics about how the body produces and utilizes energy.  The calories in the food we eat are ultimately converted into energy by a component of cells called mitochondria.  Some of the energy produced by mitochondria is in the form of a chemical compound called ATP, which stands for adenosine triphosphate.  The ATP produced by mitochondria is used to power cellular processes.  Food calories that do not end up as ATP are converted to heat by the mitochondria.    The calories in food that are not converted to ATP or heat end up as energy stored in body fat.  Because nature requires that energy be conserved,  the total calories consumed in food must equal the sum of total body energy in ATP, heat and body fat.  Thus, when caloric intake from food becomes greater than the energy expended as ATP and heat, body fat increases because the excess energy will be stored as fat..  Conversely, if calories obtained from food are less that the energy expended as ATP and heat, body fat will decrease because the energy stored in fat will be used to compensate for the difference between caloric intake and energy expenditure.    Physical activity causes muscles to work harder and this requires mitochondria in muscles to increase their ATP production in order to meet the increased need for energy.   However, when physical activity increases, mitochondria generate not only more ATP to meet the energy demands of muscles, they also generate more heat.  The heat produced by mitochondria during physical activity has an important role in managing body weight by maintaining the balance between caloric intake and energy expenditure.

The heat generated by mitochondria during physical activity can be divided into that generated by exercise, which is called exercise activity thermogenesis, and that generated by nonexercise activity, which is called nonexercise activity thermogenesis or NEAT.  Exercise activity is what we do for physical fitness, like working out in a gym or distance running.  Nonnexercise activity is what we do during everyday living.  For the average American, the time devoted to exercise is about two hours per week which amounts to a total energy expenditure of about 100 Calories per day.  However, researchers at the Mayo clinic have determined that NEAT is capable of producing energy expenditures of about 2000 Calories per day.  The amount of energy expenditure by NEAT is quite variable and can account for 15-50% of daily energy expenditure depending on the activity level.  Thus, NEAT can be a very important factor in the management of body weight.

The question is - how can people take advantage of NEAT for losing weight or preventing weight gain?  Unless you have a job or recreational pursuit that requires vigorous activity, weight management by NEAT requires some lifestyle changes.  Most of us have jobs that require us to sit more and move less.  Thus, one change we can make is to sit less and move more in spite of our jobs.  Simple physical activity like a leisurely stroll, which utilizes about 3 Cal per minute, climbing stairs, which utilizes about 4 Cal per min, and standing which utilizes about 1.5 Cal per minute can be beneficial.  The more time you spend doing simple physical activities associated with daily living, the greater the benefit you will get from NEAT.  For instance, if you can increase the time you spend leisurely walking by one hour, your energy expenditure would increase by 180 Cal.  If you did this every day your energy expenditure would be 1260 Cal per week.  This is much higher that the energy expenditure of 100 Cal per week expended by the two hours that the average person spends exercising.  While exercise activity is great for strength and heart health, increasing nonexercise activities in everyday living may provide the most benefit for weight loss.  So, if you are physically able, walk the course instead of riding a golf cart, take the stairs instead of the elevator and shovel instead of blowing light snow.  The bottom line is, create small increments of energy deficit by increasing daily nonexercise activities and let NEAT help you manage your weight.