Tag Archives: energy expenditure

Are We Fat Because We Eat Too Much, Or Lack Physical Activity?

Are we fat because we eat too much, or lack physical activity?

Most people would say, “It’s both.” Most people would be wrong, at least in terms of populations rather than individuals.

Obesity results from a protracted imbalance between energy intake (calories we eat) and energy expenditure (physical activity and resting metabolism).

Overweight and obesity have increased significantly over the last 25 years in most of the developed world. Is it because we started eating more, or that we have so many energy-saving devices that we now expend less energy on physical activity? If we are less active due to technologic advances, yet keep eating as much as in the past, we will gain weight as the excess calories are stored as fat.

Technologic advances over the last 150 years have allowed us to transform from a labor-intensive agrarian economy to one based on services and information. Computers, in particular, have made it much less labor-intensive to get our jobs done. For example, when I was a hospital intern 30 years ago, I made multiple daily trips from the patient care floors downstairs to Radiology to look at x-ray films. Now, the “films” are at my fingertips on computers close to the bedside.

Have trends in technology over the last 25 years continued to reduced the energy expenditure needed to get through our days? Alternatively, are we exercising less? Either explanation would lead to weight gain if caloric intake remained the same.

Researchers in 2008 studied populations in Europe and North America, examining trends in physical activity energy expenditure over time, since the 1980s. Energy expenditure was evaluated with a highly accurate method called “doubly labelled water.” They found that physical activity energy expenditure actually increased over time, although not by much. They conclude that the ballooning waistlines in the study populations are likely to reflect excessive intake of calories.

(All I have is the abstract of the article. I’ll try to get the full article and report back here if anything additional is interesting.)

So according to Westerterp and Speakman, the problem has not been lack of physical activity. We’re simply eating too much.

On the other hand, a 2011 study found that daily work-related energy expenditure decreased by over 100 calories in the U.S. over the last 50 years.  That could certainly contribute to our expanding waistlines.

Steve Parker, M.D.

Reference: Westerterp, K.R., and Speakman, J.R. Physical activity energy expenditure has not declined since the 1980s and matches energy expenditures of wild mammals. International Journal of Obesity, 32 (2008): 1256-1263. Published online May 27, 2008. doi: 10.1038/ijo2008.74

Are We Fat Because We’re Less Active Now?

Less active

Much of the globe has seen a significant decline in populaton-wide physical activity over the last few decades, according to Nike-sponsored research reported in Obesity Reviews.

Countries involved with the study are the U.S., U.K., Brazil, China, and India.  How did they measure activity levels?

Using detailed historical data on time allocation, occupational distributions, energy expenditures data by activity, and time-varying measures of metabolic equivalents of task (MET) for activities when available, we measure historical and current MET by four major PA domains (occupation, home production, travel and active leisure) and sedentary time among adults (>18 years).

The authors note the work of Church, et al, who found decreased work-related activity in the U.S. over the last half of the 20th century.

Inexplicably, they don’t mention the work of Westerterp and colleagues who found no decrease in energy expenditure in North American and European populations since the 1980s.

More active

My gut feeling is that advanced populations around the globe probably are burning fewer calories by physical activity over the last 50 years, if not longer, thanks to technologic advances.  We in the U.S. are also eating more calories lately.  Since the 1970s, average daily consumption by women is up by 150 calories, and up 300 by men.  Considering both these trends together, how could we not be fat?

Steve Parker, M.D.