The Obesity Paradox

According to research, obesity is to a certain extent genetically determined. The pandemic now affects a billion people and has gradually grown over the last 150 years. Interestingly, our genes have not changed over that period. So how could obesity, which is genetically determined, have appeared over a time when our genes have remained unchanged? What has changed?

Well, over 150 years ago 90% of the population lived an agricultural lifestyle. They walked to work, performed active physical work, walked home after work. Water had to be carried and clothes washed by hand. Our lifestyles were much more similar to those of our distant ancestors in that, we stood and walked for most of the day.

With the advent of industrialisation and urbanisation 50% of the world’s population moved to the cities. This figure is even higher in developed countries. Factory work became prevalent and chair-based work replaced standing just like machine operation replaced tool use. The biggest change has taken place over the last 25 years…over half the population in the developed world now sits in front of a computer for 8 hours a day. As a result of these changes, our occupational energy expenditure could have decreased by as much as 1200 kcal/day.

At home most of us have a personal computer and we spend a few more hours banking, shopping, browsing and even socialising (Facebook, Twitter, MySpace, etc)! Oh, and if we’re not sitting in front of the computer it’s probably the television…another brilliant invention that appeared in the last century. Sales of labour-saving devices like washing machines, dishwashers and cars track obesity rates and it’s estimated that mechanisation saves  around 111 kcal/day.

Obviously food has become more available (in industrialised countries) and one could assume that our intake has increased. Surprisingly, in the UK since the 1980s, energy intake seems to have decreased whereas obesity rates have doubled! Statistics in the US show that intake hasn’t changed but obesity has skyrocketed…

Here’s a quick thermodynamics refresher…when energy is added to a system it’s either used to perform work or stored…if the energy intake is greater than the energy expenditure, the excess is stored as fat…if the energy imbalance continues over several months or years it leads to obesity. It’s becoming clear that it’s the decrease in our activity that has lead to the weight gain.

How come we haven’t all been affected by this? This is where the genetics plays it’s part. Those of us that are genetically programmed to conserve energy have blossomed in this new modern environment, the rest have found other ways to replace their need for movement: walking or cycling to work, pacing about at work, getting involved in DIY at home, going to the gym or taking part in sports or active hobbies. Crucial research shows that lean sedentary people stand and walk for about 2.5 hrs/day more than obese people. If obese individuals were to stand and walk 2.5 hrs more each day it would equate to an expenditure of 350 kcal/day which is exactly the figure that was identified in a different study to determine the amount of exercise that obese people had to undertake to help weight loss.

Why should we care about obesity? Perhaps because it’s been linked to type 2 diabetes, hypertension, stroke, arthritis, sleep apnea and cancer…maybe because obesity related medical expenses are out of control and  in the US they reached $75 billion in 2003!

What’s the best way to lose weight? Is it through exercise or non-exercise activity? Or both? According to Dr Levine, the majority of people who exercise for just under 2 hours a week expend an average of about 100 kcal/day. This is a drop in the ocean compared to what it’s possible to achieve by increasing non-exercise activity. Granted, we can’t all change our jobs and become lumberjacks or tree surgeons but we can become more active both at work and at home. Our muscles are almost completely silent when seated and as a consequence, our energy expenditure is negligible…our expenditure goes up 15% when standing and doubles when ambling…purposeful walking can double or triple it! So, spending less time sitting seems to be the key to burning up more calories.

Prolonged sitting time has been linked to metabolic syndrome, type 2 diabetes, obesity and cardiovascular disease. This is thought to be the result of poor fat metabolism due to the decreased production of lipoprotein lipase in muscles when seated. Non-exercise activity reverses this process.

It appears our technological innovations have had insidious effects on our health. The antidote lies in freeing ourselves from the chair…can we afford to wait for governments and corporations to reengineer our workplaces? Probably not…we must all take responsibility for our health and those among us that have a predisposition towards energy conservation need to take active measures by simply standing and walking about more often and for longer periods during the day.

Most of the information in this post is inspired from the work of Dr James Levine, Professor in the Department of Endocrinology at the Mayo Clinic in Rochester MN