Many of us now work at desk jobs which require the expenditure of very little physical energy but need a lot of mental concentration. This sedentary lifestyle could certainly be adding to the overweight/obesity increases occurring in the UK and beyond. If we take in more calories than we use then the excess is stored in the body and our waist-lines expand. However, a very interesting study(1) has just been published which suggests that desk-jobs requiring mental, but not physical, activity could be affecting our body chemistry in ways that may lead to our overeating. If this extra energy consumption is not then expended through exercise it can lead to weight gain.
An earlier, preliminary, study(2) by the same authors last year found that knowledge-based work, sitting for 45minutes reading a document and writing a 350 word summary using a computer, required an average of only 3 calories more energy than resting in a sitting position for 45minutes. However, after the knowledge-based work individuals consumed 229calories more (at an unrestricted buffet) than after 45 minutes rest. According to the assessment questions, markers of appetite sensation had not changed between the two sitting conditions. In addition to this, the test subjects did not compensate by decreasing food intake or increasing energy expenditure for the rest of the day.
The researchers wanted to look deeper at the phenomenon and hence their most recent study(1). In this small experiment the researchers investigated 14 women (who were not over- or underweight). Each individual went through the following 45minute test ‘conditions’
-Resting in a sitting position
-Reading a document and writing a summary on the computer
-Performing a number of different computerised tests
The blood (plasma) glucose levels, insulin levels and cortisol (a hormone) levels were measured seven times during each experimental condition. Appetite sensations were also measured via a questionnaire and following the tests there was a buffet where the participants could eat what they liked.
After the reading/writing test the individuals ate, on average, 203 calories more than they did after rest. After the computerised tests they ate an average of 254 calories more than they did after a 45minute rest. There was no difference in the appetite sensations recorded among the three different test conditions. In summary the study(1) showed that knowledge-based mental work induces significant increases in calorie intake which could, over a long-term period, be a risk factor for overweight.
The interesting point is that there was also a difference between the body chemistry measured. The average cortisol levels were significantly higher in the two knowledge-based work conditions (the reading/writing and computerised test) compared to the rest condition. There was also a significant increase in variations in glucose and insulin levels compared to rest. These biochemical markers can provide insight into why mental work can induce overeating. They also present possible solutions!!
The fluctuating cortisol, glucose and insulin levels could be the trigger for over eating. Cortisol is often known as the stress hormone. Under periods of pressure our cortisol levels rise and there is suggestion that high levels can unbalance blood sugar control in the body (which has knock-on effects for the amount we consume). The fluctuating glucose and insulin levels may well be contributing to over-eating. The body is a very clever machine! Our brain uses glucose in order to function, so perhaps the fluctuations are triggering increased food intake. The problem is that; since we are not increasing physical activity there is a calorie over compensation and the extra food we take in to balance out the blood sugar fluctuations is not expended by increased physical activity.
Personally I think the key for desk-based workers is to try and provide the body with a slow and steady supply of energy throughout the day, this should prevent the blood sugar fluctuations which may be leading to over-eating. My advice would be to start the day with a breakfast containing a protein source e.g. an egg/nuts/seeds/yoghurt (be wary of low fat yoghurt as these are often packed full of added sugar) together with some unrefined carbohydrate which releases sugar slowly (one that has a low glycaemic index) such as oats or some fruit salad. If you can avoid caffeinated tea or coffee then this could also help. The caffeine can disrupt blood sugar balance. The lunchtime sandwich often leads to a mid-afternoon energy slump that leave us reaching for a sugar fix. Bread is starchy and releases sugar very quickly into the bloodstream. The body responds with a surge of insulin which can cause a subsequent sugar low a few hours later at mid-afternoon and consequent feelings of lethargy. It may be preferable to try basing your lunchtime meal around a portion of protein (unprocessed meat, fish, eggs, beans) together with 2-3 portions of vegetables/salad. This kind of meal will provide the body with a steady source of energy throughout the afternoon. If you do find your energy levels dropping try eating a few unsalted/un-blanched nuts.
Desk work needn’t cause havoc with our waistlines! Of course, trying to take some kind of daily exercise is also very important. Even a half hour walk or taking the stairs, it all helps. Exercise also helps to regulate appetite and food intake. A holistic approach is certainly the way to go!
(1)Chaput JP et al. 2008. Glycemic instability and spontaneous energy intake:association with knowledge-based work. Psychosom Med. [E-pub before print August 25 ] doi:10.1097/PSY.0b013e31818426fa
(2)Chaput JP&Tremblay A. 2007. Acute effects of knowledge-based work on feeding behavior and energy intake. Physiol Behav. 90:66-72
Written by Ani Kowal