20th April 2011 Inactivity

Unconscious Activity

Since weight gain is about eating more calories than we exercise away, when all else is the same (weight, height, amount of exercise, calorie intake) why do some gain and some lose weight?

In a study [1] on metabolism in 2005, it was discovered, using sensors, that those who don't gain weight are subconsciously moving much more than those that do. This is called non-exercise activity thermogenesis (NEAT) which includes every day activity which isn't specifically classified as 'exercises' such as walking to work, typing, gardening, or just fidgeting [2]. It was found that the obese people sat for on average 10 hours, which was two hours longer than the lean people. [1, 4]. Farmers in Jamaica had only 5 hours sitting. They had 5000 daily  movements compared with only 1500 for the obese group.

Even when lean people gained weight or obese people lost weight, their NEAT activity was unchanged. The extra NEAT activity of the lean people could burn 350 calories a day. It is suggested that the reason for this could be biological as no change was noted with the change of lean/obesity levels.[2]  This research was done with mildly obese people. I wonder if the same holds true for very obese people losing a lot of weight since it's a lot easier to actually move when you don't have a lot of extra mass getting in the way! I also wonder if it really is biological or just a case of habits taking time to change? Research has been done on looking at the possible neural and endocrine systems that control NEAT which could perhaps indicate a way treat obesity.[3]

Well ok, so some people are 'naturally' more active than others and they burn more calories so don't put on weight. So how about I just carry on sitting a lot and exercise a bit more? Does that compensate for the sitting?

Sitting

There are several things that happen to us when we sit, apart from the obvious lowering of calorie expenditure.

•  Metabolic rate drops to around 1 per minute compared with 3 for walking about.
•  Insulin effectiveness drops (by 40%) with 24 hours of inactivity when calories intake is not reduced, increasing the risk of metabolic disease and thus type 2 diabetes. [5, 9]
•  The enzymes responsible for breaking down lipids and triglycerides drop causing  HDL (good cholesterol) to fall as well. [4]

In a study of Americans, the mortality rate of men who spend 6+ hours of their leisure time per day sitting was 20% higher than the men who sat for 3 or less hours. For women, it was around 40% higher. [4]

A recent study of Australians showed a positive correlation between the amount of time spent watching TV, indicating a sedentary lifestyle, and the overall risk of death, as well as an increased risk of cardiovascular disease.[10]

The Answer?

Apart from not sitting as much, which may not be possible in work situations, we can increase our NEAT activities by fidgeting, maybe standing up more often, or perhaps install a standing or treadmill desk.[4]

We need to look at our environment and see how we can make changes to encourage ourselves to move more. [4]

Sources

1. Science. 2005 Jan 28;307(5709):584-6. Interindividual variation in posture allocation: possible role in human obesity. Levine JA, Lanningham-Foster LM, McCrady SK, Krizan AC, Olson LR, Kane PH, Jensen MD, Clark MM (Abstract)
2. Best Pract Res Clin Endocrinol Metab. 2002 Dec;16(4):679-702. Non-exercise activity thermogenesis (NEAT). Levine JA (Abstract)
3.  J Neuroendocrinol. 2007 Dec;19(12):923-40.Central neural and endocrine mechanisms of non-exercise activity thermogenesis and their potential impact on obesity.Novak CM, Levine JA (Abstract)
4. New York Times: Is Sitting a Lethal Activity?
5. Metabolism. 2010 Nov 9. [Epub ahead of print] Effects of 1 day of inactivity on insulin action in healthy men and women: interaction with energy intake. Stephens BR, Granados K, Zderic TW, Hamilton MT, Braun B (Abstract)
6. http://scienceblogs.com/thepumphandle/2011/04/stand_up_before_you_hurt_yours.php
7. http://www.scientificamerican.com/blog/post.cfm?id=can-sitting-too-much-kill-you-2011-01-06
8. J Am Coll Cardiol. 2011 Jan 18;57(3):292-9. Screen-based entertainment time, all-cause mortality, and cardiovascular events: population-based study with ongoing mortality and hospital events follow-up. Stamatakis E, Hamer M, Dunstan DW. (Abstract)
9. Am J Prev Med. 2010 Oct;39(4):379-88 Occupational sitting and health risks: a systematic review. van Uffelen JG, Wong J, Chau JY, van der Ploeg HP, Riphagen I, Gilson ND, Burton NW, Healy GN, Thorp AA, Clark BK, Gardiner PA, Dunstan DW, Bauman A, Owen N, Brown WJ. (Review of Studies April 2009 - Abstract)
10. Circulation. 2010;121:384-391Epidemiology and Prevention Television Viewing Time and Mortality The Australian Diabetes, Obesity and Lifestyle Study (AusDiab)