Is Inactivity the Main Cause of Obesity?

 
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By James J. Kenney, PhD, FACN

We have all seen the headlines quoting top researchers who have published studies that make it appear that inactivity, prolonged sitting, or a lack of exercise are largely responsible for people in America struggling with increasing body fat stores, type 2 diabetes mellitus (DM), and numerous other ills. Here’s just one example: “Lack of exercise, not diet, linked to rise in obesity, Stanford research shows.”[1] More recently we had Dr. James Levine, director of the Mayo Clinic-Arizona State University Obesity Solutions Initiative and inventor of the treadmill desk telling us that: “Sitting is more dangerous than smoking, kills more people than HIV and is more treacherous than parachuting. We are sitting ourselves to death."[2]

It is well-known that the modern food industry, including soft drink companies, fund research aimed at demonstrating that inactivity rather than what people eat and drink is the main reason so many Americans end up overweight or obese and develop type 2 DM.[3] For example, we have Stephen Blaire, a professor at the University of South Carolina and long-time Cooper's Clinic researcher telling us: “Most of the focus in the popular media and in the scientific press is, ‘Oh they’re eating too much, eating too much, eating too much’ — blaming fast food, blaming sugary drinks and so on and there’s really virtually no compelling evidence that that, in fact, is the cause.”[4] Could it be true that inactivity or prolonged sitting – and not what we eat – is largely responsible for the growing worldwide epidemic of obesity and type 2 DM?

Should We Focus on Activity Levels Rather than Diet?

Not according to Loyola University researchers Amy Luke and Richard Cooper, whose evaluation of the research about which environmental factors are most closely linked to more obesity concludes that the public health community needs to shift their message about what is promoting obesity away from inactivity, sitting, and a lack of exercise and focus instead on what the preponderance of credible scientific evidence suggests is responsible. That is the typical modern diet full of calorie-dense, low-fiber foods being washed down with more and more beverage calories. They argue that "…reduced energy expenditure [inactivity] has been removed from the list of candidate aetiological agents [that are causing obesity]."[5] An earlier study by these Loyola University researchers examined the energy expenditure and body weight of 149 rural Nigerian women and an age-matched group of 172 African-American women age18-59 in the Chicago area. They observed no significant difference in energy expenditure between these two groups of women. However, despite no significant differences in activity levels or energy expenditure, the average body weight of the African American women averaged 184 lbs, compared to only 127 lbs for the rural Nigerian women.[6] Another study by this same group of researchers measured physical activity levels in 1,944 men and women of predominantly African descent in 5 countries (Jamicia, Seychelles, Ghana, South Africa, and the USA) and then followed them for an average of 2 years. They found no significant correlation between accelerometer-measured activity levels and the gain or loss of body weight in the ensuing years. They stated: "Importantly, this is not to say, that physical activity per se is not important in the overall achievement of health such as the prevention or delay of diabetes, and cardiovascular disease, which is undisputed, but that its [activity's] role in the prevention of population level weight gain may be overstated."[7] So it appears that obesity is not largely caused by inactivity, prolonged sitting, and lack of exercise. This does not mean that inactivity is not unhealthy and it does not mean that exercise may not be of some benefit, but it does mean that far more attention needs to be put on what people are eating rather than on their activities.

Let’s look at a long-term observational study of 4,811 middle-aged and older London-based office workers who were initially free of diabetes and major cardiovascular disease. In 1998, the study participants reported the amount of time they spent on various sitting behaviors including work and commuting, leisure time, and watching television. The researchers then examined clinical data based on blood glucose levels from the same cohort until the end of 2011 to determine whether or not new cases of diabetes developed during the 13-year follow-up period. After adjusting for confounding factors such as the physical activity, quality of the diet, employment grade, alcohol and smoking habits, general health status, and baseline body mass index (BMI) of the participants, the researchers observed no significant correlation between total sitting time and increased risk of developing diabetes – except for time spent watching TV. So, for 402 cases of diabetes that developed during the follow-up period, there was little evidence for any association between sitting and diabetes, except for weak associations limited to the time spent sitting in front of the TV. Dr. Emmanuel Stamatakis stated, "Importantly, our research was among the first long-term studies to distinguish between various types of sitting behaviors – not just TV sitting, which is used in the majority of existing studies. But TV time and sitting time are practically uncorrelated so we have very good reasons to believe that the health risks attributed to TV in the past are due to other factors, such as poorer mental health, snacking and exposure to unhealthy foods advertising.”[8]

What are we to make of research finding an association between more exercise and/or activity and reduced body weight or fat stores? It may be that weight gain and obesity simply make activity more difficult, and so people naturally tend to move around less as they become more overweight. It may be that obesity causes inactivity more than inactivity promotes obesity. Correlation does not equate to causation. Even the suggestion that the low activity levels seen in modern societies today when compared to our hunter-gatherer ancient ancestors is the main reason obesity and type 2 DM are now so common is questionable. A study of a modern-day hunter-gatherer society in Africa found that calories expended per pound of body weight were not significantly different.[9]

Hunger Reduces Activity and Increases Energy Intake

It is also known that part of the physiological adaption to calorie restriction in animals is reduced activity levels. Since overweight and obese people are more likely to go on calorie-restricted diets, this too may tend to make them more lethargic and less active. In addition, there is no doubt that increased activity and weight loss both tend to increase hunger levels. It appears that any increase in calorie intake in response to this increased hunger can largely negate the weight loss benefits of increased activity or regular exercise.[10]

Data from some randomized trials has shown that regular exercise may help some overweight people to lose a bit more weight, at least over the short term. For example, a study of 320 mostly overweight and obese women randomized half to 1-year-long exercise intervention that included 45 minutes of moderate-to-vigorous aerobic exercise five times per week, with at least three of the weekly sessions supervised at the two study facilities. The control group was asked not to change their activity and both groups were asked not to change their diet. The subjects in the exercise group in this study did end up weighing 4 lbs less than those in the control group after one year.[11] However, not all controlled studies examining the impact of randomly assigning people to a calorie-restricted diet with or without either aerobic or resistance training have shown more weight loss and improved insulin sensitivity from the addition of exercise.[12] Data from the National Weight Control Registry (which is evaluating Americans who have lost a lot of weight and kept it off for an average of more than 5 years) show that only about 1% of the people who have been successful with weight management over the long term did it with increased exercise alone.[13] So it appears that reducing sitting time and/or increasing exercise alone is unlikely to be nearly as important as diet in determining BMI and the risk of developing type 2 DM.

Bottom Line: So while there is little doubt that regular exercise has many health benefits and it may help a bit at reducing body fat stores, most research suggests that regular exercise alone is unlikely to solve America’s obesity epidemic or have much impact on the growing prevalence of type 2 DM. Despite the protestations of the commercial food industry, much more attention needs to be paid to the fact that it is largely the typical modern diet and not sitting or lack of exercise that is largely responsible for obesity, insulin resistance, and the growing epidemic of type 2 DM. So instead of focusing on how much we eat, the focus needs to shift to what we eat and drink. Contrary to popular mythology, there are indeed fattening foods and drinks. Portion control and calorie counting won't lead to long-term weight control in most people. For long-term weight control, the focus needs to shift to what people eat rather than trying to use willpower to limit how much people eat and exercise more. Calorie-restricted diet and exercise programs leave many people so chronically hungry that their thinking about food becomes so irrational (or disordered) they end up with what are labeled "eating disorders."

References:

[1] https://med.stanford.edu/news/all-news/2014/07/lack-of-exercise--not-diet--linked-to-rise-in-obesity--stanford-.html.

[2] http://www.huffingtonpost.com/the-active-times/sitting-is-the-new-smokin_b_5890006.html.

[3] http://www.ajpmonline.org/article/S0749-3797(16)30331-2/fulltext?rss=yes.

[4] https://well.blogs.nytimes.com/2015/08/09/coca-cola-funds-scientists-who-shift-blame-for-obesity-away-from-bad-diets.

[5] Luke A, Cooper RS. Physical activity does not influence obesity risk: time to clarify the public health message. Int J Epidemiol. 2013;42:1831-6 or doi:10.1093/ije/dyt159.

[6] Ebersole KE, Dugas LR, Duranzo-Arvizvu, et.al. Energy Expenditure and adiposity in Nigerian and African-American Women. Obesity 2008;16:2148-54.

[7] Duga LR, Kliethermes S, Plange-Rhule J, et. al. Accelerometer-measured physical activity is not associated with two-year weight change in African-origin adults from 5 diverse populations. PeerJ 2017:5:e2902-22 or DOI 10.7717/peerj.2902.

[8] Stamatakis E, Pulsford RM, Brunner EJ, et.al. Sitting behaviour is not associated with incident diabetes over 13 years: the Whitehall II cohort study. British Journal of Sports Medicine, 2017; bjsports-2016-096723 DOI: 10.1136/bjsports-2016-096723.

[9] Pontzer H, Raichlen DA, Wood BM, et.al. Hunter-gatherer energetics and human obesity. PLoS ONE July 2012 available at: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0040503.

[10] Polidori D, Sanghvi A, Seely RJ, Hall KD. How strongly does appetite counter weight loss? Quantification of the feedback control of human energy intake. Obesity 2016;24:2289-95.

[11] https://www.ncbi.nlm.nih.gov/pubmed/20820172.

[12] Weinstock RS, Dai H, Wadden TA. Diet and exercise in the treatment of obesity. Arch Intern Med. 1998;158:2477-84.

[13] https://www.ncbi.nlm.nih.gov/pubmed/24355667/.

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