1. Cutler 2003 study: The findings of Cutler and others (2003) conclude that obesity is mainly caused by an increase in caloric intake and not mainly by reduced caloric expenditure. The conclusions were drawn from studies performed in the USA on data from obesity levels during the early 1900s to the end of the century. On average in 1965, the average married American woman who did not work outside the house spent 2 hours cooking and cleaning per day. In 1995, the same tasks took half the time to complete due to mass preparations and technological innovations. Urbanization is believed to have played a role in decreased Energy Expenditure (EE) between the years 1909 to 1950 but it was not accompanied by an increase in obesity during those years. However according to Cutler and others (2003) , increase in Energy Intake (EI) by 700 kcal between years 1965 and 1999 was not enough to explain the increase in obesity rates during those years. Thus, they argued that voluntary EE due to exercise had not changed much during 1965 to 1990 in order to explain their results and reach their conclusions.
2. Swinburn 2011 theory: Swinburn and others suggest in their (2011) Lancet publication that passive overconsumption of energy is causing the global obesity epidemic. They raise an alarm that there are no exemplar populations that have had public health success in reversing the obesity epidemic. Thus, Swinburn and others also suggest that obesity is mainly caused by an increase in caloric intake and not mainly by reduced caloric expenditure. The key points in Swinburn and others’ theory (2011) are that global food system changes have caused the obesity epidemic during the past 3-4 decades. Increased mechanisation and motorization during the first half of the 20th century along with decrease in food energy supply kept obesity rates low during that time. They suggest that in high-income countries a flipping point occurred during the years 1960-1970 with increased food energy intake and obesity. Systems for monitoring of population weight and nutrition are inadequate in almost all countries while adult obesity continues to increase almost globally.
3. DLW studies: Doubly-labelled water (DLW) studies enable direct measurement of daily EE over 1-2 weeks but these studies have been unable to convincingly influence the gluttony versus sloth debate either way. DLW-determined values of Physical Activity Level (PAL) were not significantly different in lean adults in developing countries as compared to obese adults in developed countries. These findings were very surprising and unexpected.
4. Figure 3 (Millward, 2013), Energy Expenditure and PAL: Increasing Energy Expenditure (EE) is associated with increasing Physical Activity Level (PAL) as expected. Since EE is a product of PAL and Basal Metabolic Rate (BMR), an increasing BMR will always lead to an increase in EE over the entire Weight (W) range (Fig. 3, Millward 2013). Thus, a positive slope for EE is expected with increasing weight and a negative slope is unlikely. The 3 DLW data sets in Figure 3 indeed showed similar EE-W relationships as it was data from current UK adult populations. The slope of all the data sets show increasing BMR with W which is expected and well studied. The physiological association of increasing weight causes increasing BMR and EE within the weight range (50-130 kilograms) studied in Figure 3. The underlying mechanisms which cause an increase in body weight are not adequately addressed by the authors in Figure 3.
5. Limitations of DLW studies, Table 1: The surprising finding from DLW-datasets is that there is no evidence of a fall in PAL with increasing obesity. These surprising findings were caused due to the limitations in DLW-datasets. DLW-measured PAL values have significant limitations since they are not corrected for body weight and do not relate to behavioural changes when body weight changes. The DLW-derived data in Table 1 does not explain the significant increase in Physical Activity Energy Expenditure (PAEE) with Body Mass Index (BMI) but not PAL.
6. PAEE data and Accelerometer Studies, Table 2: The data in Table 2 shows that physical activity behavior is significantly reduced in obese individuals as compared to lean ones. This significant difference is seen in DLW-measured data when adjusted for body weight and in accelerometer-measured data. This is because the amount of effect of PAEE on PAL gets smaller as size increases. Thus, adjustments for body weight are very important to adequately measure physical activity in heavier individuals.
7. Figure 5 (Millward, 2013): This figure shows the various predicted rates of energy expenditure changes between years 1955 to 2010 in UK adult populations. The values range from 2.0 PAL in very active adults in 1955 to an assumed average 1.63 PAL in 2010 UK adult population.
8. Figure 6 (Millward, 2013): This figure shows the various estimates and actual data of food energy intake between years 1950 to 2010 in the UK. The National Food Survey (NFS) conducted surveys until 2001 followed by Expenditure and Food Survey (EFS) after 2001 to get the household food purchase data. This data indicates that a simple gluttony without sloth position is not supported by the data on food energy intake to explain the obesity epidemic.
9. Future weight gain predictions from Physical Activity: The UK obesity epidemic is believed to be caused by less physical activity and unsuccessful efforts to reduce calorie intake through food and drink. If efforts are not made to increase physical activity along with reduced calorie intake then obesity prevention will not be successful in the future on a global scale.
10. Conclusions for future obesity epidemic prevention: For future obesity prevention, public health efforts have to be made which focus on both diet and exercise. Health-diet guidelines should include macro and micro nutrient adequacy with sufficient attention focused on avoiding obesogenic dietary factors. Exercise routines should start in early childhood and continue through the school years and adulthood. Adequate exercise and proper diet should become part of daily living globally in order to successfully prevent the global obesity epidemic.
Cutler D., Glaeser E., and Shapiro J., (2003) Why have Americans become more obese? Journal of Economic Perspectives, Vol. 17, pp. 93-118
Millward D. (2013) Energy balance and obesity: a UK perspective on the gluttony v. sloth debate, Nutrition Research Reviews, pp. 1-21
Swinburn B., Sacks G., Hall K., et al., (2011) The global obesity pandemic: shaped by global drivers and local environments, Vol. 378, pp. 804-814