Obesity and Lifestyle Management Strategies - Part 1: Determinants of Body Weight and Why Weight Loss is Hard

Combating unhealthy weight gain is a major public health and clinical management issue. Obesity negatively impacts cardio-metabolic health, and can increase the risk of cancer, musculoskeletal dysfunction, and a myriad of other disorders. While aspects of the environment are considered strongly obesogenic, weight gain is not inevitable for every individual. The effectiveness of diet and exercise interventions in the treatment and management of individuals with obesity are commonly questioned given the mismatch between observed and expected weight loss. Even when interventions are effective in achieving clinically beneficial weight loss, recidivism is commonly high. 

This 2-part series will examine factors explaining why some individuals experience potentially unhealthy weight gain where others, living within the same environment, remain lean. 

We will examine evidence that there is only a weak biological compensation to surplus energy supply, and the extent to which biology impacts behaviours that drive weight gain. We will then consider why weight loss is hard, and explore the biological compensation that acts in response to a reduced energy intake by reducing energy needs, in order to defend against weight loss. Finally, we will examine the relative merits of medical therapies such as surgical and pharmaceutical interventions compared with more conventional lifestyle interventions in the treatment and management of obesity. 

Part 1 - Determinants of body weight and why weight loss is hard.
This online activity will examine:
[1] determinants of weight gain
[2] reasons for the mismatch between observed and expected weight loss.

This programs provides the background upon which we will consider the effectiveness of diet and exercise strategies in Part 2.

This is a recording of an ESSA webinar presented on 26 August 2020. 

Presented by Presented by Prof Nuala Byrne, BHMS, MAppSc, PhD, AES, AEP 

Nuala has been working in the weight management field for the last 30 years. She is a Professor in Exercise Physiology and Energy Metabolism, and an Accredited Exercise Physiologist. Her current position is the Head of the School of Health Sciences at the University of Tasmania. 

Nuala's research commonly sits in the nexus between nutritional and exercise physiology.  She has published widely and in prestigious journals including JAMA Open, The Lancet Diabetes & Endocrinology (IF:24.5), Circulation (IF:23.0) Gut (IF:17.0), Diabetes Care (IF:15.3), British Journal of Sports Medicine (IF:11.6), Obesity Reviews (IF:8.2), Sports Medicine (IF:7.6), American Journal of Clinical Nutrition (IF:6.6), International Journal of Obesity (IF:5.5), Clinical Pharmacokinetics (IF:4.7), and Medicine & Science in Sports & Exercise (IF:4.5). Her research contribution has been outstanding with career outputs including over 150 peer-reviewed papers, 60 in the last 5 years, and multiple books and book chapters.

Often Nuala's research has impacted scientific maxims. In a 2005 paper in the Journal of Applied Physiology, she challenged the concept of the metabolic equivalent (MET) for estimating energy expenditure and proposed a correction factor. This paper was selected for citation in the 2006 Year Book of Sports Medicine which highlights articles identified as breakthrough developments in sports medicine, selected from more than 500 journals worldwide. In 2011, the American College of Sports Medicine (ACSM) rescaled the MET values for the Compendium of Physical Activities used internationally.

Less-than-expected weight loss (or weight loss inefficiency) is commonly observed with energy restriction interventions. Nuala's research team has shown that weight loss inefficiency in adults with obesity during severe energy restriction is, in part, explained by reductions in resting energy expenditure (REE). While the decrease in REE during energy restriction was greater with higher loss of FFM, it was also more pronounced in individuals consuming a lower protein intake. We have also published exciting research showing that combining 2-week periods of energy restriction interspersed with 2-week periods of deliberate energy balance (i.e., intermittent energy restriction) results in markedly greater weight and fat loss, and maintenance at 6-months follow-up compared with continuous energy restriction in untrained sedentary obese men 25-54 years. These research findings have been highly cited as is evidenced by Altmetric scores and media interest (including being cited as evidence for Michael Mosely’s new Fast 800 diet). 

Nuala's published research was featured in the 2011 ACSM Position Stand providing guidance for prescribing exercise, as evidence for the role of both resistance and aerobic training in optimising body composition during weight loss and to prevent visceral fat regain. Further, her research has changed recommendations regarding the amount of physical activity needed to prevent weight regain in post-obese individuals. Both the 2011 ACSM Position Stand and International Association for the Study of Obesity cited my work as evidence for the need to change the exercise dose recommendations. Additionally, the 2011 ACSM Position Stand cites my research as evidence for appropriate prescription of exercise intensity.

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Any Accredited Exercise Scientist and/or Accredited Exercise Physiologist  

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