After weight loss, total energy expenditure—in particular, energy expenditure at low levels of physical activity—is disproportionately lower than predicted by actual changes in body weight and composition. This is known as adaptive thermogenesis.* A key issue is whether this reduction, which predisposes towards weight regain, persists over time.
The increasing prevalence of obesity and its co-morbidities reflects the interaction of genes that favour the storage of excess energy as fat with an environment that provides ad libitum availability of energy-dense foods and encourages an increasingly sedentary lifestyle. Although weight reduction performed in the typical manner (Calorie restriction) is difficult in and of itself, anyone who has ever lost weight will confirm that it is much harder to keep the weight off once it has been lost.
The over 80% (thought to be closer to 95-98%) recidivism rate to pre-weight loss levels of body fatness after otherwise ‘successful’ weight loss is due to the coordinate actions of metabolic, behavioural, neuro-endocrine and autonomic responses designed to maintain body energy stores (fat) at a central nervous system-defined 'ideal'. This adaptive thermogenesis creates the ideal situation for weight regain and is evident in both lean and obese individuals attempting to sustain reduced body weights. The multiple systems regulating energy stores and opposing the maintenance of a reduced body weight illustrate that body energy stores in general and obesity in particular are actively 'defended' by interlocking bio-energetic and neurobiological physiologies.
A recent study aimed to investigate whether adaptive thermogenesis is sustained during weight maintenance after weight loss.
The study was performed using 22 men and 69 women (average age of 40 with a body mass index of 31.9) who followed a very-low-energy diet for 8 weeks, followed by a 44-week period of weight maintenance. The subjects were assessed for body-composition and metabolic rate. Measurements took place before the diet and at 8, 20, and 52 weeks after the start of the diet.
The results demonstrated a reduction in metabolic rate at the end of the dieting period (week 8 ) and this decrease was sustained after 20 weeks and 52 weeks.
The authors concluded that weight loss results in adaptive thermogenesis, and there is no indication for a change in adaptive thermogenesis up to 1 year, when weight loss is maintained.
Reference:
Stefan GJA Camps, Sanne PM Verhoef, and Klaas R Westerterp. Weight loss, weight maintenance, and adaptive thermogenesis. Am J Clin Nutr May 2013 97: 990-994.
* http://humanperformanceconsulting-uk.blogspot.co.uk/2012/01/ive-got-chills-theyre-multiplying.html
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