Physiological Adaptations to Weight Loss (Including Rapid and Slow Weight Loss)

Watch this lecture to learn about how the body responds to weight loss by defending body weight – and how this influences weight regain.

 Weight is Defended

The evidence shows us that the majority of people who are overweight or obese and lose 5-15% of their body weight through dieting and/or exercise, will regain weight to within 5% of their baseline weight within 3-5 years.^8,9 This weight regain is thought to be driven by the long-term persistence of hormonal adaptations to weight loss, which lower resting metabolic rate or energy expenditure and drive the physiological pathways for weight regain.

Researchers have reported a 15% reduction in resting energy expenditure in participants who lost 10% of their body weight.⁵ To put this in simple terms, a person with a stable weight who was obese, and successfully lost weight through dieting, would then have to reduce their energy intake by approximately 15% following a diet in comparison to what they were eating before dieting to maintain their new energy in/out equilibrium and maintain a stable weight.

The literature suggests the following physiological and hormonal pathways for the defence of weight:

1. Substrate metabolism (what is preferentially broken down for energy): After diet-induced weight loss, the body moves towards a preference for carbohydrates for energy, such that fat is stored for fatty deposits.
2. Hypothalamic pathways: Dieting has been shown to suppress the pathways from the hypothalamus that activate the thyroid, reducing resting energy expenditure
3. Appetite regulating peripheral hormones: Levels of Leptin, the hunger inhibitor, greatly reduce following dietary restriction both during weight loss and maintenance. Sumithran et al., 2011 showed a 70% reduction in leptin levels following a 10-week dietary intervention that was still 32 % lower than at baseline a year later. In contrast, Ghrelin levels were elevated during weight loss and after the active intervention, increasing hunger.
4. Subjective appetite: Increased desire to eat and preference for high calorie foods persist well beyond the weight loss period and at levels beyond those pre-diet.

Read more around the hormonal defence of weight in this key research paper: Sumithran, Priya, et al. “Long-term persistence of hormonal adaptations to weight loss.” New England Journal of Medicine 365.17 2011: 1597-1604.

There is no difference for weight regain depending on whether weight is lost rapidly through very low calorie dietary interventions or more slowly
Despite the common belief that rapid weight loss results in more rapid weight regain than gradual weight loss, evidence suggests there is no difference in the rate of weight regain, and in fact, some of the advantages of rapid weight loss (as associated with a very low calorie ketogenic diet) include people being more likely to lose weight, and more likely to be adherent to dietary interventions given the motivating element of seeing results⁸

Potential Causes of Weight Gain

Obesity can be conceptualized as the physical manifestation of chronic positive energy balance.¹⁰ However as discussed in this module, the simple equation of ‘energy in versus energy out’ does not account for all the potential factors influencing energy balance. The following table summarises potential causes and contributors to weight gain.¹⁰ These are relevant as they can be used in the assessment and management of obesity.

Read: This review article by Sharma and Padwal is a good overview of the role of these factors in the development of obesity. You can find the article here