March 28, 2026, by Susan Sargeant, BSc (Biomedical Science)
In our goal-oriented society, fitness and optimum body image have become a sought-after and demanding pursuit, resulting in many of us wanting to find the best and shortest route to a defined and lean body, with maximum muscle mass and minimal fat. Different approaches to these goals have led to the popularity of targeted diets and fasting regimes, where the goal of a lean and muscular body can be effectively achieved.
The rise of intermittent fasting is one such approach, where through prolonged periods of fasting followed by short window periods of healthy eating, the fat-burning metabolic activities of the body can be maximised. From a scientific viewpoint, this method has many advantages and can serve to efficiently achieve a lean body in a short time-span. Research highlighted by the Harvard T.H. Chan School of Public Health explains how intermittent fasting can influence metabolic health and weight management.
Energy Metabolism During Fasting
During metabolism, nutrients from the diet are broken down into glucose, glycerol and fatty acids to generate energy at a cellular level to maintain the body's natural processes. Once these are used up, the body goes into a fasting stage. Glycogen and fat are released from storage in fat cells to provide more glucose, glycerol and fatty acids. The Cleveland Clinic provides a useful overview of how the body transitions between fed and fasting states.
What Happens When Glycogen Stores Drop
Once glycogen stores are depleted, often after roughly 24 hours, the body needs to switch its metabolic activities to replenish the glucose energy supplies needed mainly by red blood cells and brain cells.
Two important processes become more prominent during this stage:
1. Gluconeogenesis
Gluconeogenesis involves the liver and kidneys generating glucose from amino acids, which are components of protein tissues. This helps the body maintain essential glucose availability when dietary intake is not occurring.
2. Ketogenesis
Ketogenesis is the production of alternative energy supplies in the form of ketone bodies from the breakdown of fatty acids. These ketones become an increasingly important fuel source during longer fasting periods.
A detailed explanation of these metabolic pathways can be found through scientific resources such as the National Center for Biotechnology Information, which explores fasting metabolism at a molecular level.
Why Intermittent Fasting Appeals to Many People
As intermittent fasting is only a temporary state of fasting, these metabolic shifts can be used to harness the body's natural processes, resulting in overall weight loss through the use of fat stores and stored body water. This is one reason why intermittent fasting has gained so much attention among people pursuing leaner body composition goals.
Guidance from the World Health Organization also reminds us that any dietary approach should consider the individual's overall health status, lifestyle, and personal needs.
A Responsible Approach
As always, intermittent fasting should take into account the overall health of the individual and should only be done responsibly and under medical advice. A method that works well for one person may not be suitable for another, especially when medical conditions, medications, or higher training demands are involved.