We have long been told to sleep well, exercise, and eat nutritiously. While these recommendations are staples of medical advice, they are often viewed as distinct prescriptions. However, modern neuroscience suggests these habits share a common purpose: they are all fundamental to maintaining the biological machinery that powers our existence.
The brain is an incredibly energy-intensive organ. Although it accounts for only about 2% of our total body weight, it consumes roughly a fifth of our resting energy. Every cognitive function—from retrieving a memory to solving a complex problem—carries a metabolic cost, making thought itself an energy-hungry process.
This energy demand is met by an evolutionary alliance dating back more than 2bn years, when a primitive cell engulfed a bacterium. Instead of being consumed, the bacterium formed a permanent partnership with its host. These descendants, known as mitochondria, now reside in nearly every cell of the human body, with the notable exception of mature red blood cells, which omit them to optimize space for oxygen transport.
For decades, biology textbooks labeled mitochondria simply as the cell’s “powerhouses”—a description that, while accurate, often undersold their true significance. We now understand that intelligence and emotional stability depend on the continuous flow of energy generated by these organelles. Healthy mitochondrial function is increasingly linked to faster processing speeds, improved working memory, greater stress resilience, and healthier brain aging.
This perspective shifts our understanding of lifestyle habits. Exercise, for instance, does more than build muscle; it expands the hippocampus, a brain region critical for learning and memory, while simultaneously encouraging mitochondria to become more numerous and efficient. We are essentially training our internal energy systems.
Sleep serves a different, equally vital role. Rather than being a period of inactivity, sleep functions as a maintenance shift. During this time, the brain consolidates memories and repairs or replaces worn-out cellular components, including mitochondria, ensuring the system is prepared for the demands of the following day.
Diet also plays a direct role in this biological chemistry. Mitochondria rely on the quality of fuel we provide to perform their energy-transformation tasks. Minimally processed foods offer the necessary ingredients for efficient function, whereas diets that overwhelm the system can degrade efficiency over time.
Neuroscientist Hannah Critchlow, author of The 21st Century Brain, notes that these three pillars of health are essentially different ways of caring for the same biological inheritance. This view aligns with the work of mitochondrial psychobiologist Martin Picard, who suggests that humans are best understood not as static molecular machines, but as dynamic energetic processes.
It is profound to consider that every idea, hope, and connection we experience relies on an alliance forged over two billion years ago. The tiny descendants of that ancient bacterium have been working within us ever since, enabling not just our physical movement, but the very capacity for thought.
This new understanding explains why traditional health advice has persisted through generations. Long before we understood the complexities of ATP or oxidative phosphorylation, we recognized that those who prioritized sleep, movement, and nutrition tended to flourish. We are finally uncovering the biological reasons why these habits remain the cornerstone of human health.
Further reading on these biological mechanisms can be found in The Song of the Cell by Siddhartha Mukherjee, Transformer: The Deep Chemistry of Life and Death by Nick Lane, and How Life Works: A User’s Guide to the New Biology by Philip Ball. The report also notes that the Song of the Cell by Siddhartha Mukherjee (Vintage, £14.99). The report also notes that transformer: The Deep Chemistry of Life and Death by Nick Lane (Profile, £14.99. The report also notes that how Life Works: A User’s Guide to the New Biology by Philip Ball (Picador, £14.99).