We all know that food gives us energy. But what does that actually mean?

Energy is not simply feeling awake, focused or sufficiently caffeinated to answer emails before 9am. At a cellular level, energy is the ability to perform biological work. Every cell needs it to transport nutrients, manufacture proteins, repair damage, communicate with neighbouring tissues and copy DNA.

The body packages much of this usable energy into a molecule called adenosine triphosphate, better known as ATP. Think of ATP as the cellular currency required to get almost anything done.

Hair follicles need ATP. They need a lot of it.

Although the hair visible above the scalp is biologically dead, the follicle producing it is highly active. And the fruits of this activity is the growing hair fibre.  During the growth phase, cells at the base of the follicle divide rapidly.  They must then mature into the different types of cells that makes the components needed to build the hair, produce large amounts of keratin, shape the developing hair fibre and stay in constant communication with blood vessels, hormones, immune cells and the surrounding tissue.

Cell division requires ATP. Keratin production requires more ATP. Tissue organisation, repair and cellular signalling require yet more and more ATP. Hair growth is, biologically speaking, an expensive business.

How the body actually produces energy

The body generates ATP through two main systems: anaerobic and aerobic metabolism.

Anaerobic metabolism allows cells to produce energy without relying directly on oxygen. Glucose is broken down through a process called glycolysis, generating a small but rapid supply of ATP. Each molecule of glucose produces a net yield of approximately two ATP molecules.

This system is useful when energy is needed quickly or when oxygen delivery cannot keep pace with demand, such as during intense exercise. It is fast, but not particularly efficient.

If ATP production remains inadequate, the follicle will struggle to sustain rapid cell division, keratin production and normal tissue repair. Hair will grow more slowly, emerge with a smaller diameter and become progressively finer, while reduced fibroblast activity may impair collagen maintenance and contribute to thinning of the surrounding dermis. Limited oxygen delivery is one possible cause, but ATP generation can also be affected by low iron, inadequate glucose availability, deficiencies in mitochondrial cofactors, chronic inflammation and impaired circulation.

Aerobic metabolism is the follicle’s main system for sustained energy production. It uses oxygen to extract energy from glucose, fatty acids and some amino acids. Through the citric acid cycle and oxidative phosphorylation, one molecule of glucose can generate approximately 30 to 32 ATP molecules.

Efficiency depends on more than oxygen alone. Iron is required for oxygen transport and mitochondrial enzymes, while B vitamins, magnesium, copper and other micronutrients support the reactions involved in ATP production. 

Hair-follicle cells use both anaerobic and aerobic metabolism, but not in equal amounts.  The balance can shift when the individual follicle is not receiving or using oxygen and nutrients efficiently. Poor microvascular supply, low iron, persistently high blood glucose, insulin resistance, elevated triglycerides and an unfavourable cholesterol profile can all impair circulation, oxygen delivery or cellular energy metabolism. Chronic inflammation may further increase energy demand while disrupting mitochondrial function. 

Food is only the beginning

Energy is not determined by the number of calories printed on the side of a protein shake. A double-shot American on the run instead of breakfast does not provide the follicle with the full range of amino acids, fatty acids, vitamins, minerals and glucose required to build new tissue.

Skipping meals, prolonged fasting, rapid weight loss, low iron, poor blood-glucose regulation, chronic inflammation and impaired vascular health can all affect how efficiently fuel and oxygen reach the follicle. They can also influence how effectively follicle cells convert those raw materials into ATP once they arrive.

This is where the NOVA food-classification system can be useful. NOVA groups foods according to how extensively they have been processed, from unprocessed or minimally processed foods through to ultra-processed products. It does not measure nutrient content directly, but it helps distinguish foods that remain close to their original form from products designed largely for convenience, shelf life and palatability.

Building meals around NOVA Group 1 foods, such as vegetables, fruit, pulses, whole grains, eggs, fish, meat, nuts and seeds, generally provides a wider range of nutrients than relying heavily on ultra-processed snacks, meal replacements and drinks. The aim is not to avoid every processed food, but to obtain most of the diet from foods capable of supplying both energy and the raw materials needed for cellular repair and hair production

Similarly, simply eating more does not guarantee that more energy becomes available to the hair follicle.  Eating supplies the raw materials. Metabolism determines whether the follicle can actually use them.