Why does a high-carbohydrate diet lead to poor hair?

When blood sugar levels are elevated, glycation occurs—a process in which glucose or fructose molecules spontaneously attach to proteins, lipids, or nucleic acids. Why this affects hair:

1. Glycation of keratin. Hair is primarily made up of the protein keratin. With chronically high sugar levels, keratin undergoes glycation, just like other proteins in the body. Glycated keratin loses elasticity and strength: hair becomes brittle, dull, and retains moisture poorly.
2. Damage to blood vessels and hair follicles. High sugar damages the walls of blood vessels (especially capillaries) through oxidative stress and the accumulation of AGEs. Hair is nourished through the microcapillaries of the scalp. If microcirculation is impaired, follicles receive insufficient oxygen, amino acids, minerals, and vitamins. This slows growth and worsens hair quality.
3. Collagen and scalp structure. Glycation affects not only keratin but also the collagen of the scalp, which provides density and stability to the dermal tissue. When it undergoes glycation, the skin loses elasticity, follicles become less stable, and hair grows weaker.
4. Inflammation and follicular stress. AGEs activate inflammatory pathways (through RAGE receptors). This creates a chronic low-grade inflammatory background in the scalp, accelerating hair thinning and worsening its structure.
5. Analogy with glycated hemoglobin (HbA1c). HbA1c is an indicator showing how long and how high blood sugar has been elevated. If hemoglobin is glycated, it means glycation is also occurring with other proteins in the body, including hair keratin and skin collagen.

High sugar not only cosmetically "damages" hair—it disrupts their biochemistry at the level of protein structure and follicle nutrition. This leads to brittleness, dullness, slowed growth, and earlier thinning.