Sugar, Glycaemic Index, and Acne

The link between sugar and acne is one of the better-evidenced nutrition–skin connections. It works through a chain: high-GI foods spike blood glucose, which raises insulin, which triggers IGF-1 (insulin-like growth factor), which increases sebum production and skin-cell proliferation — two key drivers of acne.

The mechanism

• Insulin spike: high-GI foods (white bread, sugary drinks, crisps, rice cakes) cause a rapid rise in blood glucose and a corresponding insulin surge.
• IGF-1 elevation: insulin raises IGF-1, a growth factor that stimulates oil glands to produce more sebum and accelerates the proliferation of skin cells in hair follicles — both contribute to clogged pores.
• Androgen pathway: insulin also reduces the liver's production of sex hormone-binding globulin (SHBG), leaving more free androgens in circulation. Free androgens further stimulate sebum production.
• Inflammation: high blood glucose directly promotes inflammatory signalling in the skin, worsening existing acne.

What the studies show

A 2007 RCT (Smith et al.) found that young men on a low-GI diet for 12 weeks had significantly fewer acne lesions than those on a high-GI control diet. A 2012 Korean study found similar results. These are small studies — but they are randomised controlled trials, the strongest type of evidence in nutrition research.

Practical changes

• Swap refined carbohydrates for whole-grain alternatives (brown rice, oats, wholegrain bread).
• Reduce sugary drinks — these cause the sharpest insulin spikes of any food.
• Add protein and fat to meals containing carbohydrates — this blunts the glycaemic response.
• Snack on nuts, seeds, or vegetables rather than crisps, crackers, or sweets.