A fatty deposit within the wall of an artery, the core lesion of atherosclerosis. It begins when LDL cholesterol infiltrates the vessel lining and triggers inflammation; immune cells engorge on the fat, die, and form a soft, gruel-like core covered by a fibrous cap. As atheromas grow they narrow the artery, and when a cap ruptures, a clot forms instantly, causing heart attacks and strokes. Diet influences every stage: saturated fat and excess calories raise the LDL that feeds plaques, while fiber, unsaturated fats, and plant-rich eating patterns slow their growth. Though the process unfolds silently over decades, its prevention is one of nutrition’s greatest proven achievements, with dietary change measurably reducing cardiovascular events.