This review discusses the health benefits and mechanisms of antioxidant phytochemicals in preventing and treating chronic diseases. Antioxidant phytochemicals, found in fruits, vegetables, and medicinal plants, have strong antioxidant and free radical scavenging abilities, as well as anti-inflammatory actions. These properties make them effective in reducing oxidative stress, which is a key factor in the development of chronic diseases such as cardiovascular disease (CVD), diabetes, obesity, and cancer. The review highlights the sources of antioxidant phytochemicals, their bioavailability, and potential adverse effects. It also provides an overview of the protective actions of these phytochemicals in various chronic diseases, including CVD, obesity, diabetes, cancer, aging, Alzheimer's disease, and inflammatory bowel disease. The review emphasizes the importance of consuming fruits, vegetables, and grains rich in antioxidant phytochemicals for maintaining health and preventing chronic diseases.This review discusses the health benefits and mechanisms of antioxidant phytochemicals in preventing and treating chronic diseases. Antioxidant phytochemicals, found in fruits, vegetables, and medicinal plants, have strong antioxidant and free radical scavenging abilities, as well as anti-inflammatory actions. These properties make them effective in reducing oxidative stress, which is a key factor in the development of chronic diseases such as cardiovascular disease (CVD), diabetes, obesity, and cancer. The review highlights the sources of antioxidant phytochemicals, their bioavailability, and potential adverse effects. It also provides an overview of the protective actions of these phytochemicals in various chronic diseases, including CVD, obesity, diabetes, cancer, aging, Alzheimer's disease, and inflammatory bowel disease. The review emphasizes the importance of consuming fruits, vegetables, and grains rich in antioxidant phytochemicals for maintaining health and preventing chronic diseases.