Alzheimer’s disease (AD) is a chronic neurodegenerative disorder characterized by progressive loss of cognitive function. Its main pathological features include accumulation of Amyloid-beta (Aβ) plaques, excessive phosphorylation of microtubule-associated protein tau (tau protein), and neuroinflammation. In recent years, studies have confirmed intestinal flora is closely connected to AD. Gut–brain axis has an important part in AD. Intestinal flora can achieve signal communication between gut and brain through metabolic, immune, neural, and endocrine pathways, thereby slowing down AD. It has been discovered that exercise is not only beneficial to physical health but also has a positive impact on the brain function. In recent years, more and more studies have found exercise can alleviate AD through the following four major pathways: regulating the diversity of intestinal flora, strengthening the blood–brain barrier (BBB), regulating immune homeostasis, and upregulating the brain-derived neurotrophic factor (BDNF). In this review, we have summarized intestinal flora in AD and systematically expounded potential regulatory pathways of exercise in modulating intestinal flora for AD. This provides a more theoretical basis for subsequent research targeting “gut–brain axis” to regulate AD. At the same time, this review also summarizes differences in different exercise types on improving intestinal flora for alleviating AD, providing new ideas and strategies for AD.

Parkinson’s disease (PD) is a progressive neurodegenerative disorder that is closely associated with dysfunction of the gut–brain axis. Exercise and diet exert neuroprotective effects on PD by regulating the gut–brain axis, yet the overall mechanisms underlying this regulation remain to be systematically elucidated. This article reviews the characteristic changes in gut microbiota during the progression of PD and the pathological mechanisms involving gut–brain axis dysfunction. It systematically outlines the intrinsic mechanisms by which gut microbiota modulate the onset and development of PD from the perspectives of metabolism, immunity and inflammation, neuroendocrinology, and the temporal and causal relationships between gut microbiota and PD. On this basis, the discussion focuses on the regulation of the gut–brain axis through exercise to improve PD, with emphasis on remodelling the composition and diversity of gut microbiota, enhancing gut barrier and blood–brain barrier (BBB) functions, regulating immune and inflammatory homeostasis, upregulating the expression of neurotrophic factors and promoting neuroplasticity, as well as the synergistic effects of exercise and diet. In parallel, the independent and synergistic effects of dietary interventions (e.g., high-fibre and Mediterranean diets) are discussed. In addition, the effects of different types of exercise on alleviating PD by regulating gut–brain axis are analysed. This review aims to provide new insights and a scientific basis for the prevention and intervention of PD.