Clinical and Preclinical Studies of Fermented Foods and Their Effects on Alzheimer's Disease

Abstract

The focus on managing Alzheimer's disease (AD) is shifting towards prevention through lifestyle modification instead of treatments since the currently available treatment options are only capable of providing symptomatic relief marginally and result in various side effects. Numerous studies have reported that the intake of fermented foods resulted in the successful management of AD. Food fermentation is a biochemical process where the microorganisms metabolize the constituents of raw food materials, giving vastly different organoleptic properties and additional nutritional value, and improved biosafety effects in the final products. The consumption of fermented foods is associated with a wide array of nutraceutical benefits, including anti-oxidative, anti-inflammatory, neuroprotective, anti-apoptotic, anti-cancer, anti-fungal, anti-bacterial, immunomodulatory, and hypocholesterolemic properties. Due to their promising health benefits, fermented food products have a great prospect for commercialization in the food industry. This paper reviews the memory and cognitive enhancement and neuroprotective potential of fermented food products on AD, the recently commercialized fermented food products in the health and food industries, and their limitations. The literature reviewed here demonstrates a growing demand for fermented food products as alternative therapeutic options for the prevention and management of AD.

Keywords: Alzheimer’s disease; fermented foods; gut microbiota; memory and cognition; neuroprotection; oxidative stress; probiotics.

Figure 1

Examples of fermented foods and beverages based on divergent raw food substrates found around the world.

Figure 2

The number of people with dementia living in low and middle-income countries compared to high-income countries. “Adapted with permission from International et al. [2]. 2020, Alzheimer’s Disease International”.

Figure 3

The structure of the microbiome–gut–brain axis. The HPA axis (in dashed line) in the CNS can be activated in response to environmental factors, including stress or emotion. Through a complex interaction between the AMG, HIPP, and HYP, constituting the limbic system, HPA is finalized to cortisol release. The secretion of the CRF from HYP stimulates the secretion of ACTH from the pituitary gland, leading to the release of cortisol from the adrenal glands. CNS communicates with afferent and efferent pathways with intestinal targets such as muscle layers and gut mucosa, ENS, modulating motility, permeability, immunity, and mucus secretion. The enteric microbiota has bidirectional communication with these intestinal targets that modulate the gastrointestinal functions and modulates itself by gut–brain interactions. HPA, hypothalamic pituitary adrenal; CNS, central nervous system; AMG, amygdala; HIPP, hippocampus; HYP, hypothalamus; CRF, corticotropin-releasing factor; ACTH, adrenocorticotropic hormone; ENS, enteric nervous system.