Spices Beyond Antioxidants: From the Gut to the Brain

The objective of this review was to summarize evidence of the effects of select spices/herbs on human health with a focus on the work conducted at the University of California-Los Angeles (UCLA) Center for Human Nutrition.

Herbs/spices have been used in various countries around the world for centuries. The purposes for using herbs/spices include improvement in food organoleptic properties and use as food preservatives and medicine. As interest in ethnic cuisines is gaining popularity, more Americans are interested in adding spices/herbs to their daily diets for health benefits. Health benefits conferred by herbs/spices include protection against oxidative stress, neurodegeneration, cardiovascular disease among others and may be at least partially due to their high (poly)phenolic content. (Poly)phenols are not accessible by the human digestive enzymes and are metabolized by the gut microbiome, earning them the status of "prebiotics." This is confirmed by a vast body of evidence pointing to the herbs'/spices' ability to affect gut microbiota composition/functionality.

In vitro experiments and human trials conducted at the UCLA Center for Human Nutrition were collated and results summarized. Reference lists of these publications were scanned and relevant literature extracted. Multiple additional searches relating to the select herbs/spices and their effects on human health were conducted in PubMed.

A total of 8 human trials and 12 in vitro experiments were conducted at the UCLA Center for Human Nutrition between 2010 and 2024. These experiments included interventions with individual herbs/spices, including cinnamon, chili pepper, and turmeric, as well as spice mixes. Additional relevant original research and reviews/meta-analyses were identified and included to supplement the discussions.

While further research of herbs/spices is undeniably warranted, several considerations should be kept in mind. These include the relatively small amounts of herbs/spices consumed by the general population on a daily basis, cooking methods, as well as effects of digestive/metabolic processes on the bioavailability of herb/spice (poly)phenols. While much is already known, there are still substantial gaps in knowledge that need to be addressed.