Common kitchen spices, from cinnamon and turmeric to black pepper and oregano, not only add flavor, but can also affect blood sugar, inflammation, brain function, and even the gut microbiome, researchers say.
Research: More than antioxidants, spices: From the gut to the brain. Image credit: monticello/Shutterstock.com
The researchers reviewed the available literature, particularly studies conducted at the University of California, Los Angeles (UCLA) Human Nutrition Center, to determine the effects of spices and herbs on human health. This review is available at nutrition reviews.
herbs and spices
Herbs and spices have been used around the world for centuries, with most originating from the Mediterranean, Middle East, or Asian countries, with origins dating back to ancient Egypt and Rome. Their main uses include enhancing the flavor of foods, acting as preservatives, and providing medicinal benefits.
Herbs are obtained from fresh leaves or flowers, while spices are obtained from roots, seeds, bark, stems, fruits, or buds, and are usually dried. Herbs provide a delicate, fresh flavor and are often added at the end of cooking or used raw. Spices have a stronger, more concentrated flavor and are used not only in marinades and rubs, but also throughout dishes.
Dietary guidelines in many countries recommend spices to reduce sodium intake. For example, the National Institutes of Health’s Dietary Approaches to Stop Hypertension (DASH) diet suggests replacing salt with spices and herbs to lower blood pressure. Recent studies have shown that people who like spicy foods tend to consume less salt and have lower blood pressure.
Polyphenolic compounds found in herbs and spices may help reduce oxidative stress, which is caused by excess free radicals and contributes to aging and diseases such as cancer and metabolic disorders. Antioxidants found in spices, such as phenolic acids, flavonoids, and other secondary metabolites, may help neutralize free radicals and protect against oxidative damage associated with chronic diseases.
A literature review investigating the effects of spices on human health
Between 2010 and 2024, eight human trials and 12 in vitro experiments were conducted at UCLA’s Center for Human Nutrition. These studies included interventions using individual herbs and spices, as well as mixtures of spices. All relevant articles were identified through manual bibliography review and PubMed search on the health effects of each herb and spice.
Health benefits of spices and their underlying mechanisms of action
The health benefits of common spices and their mechanisms of action are discussed below.
cinnamon
Two clinical trials conducted at UCLA’s Center for Human Nutrition found that cinnamon supplementation reduced postprandial insulin and glucagon levels in both normal weight and overweight/obese participants. Cinnamon intake was also associated with lower mean blood sugar levels and significant changes in gut microbiota composition compared to placebo. However, some participants also experienced temporary increases in blood sugar levels at certain points, highlighting the complexity of cinnamon’s metabolic effects. These findings add to broader evidence that cinnamon may help maintain healthy glucose regulation in both healthy people and people with type 2 diabetes.
In addition to its effects on blood sugar levels, cinnamon may have protective effects against respiratory and gastrointestinal infections. It also exhibits anti-inflammatory, antioxidant, hepatoprotective, and neuroprotective effects. The biological mechanisms underlying these benefits include regulation of inflammatory gene expression, inhibition of inflammatory enzymes, and regulation of various cellular signaling pathways related to metabolism, insulin sensitivity, and cellular defense. Cinnamaldehyde, the main active compound in cinnamon, is thought to play a pivotal role in these protective effects.
red chili pepper
Capsaicin, found in chili peppers, stimulates thermogenesis, but ingesting effective amounts can cause severe gastrointestinal side effects. Non-pungent CH-19 sweet chili peppers contain capsinoids such as dihydrocapsiate (DCT), which may provide similar metabolic benefits without these side effects. DCT activates TRPV1 receptors in the intestine, which can induce the sympathetic nervous system and increase thermogenesis and fat metabolism. Extracts from CH-19 peppers may increase thermogenesis, oxygen consumption, and sympathetic nervous system activity, supporting weight loss.
A 2010 UCLA study found that all overweight and obese participants who consumed a low-calorie diet lost weight, whereas only the group that consumed 9 mg of DCT showed a significant increase in postprandial energy expenditure. DCT can promote thermogenesis and fat oxidation. However, a more recent study found that DCT did not significantly affect energy expenditure or fatty acid oxidation during exercise or rest, although a small thermal effect was observed when the groups were combined.
turmeric
A 2014 UCLA study demonstrated that the combination of arctigenin, epigallocatechin gallate (EGCG), and curcumin enhanced anticancer effects in prostate and breast cancer cells compared to a single compound. This combination increased cancer cell death and further suppressed cancer-promoting pathways. Another 2018 UCLA study found that daily supplementation with a bioavailable form of curcumin for 18 months improved memory, attention, and mood in older adults, while also showing imaging changes potentially associated with amyloid and tau accumulation.
Additional studies have shown that curcumin alleviates knee pain in osteoarthritis patients and improves cholesterol profiles in metabolic syndrome patients by increasing high-density lipoprotein (HDL) levels and decreasing low-density lipoprotein (LDL) levels. Mechanistically, curcumin acts as a powerful antioxidant, neutralizing free radicals and strengthening the body’s antioxidant enzymes. It also inhibits important inflammatory pathways and promotes cancer cell death by inducing cell cycle arrest and apoptosis.
spice mix
In vitro and clinical studies have proven that mixed spices such as black pepper, cayenne, cinnamon, ginger, oregano, rosemary, and turmeric are rich in polyphenols that promote the growth of beneficial gut bacteria such as lactobacillus and bifidobacteria. Inhibits the growth of certain potentially pathogenic bacteria.
UCLA research further supports these findings, showing that incorporating polyphenol-rich spices into meat before cooking significantly reduces markers of lipid peroxidation, as shown by lower malondialdehyde (MDA) concentrations. Spice polyphenols also help reduce markers of oxidative stress and improve endothelial function.
In particular, antioxidant activity varies depending on spices and cooking methods. For example, oregano exhibits the highest antioxidant capacity. The curcumin in turmeric maintains its effectiveness after cooking, and while piperine alone has no antioxidant properties, when combined with black pepper it becomes more effective in reducing lipid peroxidation during cooking.
conclusion
Although research has highlighted the many potential health benefits of herbs and spices, much is still unknown about their effects on actual dietary patterns. As natural and widely available ingredients, they offer a promising opportunity to improve public health, but further well-designed studies are needed to clarify their role and provide future recommendations.
This review also highlights that many laboratory studies have used doses higher than those typically consumed in the daily diet, and that cooking methods, digestion, metabolism, and interactions with other foods can influence the bioavailability and efficacy of spice-derived compounds.
Ultimately, a greater focus on herbs and spices in nutrition research may provide practical strategies to support healthier food choices and promote long-term health.
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