From chillies and garlic to turmeric and cinnamon, spices add flavour, colour and scent to our meals, delighting the tastebuds and bringing ingredients to life. But could they be beneficial for our microbiome and overall health? Keep reading to find out.
- Spices: more than just seasoning
- The more, the merrier: spice blends
- Spice and the gut microbiome
- Article Summary
Of spice and men
Spice refers to aromatic substances derived from the seeds, bark or root of plants.
For example, cinnamon is derived from the bark of evergreen trees, turmeric from the Curcuma longa plant root and cardamom from the seeds of several plants.
Spices are often dried or powdered and typically used to season food, though that's only one of their uses.
Throughout history, humans have prized spices as food seasoning, fragrance and even to mummify human remains!
Their desirability has driven expeditions across the globe and fuelled wars between nations- it's not an understatement to say they have shaped the world as we know it.
Beyond their ritual and culinary uses, spices have been used medicinally for millennia in ancient Egypt, China, Greece and India.
Take Ayurvedic medicine, a traditional Indian practice dating back 3000 years. It remains a popular alternative therapy and utilises individual spices and blends to treat issues such as digestive upset, inflammation, pain and even diabetes.
Researchers have recently begun investigating these long-revered spices' purported health benefits.
Emerging research also suggests that certain spices may be able to shape the microbiome, encouraging the growth of beneficial bacteria whilst inhibiting harmful pathogens. Without further ado, let's take a look at the evidence:
☝DID YOU KNOW?☝: The Egyptians used spices such as cinnamon in the mummification process..
The best-studied of all spices is turmeric, a golden root plant with an earthy and bitter taste. It is sourced from the Curcuma longa plant, belonging to the same family as ginger.
Historically, turmeric has been used to treat conditions such as arthritis, inflammation and chronic pain, but is there any evidence to support its efficacy?
Turmeric contains a powerful polyphenol called curcumin which has anti-inflammatory, anti-cancer and antioxidant effects in vitro (outside living organisms).
The human research on turmeric is promising, with emerging research suggesting that it may be able to alleviate post-exercise muscle soreness, osteoarthritic pain and other inflammatory conditions.
Early trials suggest that turmeric may be able to mitigate the adverse effects of chemotherapy, including radiation dermatitis and oxidisation (cell damage).
Additionally, lab studies suggest that chemotherapy combined with turmeric supplementation may be better at tackling bowel cancer cells than chemotherapy alone.
There are drawbacks, however. For a start, the dose and duration of turmeric supplementation vary drastically among the studies- many of which are small-scale.
Commenting on the available research, Cancer Research UK states:
"Although some of the results look promising, they do not give enough evidence to say curcumin is an effective cancer treatment. More studies are needed and with larger numbers of people."
Moreover, curcumin is poorly absorbed in the small intestine, meaning little of the compound makes it into the bloodstream.
Interestingly, a compound called piperine in black pepper can increase curcumins bioavailability by as much as 2000%!.
Nonetheless, we recommend you steer clear of concentrated spice supplements (such as curcumin) and opt for whole spices (turmeric powder or root).
☝TOP TIP☝: Add a pinch of black pepper to enhance the availability of curcumin in your turmeric..
Ginger is a fragrant root plant used medicinally for centuries, spanning multiple cultures.
Researchers have isolated around 100 compounds from ginger, including gingerol, shogaols, zingiberene, and zingerone.
Among these, gingerol is considered the main bioactive compound, possessing antioxidant, antimicrobial, and anti-inflammatory properties.
The best available evidence seems to support its traditional use, with studies suggesting it may alleviate mild nausea and vomiting.
If you're considering taking ginger supplements during pregnancy, consult your GP first.
Whilst oral supplements have been reported as safe in some studies, the evidence is not conclusive yet. The same applies to breastfeeding.
Compared to other spices, there's a considerable amount of research exploring ginger's purported health benefits. However, almost all of these have used ginger supplements instead of foods.
Drawing on the available studies a paper published in 2020 performed a systematic review of over 100 Randomised Controlled Trials testing the health benefits of ginger.
The papers explored ginger's effect on multiple health conditions, including nausea, vomiting, inflammation, and colorectal cancer risk.
Note: Only 39.4% of the trials were deemed as having a "high quality of evidence". Moreover, the sample sizes were small across the studies (mostly under 50 and some less than 20).
The paper reports that the majority of RCTs found ginger to be efficacious, particularly the studies looking at its effect on digestive function, inflammation, pregnancy-related nausea/vomiting and colorectal cancer risk markers.
That's not to say that ginger has been proven effective for these conditions, however. For example, only 4 RCTs looked at gingers' effect on colorectal cancer risk. Pending larger and better quality studies, the jury is out.
In short, there is compelling evidence that ginger supplements may be able to alleviate mild nausea and vomiting, but consult your GP before taking them if you are pregnant or breastfeeding.
☝IMPORTANT☝According to a systematic review of RCTs, the most common side effect of ginger is heartburn, especially at doses between 500 and 2000 mg a day.
Cinnamon is sourced from the bark of evergreen trees, getting its unique aroma and flavour from an essential oil called cinnamaldehyde, a compound with antibacterial, antifungal and antiviral properties.
Moreover, one study found that consuming 1, 3 or 6g of cinnamon daily for just over a month reduced fasting blood sugar levels, LDL (bad) cholesterol and triglyceride in the bloodstream.
High levels of these markers are risk factors for heart disease, suggesting cinnamon may be cardioprotective.
A 2013 meta-analysis comprising ten studies concluded that cinnamon consumption triggered "statistically significant" reductions in blood glucose, LDL (bad) cholesterol also.
However, the amount of cinnamon and the duration of time it was taken varied drastically between studies, meaning the most effective/safe dose remains unclear.
Whilst acknowledging that the research is promising, Diabetes UK comments:
"Bear in mind that like many natural compounds, cinnamon is yet to be medically approved for prevention or treatment of any disease."
Not all cinnamon is created equal
Be aware that there are two types of cinnamon: Cassia and Ceylon or "true" cinnamon. Most of the cinnamon sold in supermarkets is of the cassia variety, which is stronger and cheaper than the alternative.
Moreover, Cassia cinnamon contains high amounts of compounds called coumarins, which can be toxic in larger doses.
The odd sprinkle of cassia cinnamon on your toast or latte won't cause any ill effect.
However, frequent and prolonged use of cassia cinnamon may cause issues in sensitive individuals long-term, such as those with liver disease. Be aware that cinnamon can interact with diabetes, liver and heart disease medication.
☝IMPORTANT☝ In higher doses, cinnamon can cause digestive issues. For reference, it is generally recommended that adults eat no more than a tablespoon a day.
Garlic is a staple of many national cuisines and has been prized for its reputed health benefits for centuries.
In particular, garlic is said to be heart-healthy and able to fight the common cold, but is there any evidence to back up these claims?
garlic and the common cold
A key compound in garlic is a sulfide called allicin, responsible for its potent aroma and flavour. Allicin is both antiviral and antibacterial, leading some to argue it can help fight infections like the common cold.
The Cochrane Institute- renowned for their rigorous systematic reviews- performed a literature review to assess these claims. Out of eight studies, only one fit the criteria for review.
The included study found that daily garlic supplementation over three months resulted in fewer colds relative to a placebo group.
For comparison, there were 24 occurrences of the common cold in the garlic group and 65 in the placebo group over the same period. The illness lasted for a similar duration in those who contracted a cold.
Due to the startling lack of clinical trials, Cochrane concluded that "claims of effectiveness appear to rely largely on poor-quality evidence."
Can garlic prevent heart disease?
The evidence for garlic's cardioprotective effects is more compelling, though not without drawbacks.
Studies suggest that garlic can reduce blood pressure and LDL" bad" cholesterol, two key markers of heart health.
Moreover, there is evidence to suggest garlic may be able to reduce clotting in the artery walls also, a risk factor for coronary heart disease.
As the American Heart Foundation (AHF) notes, the studies observing these effects use high doses of supplemental garlic- far more than you're likely to obtain from cooking with a few cloves.
Before you run to your local health food store, the AHF recommend against taking concentrated garlic supplements unless instructed otherwise by your physician.
In short, there is compelling evidence to suggest that garlic is cardioprotective, although the doses achieved by eating fresh garlic may be insufficient to achieve these effects.
That's not to say that garlic shouldn't play a part in your diet, however. Garlic is an excellent base for multiple dishes- hence why it features in cuisines worldwide, including the healthful Mediterranean diet.
Be aware that garlic can interact with blood thinning medicines such as Warfarin (Coumadin). If you are due to undergo surgery or are taking blood thinners, notify your GP before taking garlic supplements.
☝TOP TIP☝ Ageing garlic can potentially increase its antioxidant properties, enhancing its health effects.
The more, the merrier: spice blends
Eating a meal high in carbs and saturated fat has been observed to trigger short-term or "acute" inflammation.
It's unclear whether acute inflammation after eating can trigger chronic inflammation, although researchers suspect it plays a part- particularly in those who are obese.
According to a study at Penn State University, adding a diverse spice blend to a meal high in carbohydrates and fats may be able to offset post-prandial inflammation.
In short, the researchers mixed a colourful array of over ten spices and herbs, including cinnamon, ginger, oregano and turmeric.
They recruited 12 men, all overweight or obese, and randomly gave them three meals high in saturated fat and carbs; one of the meals contained no spice mix, another had 2g of the blend and the third 6g of the spice blend (roughly about a tablespoon).
Compared to meals with less or no spice, the 6g tablespoon of spice blend reduced inflammatory markers in all participants.
Whilst the researchers couldn't identify which spices were responsible for the effect or the mechanisms, the study suggests that eating a spice blend may minimise the adverse effects of meals with a high inflammatory load.
Spices and the microbiome
As we discussed earlier, certain spice compounds (curcumin) are poorly absorbed in the small intestine.
As a result, they pass undigested to the large intestine, interacting with the trillions of microbes in your gut. But what effect do spices have, and could they benefit our health?
The prebiotic effect of spices
According to an in-vitro study published in the Journal of Food Science, certain spices may be able to nourish beneficial bacteria and inhibit the growth of harmful pathogens.
The study explored the effects of seven culinary spices, including:
- black pepper
- cayenne pepper
- Mediterranean oregano
All of the spices, except for turmeric, were observed to enhance the growth of bifidobacterium and lactobacillus species in the lab- broadly considered probiotics.
Parallel to this, all the spices were observed to inhibit the growth of ruminococcus species, some of which are associated with Crohn's disease.
The researchers singled out oregano, ginger, cayenne and black pepper as having a prebiotic effect- suppressing "bad" bacteria and encouraging the growth of probiotic species.
Cinnamon also exhibited "modest" activity against clostridium difficile, an antibiotic-resistant pathogen that can cause chronic diarrhoea.
Whilst promising, the results can't simply be extrapolated to humans as spices may act differently in the human gut.
A study published in 2021 sought to fill this research gap.
To this end, the researchers recruited 15 healthy males and explored how a single serving of an Indian spice blend altered their microbiome.
The participants ate three separate meals, including a low-polyphenol, spice-free curry, a curry with 6g and a curry with 12g of the spice mix.
The dose-response study found that a single serving of the spice mix could modify the gut microbiome composition (but not overall diversity).
There was a noticeable inter-individual variability in how much gut composition changed- for example, those who didn't eat spices often saw the most pronounced changes.
Further research is needed to determine how spices interact with the gut microbiome.
In light of the research- and considering their safety- we recommend adding a colourful variety of whole spices to your meals and experimenting with different flavour combinations.
Some of my favourites are Chinese five spice (cinnamon, fennel seed, star anise, and cloves) and classic curry powder (turmeric, cumin, ginger, and black pepper.)
As we mentioned earlier, black pepper can release curcumin in turmeric, potentially enhancing its health effects.
Last but not least, cooking with a rich selection of spices can reduce your salt intake, too much of which can increase your risk for multiple health conditions.
The scope and quality of research vary drastically between different spices, with turmeric and ginger enjoying the most attention to date.
Whilst the research is compelling, many studies looking at these spices are small-scale, and questions remain about how they function when ingested, especially turmeric.
With that said, research suggests they may be able to remedy health complaints such as arthritis, nausea and digestive issues.
What's more, when eaten at normal doses as part of a healthy diet, spices have a remarkably good safety profile and can make your food more appealing.
We recommend you eat a colourful variety of whole spices instead of concentrated supplements.
This way, you will get the full range of active compounds from the original plant- including polyphenols.
You can source whole spices from your local market, alongside fresh fruit and vegetables- all of which your gut microbiome loves!
The research on spices and the microbiome is extremely scarce, but the results are promising.
Early findings suggest culinary spices can act as probiotics for your microbiome, potentially feeding good microbes and inhibiting opportunistic pathogens. Further studies are needed to confirm these findings in human subjects, however.
- Spices have been valued for their culinary and medicinal uses for millennia, featuring in both traditional Indian and Chinese medicine
- Research suggests that common culinary spices such as turmeric, cinnamon and ginger may be able to reduce inflammation, reduce blood sugar levels and remedy digestive upset, although there are drawbacks and the research quality on individual spices varies drastically
- Although the research is in its infancy, evidence suggests that spices interact with the gut microbiome, shaping its composition. In particular, cayenne, black pepper, ginger and oregano have been observed to be prebiotic in lab studies
- In one study, eating a blend of 14 spices reduced post-prandial inflammation after a high-fat, high-carb meal in obese male adults.
- Although most common spices have a good safety profile when eaten at normal doses in the diet, it remains unclear whether some spices remain safe at higher doses or taken when taken medicinally
- Experiment with a variety of spices instead of supplementing with one or treating them as pills
- Opt for whole spices over concentrated supplements