Spices Keep You Healthy

At some point, after three years in Thailand, I was convinced that science had ignored the health benefits of capsaicin - the part that makes hot peppers so spicy.  Surely, I thought, this heat helped to preserve foods, in a different way than salt does.  

Today this 24 year old paper popped up on Twitter that confirms my assumption.  What I didn't recognize was that garlic and onions are even better at the killing and/or inhibiting the growth of microbes.  Though I did assume the high use of garlic in hot climates had some health benefits too.  

The authors write in the overview:

"We wondered if there are any predictable patterns of spice use and, if so, what factors might underlie them. In this article, we summarize the results of our inquiries. We found that spice use is decidedly nonrandom and that spices have several beneficial effects, the most important of which may be reducing foodborne illnesses and food poisoning."

Prediction 1. Spices should exhibit antibacterial and antifungal activity.

And this chart shows that 

Prediction 2. Use of spices should be greatest in hot climates, where unrefrigerated foods spoil especially quickly.

They looked at cookbooks from 36 countries to see what spices were used, how many recipes included spices, how many spices per recipe, and which spices.  The used a climate atlas to rate the climate in each of the 36 countries. 

Prediction 3. A greater proportion of bacteria should be inhibited by recipes from hot climates than from cool climates.  

". . . the mean fraction of recipes that called for each one of the highly inhibitory spices used in those countries increased significantly (Figure 8a). However, this correlation did not hold for less inhibitory spices (Figure 8b). There was also a positive relationship between the fraction of bacterial species inhibited by each spice and the fraction of countries that used that spice, indicating widespread use of the spices that are most effective against bacteria."

There are a number of other things they looked into (ie. cost of spices, lemon/lime juice increases anti-microbial power of spices).  

So one question I have relates to the fact that our bodies rely on microbes to keep us healthy.  My awareness of this came well after 1999 (when the spice article was published) and I'm not sure how well it was known in 1999 or by the authors.  Do spices harm the gut biome?  

The article is written in clear language that should be easy for most people to understand most parts.  It also has pictures of spices as well as straightforward charts.  

Darwinian Gastronomy: Why We Use Spices: Spices taste good because they are good for us 

Paul W. Sherman,   Jennifer Billing  Author Notes  BioScience, Volume 49, Issue 6, June 1999, Pages 453–463, https://doi.org/10.2307/1313553   Published: 01 June 1999

They use' microbe' in some places and 'bacteria' in other places.  Since I wasn't completely sure about what each term meant, I found this American Society for Microbiology page "What Counts As A Microbe?"