Grow Youthful: How to Slow Your Aging and Enjoy Extraordinary Health
Grow Youthful: How to Slow Your Aging and Enjoy Extraordinary Health

Healthy immune system - the natural way

A few years ago I was visiting Bali in Indonesia, and happened to be waiting on a footpath to meet a friend. Right next to me, a street vendor was selling food. She had a little toddler, and gave him a corn cob she had just roasted. The little boy licked it and nibbled it a bit, then dropped it on the busy footpath. A street dog came up and sniffed it before the mother shooed the dog away. Eventually she realised her boy was not going to eat the corn cob, so she brushed it off with her hand, and put it back with the others to sell.
David Niven Miller.

To me, this boy looked healthy and active. Sure, in his circumstances he may have been exposed to a parasitic infection or more dangerous bacteria. But one thing he did have was a healthy immune system - developed through exposure to a good range of bacteria from the day he was born, through his infancy, through to his way of life that day.

Research (2) has confirmed that some level of dirt is healthy, even essential for kids. Increasing exposure to germs helps develop the young immune system, so preventing allergies and immune-related diseases like asthma and colitis later in life.

Colds prevented with bacteria - study

Another study (1) looked at just one bacteria - Lactobacillus fermentum - and its effect on common cold prevention. People took a supplement of these bacteria twice a day had less than half the number of sick days as those in the study who took a placebo.

So far there's been little study of L. Fermentum, which is only one of numerous beneficial or probiotic bacteria. More and more, research is showing that probiotics in general are immune-system enhancers, protecting you from viruses, bacteria, fungi and allergies. The richest sources of probiotics are in traditional fermented foods, like kefir, sauerkraut, rejuvelac, kombucha, miso and tempeh.

If you buy probiotic supplements, it may not always be clear which strain you are getting, or how much. You will only be getting one or a just couple of bacteria in a supplement. That's why it is so much better to get dozens or hundreds of different good bacteria from traditional fermented home-prepared foods.

Be aware that virtually all supermarket-sold foods are pasteurised, irradiated, or otherwise treated to kill all the live bacteria that they contain, including the good bacteria. For example, if you buy sauerkraut in a sealed jar, it has been pasteurised.

Centenarians have a different gut biome

Several studies show that centenarians display decreased susceptibility to ageing-associated illness, chronic inflammation and infectious disease. A study in 2021 (3) found that centenarians have a gut microbiome with high levels of microbes which generate special bile acids including iso-, 3-oxo-, allo-, 3-oxoallo-, and isoallo-lithocholic acid (LCA). The researchers found that the centenarian's faecal microbiota were high in Odoribacteraceae bacterial strains that produced these bile acids and other beneficial enzymes. One bile acid called isoallo-lithocholic acid (isoalloLCA) was considered particularly beneficial. They provided protection against gram-positive (but not gram-negative) multidrug-resistant pathogens such as Clostridioides difficile and Enterococcus faecium.


1. Cox, A. J. et al. Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes. British Journal of Sports Medicine 2008 Feb 13.

2. Torsten Olszak, Dingding An, Sebastian Zeissig, Miguel Pinilla Vera, Julia Richter, Andre Franke, Jonathan N. Glickman, Reiner Siebert, Rebecca M. Baron, Dennis L. Kasper, and Richard S. Blumberg. Microbial Exposure During Early Life Has Persistent Effects on Natural Killer T Cell Function. Science Published online 22 March 2012; DOI:10.1126/science.1219328

3. Sato Y., Atarashi K., Plichta D.R. et al. Novel bile acid biosynthetic pathways are enriched in the microbiome of centenarians. Nature (2021). Published 29 July 2021.