Prebiotics: a missing link to long-term gut health

Why probiotics aren’t enough

The power of probiotics has been all the rage in the last few years, as these beneficial microorganisms have shown to help with various conditions — such as infant colic, eczema, antibiotic-induced diarrhea, acute infectious diarrhea, and even upper respiratory tract infections.^1,2 However, the therapeutic effects of probiotics are transient: probiotics are not able to recolonise or reseed healthy bacteria populations in the gut. The strains only remain for days or, depending on the persistence of the strain, weeks after we stop taking them.^3,4

To address this, we turn to probiotics’ less spoken about, but very powerful counterpart — prebiotics. Prebiotic food sources selectively feed beneficial bacteria to build up health-promoting populations while suppressing the bad ones. To be considered a prebiotic, a food source:⁵

• Cannot be digested or absorbed in the stomach or small intestine
• Must act as a food source for one or more beneficial bacteria in the large intestine
• Must affect the composition of the colonic microflora ecosystem in a positive way
• Must induce changes that improve the health of the host

Three of the most studied prebiotics are partially hydrolyzed guar gum (PHGG), galactooligosaccharides (GOS), and fructooligosaccharides (FOS).

1. Partially hydrolyzed guar gum (PHGG)

One of our favorite prebiotics is less well known, but incredibly effective and with plenty of research to support it. Meet partially hydrolyzed guar gum — not to be confused with guar gum, as the two are processed very differently in the body.

Benefits as a prebiotic

In one study, six strains of lactic acid bacteria were studied with PHGG, and almost all showed an ability to assimilate it. Streptococcus thermophilus — a bacterium with many digestive and immune benefits — exhibited the highest growth. The researchers concluded PHGG can be considered a prebiotic source that helps grow probiotic bacteria and balance gut microflora.⁶ Other benefits:

• Relieves constipation just as well as laxatives do, but with no adverse effects.⁷
• In patients on enteral nutrition (tube feeding), lowers the incidence of diarrhea.⁸
• Useful for IBS symptoms — both constipation- and diarrhea-dominant — in adults and children.^9,10
• Increases Bifidobacterium, as FOS and GOS do.^11,12
• Promising for SIBO: a clinical trial found patients using rifaximin with PHGG had better outcomes than rifaximin alone.¹³
• Often a preferred prebiotic supplement compared to others.¹⁴

Its promise for bacterial overgrowth is one reason PHGG comes up so often in our gut work — see our overview of SIBO and how we test for it.

2. Galactooligosaccharides (GOS)

GOS are chains of galactose molecules found in all mammalian milk. Like FOS and PHGG, they aren’t absorbed or broken down in the upper GI tract, which lets them reach the colon. For supplementation, GOS is derived from lactose using the enzyme beta-galactosidase. It’s found in significant amounts in human breast milk — and recently added to some infant formulas to mimic it — as well as in legumes, Brassica-family vegetables, and pumpkin seeds.

Benefits

• Increases growth of bifidobacteria, which help digest fiber, produce short-chain fatty acids, and make important B vitamins.¹⁶
• Some research shows GOS also increases growth of lactobacilli.¹⁷
• Can significantly improve constipation.¹⁸
• In combination with FOS, has treated and helped prevent atopic eczema in infants.¹⁹
• Improves IBS symptoms — bloating, flatulence, stool consistency, and anxiety.²⁰
• Has a protective effect against GI pathogens such as E. coli,²¹ Salmonella typhimurium,²² and Vibrio cholerae.²³
• Improves calcium absorption.^24,25

3. Fructooligosaccharides (FOS)

FOS is made up of branched chains of fructose and glucose molecules. It resists digestion in the upper GI tract because of the beta configuration of its bonds (the human GI tract requires alpha configurations), so FOS is a non-digestible oligosaccharide. It’s found in over 36,000 plant species — including chicory root, dandelion, garlic, leeks, and rye. The most common supplement form is inulin, created by hot-water extraction of fresh chicory roots.

Benefits

• Increases growth of bifidobacteria — which help digest fiber, produce short-chain fatty acids, and make B vitamins.^27,28
• In combination with GOS, improved immune response in infants given prebiotic-containing formula versus formula without.²⁹
• Increases absorption of minerals such as calcium and magnesium.³⁰
• In combination with GOS, improved treatment and prevention of atopic eczema in infant-formula studies.¹⁹
• Promotes satiety, or the feeling of fullness.³¹

A documented (though apparently very rare) anaphylactic allergy to inulin exists.³² Concerns have also been raised that FOS increases Klebsiella pneumoniae — but that occurred only when the bacterium was grown in isolation in a Petri dish, not in the presence of other bacteria as in the human GI tract.³³

Other prebiotic-like foods

Some foods are prebiotic-like: they reach the colon and feed good bacteria, but don’t always feed them selectively the way true prebiotics do. They still positively shift the microbiome. These include polyphenols — phytochemicals in fruits, vegetables, legumes, tea, coffee, and chocolate — best known for their antioxidant properties but also shown to increase good bacteria like bifidobacteria and lactobacilli.³⁴ Another is resistant starch, in foods such as legumes, red kidney beans, and less-ripe bananas, which improves colonic health and increases bifidobacteria and lactobacilli.³⁵