No.5 Prebiotic Capsules

Hardly anyone asks us whether to take a prebiotic. They ask which one, and whether it'll make them gassy. These are the questions our naturopaths ask in store.

A good fit if

• Regularity is what you're after, and you can reach 10 g of fibre a day, where the trials found an effect
• You'd like to feed the bacteria you already have rather than swallow new ones
• You take an iron supplement. GOS and FOS taken with it greatly increased iron absorption
• You can give it four weeks, which is when the increase in bifidobacteria becomes clearly larger
• You'd rather start with food. Beans, leeks, onions, garlic and chicory all contain inulin

Check with us first if

• You follow a low FODMAP diet. Inulin, FOS and GOS are FODMAPs themselves, so a fermentable prebiotic works directly against the diet.
• You have medically diagnosed IBS. Two independent reviews found the prebiotic evidence limited or not significant, and we won't sell you one on an IBS promise.
• You're dairy-free or vegan. By law, galactooligosaccharides and 2'-fucosyllactose must contain lactose, so neither is dairy-free.
• You have coeliac disease. Wheat dextrin must contain gluten, and so does maltodextrin made from wheat, barley, rye or oats.
• You take medicine for blood sugar. Inulin lowered glucose tolerance test readings and improved insulin resistance in overweight adults, so it's worth mentioning to us.
• You already take a product containing GOS or 2'-FL. By law, their labels must say not to take them on the same day as another product containing the same ingredient.
• You're pregnant or breastfeeding. The research is reassuring, and any product with a regularity claim must still tell you to check with a health professional.
• You're buying for a child. GOS is capped at 8 g a day under three, 2'-FL isn't permitted under one month, psyllium needs medical advice, and fibre maltodextrin is for adults only.
• You take prescription medicine. Check with your doctor, pharmacist or our naturopaths before you start.

• Inulin (chicory root, long chain). Best known for: The name on most prebiotic labels, and the slowest of the fructans to ferment. Absorption: Increased bifidobacteria (good gut bacteria) across several trials, and improved insulin resistance at 20 g a day in 12 overweight adults. Typical use: Powders and gut blends. Allowed as an active ingredient with no limit and no warnings.
• FOS / oligofructose (short chain). Best known for: Shorter, sweeter chains that ferment quickly, early in the bowel. Absorption: Raised Bifidobacterium counts by 0.579 across 8 trials, more in adults than infants, and raised iron absorption by 51 per cent. Typical use: The common prebiotic most likely to cause wind, and its own meta-analysis flagged it.
• GOS (galactooligosaccharides). Best known for: The closest commercial match to the sugars (oligosaccharides) in breast milk. Absorption: Improved bowel movements and stool form over 4 weeks in functional constipation, and lowered gut symptom scores at 2.5 g a day in 427 students. Typical use: Made from lactose, so it isn't dairy-free. Capped at 16.2 g a day, by mouth only, and the label must warn you not to double up.
• PHGG / guar galactomannan. Best known for: Partly broken-down guar. It's thin, ferments slowly and evenly, and is the usual switch when nothing else agrees with you. Absorption: A 21-day trial in 61 adults increased complete, spontaneous bowel motions, but the same trial found the variety of gut bacteria fell. Typical use: Capped at 25 g a day, and the label must tell you to build up the dose slowly and never take the powder on its own.
• Acacia gum / gum arabic. Best known for: Not thick, mixes clear, and the slowest to ferment of the common prebiotics. Absorption: 10 g a day improved how often people went compared with placebo in 180 people; 40 g increased fullness in the short term, along with bloating and rumbling. Typical use: Allowed as an active ingredient with no limit. A sensible pick if inulin gives you wind.
• Psyllium (Plantago ovata husk). Best known for: A husk that bulks and forms a gel, and is only partly fermented, so it adds bulk without much gas. Absorption: The only fibre rated moderate for long-term constipation in a graded review of 41 trials, and the only one that formed a gel in stool. Typical use: Whenever a children's dose is given, the label must say it should only be used for children on medical advice.
• Resistant starch (high amylose maize). Best known for: Starch your digestive enzymes can't reach, which gut bacteria ferment mainly into butyrate. Absorption: Part of a diet that raised short-chain fatty acids in stool to 86.6 from 75.4 µmol/g, and blood propionate to 9.87 from 4.72 µM. Typical use: Allowed as an active ingredient with no limit. Added to a low-FODMAP diet, it raised stool output by about 50 per cent without making symptoms worse.
• 2'-FL and other human milk oligosaccharides. Best known for: The main sugar (oligosaccharide) in breast milk, now made by fermentation. Absorption: Moved formula-fed babies' gut bacteria closer to a breastfed pattern; in 89 older adults it raised bifidobacteria but missed its main immune-marker goal. Typical use: The most tightly controlled form on this list. Lactose must be declared, limits vary by age, and it isn't allowed under one month.

Reference values. There isn't one. The NHMRC reference values cover 25 vitamins and minerals and don't include a figure for prebiotics, because prebiotics aren't essential nutrients. You can live without them, so there's no recommended intake to quote.

Typical supplemental range. Trial doses ranged from 2.5 g to 30 g a day, which is more than most capsules provide: inulin and fructan blends at 9.2 to 30 g, GOS at 2.5 to 15 g, FOS at 15 g, and acacia at 10 to 40 g. The useful low-dose result is GOS at 2.5 g, which did better than 5 g on gut symptom scores in 427 students. Across 16 trials, more than 10 g a day was the point where fibre did better than the comparison for constipation. A blend with 500 mg a capsule isn't giving you a trial dose.

Upper level. Several prebiotics have a legal daily limit in listed medicines rather than a nutritional one: galactooligosaccharides 16.2 g for anyone four and over and 8 g for ages 0 to 3, guar galactomannan 25 g, larch arabinogalactan 15 g, hydrogenated polydextrose 15 g, fibre maltodextrin 50 g (adults only), 2'-fucosyllactose 12 g for ages 13 and over, and 3-fucosyllactose 5 g. Inulin, FOS, acacia, psyllium and resistant starch have no limit.

Worth knowing. Two tips matter more than the dose. Build up slowly over a week or two with plenty of water, because the discomfort, wind and loose stools depend on the dose and pass with time. And give it four weeks: the increase in bifidobacteria was clearly larger in trials that ran longer than four weeks, so a shorter try won't tell you much. What you need depends on your age, diet and health, so talk to one of our naturopaths.

Food first, where the diet allows it.

• Chicory root: inulin: the commercial source of nearly all inulin sold
• Leeks, onions, garlic, wheat and artichokes: inulin and oligofructose, as everyday dietary components
• Jerusalem artichoke: inulin: the source used in a six-month paediatric trial
• Beans, one cup daily: mixed fermentable fibre; raised gut diversity over eight weeks
• Milk: lactose, the substrate GOS is manufactured from
• Human breast milk: 2'-fucosyllactose, one of its most abundant oligosaccharides

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• Tummy pain, nausea, vomiting or new diarrhoea. Every bowel-regularity product must tell you not to use it if you have these.
• Fibre powders taken dry. Labels must tell you to mix them with food or fluid; a swelling fibre taken on its own risks a blockage.
• Raising your fibre dose. Labels must tell you to increase it gradually, and to drink more fluid as you do.
• Low-FODMAP diets and diagnosed IBS. Inulin, FOS and GOS are FODMAPs and can make symptoms worse.
• Dairy-free and vegan customers. Galactooligosaccharides and 2'-fucosyllactose both contain lactose, which must be declared.
• Coeliac customers. Wheat dextrin and maltodextrin from gluten grains contain gluten, which must be declared.
• Babies under one month. 2'-fucosyllactose isn't allowed for children under the age of 1 month.
• Children under three. Galactooligosaccharides are capped at 8 g a day, and psyllium needs medical advice whenever a children's dose is given.
• Fibre maltodextrin. It must be labelled for adults only, and carries a low blood sugar warning.
• Doubling up. GOS and 2'-FL labels must tell you not to take them on the same day as another product with the same ingredient.
• If you take medicines that lower blood sugar. In trials, inulin lowered blood sugar after a glucose load and improved insulin resistance.
• Everyone, at higher intakes. Tummy discomfort, wind and diarrhoea are common and rise with the dose.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before you start.