Jerusalem artichoke benefits: bifidobacteria rose, short-chain fatty acids did not move

Key benefits

1. 01Early research

   The bacteria changed; the substance that would carry that change did not

   2007, British Journal of Nutrition, design as above.

   Outcome	Result
   Bifidobacteria	+1.2 log10 over 21 days (p<0.05)
   Bacteroides/Prevotella	fell in number
   Clostridium histolyticum/lituseburense	fell in frequency
   Faecal short-chain fatty acids	no change
   Stool frequency	slight increase
   Flatulence	significantly more than placebo (p<0.05)

   A rise of 1.2 log10 in bifidobacteria is roughly sixteen-fold. As a prebiotic it clearly worked, and the design — double-blind, placebo-controlled — is sound.

   But the short-chain fatty acids did not move. Here is why that matters.

   When gut bacteria are said to affect health, much of the proposed route runs through the short-chain fatty acids they make by fermenting fibre — acetate, propionate and butyrate. Butyrate is fuel for the cells lining the colon and is implicated in inflammation and barrier function.

   In other words, short-chain fatty acids are the bridge between "the bacteria changed" and "this is good for you". In this trial the bacteria changed and the bridge did not move.

   That is not the same as "it does not work". Faecal short-chain fatty acid concentration measures what was left after absorption, not what was produced, so production could rise while absorption rises with it and nothing shows in stool. It is a limit of the measurement.

   But what this trial demonstrated stops at the composition of the microbiota. Weight, blood glucose, blood lipids and inflammatory markers were not measured. So "Jerusalem artichoke is good for gut health" runs one step ahead of what this trial showed.

   The scale is small too: fifteen people per group.

   The honest conclusion:

   • That Jerusalem artichoke inulin raises bifidobacteria is confirmed by a double-blind trial
   • In the same trial, short-chain fatty acids did not change
   • No clinical outcome was measured
   • Flatulence rose significantly
   • The grade is "early"
   • Since no structural difference from chicory inulin was found, this site's chicory root entry applies here too

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2. 02Nutrition data

   Do not believe the 1.6 g of fibre — and the 3.4 mg of iron is real

   Per 100 g of raw Jerusalem artichoke:

   • 73 kcal, carbohydrate 17.4 g, sugar 9.6 g, fibre 1.6 g, protein 2.0 g, fat 0.01 g
   • Potassium 429 mg, iron 3.4 mg, phosphorus 78 mg, choline 30 mg, magnesium 17 mg, calcium 14 mg
   • Thiamin 0.2 mg, niacin 1.3 mg, vitamin C 4 mg, folate 13 µg, sodium 4 mg

   Start with that 1.6 g of fibre. It does not contain the inulin.

   This is the same problem set out in this site's chicory root entry. The assay long used as the standard treats the sample with enzymes and then precipitates fibre with alcohol — and inulin dissolves in alcohol and passes straight through. So it is not counted as fibre and instead sits inside the 17.4 g of carbohydrate and the 9.6 g of sugar.

   Seeing 9.6 g of sugar and concluding it must be sweet is half right. Jerusalem artichoke does taste sweet, but a substantial part of that figure is not simple sugar that raises blood glucose — it is inulin, which is not absorbed in the small intestine. The energy actually absorbed is also lower than 73 kcal.

   Iron at 3.4 mg is very high for a tuber. Potato runs 0.8 mg. Against an adult reference of 18 mg, that is 19% in 100 g.

   But it is non-haem iron. Plant iron absorbs poorly and does better alongside vitamin C. Jerusalem artichoke's own vitamin C, at 4 mg, is negligible, so pairing it with lemon juice or raw vegetables works in its favour. Keep tea and coffee away from the meal instead.

   Potassium at 429 mg is also high. If your kidney function is reduced you may be restricting potassium; talk to your clinician.

   Choline at 30 mg is an uncommon row for a tuber.

3. 03Not established

   Gas — the most practical thing to know about this tuber

   In the trial above, flatulence was significantly more common than on placebo (p<0.05). It was mild and sometimes moderate, in some participants.

   This is not a side effect so much as a consequence of the mechanism. Inulin is not digested in the small intestine; it reaches the colon, where bacteria ferment it. Fermentation makes gas. A sixteen-fold rise in bifidobacteria and more flatulence are two faces of the same process.

   Jerusalem artichokes are notorious for this, enough that English has a joking nickname for them.

   On how to set the amount.

   The trial used 7.7 g of fructan a day for a 7-day adaptation period first, and only then raised it to 15.4 g a day for 14 days. Not starting high is the point of that design.

   • Begin with 50 g of raw tuber or less
   • Increase at weekly intervals
   • A large amount at one sitting can bring bloating and cramping

   Take particular care with irritable bowel syndrome.

   Inulin is a FODMAP — the "O", the oligosaccharides. It is one of the classic restrictions on a low-FODMAP diet, and Jerusalem artichoke is among the higher-content foods within it. Symptoms can worsen; talk to your clinician.

   Watch for daisy-family allergy. The Jerusalem artichoke is in that family, and cross-reaction is reported in people allergic to ragweed, mugwort and chrysanthemum. Chicory, globe artichoke, lettuce and sunflower seed share it.

   Notes on cooking.

   • The skin is fine to leave on. It is thin; just wash the soil off well
   • Cooking breaks down some of the inulin, raising the sweetness and leaving slightly less gas
   • Sliced raw into a salad it has a good crisp texture, but produces more gas
   • Cut surfaces brown. Keep them in lemon water — which also helps the iron

How to eat it well

What to watch out for