Rye benefits: the bread with extra bran did worst

Key benefits

1. 01Early research

   Whole grain rye beat white wheat bread on insulin; rye bran went the other way

   2009, Nutrition Journal. A crossover trial from the Division of Applied Nutrition and Food Chemistry at Lund University.

   The design:

   • 12 healthy adults
   • Rye products made from endosperm, whole grain or bran, produced by different methods — baking, simulated sourdough baking and boiling — served as breakfasts in random order
   • White wheat bread as the reference
   • Blood glucose, serum insulin, plasma ghrelin and subjective satiety measured over 180 minutes
   • A new measure, the glycaemic profile, defined as the duration of the incremental postprandial glucose response divided by its incremental peak (min/mM)

   The results:

   • Whole grain rye breads and endosperm rye products gave significantly lower insulinaemic indices than white wheat bread (p < 0.05).
   • Rye bran bread gave a significantly higher insulinaemic index than all the other rye products.
   • The acute insulin response correlated better with the glycaemic profile than with the glycaemic index.
   • Endosperm rye bread and whole grain rye bread with lactic acid produced a significantly higher glycaemic profile than rye bran bread, white wheat bread, and the wheat and whole grain rye porridges.
   • A lower insulin peak went with less severe late postprandial hypoglycaemia (r = 0.38, p < 0.001), and that hypoglycaemia correlated negatively with subjective satiety at 180 minutes (r = −0.28, p < 0.05).
   • A lower insulin peak also went with a milder recovery of plasma ghrelin at 180 minutes (r = 0.34, p < 0.01).

   How to read the bran result. Rye bran is the fibre-rich fraction. It produced the worst insulin response of the rye products tested. It is a case where whole grain being good does not mean that adding more bran is better. A grain with its structure intact is not the same as flour with bran stirred back in.

   The satiety observation is also interesting. When insulin spiked and fell, late hypoglycaemia followed, and that hypoglycaemia ate into fullness three hours later. It is data that speaks to the folk claim that a glucose spike leaves you hungry sooner — but the correlation is weak at −0.28.

   The limits are clear.

   First, twelve people. It points a direction, no more.

   Second, it is an acute study of three hours after one meal. It does not answer what happens to diabetes or weight over time.

   Third, all were healthy adults. People with diabetes may respond differently.

   Hence the early grade.

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2. 02Nutrition data

   15.1 g of fibre — more than whole wheat

   Per 100 g of dry rye grain:

   • 338 kcal, protein 10.3 g, fat 1.63 g
   • Of 75.9 g of carbohydrate, 15.1 g is fibre — sugar is 0.98 g
   • Magnesium 110 mg, potassium 510 mg
   • Manganese 2.58 mg — above the adequate intake
   • Iron 2.63 mg, zinc 2.65 mg, selenium 13.9 µg
   • Thiamine 0.316 mg, niacin 4.27 mg, vitamin B6 0.294 mg
   • Sodium 2 mg

   The 15.1 g of fibre is the core of this grain. More than whole wheat (12.2 g) and more than oats (10.6 g) — near the top of commonly eaten grains.

   Rye's fibre is mostly arabinoxylan. It holds water and makes the dough sticky, which is why rye bread is denser and heavier than wheat bread.

   Sugar is effectively absent at 0.98 g.

   One distinction matters here: these figures are for the grain. Most shop "rye bread" is blended with a substantial proportion of wheat flour, which drops the fibre considerably. Check where rye flour sits in the ingredient list. If rye is not first, it is closer to wheat bread.

   Do not judge by colour. Caramel colouring and molasses darken many loaves.

   Magnesium at 110 mg and manganese at 2.58 mg are the mineral strengths.

3. 03Not established

   Rye contains gluten — and a word on sourdough

   This entry corrects a common belief.

   "Rye is gluten-free" is false. Rye, with wheat and barley, is a gluten-containing grain. People with coeliac disease must avoid rye too.

   The confusion arises because rye's gluten behaves differently from wheat's. Rye has gliadin but little glutenin, so it cannot form the elastic gluten network wheat does. That is why rye bread is dense and does not rise — not because there is no gluten in it.

   A word on sourdough. Rye bread is traditionally made with a sourdough starter. Rye dough has to be acidic for its enzyme activity to be controlled and for the loaf to bake properly — the practice began as a baking necessity, not a flavour or health choice.

   The claim that sourdough fermentation reduces phytate and so aids mineral absorption has laboratory support. But randomised evidence that eating sourdough bread improves people's iron or zinc status is thin.

   That the whole grain rye bread with lactic acid sat on the favourable side of the glycaemic profile in the trial above is interesting, but it is one condition in a twelve-person study.

   The honest summary: what can be said about rye today is the composition table (15.1 g of fibre) and one acute trial in twelve people. The health effects of sourdough are not yet at that level.

How to eat it well

What to watch out for