Dietitian Sophie Turigel and Chris Young look at two potential benefits of sourdough fermentation.
Phytate (aka phytic acid) is a phosphorus storage compound in plants. It is found in high concentrations in grains and other seeds, particularly the bran coating of cereals. The challenege is that phytate binds with certain minerals (including iron, magnesium and zinc) in food, making them less bioavailable - reducing the amount that can be absorbed during digestion. For this reason, some people refer to it as an anti-nutrient.
Phytate is degraded by the enzyme phytase, which is found in relatively high levels in the digestive systems of cows and other ruminants, allowing them to absorb more of those micronutrients. The human digestive system contains far less phytase, meaning that the phytate in generally healthy foods such as pulses and wholemeal bread can have a negative impact in this respect. This can be a particular issue for people on a vegetarian or vegan diet, who do not eat foods rich in these micronutrients, such as meat and eggs, leading or contributing to conditions such as iron-deficiency anaemia.
A number of studies have concluded that lactic acid bacterial fermentation can create conditions favourable to phytase activity and, therefore, a reduction in phytate levels.
Does this mean bakeries can advertise that genuine sourdough bread is more nutritious or, at least, helps the body make the most of the nutrients in the food we eat? Sadly not. Though each of the studies offers compelling evidence, this shouldn’t be confused with conclusive proof. Something else to note is that, as each study was conducted under carefully-controlled conditions and according to set of specific criteria (a particular bacterium or group of bacteria, at a certain temperature, for a specific period of time etc.), the findings cannot necessarily be extrapolated to apply to all sourdough bread. Much more research is needed.
FODMAPs and IBS
There is also emerging evidence that eating genuine sourdough bread might be beneficial for some people who have Irritable Bowel Syndrome. IBS is a debilitating condition that can cause symptoms including diarrhoea, bloating and excess wind production. These can be triggered by fructans, oligosaccharides, disaccharides and polyols (FODMAPs) fermenting in the large bowel.
People living with IBS are often advised to follow The Low FODMAP Diet, developed and trademarked by Monash University in Australia. This involves avoiding foods high in FODMAPs, such as wholemeal bread made from 'common' wheat (Triticum aestivum) or rye. In Australia, the US and Canada, tests are conducted on specific foods to determine their FODMAP levels and have found that some particular brands of sourdough bread are suitable for people on The Low FODMAP Diet.
Unfortunately, the situation in the UK is very different. The NHS website advises that, other than oats, people with IBS should avoid wholegrain foods – listing ‘brown bread’ (a vague term with no legal definition) amongst its examples. Other sources note that spelt wheat (Triticum aestivum ssp. spelta aka T. spelta) has lower FODMAP levels than modern wheat, pointing to Monash University guidance suggesting that genuine sourdough spelt bread is lower still. It is still only specific brands of spelt sourdough that have been tested and approved for the branded The Low FODMAP Diet. This leaves many people in the UK with IBS turning to gluten-free products, most of which are low FODMAP but tend to be full of additives and can be of questionable nutritional value.
Separating wheat from the chaff
In a society where many people are avoiding Real Bread for a range of reasons, not all of which are founded in hard fact, we need to work together to tackle misinformation about this staple food. One thing we can say with a level of certainty is that any beneficial effects of sourdough fermentation cannot occur to the same extent (or perhaps at all) if the period of lactic acid bacterial fermentation of a dough is shortened by the addition of yeast or chemical raising agents.
Sophie is campaigning to get FODMAP testing equipment in the UK so that bakeries can demonstrate which of their products are suitable for people living with IBS. Meanwhile, the Real Bread Campaign continues to call for more research into the potential benefits of sourdough fermentation to separate the grains of truth from the chaff.
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- Is sourdough ‘better’ than other bread?
- Sourdough: the case for a legal definition
Bakers and health claims
Please note that when labelling, advertising or otherwise marketing food in the UK, it is only legal to make health or nutrition claims listed on the Great Britain Nutrition and Health Claims Register. At the time of publication, none of those listed in the register is related to sourdough.
Whether your understanding or belief is based on personal experience or another source, it is not legal to claim, for example, that sourdough bread is more digestible, nutritious, or lower in FODMAPs.
A high fibre claim can be made about a food but only as long as it contains 6g of fibre per 100g, so the food needs to be tested so you can prove this. You can find information and guidance at www.gov.uk and on the Advertising Standards Authority website.
Please also remember that only a qualified, registered health professional should be issuing dietary or other medical advice.
Published 16 Oct 2023
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