Caesar’s mushrooms, foraged in the Appenine forests
Trehalase deficiency (TREHD) — or trehalose intolerance — is one of the more curious of the many food sensitivities which affect us, albeit also one of the rarest.
As with the far more common and well-known lactose intolerance (lactase deficiency), trehalose intolerance is caused by a deficiency of the enzyme trehalase, which is required to break down the dietary sugar trehalose into glucose in the gut, for absorption.
Trehalose sugar is found mainly in mushrooms, particularly shiitake and oyster mushrooms, but also seaweed / algae, shellfish, insects, sunflower seeds and yeasts. As an additive, it is sometimes used to prolong the shelf life of dried food — especially in Japan.
As you might expect, the symptoms of trehalose intolerance are similar to those experienced by those with lactose intolerance — diarrhoea, abdominal disturbance and sickness.
There is an association with coeliac disease, again analogous to the lactose / lactase situation, in that trehalase production in undiagnosed coeliac disease can be hampered, but it does recover when the patient is established on a gluten-free diet. This is secondary (transient) trehalose intolerance, and can also be caused by severe gastroenteritis and other gut diseases.
Primary trehalase deficiency is an inherited genetic condition. It is relatively unknown in most Western nations, but is common among Greenlandic peoples, where around 10% of the population may be affected, and other Nordic / Scandinavian peoples appear to show higher rates too. Although thought to be rare elsewhere, the real degree of prevalence is unknown, partly because consuming a large quantity of trehalose is not common, and many who find mushrooms don’t ‘agree’ with them merely avoid consuming them.
There’s no need to moderate your mushroom intake if you enjoy them and have no symptoms. In fact, it has been proposed that trehalose might be a powerful tool in the fight against Covid-19, so with winter just around the corner, it may well be a good plan to keep your fungi firmly on the menu …