Maldigestion: means „inefficient digestion” – a certain substance is not being broken down efficiently in the stomach or in the small intestine and can therefore not be digested properly
Malabsorption: means „inefficient absorption or intake” – a certain substance is either poorly absorbed, or not absorbed at all via the digestive system, and can therefore not be ingested by the system.
Intolerance: the medical term for food intolerance is non-allergic food hypersensitivity (in short: food hypersensitivity), sometimes referred to as „pseudoallergic reaction”. This means that a certain substance cannot be tolerated well and thus causes symptoms.
Additional info - Food Allergy: A food allergy is an adverse immune response to a food, it's not a food intolerance! Allergies always are immune reactions (IgE). The most common food allergies are a sensitivity to peanuts, fish, milk, eggs, nuts, seafood, shellfish, soy and wheat.
The difference between terms is in the detail and under normal circumstances this is not relevant to those affected. The terms are thus frequently interchangeable. For example, fructose malabsorption is the same as dietary fructose intolerance (DFI) (see article „What is fructose malabsorption?”). The same happens with the term intolerance. Fructose malabsorption is thus also referred to as fructose intolerance, but "fructose malabsorption" is more commonly used.
The same principle applies to lactose intolerance or lactose maldigestion.
Attention: Hereditary fructose intolerance (HFI) is something completely different than fructose malabsorption (also known as dietary fructose intolerance).
Laktose intolerance is also known as lactase deficiency (see more in article „What is lactose intolerance”). Several other terms are used which are all connected to lactose intolerance including, for example, lactose maldigestion, lactose malabsorption, lactase deficiency syndrome, lactase non-persistence, hypolactasia and more...
The types of lactose intolerance do of course need to be separated in order for the medical professional to be able to make an exact diagnosis. Maldigestion can result in malabsorption, and this can – but does not necessarily have to – result in intolerance.
This means that there can be patients who may have mild fructose malabsorption, but because they do not experience any noticeable symptoms, they do not suffer from an intolerance. In medical practice such cases will, however, appear very rarely, as patients only visit their doctor if they experience symptoms, and thus already have some form of intolerance. Malabsorption should, however, always be treated as it can lead to more serious problems – even when the patient does not experience any symptoms. This certainly needs to be taken into account in the case of patients with multiple intolerances and also in patients who have dysfunctional self-perception!
The correct terms should therefore be used as precisely as possible for the diagnosis of the patient, but during communication with the patient definitions that are non-medical and clear should be used. The diagnosis itself should be itemised more clearly than has been specified here.
(1): Klinisches Wörterbuch Pschyrembel, 261.Auflage, 2007; verlag Walter de Gruyter
(2): Ernährungsmedizin, K.Widhalm (Hrsg.), Verlagshaus der Ärzte, 3.Auflage, 2009
(3): Zechmann M., Masterman G., "Food Intolerances: Fructose Malabsorption, Lactose and Histamine Intolerance: living and eating well after diagnosis & dealing with the elimination diet", 2013