Histamine is a biogenic amine, a naturally occurring chemical that plays a role in human physiology. It is commonly known for its function in the immune system, where it is released by mast cells during an allergic reaction to increase blood flow and trigger inflammation. Beyond this immune function, histamine also acts as a neurotransmitter in the central nervous system, helping to regulate the sleep-wake cycle and various cognitive functions. Since histamine is present in many foods, dietary histamine is a growing concern for people whose bodies struggle to process it efficiently.
The Role of Histamine in the Body
The body has two mechanisms to metabolize and break down both the histamine it produces and the histamine consumed through food. The enzyme Diamine Oxidase (DAO) is the main enzyme for metabolizing dietary histamine, primarily operating in the intestinal lining. The second enzyme, Histamine N-methyltransferase (HNMT), is responsible for breaking down histamine within the body’s cells, including the central nervous system.
Histamine intolerance is not a true allergy but an imbalance that occurs when the body’s capacity to break down histamine is overwhelmed. A deficiency or inhibition of the DAO enzyme is often the underlying cause, leading to an accumulation of histamine in the bloodstream. When histamine levels exceed an individual’s tolerance threshold, it can trigger a wide range of non-specific symptoms.
These symptoms can affect multiple body systems because histamine receptors are found throughout the body. Common reactions include digestive issues like bloating, diarrhea, or abdominal pain, and neurological symptoms such as headaches or migraines. Other manifestations involve the skin (hives or itching) and the respiratory system (congestion).
Inherent Histamine Content of Rice Varieties
Plain, freshly cooked rice is generally considered a low-histamine food. For this reason, rice is a common staple often recommended as a base for low-histamine elimination diets. The inherent histamine level in the raw or freshly prepared grain is minimal.
White rice, which has had the outer bran layer removed during milling, is typically the lowest risk option and is accepted in a low-histamine diet. Brown rice contains the bran and germ, which provides more nutrients and fiber but slightly increases the risk. This elevated risk is due to the greater presence of free amino acids, including histidine (the precursor to histamine), and the possibility of bacterial action on the outer layer.
Wild rice, which is technically a grass seed, is also regarded as safe for people managing histamine sensitivity. For any variety, the most important factor in determining its safety is the freshness and handling of the cooked product, not the grain type.
How Preparation and Storage Affect Rice Histamine Levels
Improper handling after cooking is the main factor that can turn safe, low-histamine rice into a problem food. Histamine levels increase not from the heat of cooking, but from the growth of certain bacteria after the rice cools. These bacteria convert the naturally occurring amino acid histidine into histamine through an enzyme called histidine decarboxylase.
Cooked rice is susceptible to this bacterial proliferation. Allowing cooked rice to cool slowly at room temperature or keeping it refrigerated for multiple days provides an ideal environment for histamine-producing microbes to multiply rapidly. This microbial activity significantly elevates the histamine concentration in the leftovers.
To keep rice low in histamine, minimize the time spent in the temperature danger zone between 40°F and 140°F (4°C and 60°C). Experts recommend cooling cooked rice as quickly as possible, such as by spreading it thinly on a tray, and refrigerating it promptly within one hour of cooking. If storing cooked rice, freezing leftovers immediately after rapid cooling is the most effective way to halt histamine formation, as refrigeration alone will only slow the process.