Why Are You Always Tired? This Might Be the Reason!

Histamine intolerance, the DAO enzyme, and the hidden cycle of fatigue

You ate your meal—seafood, fish, various vegetables, maybe tomatoes, eggplants, spinach… You leave the table feeling well-nourished. But shortly after, things change: fatigue, persistent tiredness, heart palpitations, even diarrhea… For some people, this becomes a repeating cycle after nearly every meal.

For those who say, “I run to the bathroom right after eating,” or experience widespread rashes, itching, dizziness, or brain fog after meals, one of the possibilities to consider is histamine intolerance. This is not a classic food allergy; it is more of a metabolic issue related to the body’s ability to balance histamine load.

Proteins break down into smaller units during digestion—these smaller components are called amines. One of these amines is histamine. Histamine is a natural molecule that activates the immune system, enables communication in the brain, and regulates sleep–wake cycles and arousal levels.

To keep histamine in balance, another player enters the scene: the DAO enzyme (diamine oxidase). DAO is the enzyme that breaks down histamine and prevents its toxic accumulation. It is primarily produced in the intestinal lining and in the placenta, serving as a protective barrier for both the digestive system and the fetus.

If you frequently consume foods high in histamine—such as aged cheeses, fermented foods, yogurts, fermented products, seafood—your body may suddenly encounter a large histamine load. This can lead to itching, flushing, diarrhea, fatigue, dizziness, tiredness, heart palpitations, and vasodilation.

There is also a second dimension to the issue: insufficient DAO production. Certain medications may reduce DAO levels; for example, aspirin, some anti-rheumatic drugs, and metformin used for diabetes can suppress DAO production. When histamine intake is high and DAO levels are low, the condition becomes even more pronounced; the body’s ability to balance histamine is strained.

It is important to distinguish histamine intolerance from a food allergy. In classical food allergies, IgE levels—an immune marker—tend to rise, but in histamine intolerance this usually does not occur. What we see here is not an allergic immune response, but a metabolic overload—an exceeded tolerance threshold.

In recent years, DAO-containing supplements have been introduced to help regulate histamine load. Some are animal-derived—usually extracted from pig kidneys—and therefore may not be suitable for vegans, vegetarians, or those with religious considerations. Plant-based options, reportedly derived from pea sprouts, also exist. However, whether their laboratory (in vitro) effects translate into actual human (in vivo) effects remains uncertain. The use of such supplements should always be evaluated under medical guidance.

In daily practice, the first step is usually to alleviate symptoms with antihistamines. If the same complaints persist after meals and are triggered by specific foods, histamine intolerance may be considered. In such cases, you should not self-diagnose; instead, consult your physician for a detailed evaluation, as many different conditions can produce similar symptoms.

Foods that increase histamine levels, as well as medications and lifestyle factors that reduce DAO, can all influence the situation. A long-term approach may include reviewing high-histamine foods and DAO-suppressing medications with your physician, forming part of a personalized nutrition and treatment plan.

In conclusion, if constant fatigue, exhaustion, post-meal palpitations, diarrhea, and brain fog accompany the picture, the issue may not simply be “I ate too much” or “the meal was heavy.” Your body may be trying to manage a subtle and complex balance involving histamine and DAO. Understanding this balance—and evaluating it with your physician when necessary—is important not to prolong life, but to avoid shortening the life entrusted to you.

Remember: You cannot extend life. But you can prevent the life entrusted to you from being shortened by unnecessary burdens, metabolic imbalances, and ignored warning signals.