Understanding What Foods Deplete Vitamin B1

October 28, 2025 •

5 min read

An estimated 80% of individuals with chronic alcohol abuse will develop a thiamine deficiency, but alcohol is not the only cause. Beyond this well-known factor, several types of foods, beverages, and specific dietary patterns can also contribute to a decrease in vitamin B1 (thiamine) levels in your body. This happens either by containing thiaminase enzymes that destroy the vitamin or by increasing the body's metabolic demand for it.

Quick Summary

This article explores the foods and beverages that interfere with vitamin B1 absorption or increase its consumption by the body. It discusses the role of thiaminase enzymes found in certain raw seafood and plants, the impact of processed carbohydrates and sugars, and the significant effect of excessive alcohol intake on thiamine levels. Practical dietary strategies for prevention and management are also covered.

Key Points

Thiaminase Enzymes: Raw fish, raw shellfish, and certain plants like bracken ferns contain enzymes called thiaminases that destroy vitamin B1.
Refined Carbs and Sugars: Processed foods like white rice, white flour, and sugary items lack thiamine and increase the body's metabolic demand for the vitamin, leading to depletion.
Alcohol Use: Excessive and chronic alcohol consumption is a leading cause of thiamine deficiency, as it impairs absorption, increases metabolism, and often coincides with poor dietary intake.
Tea and Coffee: Both coffee and tea contain anti-thiamine factors, and excessive consumption can contribute to lower thiamine levels over time.
Cooking is Key: Cooking thiaminase-containing foods, like fish and shellfish, deactivates the destructive enzymes, preserving the vitamin content.
Whole Foods are Best: A balanced diet rich in whole grains, lean meats, and legumes provides natural sources of thiamine and helps prevent depletion caused by processed foods.

The Silent Culprits: How Foods Can Interfere with Thiamine

Thiamine, or vitamin B1, is a crucial water-soluble vitamin that plays a central role in energy metabolism and the proper function of the nervous system. Because the body stores only a small amount, regular dietary intake is essential. However, certain foods and dietary habits can actively work against this process, either by containing thiaminase enzymes that break down thiamine or by increasing the body's demand for the vitamin. Being aware of these culprits is the first step toward safeguarding your thiamine status.

Foods and Beverages Containing Thiaminase Enzymes

Certain foods naturally contain thiaminases, enzymes that break down the thiamine molecule before the body can absorb and use it. These factors are primarily of concern when the food is consumed raw or in large quantities. The heat from cooking typically deactivates thiaminase enzymes.

Raw Fish and Shellfish: This is one of the most well-documented sources of thiaminase. Raw freshwater fish, raw shellfish, shrimp, mussels, and clams contain these enzymes. While rare in developed countries, populations with diets heavily reliant on raw fish are at higher risk of deficiency.
Tea and Coffee: These popular beverages contain anti-thiamine factors, such as polyphenolic substances, that can destroy thiamine. While a moderate intake is unlikely to cause a deficiency in healthy individuals with a balanced diet, excessive consumption can contribute to lower levels over time.
Betel Nuts: These contain anti-thiamine factors that can inhibit thiamine. This is a particularly relevant factor in areas where betel nut chewing is a common cultural practice.
Bracken Ferns: In some regions, bracken ferns are consumed as food, and they contain thiaminase enzymes. For ruminant animals, bracken fern ingestion can lead to thiamine deficiency, though human cases are rare.

Processed Carbohydrates and Sugars

A diet high in processed carbohydrates and refined sugars is a major contributor to thiamine depletion. Thiamine is essential for the body to metabolize glucose, and a large intake of simple sugars and starches increases the body's need for the vitamin. At the same time, processing often removes thiamine from these foods.

Polished White Rice: The milling process that transforms brown rice into white rice strips away the nutrient-rich outer layers, removing a significant amount of thiamine. This is why beriberi, a disease caused by severe thiamine deficiency, became prevalent in Asian populations with a diet centered on polished rice.
White Flour and Sugar: Like polished rice, products made from white flour and white sugar are depleted of natural B vitamins, including thiamine. Consuming large amounts of foods like white bread, pastries, and sugary drinks requires the body to use more of its thiamine stores for metabolism, without providing a fresh source of the nutrient.

Alcohol's Complex Relationship with Thiamine

Chronic and excessive alcohol consumption is arguably the most significant dietary factor contributing to thiamine deficiency in industrialized nations. The impact is multifaceted:

Inadequate Intake: Individuals with alcohol use disorder often have a poor diet, replacing nutrient-dense foods with alcohol.
Impaired Absorption: Alcohol damages the lining of the stomach and digestive tract, reducing the body's ability to absorb thiamine from food.
Increased Metabolism: The process of metabolizing alcohol places a heavy burden on the liver and rapidly depletes the body's thiamine stores.
Reduced Utilization: Alcohol interferes with the conversion of thiamine into its active form, thiamine pyrophosphate.

Comparison Table: Foods That Deplete vs. Support Thiamine


Feature	Foods That Deplete Thiamine	Foods That Support Thiamine
Mechanism	Contain thiaminase enzymes, increase metabolic demand, or lack inherent thiamine.	Contain natural thiamine, assist in absorption, or are fortified.
Examples	Raw fish, raw shellfish, tea, coffee, refined carbohydrates (white rice, white flour), high-sugar items, alcohol.	Pork, legumes (black beans, lentils), nuts (sunflower seeds, macadamia), whole grains, enriched cereals, fortified rice, eggs, trout.
Impact on Absorption	Active inhibition (thiaminase) or impaired absorption (alcohol).	Optimal conditions for absorption.
Nutrient Density	Often low in nutritional value, especially processed items.	High in overall nutrients, providing more than just thiamine.
Risk Factor	High consumption increases risk of deficiency, especially with other health issues like chronic alcoholism.	Regular consumption helps prevent deficiency and supports overall health.

Mitigating Thiamine Depletion

Protecting your thiamine levels involves a combination of smart food choices and lifestyle adjustments. Focusing on a diet rich in whole, unprocessed foods is the most effective strategy.

Prioritize Thiamine-Rich Foods: Incorporate excellent sources like pork, whole grains, nuts, legumes, and fortified cereals into your daily meals. For example, add black beans to a salad or choose whole wheat bread over white.
Cook Thiaminase-Containing Foods: When consuming fish or shellfish, cooking them thoroughly will inactivate the thiaminase enzymes, preventing vitamin destruction.
Limit Refined and Sugary Foods: Reduce your intake of highly processed carbohydrates and sugary beverages to decrease the metabolic demand for thiamine. Opt for complex carbohydrates from whole grains, which provide a slower release of energy and are often naturally higher in B vitamins.
Moderate Alcohol and Caffeine Intake: Keep alcohol consumption to a minimum and be mindful of excessive coffee and tea consumption, especially if your diet is otherwise limited in B vitamins.
Consider Supplementation: For those at high risk of deficiency, such as individuals with chronic alcoholism, malabsorption disorders, or those who have had bariatric surgery, supplementation may be necessary and should be discussed with a healthcare provider.

Conclusion: A Balanced Approach to Nutritional Health

Thiamine depletion is not solely a result of lacking vitamin B1 in the diet but can also be caused by consuming specific foods and beverages that actively interfere with its absorption or metabolism. Chronic alcohol use, diets high in refined carbs and sugar, and excessive intake of raw fish, tea, and coffee are all significant factors that can lead to depleted thiamine levels. By understanding these factors and making conscious, balanced dietary choices, you can effectively protect your body's thiamine stores and support overall nervous and cardiovascular health. Prioritizing whole foods and limiting processed items is a fundamental step toward preventing deficiency and maintaining optimal wellness.

For more information on the functions and benefits of thiamine, consider consulting reliable sources like the National Institutes of Health.(https://ods.od.nih.gov/factsheets/Thiamin-HealthProfessional/)

Frequently Asked Questions

Yes, both coffee and tea contain compounds that can interfere with thiamine (vitamin B1) levels. While moderate intake is unlikely to cause a problem for most people, excessive consumption, especially alongside a poor diet, can contribute to depletion over time.

Alcohol depletes vitamin B1 by multiple mechanisms, including reducing its absorption in the gut, increasing the body's metabolic use of the vitamin, and impairing its storage and activation in the liver. This is compounded by the poor diet often associated with chronic alcohol use.

No, only certain fish and shellfish, particularly when eaten raw, contain thiaminase enzymes that destroy thiamine. Cooking fish inactivates these enzymes, making it a safe and often beneficial part of a balanced diet.

Refined carbohydrates like white rice and white flour are processed in a way that removes the bran and germ, where much of the thiamine is stored. Additionally, metabolizing these quick-burning carbs requires thiamine, so a diet high in them increases the body's demand for the vitamin.

Yes, a diet with a high intake of sugar can contribute to thiamine deficiency. Thiamine is necessary for glucose metabolism, so consuming a large amount of sugar increases the body's need for thiamine while providing very little of it.

Early symptoms of thiamine deficiency can be vague and non-specific, including fatigue, irritability, poor appetite, memory issues, and abdominal discomfort. Severe deficiency, or beriberi, can lead to more serious neurological and cardiovascular problems.

To prevent thiamine depletion, focus on a diet rich in whole grains, lean meats, nuts, and legumes. Limit your intake of alcohol, processed carbohydrates, and sugary foods. Ensure that any raw fish or shellfish you eat is cooked, as heat deactivates thiaminase enzymes.