Which food is not a good source of thiamin? A complete guide

December 11, 2025 •

3 min read

According to the NIH, while many foods naturally contain thiamin, highly refined and processed items, such as white rice and white flour products, are not good sources because the vitamin is stripped away during processing. Understanding which food is not a good source of thiamin can help you make better dietary choices to prevent deficiency.

Quick Summary

Processed foods like white rice and sugar are poor sources of thiamin, and some raw seafood and alcohol can interfere with its absorption. This article explains which foods lack this essential vitamin and highlights how cooking and processing methods can affect its content.

Key Points

Processed Carbs Lack Thiamin: Highly refined foods like white rice and white flour products are stripped of most of their thiamin during processing.
Some Beverages Interfere: Consuming large quantities of coffee, tea, and alcohol can hinder the body's absorption and use of thiamin.
Raw Fish Contains Enzymes: Certain raw fish and shellfish contain thiaminases, enzymes that destroy thiamin, but cooking neutralizes them.
Cooking Affects Content: Thiamin is sensitive to heat and dissolves in water, so boiling and prolonged, high-heat cooking can reduce its levels in food.
Whole Foods are Key: The best sources of thiamin are whole grains, legumes, nuts, lean pork, and fortified cereals.
Fat and Oil Have None: Most pure fats and oils, like lard and vegetable oil, contain zero thiamin and offer no dietary contribution of this vitamin.

The Role of Thiamin in the Body

Thiamin, also known as Vitamin B1, is an essential water-soluble vitamin that plays a vital role in our health. It is crucial for carbohydrate metabolism, helping the body convert food into energy, and it supports the proper functioning of the nervous system and muscles. Since the body has a very limited storage capacity for thiamin, a regular dietary intake is necessary to avoid deficiency. A lack of thiamin can lead to serious health issues, including beriberi, which affects the heart and nervous system.

Why Processed and Refined Foods Fall Short

The primary culprits for being poor thiamin sources are highly processed and refined foods. During the milling and refining process, the outer layers of grains, which contain most of the vitamins, are removed.

Polished White Rice: This is a classic example of a refined carbohydrate that is notoriously low in thiamin. The polishing process removes the bran and germ, along with nearly all the naturally occurring B vitamins. While many brands add thiamin back through 'enrichment,' it's still not comparable to whole grains.
White Flour and Sugar: Similar to white rice, products made from white flour and high in refined sugars, such as cakes, pastries, and candy, contain minimal thiamin. Diets heavily reliant on these items significantly increase the risk of deficiency.
Fats and Oils: Fats, oils, and foods with high saturated fat content contain virtually no thiamin. This includes items like lard, mayonnaise, and most salad dressings.

Foods That Inhibit Thiamin Absorption

Beyond simply lacking thiamin, some foods contain compounds that actively interfere with its absorption or destroy it altogether. These are known as antithiamin factors (ATFs).

Raw Fish and Shellfish: Certain raw seafood, including some types of fish, shellfish, and clams, contain enzymes called thiaminases. These enzymes break down and inactivate thiamin, though cooking typically destroys them. For most people in Western diets, this is not a major concern, but it is a factor in regions where these foods are consumed raw and frequently.
Tea and Coffee: Both caffeinated and decaffeinated tea and coffee contain polyphenolic compounds that can interact with and degrade thiamin. While moderate consumption is unlikely to cause a problem for those with a healthy diet, excessive intake can pose a risk for those with already low thiamin levels.
Alcohol: Chronic and excessive alcohol consumption is a leading cause of thiamin deficiency in industrialized countries. Alcohol impairs the absorption and utilization of thiamin and increases its excretion through urine.

Comparison of Thiamin Content in Common Foods


Food Type	Example	Thiamin Content	Thiamin Availability	Notes
Excellent Source	Fortified Cereal	High (up to 100% DV)	High	Added synthetically, high absorption
Good Source	Pork Chop	Moderate (up to 33% DV)	High	Bioavailable form, naturally occurring
Good Source	Black Beans	Moderate (up to 33% DV)	High	Naturally occurring, plant-based
Low Source	Unenriched White Rice	Very low (1/10 of brown rice)	Low	Milled and stripped of nutrients
Low Source	White Bread	Low (8% DV per slice)	Low	Refined and enriched, not as good as whole grain
Very Poor Source	Butter/Oils	Zero	N/A	High-fat items contain no thiamin

Impact of Preparation on Thiamin Content

Thiamin is a water-soluble and heat-sensitive vitamin, meaning cooking methods can significantly impact its retention.

Boiling and Soaking: Because thiamin dissolves in water, much of it can be lost if food is boiled and the water is drained away, such as with vegetables or pasta.
High-Heat Cooking: Prolonged cooking or high-temperature methods like deep-frying can destroy thiamin. This is why overcooking meat can reduce its vitamin content.
Proper Preparation: To maximize retention, opt for steaming, roasting, or grilling and avoid overcooking. Steaming or using the cooking liquid for a sauce can help retain leached nutrients.

Conclusion

When considering which food is not a good source of thiamin, the most definitive answer points to highly processed and refined carbohydrates like white rice, white flour products, and refined sugars. Additionally, consuming a high amount of raw fish or certain beverages like tea and coffee, particularly when coupled with an otherwise poor diet, can inhibit thiamin absorption. For optimal thiamin intake, it is best to favor whole grains, legumes, and lean meats, while being mindful of cooking methods and excessive alcohol or raw fish consumption. Building a diet around whole foods is the most effective strategy for ensuring adequate thiamin levels and supporting overall health. Learn more from the NIH Office of Dietary Supplements about Thiamin.

Frequently Asked Questions

Common foods with very little or no thiamin include refined sugars, pure fats like lard and butter, and highly processed carbohydrates such as unenriched white rice and white flour products.

Yes, thiamin is a heat-labile vitamin, meaning it can be destroyed by high temperatures or prolonged cooking. Since it is also water-soluble, boiling foods can cause a significant amount of thiamin to leach into the cooking water, which is then discarded.

While fruits and vegetables contain a variety of vitamins and minerals, most are not a primary source of thiamin. Foods like legumes and nuts are better plant-based sources, and fortified cereals often contain more.

Excessive consumption of coffee and tea can negatively impact thiamin levels. These beverages contain compounds that can degrade thiamin, though the effect is most notable in individuals with already low thiamin intake.

During the milling and processing of grains, the nutrient-rich outer bran and germ layers are removed to create white rice or white flour. This process strips away most of the natural thiamin.

Dairy products, particularly milk and cheese, have a relatively low thiamin content. While they offer other important nutrients like calcium, they are not a significant source of vitamin B1.

Chronic alcohol use interferes with thiamin absorption from the intestine, inhibits its utilization by cells, and increases its excretion via the kidneys. This makes chronic alcoholics highly susceptible to thiamin deficiency.