Thiamine is one of the B vitamins and plays an important role in energy metabolism and tissue building. It combines with phosphate to form the coenzyme thiamine pyrophosphate (TPP), which is essential in reactions that produce energy from glucose or that convert glucose to fat for storage in the tissues. When there is not enough thiamine in the diet, these basic energy functions are disturbed, leading to problems throughout the body.
The non-glucose related TPP-dependent enzyme, branched-chain ketoacid dehydrogenase, catalyses the production of acyl-CoA derivatives from branched-chain amino acids in liver and muscle.
Professor Bruce Ames has published a number of reviews on the Micronutrient Triage theory; that micronutrients are apportioned differently when scarce. Mild deficiency of selenium, for example, spares the systems affected by severe deficiency. Short-term survival takes precedence over long-term survival. In the case of thiamine, fat storage is a long-term survival project.
In fact, high-fat diets can be used to prevent thiamine deficiency: http://www.jbc.org/content/206/2/725.full.pdf
Thiaminase can also be produced by some gut bacteria, perhaps as a way of competing with other commensal species for carbohydrate released from resistant starch.
Thiamine is released by the action of phosphatase and pyrophosphatase in the upper small intestine. At low concentrations, the process is carrier-mediated, and, at higher concentrations, absorption occurs via passive diffusion. Active transport is greatest in the jejunum and ileum (it is inhibited by alcohol consumption and by folic deficiency). Decline in thiamine absorption occurs at intakes above 5 mg. _ Wikipedia
The presence of anti-thiamin factors (ATF) in foods also contributes to the risk of thiamin deficiency. Certain plants contain ATF, which react with thiamin to form an oxidized, inactive product. Consuming large amounts of tea and coffee (including decaffeinated), as well as chewing tea leaves and betel nuts, have been associated with thiamin depletion in humans due to the presence of ATF. Thiaminases are enzymes that break down thiamin in food. Individuals who habitually eat certain raw freshwater fish, raw shellfish, and ferns are at higher risk of thiamin deficiency because these foods contain thiaminase that normally is inactivated by heat in cooking.
In fact, it looks as though anti-thiamine factors of all classes might be prevalent in precisely those diets most often called in evidence to falsify the carbohydrate-insulin hypothesis of obesity: for example,
In the Philippines, the Tagalog word for beriberi is 'bangungut' which means nightmare and classically death occurs in sleep after a heavy meal consisting of rice and fish (Lonsdale, 1990). The thiaminase in the fish may compound an initial marginal dietary thiamine deficiency and can be fatal.
Some bacteria (e.g. Bacillus thiamineolyticus) are also capable of destroying thiamine. It has been reported that 3% of Japanese show a thiamine deficiency due to this cause. Thiaminase bacteria have been frequently isolated from human stools in Japan and it was reported that the thiamine levels in the blood of these patients was low in spite of adequate intake largely due to the destruction of thiamine in the intestines (Bhuvaneswaran and Sreenivasan, 1962).