Overview. Vitamin B1, also called thiamine or thiamin, is one of 8 B vitamins. All B vitamins help the body convert food (carbohydrates) into fuel (glucose), which the body uses to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body metabolize fats and protein.he most important use of thiamine is to treat beriberi, which is caused by not getting enough thiamine in your diet. Symptoms include: 1  Swelling, tingling, or burning sensation in the hands and feet. 2  Confusion. 3  Trouble breathing because of fluid in the lungs. 4  Uncontrolled eye movements (nystagmus).