Similar to the other B-complex vitamins, vitamin B-1 helps your body to break down fats, protein and carbohydrates. However, no research suggests that taking vitamin B-1 will help you to lose weight. Instead, it seems as though some weight loss diets might affect your vitamin B-1 status in a negative way. As a result, although you should try to ensure that you get enough vitamin B-1 when losing weight, taking vitamin B-1 will not cause weight loss.
Nutrient Metabolism and Weight Loss
Vitamin B-1 plays an essential role in converting carbohydrates to adenosine triphosphate, which can help fuel any exercise-related attempts to burn calories and lose weight. However, taking vitamin B-1 does not cause weight loss. In fact, a 2010 review in "The American Journal of Clinical Nutrition" indicates that following a low-calorie diet when trying to lose weight can result in an insufficient vitamin B-1 intake. As this is particularly true for low-carb diets, you can potentially avoid low vitamin B-1 status by cutting down on fats, not carbohydrates, when dieting to lose weight.[Ref 2]