B1 dietary needs should be calculated as a function of personal carb intake.
According to the WHO, the number is:
"The RDA for thiamine based on the energy intake is 0.4 mg/ 1000 kcal"
(If one eats those kcal as fat and not as carbs, then thiamine requirements will be less. I do not know how much less, but based on the
biochemical explanations of Chris Masterjohn (thanks
@Gondwanaland for the video) I could imagine 50%)
If you want details............
There is a lot of discussion on the details of that 0.4mg / 1000kcal number... So, if you want to dig deeper, here you go:
I. the attached WHO document says:
Foltz and others (1944) reported that thiamine deficiency occurred within 8 weeks in the majority of humans kept on an intake of 0.20 mg thiamine/1000 kcal or less (total intakes of 0.6 mg thiamine or less daily).
The minimum requirement was stated as ranging from 0.33 to 0.45 mg thiamine/1000 kcal (1.0 to 1.5 mg thiamine daily) which was necessary for maintenance and for well-being.
Anderson and others (1986) recommended a minimum thiamine intake of 1.22 mg/day for men and 1.03 mg/day for women.
Values for thiamine intake ranging between 0.2 and 0.5 mg per 1000 kcal have been reported as those needed to satisfy requirements. The large differences can be explained by differences in approach and in experimental procedures used to estimate thiamine requirements.
II. there is a book chapter on setting the recommendations for B1 requirements
https://www.ncbi.nlm.nih.gov/books/NBK114331/
No studies were found that examined the effect of energy intake on the thiamin requirement. Some studies provided thiamin in graded doses that kept the ratio of thiamin to energy constant for those studied who had different energy requirements. Other studies provided total amounts of thiamin (and sometimes energy) that were the same for all individuals.
Sauberlich and colleagues (1979) adjusted activity levels rather than energy intake to maintain weight in their subjects. Several investigators examined their data to assess whether it would be better to express thiamin as an absolute value or in relation to energy. For example,
Dick and colleagues (1958) reported that the coefficient of variation of the estimated thiamin requirement for adolescent boys was 14.2 percent/person, 15.5 percent/1,000 kcal, 27.5 percent/kg body weight, 19.5 percent/m2 surface area, and 19.2 percent/mg of creatinine excretion.
Elsom and coworkers (1942) noted that they could not distinguish whether it was better to express thiamin in absolute values or per 1,000 kcal but that thiamin intake expressed per body weight did not discriminate between those who were deficient and those who were not.
Anderson and colleagues (1986) presented evidence that expressing the thiamin requirements in absolute terms is more useful for predicting biochemical thiamin status than expressing it in relation to energy intake, and data from individuals presented by
Henshaw and coworkers (1970) appear supportive.
Despite the lack of direct experimental data, the known biochemical function of thiamin as thiamin pyrophosphate (
TPP) in the metabolism of carbohydrate suggests that at least a small (10 percent) adjustment to the estimated requirement to reflect differences in the average energy utilization and size of men and women, a 10 percent increase in the requirement to cover increased energy utilization during pregnancy, and a small increase to cover the energy cost of milk production during lactation may be necessary.
It has been observed that during periods of starvation such as in war, larger individuals present signs of beriberi more rapidly than do those with smaller body builds, indicating their greater needs for thiamin and other energy-related nutrients (Burgess, 1946). Many studies report thiamin intake per 1,000 kcal; others report total intake. Thus, the evidence below is presented as it was done in the studies and not because the ratio is considered important
Eating does not seem to influence the lactate levels. Exercise does have an effect: 
