Does fermented capsaicin help speed up your metabolism?
Capsaicin slightly and temporarily increases fat burning. No research has been done on fermented capsaicin specifically, so whether fermentation changes anything about how it works is unknown.
Capsaicin raises your resting metabolism measurably, but modestly. Many studies combined, covering thirteen groups of people, show that capsaicinoids and their milder cousins (capsinoids, from mild peppers) increase the energy your body burns at rest by around 34 kilocalories per day on average. That is a real but small effect: roughly the equivalent of one extra slice of bread.
The effect on fat burning is more consistent. Both across those thirteen studies and in a broader look at 24 studies in people, the ratio of fat to carbohydrates burned shifts slightly but demonstrably in favour of fat. This effect is stronger when you are already on a diet and eating less than you burn. Capsaicin also appears to partly make up for the reduced feeling of fullness that comes with dieting, especially when combined with a higher protein intake.
What capsaicin does not do is meaningfully raise total energy expenditure over the long term. Across 24 studies in people, no statistically clear effect emerges when all results are taken together, even though some individual studies show a modest rise. So 'speeding up your metabolism' does not work as a lasting turbo effect.
There is also an unexpected caveat. Research among people in a cold region of China found that those who eat spicy food regularly are actually more likely to be overweight, not less. Animal studies from the same research suggest that capsaicin in a cold environment may worsen fat accumulation and throw the gut bacteria out of balance. That does not fit the popular image of capsaicin as a slimming aid and shows that the surrounding environment plays a role.
On fermented capsaicin specifically, the available studies say nothing. The findings that do exist apply to red pepper in meals or in capsule form, not to a fermented version. Whether fermentation changes how it works has not been studied.
This answer draws on two large summaries of thirteen and twenty-four studies in people respectively, plus one study following people over time in China combined with animal studies. The summaries provide reasonably strong evidence for short-term effects on resting metabolism and fat burning, but also show that the long-term effect on total energy expenditure disappears. The study following people over time and the animal studies are weaker in design and show only an association, not proof of cause and effect. No evidence is available on fermented capsaicin specifically.