“Drinking espresso with a pinch of sea salt and grass-fed butter before cardio turns your body into a fat-burning furnace." (Post caption: "Drinking espresso before cardio can increase fat oxidation during exercise, while the added butter provides dietary fat that can be used as an energy source. Together, this combination can support a…”

The cited paper exists, but the title in the post is wrong and, more importantly, the paper argues against the mechanism the post attributes to it. Graham's 2001 Sports Medicine review is titled "Caffeine and exercise: metabolism, endurance and performance," not "Caffeine, Its Effects on Metabolism, Exercise and Performance." In its abstract, Graham states that the mechanisms by which caffeine produces its ergogenic effects are unknown, and the popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best. A secondary review quoting the paper reproduces the same point and adds Graham's alternative suggestion that caffeine may work partly by creating a more favourable intracellular ionic environment in active muscle, which could facilitate force production by each motor unit. Separately from the cited paper, more recent evidence does support a modest caffeine effect on fat oxidation during exercise, under specific conditions. A 2020 meta-analysis found caffeine significantly increased the fat oxidation rate (standardized mean difference 0.73; 95% CI 0.19 to 1.27), but doses at or below 3.0 mg/kg showed a non-significant effect, while doses above 3.0 up to 5.9 mg/kg and 6.0 to 7.0 mg/kg produced statistically significant effects. A controlled trial reported that maximal fat oxidation was 16% higher with caffeine than placebo, occurring at about 40% of VO2max, with elevated fat oxidation up to 70% of VO2max. The literature is not unanimous. The larger 2022/2023 review notes that numerous studies reached the opposite conclusion based on gas exchange variables, finding either no change or significant decreases in fat metabolism after caffeine, and that while caffeine likely mobilizes fatty acids from adipose tissue, respiratory exchange ratio measures have limits. It also observes that a 2020 meta-analysis of 19 studies indicated caffeine increased fat metabolism during exercise based on whole-body gas exchange, but fitness level modulated the effect, with less effect in trained individuals. On the butter component specifically, a dedicated review of butter coffee reports that the only trial examining substrate utilization found that Bulletproof Coffee, but not black coffee, produced significant increases, yet effects on fat oxidation appeared equivocal and were offset by the additional calorie intake of Bulletproof Coffee, with the authors calling for further research using more rigorous designs, larger samples and more diverse populations. On whether higher fat oxidation during a workout produces fat loss, controlled chamber research found that when subjects were studied in energy balance, 24-hour fat oxidation did not differ between control and exercise days in lean sedentary, lean trained or obese sedentary groups, and 24-hour fat balance was actually significantly more positive on the exercise day. The authors note the governing principle: to achieve negative fat balance, intake or expenditure must be altered such that fat oxidation exceeds fat intake. A related paper concludes that although exercise improves the capacity of muscle to oxidize fat, moderate duration exercise of one hour or less has little impact on 24-hour fat oxidation. On salt, no credible source links adding salt to coffee with fat burning. Coverage of the related viral "salt trick" genre states plainly that there is no evidence that pink salt water burns fat or resets metabolism, and a coffee industry source acknowledges that salt in coffee relates to weight loss only through sugar replacement, not fat burning, with its documented mechanism being sodium's effect on bitter taste receptors, documented in taste science research.