In particular, caffeine intake at 3mg/kg was found to be superior to higher doses of 5mg/kg and 9mg/kg, as it could promote fat oxidation during exercise without causing cardiovascular strain.
However, caffeine intake did not affect fat and carbohydrate oxidation when the participants were at rest, regardless of the dose taken.
The study, conducted by researchers from Jiangxi Normal University and the University of the Pacific, Stockton, assessed how different caffeine doses could affect fat oxidation and cardiovascular responses at rest and during exercise.
Writing in the Journal of the International Society of Sports Nutrition, researchers highlighted that a dose of 3mg/kg appeared to offer an optimal balance between stimulating fat oxidation and maintaining cardiovascular safety.
Study method
In this double-blind, placebo-controlled, randomized crossover study, each participant took caffeine capsules at dosages of 3mg/kg, 5mg/kg, 9mg/kg and a placebo, with each intervention separated by a one-week washout period.
During each intervention, participants took the assigned capsules and remained seated for 60 minutes before going for a 40-minute treadmill run at the FATmax (maximal fat oxidation) intensity.
The caffeine capsules used in this study were commercially available products from Piping Rock Health Products, while fiber tablets from Amway Nutrilite Inc served as the placebo.
A total of 11 overweight or obese female college students with a body mass index (BMI) of 26.4 kg/m² and a body fat percentage of 37.8% took part in the study.
A BMI of over 24 kg/m² and a body fat percentage exceeding 30% is classified as overweight or obese according to Chinese criteria.
The optimum dose
Findings showed that a caffeine dose of 3mg/kg was optimal to 5 mg/kg and 9 mg/kg as it could significantly increase fat oxidation rates during exercise without causing cardiovascular strain.
Caffeine intake at both 3mg/kg and 5 mg/kg had significantly increased fat oxidation rates as compared to the placebo group at most time points during exercise.
The highest dose of 9 mg/kg, however, showed no additional metabolic benefit, since the fat oxidation rate in the 5 mg/kg group was markedly higher at most time points.
“The fat-oxidizing effect increased from 3 to 5 mg/kg but diminished at 9 mg/kg, which may exceed the optimal range and potentially trigger counter-regulatory responses,” the researchers wrote. “Thus, to maximize fat oxidation during exercise at FATmax, caffeine doses in the range of 3–5 mg/kg appear optimal, whereas a dose of 9 mg/kg provides no further benefit."
Caffeine and cardiovascular strain
Caffeine at doses of 5 and 9 mg/kg was associated with increased cardiovascular strain, which researchers said was not observed in those taking caffeine at 3 mg/kg.
This could be seen from how the systolic blood pressure (SBP) of these two groups remained significantly higher than the placebo at the 60th and 100th minute after taking caffeine.
Although SBP did significantly increase in the 3mg/kg caffeine group as compared to the placebo 60 minutes after taking caffeine, the increase was not sustained
“Caffeine at 3 mg/kg led to a slight increase in resting systolic blood pressure post-absorption, though both systolic and diastolic pressures remained unchanged immediately after exercise,” the researchers wrote. “In contrast, caffeine at 5 and 9 mg/kg resulted in significant increases in blood pressure, both at rest after absorption and immediately post-exercise.”
The post-trial questionnaire results also showed that specific adverse events were reported only following the 9 mg/kg caffeine trial.
These adverse events included difficulty initiating sleep and increased diuresis.
“Given that the 9 mg/kg dose provided no additional fat-oxidation benefit but was associated with a higher likelihood of side effects, it cannot be recommended for this population,” researchers wrote.
They concluded that caffeine is recommended only for individuals seeking to improve fat oxidation during exercise who have no history of cardiovascular issues or heightened caffeine sensitivity.
“For overweight or obese female college students, a caffeine dose of 3 mg/kg during FATmax exercise is advisable as a safer option.”
Source: Journal of the International Society of Sports Nutrition. doi: 10.1080/15502783.2026.2670558. “Effects of different caffeine doses on fat oxidation and cardiovascular response during exercise at FATmax in overweight/obese female college students.” Authors: Gong, Z., Yu, S., Lyu, Z., Huang, W., & Zhang, T.
