p‐Synephrine, the main protoalkaloid of Citrus aurantium, raises fat oxidation during exercise in elite cyclists

Abstract

Purpose:The aim of this study was to investigate the acute effects of p-synephrine ingestion on substrate oxidation during exercise in elite cyclists. Methods: Fifteen elite cyclists volunteered to participate in a double blind, crossover, randomized and placebocontrolled experimental trial. During two different trials, participants either ingested a placebo (cellulose) or 3 mg/kg of p-synephrine. After 60 min for substances absorption, participants performed an incremental maximal cycle ergometer test until volitional fatigue (25 W/min). Breath-by-breath gas exchange data was continuously recorded during the entire test to estimate energy expenditure, carbohydrate oxidation, and fat oxidation rates by stoichiometric equations. Heart rate was continuously measured by using a heart rate monitor. Results: The ingestion of p-synephrine had no significant effects on energy expenditure (F=0.71, P=0.40) or heart rate (F=0.66, P=0.43) during exercise. However, there was a main effect of p-synephrine to increase the rate of fat oxidation over the placebo (F=5.1, P=0.04) and the rate of fat oxidation was higher with p-synephrine in the following loads: 45±2%, 51±3%, 62±3%, 67±4%, 79±5% and 85±5% of the maximum wattage obtained in the test (all P<0.05). The ingestion of p-synephrine did not modify the maximal rate of fat oxidation during the ramp test (mean value; 95%CI = 0.91; 0.79-1.03 vs 1.01; 0.91-1.11 g/min, respectively, P=0.06) nor the exercise intensity at which maximal fat oxidation was achieved (i.e., Fatmax= 49; 48-53 vs 50; 47-51% Wmax, P=0.52). 3 Conclusion: Acute p-synephrine ingestion moved the fat oxidation-exercise intensity curve upwards during an incremental cycling test without affecting Fatmax.

Effects of p-Synephrine during Exercise: A Brief Narrative Review

“…For example, the acute intake of p -synephrine (3 mg/kg of body mass) did not change running performance during 60-m and 100-m sprint races and it did not affect single and repeated jumping capacity of sprinters when compared to a placebo [ 27 ]. In addition, the ingestion of the same dose of p -synephrine did not increase peak wattage nor the maximum oxygen uptake (VO 2max ) obtained during a ramp exercise test in elite cyclists [ 28 ]. The only evidence demonstrating an increase in performance with p -synephrine is a study reporting a higher capacity to perform squat repetitions during six sets of exercise with a load equivalent to 80% of participants’ one-repetition maximum [ 29 ].…”

“…It is well established that aerobically trained individuals have higher rates of fat oxidation during exercise than untrained individuals [ 30 ] due to the different adaptations that aerobic training induces in the cardiorespiratory system and within the skeletal muscle. The comparison of these two studies [ 5 , 28 ] suggests that acute p -synephrine intake has the capacity of increasing the rate of fat utilization during exercise irrespective of the fitness level of the individual. Hence, it seems that the adaptations induced by aerobic training do not prevent the benefits of acute p -synephrine intake on fat oxidation during exercise.…”

“…Additionally, it has been found that there is needed ingesting of at least 2 mg/kg of body mass of p -synephrine to significatively increase the rate of fat oxidation during exercise of increasing intensity, while it sems that the effect of this substance on fat oxidation plateaus at 3 mg/kg of body mass [ 31 ]. In all these investigations [ 5 , 28 , 31 ], the acute intake of p -synephrine moves upwards the fat oxidation–exercise intensity curve and the effect of p -synephrine was present at several exercise intensities between 30% and 80% of VO 2max . As a result, it seems safe to indicate that p -synephrine is effective to enhance fat utilization during exercise of low to moderate intensity.…”

“…In all the abovementioned investigations, the increases in fat oxidation rate with p -synephrine were accompanied by a concomitant reduction in carbohydrate oxidation rates [ 28 , 30 , 31 , 32 ]. This is because p -synephrine does not modify energy expenditure rates at any exercise intensity, which contradicts its potential thermogenic effect, at least during exercise.…”

“…Hence, it seems that p -synephrine produces a shifting in substrate oxidation during exercise without affecting the energy expended with exercise [ 32 ]. The reduction of carbohydrate oxidation is evident during exercise of increasing intensity [ 28 ] and during steady-state exercise [ 32 ], and it may help individuals to spare muscle and liver glycogen during exercise. Glycogen sparing through feeding or training with low carbohydrate availability has been found effective to increase some forms of aerobic exercise performance [ 35 ].…”