A low-carbohydrate, high-fat (LCHF) diet is thought to have a role in sports nutrition, with some believing that in trained athletes, controlled carbohydrate consumption can lead the body to rely on its relatively unlimited stores of fat instead of on the usual glycogen.
Previous studies have showed that maintaining an LCHF diet for three weeks to several years leads to such changes in exercise fuel use, but any positive impact it may have on athletic performance is still unsubstantiated.
Another nutritional support method for endurance sport is the periodised carbohydrate (PCHO) diet, which is said to ensure high carbohydrate availability to sustain high-intensity training sessions, and low carbohydrate availability for low-intensity sessions.
However, this has been found to benefit performance only in sub-elite but not elite athletes, suggesting that this diet alone does not affect sports performance across the board.
Based on this, researchers in Australia conducted a non-randomised parallel study to assess the impact of a 21-day ketogenic LCHF diet and 21-day PCHO diet on pre- and post-exercise blood pH (indicated by acid-base status), bicarbonate and lactate concentrations — compared with a high-carbohydrate control diet — in elite athletes.
They recruited 24 (17 male, seven female) elite-level race walkers, most of whom they said "had represented their countries at World Championships, Olympic Games, and International Association of Athletics Federations (IAAF) World Cup events". This was in contrast to previous studies, whose subjects were "healthy but untrained".
Nine of the elite athletes were placed on an LCHF diet, seven on a PCHO diet, and eight on the control diet.
Their blood pH, bicarbonate and lactate levels were measured at baseline and post-intervention, before and after they took a graded exercise test.
The researchers subsequently observed that the LCHF diet was not linked to significant differences in blood pH, bicarbonate or lactate when compared to the control diet, both pre- and post-exercise.
As for the PCHO diet, they noted that post-exercise, blood pH was lower and lactate levels were higher in the PCHO group, while no significant difference was seen in terms of bicarbonate levels.
However, they said such differences could be attributed to differences in work capacity: the PCHO group put in more work during the post-intervention graded exercise test, with a mean test duration of 17.6 minutes, longer than the LCHF group's 15.8 minutes.
The researchers wrote that based on these findings, "sustained manipulation of macronutrient intake is unlikely to influence acid–base status in elite athletes, which may be due to pre-existing training adaptations…or the actions of respiratory and renal pathways, which have a greater influence on regulation of acid–base status than nutritional intake".
In conclusion, they wrote: "Any performance implications of a LCHF diet are unlikely to result from perturbations in acid–base status, a system which is tightly regulated via the interaction of the blood and tissues, plus respiratory and renal systems."
"Chronic Ketogenic Low Carbohydrate High Fat Diet Has Minimal Effects on Acid–Base Status in Elite Athletes"
Authors: Amelia J. Carr, et al.