Short-Term Low-Carbohydrate Diet Dissociates Lactate and Ammonia Thresholds in Men

Abstract

A low-carbohydrate (L-CHO) diet has been shown to shift the lactate threshold toward higher workloads. The aim of the present study was to examine the effect of an L-CHO diet on the ammonia threshold and to compare it with the lactate threshold in men. The plasma catecholamine threshold was also measured. Eight young, untrained men participated in the study. Two exercise tests with graded workload were performed. The workload was increased every 3 minutes by 40 W until volitional exhaustion. The first test was performed after 3 days of a controlled mixed diet. After the first test, the mixed diet was switched to a L-CHO diet. Three days later the same test was repeated. The blood concentration of lactate, ammonia, noradrenaline, and adrenaline was measured before and after each workload in both groups. It was found that the concentration of the examined compounds in the blood increases exponentially with graded workload after each kind of diet. This led us to calculate the blood ammonia, lactate, epinephrine, and norepinephrine thresholds. The thresholds were defined as points at which the concentration of a given compound starts to increase in a nonlinear fashion, which is calculated using 2 segmental linear regressions. After the mixed diet, the threshold for each compound occurs at the same workload. The L-CHO diet resulted in dissociation of the lactate threshold from the ammonia threshold: the lactate threshold was shifted toward a higher workload, whereas the ammonia threshold was shifted toward a lower workload. The norepinephrine threshold was also shifted toward a lower workload, and the epinephrine threshold remained unchanged. The results obtained indicate that an L-CHO diet accelerates production of ammonia and delays production of lactate during graded exercise, as well as that diet must be strictly controlled when ammonia and lactate thresholds are measured.

Effect of a Reduced-CHO Diet on the Rate of Perceived Exertion Curve During an Incremental Test

“…The estimated sample size required to achieve α = .05 and β = 0.80 was > 52 participants, an unrealistic sample size for studies involving diet manipulation. In fact, several studies of dietary manipulation have been developed using relatively small sample sizes because investigations of this nature involve many days of testing and a high level of diet control (Langfort et al, 2004;Lima-Silva et al, 2009;Lima-Silva et al, 2013;Sabapathy et al, 2006). Although we cannot ensure that Type II error did not occur, the ES values indicate that diet had a small effect on the thresholds.…”

“…Several studies lead us to the notion that diet manipulation would dissociate RPE and lactate thresholds (Langfort et al, 2004;Langfort et al, 2001;Prusaczyk et al, 1992), although the effect of CHO availability on RPE and lactate thresholds has never been investigated. It has been suggested that the anaerobic metabolic pathway increases its contribution after 80% of Wmax (Zagatto et al, 2011), but reduced CHO availability from the diet reduces the use of CHO during exercise performed at intensities above 70% of VO2max (Maughan et al, 1997;Pizza et al, 1995).…”

“…A reduction in the maximum power output reached during the incremental test after a reduced-CHO diet reinforces that the diet protocol was effective. In addition, a large body of evidence has demonstrated that 2 to 4 days on a reduced-CHO diet is effective to alter the glycogen levels in skeletal muscle and physiological responses during exercise (Langfort et al, 2004;Langfort et al, 1996;Langfort et al, 1997;Langfort et al, 2001;Lima-Silva et al, 2010b;Maughan & Poole, 1981;Prusaczyk et al, 1992;Ratz et al, 1989;Sadamoto et al, 2000).…”

“…The mechanism by which this occurs is not fully understood, but it has been suggested that it may be due an inhibition of the enzyme phosphofructokinase 1 (PFK1) caused by reduced CHO availability to the muscle cell, which reduces glycolysis and blood lactate accumulation (Langfort et al, 1996). Notably, although LT is identified at higher power outputs after a reduced-CHO diet (Langfort et al, 2004), maximal power output is reduced, suggesting that the reduced glycolysis resulting from reduced CHO availability is detrimental to performance (Sabapathy et al, 2006).…”

Effects of carbohydrate quality and amount on plasma lactate: results from the OmniCarb trial

“…28 In another study of eight subjects undergoing exercise, a low carbohydrate diet, compared with a regular carbohydrate diet, led to delayed production of lactate after exercise. 29 It has been hypothesized that reduced lactate levels may be due to decreased glycogen levels or decreased flux through glycogenolysis or anaerobic glycolysis. 30 Alternatively, the shift in substrate for oxidative phosphorylation resulting from reduced carbohydrate availability may mean that a greater portion of acetyl coenzyme A may be derived from fat and protein resources, thereby bypassing glycolysis.…”