Effect of low- and high-carbohydrate diets on swimming economy: a crossover study

Abstract

Background Swimming economy refers to the rate of energy expenditure relative to swimming speed of movement, is inversely related to the energetic cost of swimming, and is as a key factor influencing endurance swimming performance. The objective of this study was to determine if high-carbohydrate, low-fat (HCLF) and low-carbohydrate, high-fat (LCHF) diets affect energetic cost of submaximal swimming. Methods Eight recreational swimmers consumed two 3-day isoenergetic diets in a crossover design. Diets were tailored to individual food preferences, and macronutrient consumption was 69–16-16% and 16–67-18% carbohydrate-fat-protein for the HCLF and LCHF diets, respectively. Following each 3-day dietary intervention, participants swam in a flume at velocities associated with 50, 60, and 70% of their maximal aerobic capacity (VO2max). Expired breath was collected and analyzed while they swam which enabled calculation of the energetic cost of swimming. A paired t-test compared macronutrient distribution between HCLF and LCHF diets, while repeated-measures ANOVA determined effects of diet and exercise intensity on physiological endpoints. Results Respiratory exchange ratio was significantly higher in HCLF compared to LCHF (p = 0.003), but there were no significant differences in the rate of oxygen consumption (p = 0.499) or energetic cost of swimming (p = 0.324) between diets. Heart rate did not differ between diets (p = 0.712), but oxygen pulse, a non-invasive surrogate for stroke volume, was greater following the HCLF diet (p = 0.029). Conclusions A 3-day high-carbohydrate diet increased carbohydrate utilization but did not affect swimming economy at 50–70% VO2max. As these intensities are applicable to ultramarathon swims, future studies should use higher intensities that would be more relevant to shorter duration events.

Reliability and Validity of a Flume-Based Maximal Oxygen Uptake Swimming Test

“…Therefore, these results may not be generalizable to a novice-level swimming population. Since maximal/peak physiological responses in water are comparatively different than land-based (i.e., cycle or treadmill) measures [ 13 , 18 , 30 , 31 ], an alternative paradigm was employed presently that utilized freestyle swimming performance time to establish “performance validity” as predicted by the swimming flume protocol. It was also expected that physiological responses to maximal swimming efforts in both the flume and pool were likewise controlled by the rate limiting links within the oxygen kinetic chain [ 30 , 31 ].…”

“…VO 2 max sw was identified as a change in VO 2 of <2.1 mL∙kg −1 ∙min −1 with increased exercise intensity and/or the highest VO 2 reached at maximal swimming intensity. Secondary VO 2 max sw test criteria included one or more of the following: 1) a respiratory exchange ratio (RER) > 1.10 (defined as ratio of (CO 2 ): (O 2 )); (2) HR ± 5 b·min −1 of the age-predicted maximum; (3) a RPE (OMNI scale) > 9; (4) volitional test termination due to exhaustion, and (5) blood lactate > 8.0 mmol∙L −1 [ 13 , 26 , 27 ]. When the test was terminated (i.e., unable to maintain stationary position in the swimming flume), the participant lifted their head out of the water, whereby investigators immediately stopped the swimming flume and removed the mouthpiece and nose clip.…”

“…However, more recent advanced studies have employed flume-based tests to both energetics and stroke mechanics in a temporal fashion [ 10 , 11 , 12 ]. A continuous graded swimming flume test protocol can assess cardiorespiratory and metabolic factors that determine maximal oxygen uptake, energy expenditure, as well as the economy of a swimmer’s stroke (i.e., stroke efficiency) [ 8 , 12 , 13 ].…”

The Low-Carbohydrate Diet: Short-Term Metabolic Efficacy Versus Longer-Term Limitations

“…One hypothesis is that the reduced glycogen stores that associate with the adoption of the LCD [ 25 ] result in reduced physical activity and increased fatigue [ 24 ], with consequent reduced energy expenditure. However, no consistent evidence from human-based studies supports any assumption that dietary composition and quality has an appreciable impact on physical activity, performance or endurance in people adopting dietary modification (including the LCD) for the purpose of weight loss [ 26 , 27 , 28 ]. There is also controversy regarding the effects of the LCD on the capacity for physical activity in sportsmen [ 29 , 30 , 31 ].…”

The Effects of Concurrent Training Combined with Low-Carbohydrate High-Fat Ketogenic Diet on Body Composition and Aerobic Performance: A Systematic Review and Meta-Analysis

“…For example, CT combined with a high-carbohydrate diet can increase muscle glycogen stores and thus benefit aerobic capacity in trained participants (e.g., with experience of at least two-month regular training/exercise) [ 13 ]. However, several other studies suggested that the endurance capacity may not benefit from a high-carb diet due to limited glycogen stores, especially since it also increases the risk of obesity [ 14 , 15 , 16 , 17 ]. Therefore, it is critical to implement appropriate dietary strategies during the CT protocol.…”