Updated: Mar 30
By: William Sanders RD, LD, ACSM-CPT
Low Carb Ketogenic Diets (LCKDs) have gained popularity among athletes; however, there is no ergonomic or athletic advantage to consuming a LCKD in either strength/power or endurance sports (Kang, et al. 2020). In fact, athletes are more likely to face performance declines following a LKCD in sport (Murpy, Carrigan, & Margolis, 2020). Although they provide no athletic advantage, keto diets are proven to assist with short term weight loss and improve body composition when paired with an adequate physical activity regimen (Kang, et al. 2020).
The LCKD has been claimed as advantagous in endurance sports by some, because the LCKD can preserve endurance performance in activities that do not exceed 65-70% VO2max; however, activities with intensity exceeding 70-80% VO2max result in greater carbohydrate expenditure (Rebic, Ilic, & Zlatovic, 2021). Keto diets result in decreased glycogen stores, limiting sports performance for activities that exceed 70-80% VO2max (Kang, et al. 2020).
Very high intensity activities (ex: jumps and sprints) abilities typically remain the near level between LCKD and High Card (HC) diets simply because the phosphagen (creatine) energy system is primarily utilized; however, this systems capabilities are diminished within seconds. After creatine is used up, the body uses glucose from stored glycogen to support continue high intensity activity (Rebic, Ilic, & Zlatovic, 2021).
In addition to decreased performance, decreased glycogen stores from the LCKD make it significantly more difficult to build and preserve strong muscle (Rebic, Ilic, & Zlatovic, 2021). Bone health and increased fracture risk is also a concern for those following a keto diet, as negative effects on bone modeling and remodeling are possible. Negative effects on iron metabolism, potentially inhibiting aerobic performance are also possible (Bowler & Polman, 2020). Increased LDL cholesterol is common (O’Neill & Raggi, 2020). People consuming a ketogenic diet must evaluate their own diet for balance to ensure they make appropriate food choices to receive adequate micronutrient intake from omission of nutrient-rich high-carb foods (Kenig, et al. 2019).
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