"The IAAF has today released a comprehensive guide to sports nutrition designed to offer athletes the latest information on fueling their training and performance."

IAAF press release here: https://www.iaaf.org/news/press-release/iaaf-consensus-statement-nutrition-for-athlet

Read the articles at Human Kinetics Journals: https://journals.humankinetics.com/doi/full/10.1123/ijsnem.2019-0065

A few of the key findings highlighted in the IAAF release:
*"No direct benefits have been associated with the avoidance of gluten by clinically healthy athletes."
*emphasis on a "food first philosophy" that prioritizes food before supplements, stating that "Only five supplements have an evidence base of contributing to performance: caffeine, creatine, nitrate/beetroot juice, beta-alanine and bicarbonate."
*caution that "Vegetarian diets can theoretically support athletic demands, but special attention and good planning are required to ensure adequate intake of energy and specific nutrients that are less abundant or less well absorbed from plant sources (eg. iron)."

There is a lot of info here and I would suggest reading the full text at HK when you have time.