You don't want to go down this road. It just so happens it's something I'm pretty well versed on. And two, unless you're also agreeing on the notion that plant based diet, with fat and protein from whole foods is the ideal nutrition for athletes, we're going to but heads. And your skull will be crushed, your existing appreciation for what an athlete 'should eat' disintegrated and if you're a fella open minded to robust science and changing his mind, maybe reborn like the Phoenix.
Bah. Feck it. Here's a few places for you to start. Once you've read and understood these appetizers we can look at Lukaku's eating and consider whether he is off the mark:
Lynch HM, Wharton CM. Cardiorespiratory fitness and peak torque differences between vegetarian and omnivore endurance athletes: a cross sectional study. Nutrients. 2016;8(11)
Nieman DC. Implications of the vegetarian diet for athletes. Vegetarian Nutrition. 2001. CRC Press LLC
Nieman DC. Physical fitness and vegetarian diets: is there a relation? American Journal of Clinical Nutrition. 1999; 70: 570S-575S
Craddock JC, Probst YC, People's GE. Vegetarian and Omnivorous Nutrition - Comparing Physical Performance. International Journal Sport Nutr Exercise Metab. 2016; 26(3):212-20
Baguet A, Everaet I, De Naeyer H et al. Effects of sprint training combined with vegetarian or mixed diet on muscle carnosine and buffering capacity. European Journal of Applied Physiology. 2011; 111(10): 2571-80.
Raben A, Kiens B, Richter EA, et al. Serum sex hormones and endurance performance after a lacto-ovo vegetarian and a mixed diet. Med Sci Sports Exerc. 1992; 24(11): 1290-7
Trapp D, Knez W, Sinclair W. Could a vegetarian diet reduce exercise-induced oxidative stress? A review if the literature. J Sports Sci. 2020; 28(12): 1261-8.
Fisher I. The influence of flesh eating on endurance. Yale Medical Journal. 1907; 5: 205-221
And here's a special one that I love: Roman Gladiators were practically vegan eating barley and beans! How cool is that?!
Longo UG, Spiezia F, Mauffulli N, Denaro. The best athletes in Ancient Rome were vegetarian! J Sports Sci Med. 2008; 7(4):565