The recent marathon world records are apparently due to improved nutrition.

Here's the producer of the hydrogels talking about the exact process of getting the maximum carbohydrates into the runner:

https://maurten.no/blogs/m-magazine/how-sabastian-sawe-fuele...

> At the elite level, marathon performance is defined by energy availability as much as physiology.

> Maintaining a pace of 2:50 per kilometer requires a constant supply of fuel. Even small disruptions in energy delivery can result in significant time loss.