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It's a real science for distance swimmers - needing to take on a mix of water, hot drinks, energy-dense foods that you can imbibe really quickly and your body can handle while constantly swimming. Feeds are usually done hourly and last 20 seconds max as every second you're not swimming, you're drifting. A lot of Channel training involves experimenting with nutrition. Probably a bit more straightforward for the 10km swimmers.
How do you think people get across the Channel in cold water without fuelling? I know people who’ve taken over 20 hrs to cross, that’s a heavy required food intake. I also know of a Japanese swimmer whose food stops involved treading water eating bowls of noodles - with chopsticks!