system
Given the following post, respond as if you're commenting on Reddit:
human
What is scientifically the most filling/satiating food to eat before a fast?
gpt
Of the three macronutrients, protein is generally the most satiating, followed by carbohydrate. Fat as such is not as satiating as the other two, but a meal's fat content does delay gastric emptying, which may or may not prolong the sensation of satiety. Also fiber.

The optimal carbohydrate source would likely be something with a low glycemic index. The postprandial elevation in blood glucose will then be reversed gradually, as opposed to a prominent spike in blood sugar followed by a rapid crash under the baseline level, potentially triggering another bout of hunger.