To clarify: The increased nutrient absorption they observed wasn’t actually a good thing. Our stomachs evolved to very efficiently extract as many nutrients as possible from the food we eat, so these nutrients weren’t being wasted. Rather, the excess fructose overwhelmed the normal nutrient breakdown process and resulted in an abnormal nutrient absorption pattern:

> Moderate amounts of fructose — for example, those ingested when consuming fruits — are taken up and broken down by intestinal cells. Excess amounts, such as those that might be ingested after drinking a sugary beverage, overwhelm the intestine’s absorptive capacity and the fructose either ‘leaks’ into the bloodstream to reach the liver intact, or it spills over from the small intestine and reaches the colon

Basically: Too much fructose at once, especially without all of the fiber and structure of fruit to slow it down, ends up in places it shouldn’t because the normal digestive processes can’t keep up. Spilling bursts of fructose into your bloodstream and your liver isn’t great for your body.

Excess Fructose spilling into the colon creates another set of problems as this can do weird things to the microbiome. Ideally the small intestine would be able to handle the fructose and leave the colonic bacteria to feed on the leftover complex carbohydrates, but if you eat too much fructose some of it spills into the colon.