Modifying the Gut through Diet

 Our gut is apparently modified by what we eat. This makes a lot of sense. If we usually eat a lot of some food and the body ramps up the enzymes that digest that food, then we should get more energy from that food, and until relatively recently, getting as much energy from our food as posible was the body's goal. It's only in the recent past that most of us have too much food available so that obesity and not starvation is the problem.

Here is a study showing that if you eat a lot of food, your gut expands so you can digest more food. It had previously been shown that cold does the same, which makes sense because you need to burn more calories to stay warm when it's cold. The interesting thing is that this process seems to be reversible, meaning that if you limit your food intake for a bit, your gut may change its structure again (reducing the number of absorptive villi and hence surface area) so that it absorbs fewer calories.

Interestingly, fructose seems to do the same thing, increasing the villus length: "the increase in villus length was associated with increased nutrient absorption, weight gain and fat accumulation in the animals" wrote the authors of this study. They note that this makes sense evolutionarily because fruit, which contains a lot of fructose ("fruit sugar"), is most available in the fall, when animals want to fatten up so they can survive the lean times of winter.

Eating a peach is not likely to fatten you up, but overeating fructose by drinking a lot of high-fructose corn syrup--sweetened sodas could.

The abstract of the paper can be found here. Note that the authors suggest that fructose also promotes tumor growth.

Of course, if you have diabetes, any sugars like glucose, sucrose, or fructose are not a great idea.