Not all calories are created equal

The calorie content of a food measures how much energy your body can extract from that food — energy that’s either used to turn the gears of the body’s current metabolism or is stored for later use as glycogen in your muscles or fat in your fat cells. At this first level of analysis, all calories are equal, because each calorie represents the same amount of potential energy.

But, apart from their potential energy content, foods also initiate three types of signals in the body, and those signals determine how the body makes use of the foods it eats.

1. Different foods stimulate the production or suppression of various hormones.
2. The tastes and smells picked up by your tongue and nose start a cascade of nerve signals.
3. The bacteria in your gut react differently to different foods.

All of these signaling pathways have to be taken into consideration in order to analyze the effects of different foods.

What we’re learning about fructose

The fructose molecule signals to the body: “let the good times roll.” A review article in Nature Metabolism from April, 2026 reveals the latest we’ve learned about this. It makes sense because, throughout most of our evolutionary history, the periods when fructose was plentiful coincided with the season when food and calories were most abundant overall.

At these times of “metabolic plenty,” our metabolism was tuned to stock up on nutrients and store energy for the future. The fructose we consumed had a meaning beyond the extra calories it contained; it was the signal to shift our metabolic style. Building fat reserves was necessary because, invariably, there were lean times ahead.

Nowadays, for most of us, truly lean times never roll around. If we put on an extra layer of fat, it just sits there forever, or at least until the next cycle comes around and we pile on even more fat. Empty calories, such as sucrose and other simple sugars, are bad enough. But fructose plays an even more damaging role due to its signaling function.

Wait — is it bad to eat fruit?

No it isn’t bad to eat fruit. It’s true that a lot of the fructose in our diet comes from fruit. But whole fruits contain lots of fiber and other nutrients to go along with the fructose. And the sugars in fruit take longer to digest and process as compared to sugar that’s added to soda, candy, and the like. On the whole, fruits are a healthful component of your diet. You should perhaps limit your intake of fruit juice, however, since you’re not getting the fiber component of the whole fruit.

What are other health problems concerning fructose?

Read all about it.