Opinion – Suzana Herculano-Houzel: Eating at night makes you fat

One of the beauties of science is that the account always closes. People lose weight when they use more energy than they take in and gain weight when they take in more energy than they use. That simple.

A real mystery is when two individuals eat the same food, but one gains weight and the other does not. “So-and-so is wickedly thin,” they say; he eats what he wants and doesn’t get fat.

But it’s not bad, no. At least one of the factors is now known to science: when you eat it makes all the difference. Apparently, what is eaten during periods of activity is immediately used, either because it sustains the current activity or because, if there is no great activity, what is left over becomes heat, and the energy is lost to the environment. Balance? Practically zero. But the same amount eaten during inactivity becomes… reserve, in the form of fat.

The difference comes from the metabolism of adipocytes, the cells that store fat in the body, controlled by the brain, according to a recent study by researchers at Northwestern University, in the USA, published in the journal Science. The researchers found that even when mice live in an environment at 30°C, which for them requires no effort from the body to maintain its temperature, eating during the active period (which for them is at night) increases the activity of futile cycles that consume energy without going anywhere—that is, they don’t produce work, just heat, which dissipates.

But if the same amount of food is eaten during the period of inactivity, when the hypothalamus’ biological clock keeps the body in a state of rest and recovery, the futile cycles are not triggered. All the energy needed at the moment will be used, of course—always. But if there is energy ingested in excess at these times, when futile cycles cannot be activated, what is left becomes extra weight.

It’s just like a gas-guzzling car that runs around getting fuel by vein all the time. What goes in while the car is running, or at least idling, ready to start all over again, is consumed by the metabolism that keeps the car’s engine warm and running. The tank neither empties nor overflows. But if the fuel keeps coming in after the car shuts off, it’s obvious that the tank is going to overflow — and the garage or the rest of the body around it picks up the leftovers and puts it away for another day. It can be a lifeline in lean times and uncertain circumstances.

But for those who exist in the abundance of the industrial world, getting fat seems like nature’s revenge against those who start to have more food available than they need. After all, those who are hungry and find food don’t wait to eat later: they eat as much as they can as soon as they find food, which will happen, by definition, while they are active. Accumulating food to eat later, at the end of the day, during rest, is for those who can afford to save it for later.

The solution is simple. It will be difficult to beat the lobby of bars and restaurants for the night crowd…