The pitfalls of late-night snacking
A growing body of research suggests that our bodies function optimally when we align our eating patterns with our circadian rhythms.
NUTRITION scientists have long debated the best diet for optimal health. But now some experts believe that it’s not just what we eat that’s critical for good health, but when we eat it.
A growing body of research suggests our bodies function optimally when we align our eating patterns with our circadian rhythms, the innate 24-hour cycles that tell our bodies when to wake up, when to eat and when to sleep.
Studies show that chronically disrupting this rhythm– by eating late meals or nibbling on midnight snacks, for example – could be a recipe for weight gain and metabolic trouble.
That is the premise of a new book, The Circadian Code, by Satchin Panda, a professor at the Salk Institute and an expert on circadian rhythms research.
Panda argues that people improve their metabolic health when they eat their meals in a daily 8- to 10-hour window, taking their first bite of food in the morning and their last bite early in the evening.
This approach stems from the idea that human metabolism follows a daily rhythm, with our hormones, enzymes and digestive systems primed for food intake in the morning and afternoon.
Panda has found in his research that the average person eats over a 15-hour or longer period each day, starting with something like milk and coffee just after rising and ending with a glass of wine, a late night meal or a handful of chips, nuts or some other snack just before bed.
That pattern of eating, he says, conflicts with our biological rhythms. Scientists have long known that the human body has a master clock in the brain, located in the hypothalamus, that governs our sleep-wake cycles in response to bright light exposure. A couple of decades ago, researchers discovered that there was not just one clock in the body but a collection of them.
During the day, the pancreas increases its production of the hormone insulin, which controls blood sugar levels, and then slows it down at night. The gut has a clock that regulates the daily ebb and flow of enzymes, the absorption of nutrients and the removal of waste.
The communities of trillions of bacteria that comprise the microbiomes in our guts operate on a daily rhythm as well. These daily rhythms are so ingrained that they are programmed in our DNA: studies show that in every organ, thousands of genes switch on and switch off at roughly the same time every day.
Panda said: “We’re designed to have 24-hour rhythms in our physiology and metabolism. These rhythms exist because, just like our brains need to go to sleep each night to repair, reset and rejuvenate, every organ needs to have down time to repair and reset as well.”
Most of the evidence in humans suggests that consuming the bulk of your food earlier in the day was better for your health, said Dr Courtney Peterson, an assistant professor in the department of nutrition sciences at the University of Alabama at Birmingham.
Dozens of studies demonstrate that blood sugar control is best in the morning and at its worst in the evening. We burn more calories and digest food more efficiently in the morning as well.
At night, the lack of sunlight prompts the brain to release melatonin, which prepares us for sleep. Eating late in the evening sent a conflicting signal to the clocks in the rest of the body that it was still daytime, said Peterson.
Most people know what happens when we disrupt the central clock in our brains by flying across multiple time zones or burning the midnight oil: fatigue, jet lag and brain fog set in.
Eating at the wrong time of day placed similar strain on the organs involved in digestion, forcing them to work when they were programmed to be dormant, which could increase the risk of disease, said Dr Paolo Sassonecorsi, the director of the Center for Epigenetics and Metabolism at the University of California, Irvine.
“It’s well-known that by changing or disrupting our normal daily cycles, you increase your risk of many pathologies,” said Sassone-corsi.
A classic example of this is shift workers. Night-time shift work is linked to obesity, diabetes, some cancers and heart disease.
In one experiment, scientists found that assigning adults to delay their bedtimes and wake up later than normal for 10 days – throwing their circadian rhythms and their eating patterns out of sync – raised their blood pressure and impaired their insulin and blood sugar control.
Another study found that forcing people to stay up late just a few nights in a row resulted in quick weight gain and reduced insulin sensitivity.
In 2012, Panda and his colleagues at the Salk Institute took genetically identical mice and split them into two groups. One had round-the-clock access to high-fat, high-sugar foods. The other ate the same foods, but in an eight-hour daily window. The mice that ate whenever they wanted got fat and sick while the mice on the time-restricted regimen did not.
Inspired by this research, Peterson conducted an experiment in a small group of pre-diabetic men. In one phase, the subjects ate their meals in a 12-hour daily window for five weeks. In the other phase, they were fed the same meals in a six-hour window beginning each morning.
The researchers had the subjects eat enough food to maintain their weight so they could assess whether the time-restricted regimen had any health benefits unrelated to weight loss.
It did. On the time-restricted regimen, the men had lower insulin, reduced levels of oxidative stress, less night-time hunger and lower blood pressure.
Researchers in Israel found that overweight adults lost more weight and had improvements in blood sugar, insulin and cardiovascular risk factors when they ate a large breakfast, modest lunch and small dinner compared to a small breakfast and a large dinner.
Peterson said it confirmed an age-old adage: eat breakfast like a king, lunch like a prince and dinner like a pauper. – The New York Times