The inner clock of obesity


It’s kind of neat to find that despite being surrounded by artificial constructions and technologic marvels we remain deeply connected to our natural environment -- we’re still fixedly linked to Earth’s 24-hour rotation about its axis. There are mysterious clocks inside our brain, and in every cell in our body, and those regulate not only sleep and wakefulness, but also hormones and metabolic pathways. They organize our bodily functions and behaviors so that we should be optimized for the time of day.

And messing with this governing clock comes at a price. Jet lag is an obvious example: Moving rapidly across time zones can cause fatigue, headache, irritability and indigestion. Shift work that involves a nocturnal lifestyle is associated with obesity, type 2 diabetes and heart disease.

We now live a 24-hour lifestyle, where darkness and nighttime are no longer a constraint, and we can find food day and night. This led researchers to ask the question: Could messed up internal clocks be involved in the obesity epidemic?

A recent article in Obesity Reviews (207 references) gathers interesting findings.

Eating the right thing at the right time

Most people have realized that they are better at some tasks, such as complex math or writing, in the morning, and that other times of the day are better suited for other types of mental tasks.

Eating, it seems, is also time-of-day dependent.

Studies have shown that eating breakfast is associated with lower BMI, and skipping it with obesity. Likewise, there’s some research support to the notion that eating big meals close to bedtime increases blood sugar and insulin when our body is less active, and therefore dinner is best eaten 3 hours or more before sleep.

There’s some research (animal models and also human) that suggests that carbs during dinner improve satiety during the next day. A 6-month study of 78 police officers showed that those that reserved their daily carb intake to dinner lost more weight, felt more full, and had better insulin sensitivity than those on the same calorie-restricted diet in which the carbs were divided throughout the day.

Nutritional jetlag

But here’s a fascinating understanding of our enigmatic inner clocks: The more they are studied, the more apparent it becomes that although they regulate our energy and metabolic rate, we also regulate them. It’s a two-way interaction, in which food functions as a clock regulator. What we eat and when we eat can disrupt our circadian rhythm, and the modern 24/7 lifestyle – and non-stop consumption of calorie-dense food – can throw us into a social jetlag, with disrupted internal clocks that lead to obesity.

Animal studies have proven that. Rats on a high fat diet lose normal daily fluctuations of hormones – such as insulin and leptin – and other cellular communication mechanisms. The genes that express these cellular clocks are disrupted. This loss of variation between night and day might be the behind the development of obesity.

Our gut microbes also show circadian variation, and their communities can also be upset when day and night feeding become disorganized, leading to a vicious cycle in which a disturbed microbiome further contributes to obesity.

The metabolic price of disrupted internal clocks is called Chronobesity, and I suspect we’ll learn lots more about circadian rhythms and weight control in the years to come.

In the meantime, I think it’s safe to say that we should work towards regaining more balance and regularity in eating, sleep, and activity. Our inner clock seems to demand it.

Dr. Ayala

Eating, it seems, is also time-of-day dependent.