Festive bulge: scientists offer advice on how to beat overeating

Christmas and New Year are holidays with dietary excesses that many of us cannot control. This often leads to the “festive bulge”. As the holidays approach, could there be a recipe to contain this weight gain and pave the way to sustainable nutrition-based health at the same time? There’s a lot of focus on what we eat and how much we eat – but what about when we eat? Chrononutrition is the science of how timing affects our responses to nutrients. Scientific insights into when we eat suggest it may be worth exploring for better health.

While the idea of getting started on Chrono nutrition over Christmas can sound challenging, the guilty conscience that tends to follow feasting over the holidays may provide the needed motivation for the year ahead.

So for better health in the new year, why not try out time-restricted eating (TRE)? TRE is a type of intermittent fasting: a person eats all their meals and snacks within a particular time window, ranging from six to 12 hours each day. This implies 12 to 18 hours of fasting.

More and more research suggests that this kind of timing may have a significant influence on our health via interplays between our body clocks and nutrition.

As researchers with a focus on circadian biology, we have identified the festive season as a suitable starting point for a lifestyle change to time-restricted eating.

What is chrononutrition? The basic idea of chrononutrition is that the body’s response to the timing of meals can promote well-being and health via the circadian timing system. This timing system refers to the internal 24-hour mechanism that primes our bodies for the challenges and stimuli of the 24-hour day. This includes when nutrients are likely to be consumed, how they are used within the body at a given time and how the body responds to them at a given time.

A rodent experiment in the 1930s led to a focus on counting calories and calorie-restricted eating. This dietary restriction extended the lifespan of rats in this case. It was subsequently shown in a wide range of species. The promise is large: if you eat less, then weight loss, better health and a longer life may follow.

The rodent experiment was followed by research into diets that foster health and prevent disease. Interest in “meal-timing, circadian rhythms and lifespan” was sparked by Franz Halberg (known as the father of American chronobiology), among others, in the 1980s.

These studies around food and behaviour take evolutionary considerations into account. For instance, rodents gain fitness when fed in a time-restricted manner. In contrast, human behaviour tends to involve more erratic eating patterns during the hours when people are awake.

Lifestyle changes So what practical advice can we give on the occasion of Christmas and New Year from the 2017 Nobel Prize-winning field of chronobiology? The field gained recognition for its discoveries into how internal clocks organise our physiology and enable us to live in harmony with the external rhythms of day and night.

Findings from this field point to a simple lifestyle change: limiting when you eat to eight to 10 hours a day could protect you from developing obesity, or even lessen the negative health impacts of existing obesity. And time-restricted eating can work even if practised for only five days per week.

Importantly, if you can reduce a long habitual eating window (for instance, 15 hours) to a time-restricted eating window of eight hours, you are likely to benefit more than someone who reduces a habitual eating window of 10 hours to eight hours. Reductions in eating-time windows have already been found to help some overweight humans lose weight, sleep better and feel more energised.

Granted, much of the evidence comes from animal studies – and humans are certainly not big mice. Nonetheless, there have been no reports of detriments to this practice in humans. However, there has been one report of possible disadvantages to offspring in a pregnant animal model of time-restricted eating.

Late breakfast and early supper Why not try what some studies suggest and start time-restricted eating over Christmas, or put it on your New Year’s resolution list? To get started, consider having a late breakfast and an early dinner. Of course, if in doubt about the impact of time-restricted eating – or if you have medical or dietary restrictions, or are pregnant – talk to your doctors first for advice.

Beyond paying attention to calorie intake and food composition, “when we eat” is a relatively simple and potentially sustainable approach.