Longevity Briefs: Does The Timing Of Meals Correlate With Rates Of Ageing?

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Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

Not everyone experiences biological ageing at the same rate. Some people develop age-related disease relatively early in life, while others manage to maintain organ function equivalent to someone a decade younger than them. This difference is captured by the concept of “biological age”, which reflects the functional health of our cells and tissues, often differing from our chronological age (the number of years we’ve lived). It is hoped that by exploring which lifestyle factors influence estimates of biological age, we will uncover practices that can be adopted to delay the ageing process and live longer, healthier lives.

We know that diet plays a significant role in overall health and ageing, with calorie restriction (a sharp reduction in calorie intake without causing malnutrition) appearing to slow ageing and extend lifespan in animal models. The timing of our meals remains a less explored variable. Many aspects of our biology operate on a roughly 24-hour schedule known as a circadian rhythm, and this includes digestion and metabolism. In this study, researchers comb through large observational datasets to investigate whether a relationship exists between timing of meals and estimates of biological age.

The discovery:

Researchers used data from just over 14,000 individuals from the National Health and Nutrition Examination Survey (NHANES), a nationally representative health database from the United States. This data included self-reported dietary intake throughout the day, including the timing of the first and last meals. Researchers then used various biomarkers that are associated with function in different organ systems in order to estimate biological age in the heart, liver and kidneys. In brief, this involves looking at markers that are linked to health in a specific organ and comparing those to the population average. If a 40 year-old has liver function markers equivalent to those of a 50 year old, we estimate that the biological age of their liver is 50. It is important to note that this is not a measurement of ‘true’ biological age – just an estimate of how well a given organ functions based on certain markers.

When comparing meal timing to biological age in this sample, researchers found that consuming one’s last meal of the day between 3pm and 5pm appeared to be the sweet spot. Compared to those eating their last meal after 9pm, the 3pm-5pm timing was associated with significantly slower biological ageing in the heart and whole body, while those eating their last meal between 5pm and 7pm showed higher risk of biological ageing in the liver. Unsurprisingly, given the previously measured association between fasting and biological age estimates, a narrower feeding window (in other words, longer fasting period) was associated with slower estimated biological ageing in the whole body, heart and liver. Despite this, later consumption of the first meal of the day (which would extend the fasting period) was associated with faster biological ageing in the whole body, heart and liver.

Graph showing the likelihood of accelerated or decelerated biological ageing in different organs based on timing of the last meal of the day. Timings are shown on the left. The black diamonds in the centre of the graph represent the odds ratio (OR), the probability of accelerated or decelerated biological ageing relative to eating after 21:00. Diamonds to the left of the graph signify reduced risk of accelerated biological ageing. For example, an odds ratio of of 0.5 means 50% reduction in biological ageing risk.
*Dietary rhythms and biological aging risk across multiple organs*

These findings didn’t generalise to everyone – participants were affected by meal timing to different degrees based on age, sex and total calorie intake:

The effects of meal timing on biological age were greater in those with lower calorie intake.
The effects of meal timing were greater in male participants, while the effects of feeding window were greater in female participants.
The effects of meal timing and feeding window were not statistically significant in participants under the age of 40.

The implications:

This study suggests that shorter feeding windows are associated with beneficial changes in biomarkers of ageing, but that this feeding window should ideally be achieved by moving both the first and last meals of the day to earlier hours, with the ‘optimal’ timings appearing to be around 8am and 3-5pm respectively, based on this data. The proposed biological explanation for this is that the body follows a circadian rhythm with hormonal and metabolic changes typically favour eating earlier in the day. For example, sensitivity to the blood sugar-lowering hormone insulin is typically higher earlier in the day, meaning that blood sugar spikes higher when eating later in the day.

Research concerning meal timing can be difficult to interpret due to the presence of confounding factors, even when researchers make their best efforts to control for them. There is obviously a difference between someone who eats supper at 9pm because that’s when they get hungry, and someone who eats at 9pm because they have a three-hour commute. This is also further complicated by the existence of chronotypes (whether you are a ‘lark’ or an ‘owl’). Research suggests that chronotype influences those aforementioned biological rhythms, so while eating your last meal at 9pm might be harmful for a lark, it might not be so bad for an owl whose activities align with their natural circadian rhythm. Unfortunately, since standard working hours oblige most owls to behave like larks, even studies that look specifically at chronotypes may not paint a complete picture.