“Time is the longest distance between two places.”
– Tennessee Williams, The Glass Menagerie
For many of us food-centric types, it may perhaps be better stated that time is the longest distance between two meals.
With all the buzz about intermittent fasting, long fasts, short fasts, and multiple meals, it raises the question of an optimum “distance” between eating. Specifically, does the time between meals impact our health, irrespective of what we consume? Previously in this column, the topic of chrononutrition (the timing of our meals) was discussed along with the effects of chrono-disruptors like social jet lag.
This week, the focus is specifically on the timing of our daily fast between meals. We all fast at some point when we sleep. Our word for the first meal of the day after arising from sleep, breakfast, comes from the very act of breaking the fast of the night before. It turns out that this cycle of eating and sleeping/fasting is involved in the synchronization of our circadian clocks. This, in turn, has important effects on our cardiovascular system and blood pressure, as well as other peripheral systems involving the liver, kidney, and pancreas.
As a result of increasing data on chrononutrition, practices like intermittent fasting (also known as time-restricted eating or TRE) have gained in popularity and delivered confusing and, at times, contradictory information regarding the most beneficial regimen. TRE specifically refers to the practice of extending the nighttime fast beyond twelve hours. Previous literature using animal models has shown that eating only within an 8-10 hour window during the day results in improved metabolic health and protection against obesity. In human studies, TRE has been linked to reduced body weight, blood pressure, and a reduction in markers of inflammation.
The current study sought to explore the associations between the time of the first and last meal of the day, the number of eating occasions, and nighttime fasting duration with the risk of cardiovascular disease (CVD). Thus, there were four variables examined: the length of the evening fast, the start & finish times (the time the fast was broken and the time of the last meal, early versus later in the day), and the number of meals/snacks during the active eating window.
- The study examined 103,389 participants from the prospective NutriNet-Santé cohort.
- The cohort was 79 percent female, with an average age of 42.6 years.
- The data was obtained by using dietary records, with an average of 5.7 records per participant over a median follow-up time of 7.2 years.
- CVD events were comprised of cerebrovascular events (stroke and transient ischemic attacks (TIAs)) and coronary heart disease events (coronary heart disease (CHD), heart attack, receiving an angioplasty, acute coronary syndrome, or chest pain (angina)).
- Breaking the fast later in the day (after 8 AM) and eating a last meal later in the evening (after 8 PM) were associated with an increased risk of overall CVD.
- These findings were more pronounced in women compared to men.
- The time of consuming the last meal of the day affected the risk for cerebrovascular disease; specifically, eating after 9 PM compared to having the last meal no later than 8 PM increased the risk of cerebrovascular disease by 28 percent.
- There was no effect (positive or negative) associated with the number of meals consumed during the active eating time.
There are three specific measures reported in this study: CVD, which includes both cerebrovascular risk and coronary heart disease risk as a composite endpoint; cerebrovascular risk as an independent measure; and coronary heart disease (CHD) as an independent measure.
The time of breaking the evening fast did statistically significantly affect CVD, with a later breakfast time associated with an increased overall risk of CVD by 6 percent. The time of the last meal (eating the last meal later in the evening) increased the risk of CVD by 13 percent, but this value was remarkable only as a trend and did not reach statistical significance (p=0.06). There was no effect, positive or negative, of eating a few meals versus many.
For cerebrovascular disease, unlike the composite endpoint of CVD, there was no impact related to the time of breakfast. However, there was an impact regarding the timing of the last meal, e.g., eating after 9 PM as opposed to finishing mealtime by 8 PM or earlier, increased the risk of a cerebrovascular event by 28 percent. There was also an inverse association between the length of fasting time and cerebrovascular risk. Each additional hour of fasting reduced cerebrovascular disease by 7 percent. Similar to the findings for CVD, there was no difference between eating a few meals or eating multiple meals.
For CHD, there was no association between meal timing, the length of fasting, or the number of meals consumed during the active eating window for the study group as a whole.
The results were more pronounced in women versus men. For women, eating later in the evening and having breakfast later in the day did increase the risk of overall CVD and specifically cerebrovascular disease, while a longer fasting time correlated to a reduced risk of CHD.
Interestingly, the greater the time between the last meal and bedtime correlated to a decreased risk of overall CVD.
This study is one of the first large trials to investigate the role of chrononutrition and health outcomes, specifically CVD. The study found an inverse association between nighttime fasting duration and the risk of cerebrovascular disease, which was a potent driver of outcomes.
Stimulatingly, this introduces the possibility of other variables and their relation to diet, digestion, and health outcomes. For example, the glymphatic system is a recently discovered system in the brain that plays a crucial role in the clearance of waste and toxins. It functions somewhat like the lymphatic system in the rest of the body but with unique characteristics specific to the brain. It is particularly active during sleep. Thus, these findings may reflect at least a partial role of the glymphatic system during sleep versus an effect due solely to the length of fasting time. The length of nighttime fasting had no impact on coronary heart disease or the composite variable of overall cardiovascular disease. The relationship between our circadian rhythm, the glymphatic system, and digestion remains unknown.
This study raises many intriguing avenues for further research into the blossoming field of chrononutrition, highlighting the importance of not only what we eat but the importance of how, why, where, with whom, and in this case, when we choose to engage with our personal food experience.
Palomar-Cros, A., Andreeva, V.A., Fezeu, L.K. et al. Dietary circadian rhythms and cardiovascular disease risk in the prospective NutriNet-Santé cohort. Nat Commun 14, 7899 (2023). https://doi.org/10.1038/s41467-023-43444-3