A recent study in Nature Communications explored how eating and fasting fluctuations affect the incidence of cardiovascular disease (CVD).
Introduction
Human bodies have physiological cycles that span approximately 24 hours, termed circadian cycles.
These include fasting/eating cycles that set peripheral clocks in various tissues, and the latter, in turn, help regulate the working of the heart and blood vessels. A new study seeks to throw more light on this topic by exploring how alterations in the timing of eating and fasting affect the incidence of CVD.
CVD is the leading reason for disease and death worldwide. Dietary patterns contribute significantly to cardiovascular risk, with almost 8 million deaths from CVD being linked to faulty diet. In recent years, many parts of society have become less focused on traditional meal times, and diets have become commonplace, meaning that meal timings are often irregular.
However, the link between cardiovascular health and the eating/fasting cycle is part of the important new field of chrononutrition that seeks to elucidate the network of connections between meal timings and health.
Research has shown that breakfast is essential to maintaining normal metabolism and cardiovascular health, while late-night meals promote arteriosclerosis, obesity, and abnormal lipid profiles. In women, it also leads to metabolic syndrome. However, there is considerable confusion over what timing identifies each meal and what defines late-night eating.
Time-restricted eating (TRE) could be a method of improving cardiometabolic health. It refers to extending nighttime fasting to over 12 hours, and in humans, it has shown corresponding reductions in body weight, blood pressure, and inflammation.
The relative paucity of data on how CVD risk is impacted directly by nighttime fasting duration and specific meal timings motivated the current study. The study, published in Nature Communications, used data from the NutriNet-Sante study involving over 100,000 adults. Their dietary records were used to build a database on eating frequency and meal timing.
What did the study show?
People who were younger, single, without a family history of CVD, smoked regularly, were more active, better educated, had lower monthly incomes, and were more likely to eat later breakfasts and late-night meals.
Individuals eating later meals were also at higher risk of having more variable meal timings, binge drinking, and higher mean alcohol consumption, as well as later bedtimes.
The median follow-up period was 7 years. This covered almost 700,000 person-years. During this period, there were just over 2,000 new cases of CVD, almost equally distributed between cerebrovascular diseases, including strokes and transient ischemic attacks, and coronary heart diseases (CHD), including heart attacks, angioplasty, acute coronary syndrome, and angina.
The later the first meal, the higher the risk of CVD was, but no such trend was observed with the timing of the last meal. However, when it was eaten after 9 pm, there was a 13% increase in risk compared to before 8 pm. The risk of cerebrovascular disease rose by 8% with each hour of delay of the last meal, and at the inflection point (after 9 pm vs. before 8 pm), it was 28% higher.
Increased nighttime fasting was linked to a reduction of cerebrovascular disease risk by 7%, but no similar decrease was observed for either CVD overall or CHD.
Thus, if the first meal was eaten after 9 am as compared to before 8 am, and if the last meal was taken after 9 pm vs. before 8 pm, the risk of cardiovascular outcomes was increased, more so among women compared to men. The benefits of increased nighttime fasting interval were also more prominent among women.
The maximum benefits would appear to be when nighttime fasting periods were prolonged by advancing the time of the evening meal rather than delaying or skipping the first meal of the day. This is probably because people are most sensitive to insulin and higher glucose levels early in the morning, becoming less so as the day progresses.
In fact, animal studies demonstrate the onset of weight gain, increased fat mass, fat deposition in the liver, and a delay in the rhythmic expression of lipid metabolism genes when breakfast was routinely delayed by four hours.
Human studies indicate that aberrations in glucose regulation and insulin sensitivity, dyslipidemia, and weight gain beyond normal limits occur when evening meals are delayed.
This may be linked to food intake during the body’s rest phase, when melatonin secretion is at its peak, causing prolonged elevations of glucose in the blood after the meal.
What are the implications?
It appears that cardiometabolic health is best served by early TRE, with early first and last meals, and this is supported by an earlier finding from the same cohort that people who ate breakfast before 8 am and fasted for >13 hours overnight had a lower risk of type 2 diabetes mellitus.
The findings that later first and last meal timing are both separately linked to a higher risk of overall CVD corroborate earlier studies showing improved cardiometabolic risk factors with earlier breakfasts and last meals. Timely meals promote the metabolism of food, as food has been established to set peripheral circadian rhythms that regulate blood pressure.
While these findings are suggestive, because of the large sample size and the prospective design, confounding factors must be considered, such as the possibility of night shift work among those who eat later in the night.
This is an independent correlate of cerebrovascular disease and impaired sleep. However, no participant in this study ate meals exceptionally early or late in an attempt to rule out such shift work.
Other factors such as light exposure at night, nighttime awakenings, timing of exercise or other activity, drinking, and substance abuse could all potentially cause disturbances of the circadian rhythms and were not controlled in this study.
These findings suggest that, beyond the nutritional quality of the diet itself, recommendations related to meal timing for patients and citizens may help promoting a better cardiometabolic health.
Palomar-Cros et al. (2023)
Further studies are needed to validate these findings.
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