Eating habits are a well-researched lifestyle factor contributing to CVD [63]. Poor eating habits, such as poor diet quality, have been linked to key cardiometabolic risk factors for CVD [11,12,64,65], including increased blood pressure, body mass index, serum lipids, total cholesterol, and low-density lipoprotein cholesterol [12,66,67]. As such, improving eating habits is a critical part of reducing CVD risk [13,68]. However, it has become apparent that the timing of food intake is also an important consideration [38], primarily due to the burden of altered eating patterns on the circadian system [14].

Eating at times when our body is not primed to digest food (e.g., at night [16]) can compromise metabolism and thus lead to an increase in the likelihood of developing CVD [38,44]. Indeed, observational studies have reported a relationship between irregular eating patterns and increased risk for metabolic syndrome [69,70,71], in addition to a relationship between habitual night eating and arterial stiffness, a preclinical sign of CVD [72]. Altered eating patterns are characteristic of shift work [55,73,74,75], with shift workers reporting that they change the timing of eating to accommodate their shift schedule; for example, eating during the night when working night shifts [55]. Misalignment of eating rhythms with the internal circadian system is thought to contribute to the relationship between shift work and CVD [73]. Research in non-shift workers has shown that erratic eating patterns are associated with increased CVD risk after controlling for dietary composition [76]; thus, highlighting that in addition to ‘what is eaten’, ‘when eating occurs’ also influences CVD risk. Collectively, recent research highlights the need to optimise eating time to reduce circadian disruption and consequently reduce the prevalence of CVD.

As previously discussed, TRE is a unique strategy that has gained popularity as a way to optimise the timing of food intake [14,16,38]. While typical eating windows for most individuals span 14 h of the day, a TRE approach shortens the eating window to between 4 and 10 h [14,77] (Figure 1, example 8 h eating window). It is important to note that the optimal timing of a shortened eating window (i.e., starting the eating window early in the day or later in the day) requires systematic study [44]. In a recent review by Regmi and Heilbronn [78], the authors argued that while the early morning (e.g., Figure 1, middle panel) may be considered an optimal time to start the eating window for maximal metabolic benefits (e.g., improving insulin sensitivity and lipid absorption), this would mean that people would miss eating dinner at a traditional time (6–8 pm), which is a typical family and group eating time [79]. This may therefore present social challenges. In contrast, the same 8 h eating window could start at 12 pm and include the typical dinner time (e.g., Figure 1, right panel). While this arrangement extends the overnight fast to the same degree and may be perceived to be less socially challenging, metabolic benefits may be reduced due to circadian considerations [78].

TRE may lead to improved cardiovascular outcomes [16]. For example, a recent systematic review and meta-analysis of eleven studies found significantly lower fasting glucose values for participants on a TRE pattern (with eating windows ranging from 6 h to 12 h) compared to those eating ad libitum [50]. Other studies have similarly demonstrated improvements following TRE in blood pressure, body weight, cholesterol, glucose metabolism, and the gut microbiome [22,50,51,78,80,81]. Furthermore, TRE circumvents some of the challenges of typical dieting approaches, which often require individuals to employ restrictive behaviours, because the quality and quantity of the food eaten in TRE regimes does not change [77,82], as only the window of eating is altered.

In shortening the eating window, TRE reduces the amount of time the body is required to metabolise food and lengthens the daily fast period, arguably allowing for greater metabolic recovery [14,16,22,41,50]. As introduced in Figure 1, a further opportunity for improving cardiometabolic outcomes arises from the ability to consider the timing of the eating window to reduce circadian disruption. In people with typical diurnal rhythm, starting a shortened eating window early in the day avoids circadian misalignment of eating behaviours and related impairment in the way in which food is processed by the body [15,38]. Indeed, evidence suggests that an earlier eating window is associated with more effective cardiometabolic outcomes compared to a later eating window [14,16,41,77]. As previously discussed, circadian disruption plays a significant role in the development of CVD due to misaligned daily rhythms, such as metabolism, digestion, and blood pressure [1]. Since food acts as a signal for peripheral circadian clocks [16,18], eating food at biologically inappropriate times can lead to misalignment between central and peripheral clocks [83]. Therefore, carefully timed TRE may be an effective and relatively straightforward strategy to minimise circadian disruption [48] and ultimately contribute to a reduced burden of CVD [38,77]. However, while day interventions are the focus of much of the existing TRE literature [14,38,45,50,84], consideration of the impacts of practicing TRE at other times, such as during the night, has been less well-documented. Research in this area is of particular interest for night workers who typically eat during the night [55]. Recent laboratory research has demonstrated the beneficial effect for glucose metabolism of maintaining a daytime eating window even while working (simulated) night shifts [85,86,87,88]. To extend this research, additional consideration of TRE for those working night shifts is needed; in particular, this would determine the impact and feasibility of shortening the daytime eating window while supporting the need to sleep during the day (Figure 2).

Consideration of sleep in the context of night work is critical. While TRE can be designed to reduce circadian disruption, one of the biggest contributors to circadian disruption is an altered sleep–wake cycle [23,26]. We hypothesise that TRE may not have the same benefits for cardiometabolic health if individuals are experiencing circadian disruption due to inadequate sleep.

Inadequate sleep is highly prevalent globally, with adults commonly obtaining less than the optimal 7–9 h of sleep per night [89,90,91,92,93]. For example, up to one-third of Australians do not achieve 7 h of sleep per night [89,90]. This is problematic, as chronic inadequate sleep challenges the circadian system [19] and consequently impacts cardiometabolic health [1,10,19,94]. Several studies have demonstrated the link between short sleep (considered sleep of ≤6 h in duration [95]) and adverse cardiometabolic outcomes including obesity, hypertension, poor glucose regulation, and insulin resistance [19,95,96,97,98,99,100]. Importantly, extended sleep (i.e., sleep >9 h) is also associated with adverse cardiometabolic health effects [101,102], such as increased blood pressure [103,104], and this could be a bi-directional relationship, with long sleep a symptom of CVD [105]. This suggests a U-shape relationship between sleep and cardiometabolic health, with 7–9 h considered an optimum amount for favourable cardiometabolic outcomes [102]. Ensuring adequate sleep duration (i.e., 7–9 h per 24 h) is therefore a key strategy to reduce the risk of CVD.

Inadequate sleep is a common outcome of shift-work schedules [37]. Many shift workers, particularly those engaged in night work, experience some degree of circadian disruption [9,106]. This is thought to be a major contributor to the prevalence of cardiometabolic issues in shift workers, such as elevated post-prandial glucose levels, obesity, and CVD in the long-term [9,19].