Unlike previous studies, which focused on body weight and blood glucose levels, this meta-analysis primarily focused on the effects of TRE on BP. To the best of our knowledge, this is the first meta-analysis to investigate this relationship. The results of a meta-analysis of ten studies showed that TRE significantly reduced SBP. Furthermore, this relationship remained consistent across the subgroup analyses. Meanwhile, TRE significantly reduced DBP in patients with an intervention duration of 12 weeks. These findings are critical because they provide a new perspective on decreasing BP.
In recent years, TRE, a weight loss method, has shown enormous promise in fighting obesity and metabolic diseases. The concept of TRE stems from studies of the effects of food timing on the circadian system. One of the major adverse consequences of circadian rhythm disturbances is an increased risk of cardiovascular diseases [36]. Cardiovascular diseases remain a leading cause of death globally in the general population; consequently, there is growing interest in the circadian regulation of cardiovascular health.
However, TRE was shown to have little beneficial effect on heart rate. Therefore, lower BP may be attributed to distinct weight loss. As is well known, there is a strong link between body weight and BP in obese patients [37]. Several mechanisms may lead to hypertension, such as insulin and leptin resistance, perivascular adipose tissue dysfunction, renal impairment, renin-angiotensin-aldosterone activation, and sympathetic nervous system activity [37]. Weight loss has beneficial effects on BP. In this study, we further analyzed the effect of TRE on blood lipid levels (total cholesterol, triglycerides, LDL-C, and HDL-C). Unfortunately, we found no obvious effects in our study. Recent studies [38] using metabolomics and lipidomics platforms have shown that the levels of hundreds of lipid species in the plasma are regulated by circadian rhythms, although the timing and magnitude of the lipid rhythms vary widely among individuals. A prior meta-analysis by Chen et al. [39] demonstrated that LDL-C levels were increased in the TRE group, which may partially explain our poor results.
Broadly speaking, the results of previous animal experimentation were consistent with the conclusions of the present study. An animal model conducted by Cote et al. [40] illustrated that limiting feeding in the active phase reduces BP. Hou et al. demonstrated [41] that TRE protects the circadian rhythm of BP in db/db mice by suppressing sympathetic activity during the light phase. Furthermore, Mager et al. [42] demonstrated that intermittent fasting reduces heart rate in rats. The increased variability in heart rate in rats caused by TRE may result from the enhanced activity of brainstem cholinergic cardiovagal neurons [43]. Godar et al. [44, 45] showed that intermittent fasting improved myocardial ischemia-reperfusion injury and reduced circulating cholesterol and triglyceride levels. In general, animal studies have demonstrated significant cardioprotective effects of TRE.
Our study has several limitations which should be mentioned. Firstly, as shown in Table 1, the vast majority of our subjects were overweight or obese, while patients with hypertension were excluded from the present study. Therefore, it is prudent to conclude that TRE improves BP in obese individuals. Whether this conclusion can be extended to hypertensive populations requires further investigation. Secondly, the heterogeneity of the studies was significant; this was attributed to the different time ranges and durations of the TRE interventions. The longest intervention period in the included studies lasted 12 months, whereas the shortest was 1 month. These factors may have had different degrees of influence on the results. Despite this, our results remained statistically significant. Furthermore, compared with DBP, TRE significantly reduced the SBP. Heart rate and peripheral resistance had a significant effect on DBP. This appears to explain the DBP changes with inconspicuous improvement in heart rate. At the same time, the included participants were generally younger with higher peripheral resistance; therefore, the changes in DBP were not distinct. In addition, intervention components such as calorie restriction or exercise are thought to influence BP, weight, lipids, and glucose. Kotarsky et al. [33] reported that participants in both the TRE and normal eating groups completed eight weeks of aerobic exercise and supervised resistance training. As both the experimental and control groups exercised, we excluded the liability of exercise on BP, weight, lipids, and glucose. Finally, the effect of different TRE restriction times (e.g. 4 h, 6 h, 8 h, 12 h) would have had an effect on the outcome. However, owing to the number of original studies, the TRE restriction time could not be refined further. Our results need to be validated by RCT studies with large samples and long-term follow-up.
There is already a wealth of evidence, both in the basic and clinical fields, to suggest the effects of TRE. However, there is still room for improvement in the following aspects. First, the effects of TRE on the heart rate and blood lipid levels were not apparent in our study, which was not consistent with the results of basic research. More convincing data on the effects of TRE on heart rate and blood lipids are still required. Simultaneously, we generalized our conclusions to patients with prehypertension and hypertension. As a simple and accessible means, TRE promises to improve the lifestyle of prehypertensive and hypertensive patients.