Persistent postprandial hyperglycemia is an important risk factor for type 2 diabetes mellitus (T2DM) and its complications, which include cardiovascular diseases and mortality [1,2,3]. In fact, postprandial glucose is often considered a more dynamic indicator of metabolic health and cardiovascular disease risk compared to glycated hemoglobin (HbA1c) or fasting glucose [4,5,6]. Impaired postprandial glycemia is also associated with inflammation, oxidative stress, and impaired endothelial function [7]. Longitudinal studies have demonstrated that reducing postprandial glucose not only improves glycemic control but also reduces cardiovascular disease risk in patients with T2DM [8,9]. Given the recurrent exposure to postprandial hyperglycemia throughout the day, the postprandial phase has emerged as a pivotal focus for the prevention and treatment of diabetic conditions.

Exercise is vital in the prevention and treatment of T2DM. Both endurance and resistance exercise can acutely enhance insulin sensitivity and glucose tolerance [10,11,12]. These improvements have been attributed to the activation of the skeletal muscle glucose transporter system [13], the depletion of muscle and liver glycogen stores [14,15], and/or increased skeletal muscle blood flow [16] following the cessation of exercise. In adults with prediabetes or T2DM, a net reduction in blood glucose concentration during exercise is usually observed [17]. It has been suggested that strategies to combat T2DM should consider exercise after meals to more effectively tame postprandial glucose excursions [18,19]. When exercise is performed postprandially, both contraction- and insulin-mediated glucose uptake are stimulated, resulting in an additive effect on skeletal muscle glucose uptake [20]. Exercise after a meal is also linked to an elevated insulin-to-glucagon ratio, which can suppress hepatic glucose output, thereby lowering blood glucose levels [21,22].

A key objective of adopting postprandial exercise (PPE) is to effectively balance the rate of meal-derived glucose entering the bloodstream with the rate at which exercise utilizes this fuel. In this context, the impact that exercise has on postprandial glucose profile will depend in part on the time elapsed between the start of the preceding meal and the initiation of subsequent exercise. If exercise occurs too soon while meal-derived glucose levels are still low, or if it occurs too late, i.e., beyond the peak blood glucose period, the opportunity to effectively blunt postprandial hyperglycemia can be lost [23]. Recent reviews suggest that exercise initiated 30 min after a meal may produce the greatest improvements in glycemic control for individuals with T2DM [24,25]. However, this view is based on a limited number of studies that mainly compare the effect of pre- and post-meal exercise on glycemic responses in individuals with T2DM [26,27,28]. Studies involving an exercise regimen 60 min or more after a meal have also shown a significant reduction in glucose response in this population [29,30,31,32,33,34,35,36].

While managing postprandial hyperglycemia holds crucial significance in treating and preventing T2DM, exercise strategies during this phase that could be most effective in mitigating blood glucose levels have yet to be fully established. Among the studies exploring the acute effect of postprandial exercise on glycemic control, substantial heterogeneity exists in aspects such as participant demographics, exercise protocols, and exercise timing post-meal, making it challenging in directly applying the findings. Among the studies in the literature, there are also disparities in how postprandial glycemic responses have been determined. Glycemic responses following PPE can be assessed by quantifying the area under the curve (AUC) for glucose a few hours after exercise or by determining the mean glucose concentration over a 24 h period that includes the exercise treatment. These two measures, however, do not always yield the same results [29,37,38,39].

Through combining multiple studies that have investigated the acute metabolic effects of PPE, a modest yet significant reduction in blood glucose response following PPE was detected in those with and without T2DM. The reduction was evident in both the postprandial glucose AUC, which quantifies the immediate glycemic response to PPE, and the 24 h mean glucose concentration, which provides a more comprehensive assessment of glycemic control. Taken together, these findings suggest that exercise post-meal can not only lead to a transitory reduction in postprandial glucose levels but also contribute to positive glycemic control throughout the day. The underlying mechanism for the glucose-lowering effect of PPE can be attributed to the muscular activity that occurs concurrently with the buildup of glucose in the blood from the meal. When this occurs, it stimulates both contraction- and insulin-mediated glucose uptake, thereby removing glucose from the bloodstream more effectively [20]. During this time period, the insulin-to-glucagon ratio is also elevated, which could further reduce blood glucose concentration by inhibiting hepatic glucose output [23].

Exercise protocols in studies demonstrating a significant reduction in postprandial glucose AUC or 24 h mean glucose concentrations following PPE exhibited wide variations in intensity, duration, and modality. These protocols can be broadly categorized as either more vigorous shorter-duration exercises or less intense exercises for a longer duration. While the majority of studies utilized treadmill walking and stationary cycling, the glucose-lowering effects of alternative exercises, including bodyweight exercises, exercises involving medicine balls or elastic bands, and daily activities such as stair climbing, gardening, and household tasks, have also been demonstrated. In general, higher-intensity exercises are more effective in enhancing cellular glucose uptake due to their high demand for glycogen [66,67,68]. However, this evidence may not directly apply in the context of PPE, where the overall exercise volume is relatively small. Characterizing a generalized dose–response relationship for PPE is challenging due to the diverse exercise protocols used in the selected studies.

There has been a growing interest in using HIIE following meals as a time-efficient approach to counter postprandial hyperglycemia, as HIIE has been shown to enhance glucose tolerance and insulin sensitivity [69,70,71]. Given the high-intensity nature of HIIE, incorporating it into a PPE should theoretically enhance glucose disposal into skeletal muscle, reducing meal-induced glucose responses. On average, the intensity and duration attained were ~90% VO₂max and ~28 min, respectively, in HIIE and ~60% VO₂max and ~45 min, respectively, in CMIE. Notwithstanding these disparities between HIIE and CMIE, a similarity was observed in their glucose-lowering effects (as measured by the postprandial glucose AUC and the 24 h mean glucose concentrations combined). This finding is consistent with an earlier review by Borror et al. [17] and suggests that the combination or interaction of intensity and duration or the total exercise volume are the most critical factors in determining the effectiveness of PPE. Caution should be used when interpreting the results on this issue, as only six studies were used for the comparison. One should also be cognizant that despite HIIE protocols being time-efficient, their intense nature could potentially increase hepatic glucose output and worsen postprandial hyperglycemia [72,73].

Knowing an ideal time frame when exercise should commence after a meal can help further increase the metabolic benefits from the same exercise. The secondary analysis based on the five studies that implemented an exercise trial before and after a meal revealed a significantly larger glucose-lowering effect associated with exercise being carried out post-meal [26,28,54,57,61]. This finding agrees with many earlier reports suggesting that exercise undertaken postprandially confers better glycemic control than exercise initiated before a meal [18,24]. Pre-meal exercise may not be as effective in part because exercise in the post-absorptive state has been associated with more activated counterregulatory hormones such as glucagon and epinephrine, which trigger a greater hepatic glucose output [22].

When exploring the optimal timing for initiating PPE, the answer appears to diverge widely across the selected studies, ranging from 20 min to 150 min after a meal. Earlier studies involving healthy humans suggest that commencing exercise within 30–45 min after a meal is more effective in blunting postprandial hyperglycemia because it coincides more closely with the time when the blood glucose level reaches its peak [74,75,76]. However, based on the subgroup analysis of exercise timing post-meal, the reduction in glucose AUC appears unaffected by exercise timing, that is, whether postprandial exercise is initiated within the first hour after a meal or later, it remains equally effective in eliciting a transient reduction in blood glucose levels during the postprandial period. As for the 24 h mean glucose concentration, it demonstrated a significantly greater reduction following PPE initiated ≥60 min compared to <60 min after a meal. It has been suggested that individuals with impaired insulin action may experience a more prolonged and higher peak in postprandial glucose levels between 60 and 90 min after a meal [77,78,79].