The order in which foods are consumed during a meal may influence post-meal blood glucose levels through coordinated interactions between gastrointestinal hormones, gastric emptying, and neural signaling, according to new research published in Diabetes. The study found that consuming olive oil before glucose reduced the subsequent rise in blood glucose in mice, with glucagon, glucagon-like peptide-1 (GLP-1), and vagal nerve signaling contributing to the observed effects. The findings provide new insights into the physiological mechanisms underlying meal sequencing and its potential application as a dietary strategy for improving glycemic control.
Postprandial hyperglycemia is an important concern in diabetes management, as repeated elevations in blood glucose following meals contribute to overall glycemic burden. Although dietary recommendations traditionally emphasize carbohydrate quantity and quality, growing evidence suggests that the sequence in which different nutrients are consumed may also influence glucose regulation. Previous clinical studies have shown that eating vegetables, protein, or fat before carbohydrate-rich foods can attenuate post-meal glucose excursions. However, the hormonal and neural mechanisms responsible for these effects have remained incompletely understood.
One proposed explanation is that consuming non-carbohydrate nutrients before carbohydrates slows gastric emptying, thereby delaying glucose delivery to the small intestine and its subsequent absorption into the bloodstream. Fat intake also stimulates gastrointestinal hormones, including glucose-dependent insulinotropic polypeptide (GIP) and GLP-1, which participate in nutrient sensing and metabolic regulation. However, whether these hormones act independently or through coordinated interactions with other endocrine and neural pathways has not been fully established.
To investigate these mechanisms, an international research team led by Liu and colleagues examined the metabolic effects of consuming dietary fat before or after glucose administration in mice. Following an overnight fast, the animals were assigned to three experimental groups. The control group received water followed by glucose, the fat-preload group received olive oil followed by glucose 15 minutes later, and the third group received glucose followed by olive oil after the same interval. Blood samples were collected to assess glucose concentrations and changes in insulin, glucagon, GIP, and GLP-1 secretion.
The investigators also evaluated gastric emptying using an acetaminophen absorption test. Because orally administered acetaminophen is absorbed primarily in the small intestine, its appearance in the bloodstream serves as an indirect indicator of gastric emptying. Additional experiments involving mice with type 2 diabetes and severe insulin deficiency were conducted to determine whether the metabolic effects of fat preloading persisted under conditions of impaired glucose regulation.
The results demonstrated that consuming olive oil before glucose substantially attenuated the early rise in blood glucose compared with administering glucose before olive oil. This effect was accompanied by delayed gastric emptying and increased early secretion of glucagon, GIP, and GLP-1, indicating that the timing of fat consumption influenced both gastrointestinal hormone responses and the rate at which ingested glucose entered the intestine. The glucose-lowering response was also observed in mice with type 2 diabetes and those with severe insulin deficiency. These findings suggest that the benefits of fat preloading may not depend exclusively on insulin secretion and that additional gastrointestinal and neuroendocrine mechanisms contribute to postprandial glucose regulation.
To clarify the roles of individual hormones, the researchers performed experiments involving pharmacological inhibition of glucagon and GLP-1 signaling. Blocking either pathway independently did not abolish the glucose-lowering effect of olive oil preloading. However, simultaneous inhibition of both pathways attenuated the response, suggesting that glucagon and GLP-1 exert partially redundant effects in mediating the metabolic benefits of consuming fat before glucose.
The involvement of glucagon is particularly noteworthy because the hormone is conventionally associated with increasing blood glucose by stimulating hepatic glucose production. The findings indicate that its physiological contribution may be more complex in the context of nutrient sequencing, particularly when glucagon signaling occurs alongside GLP-1 secretion and changes in gastrointestinal function. Rather than acting solely as a counterregulatory hormone, glucagon may participate in an integrated response that influences the handling of subsequently ingested carbohydrates.
The investigators further explored the contribution of neural signaling by examining the effects of bilateral subdiaphragmatic vagus nerve ligation. Disruption of vagal signaling altered the metabolic responses associated with fat preloading, supporting the involvement of communication pathways linking the gastrointestinal tract, nervous system, and metabolic organs. These observations suggest that the glucose-lowering effects of nutrient sequencing cannot be explained by hormonal changes alone.
The study adds a mechanistic dimension to existing clinical observations supporting meal sequencing as a potential strategy for moderating postprandial hyperglycemia. It also highlights the importance of considering nutrient timing and interactions, rather than focusing exclusively on the individual nutritional components of a meal. The findings provide a physiological basis for further investigating meal sequencing as a practical, potentially low-cost dietary approach to managing post-meal glucose excursions. Understanding how nutrient order influences gut hormone secretion, gastric emptying, and neural signaling may also help refine nutritional recommendations for individuals with diabetes and those at increased risk of impaired glucose regulation.
Reference
- Liu Y, Tsuchida H, Kubota S, Kubota-Okamoto S, Kato T, Horikawa Y, et al. Olive oil before oral glucose delays gastric emptying and lowers glycemia through partially redundant glucagon and GLP-1 signaling in mice. Diabetes. doi:10.2337/db26-0531.