The rising prevalence of obesity and diabetes has made pre-diabetic adults who spend much of their day in a state of postprandial hyperglycaemia a target demographic for preventive lifestyle interventions against type 2 diabetes and related cardiovascular conditions.
Researchers at the Australian Catholic University and Baker Heart and Diabetes Institute conducted a study whereby they compared the effect of high-energy versus low-energy first meals on glucose and insulin responses during prolonged sitting in pre-diabetic individuals.
Which way to go — high or low?
They recruited 13 overweight and obese pre-diabetic adults aged 60 to 66, with a BMI of between 33kg/m2 and 37kg/m2, to complete two randomised trials, both of which entailed 10 hours of uninterrupted sitting.
One involved incorporating three meals with matching macronutrient compositions but different energy distributions: a high-energy breakfast (50% of the daily energy intake), followed by lunch (30%) and dinner (20%).
The other involved a low-energy breakfast (20%), followed by lunch (30%) and dinner (50%).
The researchers then took venous blood samples between 8 AM and 6 PM to determine the participants' plasma glucose and insulin concentrations, alongside 24-hour continuous glucose monitoring (CGM).
They then reported that total glucose and mean plasma glucose concentrations were greater after the high-energy breakfast, compared to the low-energy breakfast.
Those who had consumed the high-energy breakfast were also found to have higher plasma glucose levels after breakfast, but lower levels after lunch.
In addition, total insulin was greater following the high-energy breakfast than after the low-energy breakfast. At the same time, 24-hour CGM found no differences in mean and total glucose between conditions.
The researchers wrote: "Compared to a low-energy first meal, a high-energy first meal elicited exaggerated plasma insulin and glucose responses until lunch, but had little effect on 24-hour glycaemia.
"During periods of prolonged sitting, adults with pre-diabetes may have more beneficial postprandial insulin responses to a low-energy first meal."
Issues of size and timing
One of the study's limitations was that its sample size was smaller than initially planned, and there was a lack of venous sampling after 6 PM, leading to the inability to characterise the postprandial insulin, C-peptide or GLP-1 responses after dinner.
The timing of the meals was also similar to a time-restricted feeding protocol that could have compounded the postprandial hyperglycaemic response to lunch and dinner.
The researchers concluded: "Our results support a role for first-meal energy intake to influence postprandial glucose and insulin responses in adults with pre-diabetes, independent of macronutrient composition.
"In contrast to the results of studies of meal energy distribution, the clinical advantage of a high-energy first meal to improve daily blood glucose regulation was not evident in this investigation in individuals with pre-diabetes.
"For adults with pre-diabetes who experience prolonged sedentary periods, particularly in the hours leading to lunch, a low-energy first meal may be desirable for postprandial glucose and insulin regulation, although 24-hour glycaemic control was not impaired or improved by a high-energy first meal of the same composition.
“These considerations highlight the need for a larger, longer-term intervention, where meal size is the modifiable factor and each meal composition is controlled.
"However, food availability / choices at mealtimes often dictate the composition, so there is also a need to investigate meal size with the consideration of typical meal compositions (i.e., higher carbohydrate intakes at breakfast and higher protein at dinner)."
"Impact of First Meal Size during Prolonged Sitting on Postprandial Glycaemia in Individuals with Prediabetes: A Randomised, Crossover Study"
Authors: Evelyn B. Parr, et al.