Having high blood sugar levels after eating is linked to health problems, such as diabetes, heart disease and obesity. Previous research has shown that a snack a few hours before a meal can help control blood sugar levels, which may partly explain why the first thing we eat each day (i.e. breakfast) tends to increase blood sugars more than other later meals, yet the effect of nocturnal protein ingestion on morning glycaemic control has never been examined.
Researchers from the Federal University of Uberlândia, in Brazil, conducted a randomised crossover study to compare the acute effect of consumption of a high-protein/moderate carbohydrate (HP-MCHO) versus low-protein/high-carbohydrate (LP-HCHO) meal at night on the postprandial metabolic response of male night workers the following breakfast.
They found no significant differences in glucose, insulin, triglyceride, and HOMA-IR levels were found between interventions. A night meal with a higher percentage of protein and a lower percentage of carbohydrate led to minor postprandial glucose levels during the night shift but exerted no effect on the metabolic response of the following meal.
Their study involved 14 male night workers aged 30-50. Participants underwent two different isocaloric dietary conditions at 1am during their night shift: HP-MCHO (45% carbohydrate, 35% protein and 20% fat) and LP-HCHO (65% carbohydrate, 15% protein and 20% fat).
Postprandial capillary glucose levels were determined immediately before the intake of the test meal and 30, 60, 90 and 120 min after the end of the meal. At the end of the work shift (6:30am), participants received a standard breakfast and postprandial levels of glucose, insulin and triglycerides were determined immediately before and then every 30 min for two hours.
Higher values of capillary glucose were found after the LP-HCHO condition compared to the HP-MCHO condition.
Unexpected negative effect
This Brazilian study was published just a few days after another similar study - currently under review - which was presented during an online conference last week.
The study, conducted by researchers from the University of Bath, looked into the effect of nocturnal whey protein shake consumption on postprandial responses to breakfast.
The results of the study actually suggested that consuming protein at night increased blood sugar levels in the morning.
Eleanor Smith, a Uni of Bath graduate, presented the work during the Physiological Society's Future Physiology conference last week. She said the randomised cross-over study involved fifteen healthy young men and women (eight females and seven males). The participants were woken up at 4am to drink 300ml of a water solution, either with or without 63 grams of whey protein.
They then went back to sleep and at 9am were provided with a standard amount of porridge for breakfast, with blood samples collected for two hours afterwards to check the blood glucose response.
When they looked at their data, the researchers were surprised to discover the blood sugar response to breakfast was higher when participants consumed the protein shake rather than plain water at 4am.
Smith said this revealed a paradoxical second-meal phenomenon whereby nocturnal feeding impaired subsequent glucose tolerance.
One explanation she suggested for the result is that the body does not expect or need much food to be consumed during the night and so the protein itself was turned into sugar. This may result in the body having more carbohydrate already available upon waking such that the energy in the breakfast can less easily be used or stored, so it builds-up more in the blood.
She added: "Future research will look at whether this applies to older and overweight people who tend to have more problems controlling their blood sugar levels. It would also be interesting to know to what extent our findings are due to eating at an unusual time or the type of protein consumed."
Crispim. C. A., et al
"A High-Protein Meal during a Night Shift Does Not Improve Postprandial Metabolic Response the Following Breakfast: A Randomized Crossover Study with Night Workers"