Snacking and grazing throughout the day, as opposed to structured mealtimes, could limit children's growth, finds new research by Cardiff University.
A new study has investigated the influence of structured mealtimes and continuous grazing on hormones that control growth, indicating that the shift from regular meals to snacking behaviour may be detrimental to growth.
Given the contemporary shift away from regular meals at breakfast, lunch and dinner, towards snacking behaviour, we wanted to understand if and how this shift could have potential implications for growth.
Researchers investigated how grazing (small, frequent portions) and meal-feeding (three large meals) influence growth in mice and rats by analysing changes in the levels of two hormones that control growth - growth hormone and ghrelin.
Ghrelin is released from an empty stomach and represents a hunger cue. It promotes the release of growth hormone – which accelerates childhood growth and helps to maintain tissues and organs throughout our lifespan.
Along with the animal models, the team also undertook a separate study measuring hormone levels in humans, comparing graze feeding or meal-feeding in volunteers fed through a nasogastric tube.
We were able to measure the impact of grazing and meal-feeding in rats and mice by measuring the width of the growth plate in the tibial bone - this is an accurate growth marker in rats and mice. We saw that skeletal growth was accelerated in mice that ate meals.
"We also looked at this in mice that were genetically engineered to not produce receptors for ghrelin - these changes in growth were reversed in these mice. In the absence of the action of ghrelin, meal-fed mice grew less well and grazing mice show no reduction."
In grazing rats, growth hormone was tripled in meal-fed rats, with two extra bursts of growth hormone released a day.
The researcher's findings in rats and mice were also supported in the parallel human study by the team, which looked at continuous feeding compared to meal-feeding in volunteers fitted with a nasogastric tube - a tube inserted through the nose into the stomach, used for feeding and medication administration.
"We found that continuous feeding caused levels of the hunger hormone ghrelin to stay high in humans – as if they were still hungry. This led to continuously high growth hormone levels. To be effective in promoting growth, growth hormone levels need to show natural ups and downs – rhythmic bursts. Therefore, the lack of growth hormone bursts produced by continuous feeding could impede growth in humans," added Dr Wells.
When volunteers with nasogastric tubes received the same nutrition, but in separate meals, ghrelin levels dropped after each meal, which facilitated bursts of growth hormone release.
This study was performed exclusively with male rats, mice and humans.
Our findings show that the on-off exposure to ghrelin produced by meals, amplifies the hormone rhythms that normally promote skeletal growth.
"In contrast, the continuously high ghrelin levels produced by grazing represent a starvation signal that can slow growth, even when sufficient nutrients are being provided.
"This research has wider implications for how we should be feeding our children, the maintenance of structured mealtimes boosting healthy growth, however further research is needed
"This study was performed exclusively in males, additional research will demonstrate the impact of these feeding patterns in females."
Meal-feeding promotes skeletal growth by ghrelin-dependent enhancement of growth hormone rhythmicity , was published in the Journal of Clinical Investigation. The research was conducted in collaboration with Swansea University, University of Bath, and the University of Exeter.
