Evening exercise will not ruin sleep and might even reduce appetite
February 21, 2019
Science Daily/The Physiological Society
With growing time demands, many middle-aged adults are finding time to engage in exercise increasingly difficult. For many, even the thought of fitting exercise in after a busy day at work can be as tiring as it is unappetizing. The standing belief that high-intensity exercise should be avoided in the early evening due to its effect on sleep only serves to act as another barrier to exercise at this time.
Must cook dinner. Need to pick the kids up from school. Have to catch up on my favourite TV series. Live too far from the gym. Any of these sound familiar? With growing time demands, many middle-aged adults are finding time to engage in exercise increasingly difficult. For many, even the thought of fitting exercise in after a busy day at work can be as tiring as it is unappetising. The standing belief that high-intensity exercise should be avoided in the early evening due to its effect on sleep only serves to act as another barrier to exercise at this time.
However, encouraging new research published in Experimental Physiology has suggested that 30 minutes of high-intensity exercise performed in the early evening does not negatively affect subsequent sleep, and may also reduce feelings of hunger.
Researchers at Charles Sturt University in Australia recruited eleven middle-aged men to complete three experimental trials to investigate sleep and appetite responses to exercise performed in the morning (6 -- 7 am), afternoon (2 -- 4 pm) and evening (7 -- 9 pm). Participants were required to perform high-intensity cycling involving six one-minute, maximal intensity sprints interspersed by four minutes of rest. Blood collections were taken prior to exercise and following exercise to examine appetite-related hormones, and multiple tests were performed during sleep to assess sleep stages.
The results not only showed that evening exercise did not have a detrimental impact on subsequent sleep, but also that afternoon and evening high-intensity exercise were associated with greater reductions of the hunger stimulating hormone, ghrelin. It is important to note that a single bout of exercise was not linked to reduced hunger, but nevertheless, the observations from this study support high-intensity exercise early in the evening as a viable time-of day for exercise.
As this study's sample size was relatively small, the findings extrapolated to other population groups beyond middle-aged men may be limited, given that sleep and appetite regulation are influenced by sex and age.
Penelope Larsen, lead author of the study, commented said:
"In the future, we hope to conduct similar studies recruiting women, to determine whether sleep and appetite responses may be different depending on sex. Also, this study only considered a single bout of exercise; therefore, it would be beneficial to investigate long-term sleep and appetite adaptations to high-intensity exercise training performed either in the morning, afternoon or evening."
Interestingly, power output during the sprint efforts was higher for the afternoon and evening trials compared to the morning trial, indicating that participants were able to perform better during latter parts of the day. Therefore, time-of-day may also need to be considered when planning training schedules."
https://www.sciencedaily.com/releases/2019/02/190221083411.htm
'Hunger hormone' enhances memory
July 9, 2019
Science Daily/Society for the Study of Ingestive Behavior
A team of neuroscience researchers at the University of Southern California have identified a surprising new role for the "hunger hormone" ghrelin. Ghrelin has previously been recognized for its unique role in sending hunger signals from the gut to the brain, but, as presented this week at the annual meeting of the Society for the Study of Ingestive Behavior, these new findings suggest that it may also be important for memory control.
Ghrelin is produced in the stomach and secreted in anticipation of eating, and is known for its role to increase hunger. "For example, ghrelin levels would be high if you were at a restaurant, looking forward to a delicious dinner that was going to be served shortly," said Dr. Elizabeth Davis, lead author on the study. Once it is secreted, ghrelin binds to specialized receptors on the vagus nerve -- a nerve that communicates a variety of signals from the gut to the brain. "We recently discovered that in addition to influencing the amount of food consumed during a meal, the vagus nerve also influences memory function," said Dr. Scott Kanoski, senior author of the study. The team hypothesized that ghrelin is a key molecule that helps the vagus nerve promote memory.
Using an approach called RNA interference to reduce the amount of ghrelin receptor, the researchers blocked ghrelin signaling in the vagus nerve of laboratory rats. When given a series of memory tasks, animals with reduced vagal ghrelin signaling were impaired in a test of episodic memory, a type of memory that involves remembering what, when, and where something occurred, such as recalling your first day of school. For the rats, this required remembering a specific object in a specific location.
The team also investigated whether vagal ghrelin signaling influences feeding behavior. They found that when the vagus nerve could not receive the ghrelin signal, the animals ate more frequently, yet consumed smaller amounts at each meal. Dr. Davis thinks these results may be related to the episodic memory problems. "Deciding to eat or not to eat is influenced by the memory of the previous meal," says Davis. "Ghrelin signaling to the vagus nerve may be a shared molecular link between remembering a past meal and the hunger signals that are generated in anticipation of the next meal."
These novel findings add to our understanding of how episodic memories are generated, as well as the relationship between memory and eating behavior. In the future, researchers may be able to develop strategies for improving memory capacity in humans by manipulating ghrelin signaling from the gut to the brain.
https://www.sciencedaily.com/releases/2019/07/190709171807.htm
Gut hormone increases response to food
Ghrelin promotes conditioning to food-related odours
December 12, 2018
Science Daily/McGill University
The holiday season is a hard one for anyone watching their weight. The sights and smells of food are hard to resist. One factor in this hunger response is a hormone found in the stomach that makes us more vulnerable to tasty food smells, encouraging overeating and obesity.
New research on the hormone ghrelin was published on today in Cell Reports on Dec. 4, 2018, led by Dr. Alain Dagher's lab at the Montreal Neurological Institute and Hospital of McGill University.
Previous research by Dr. Dagher's group and others demonstrated that ghrelin encourages eating and the production of dopamine, a neurotransmitter that is important for reward response. In the current study, researchers injected 38 subjects with ghrelin, and exposed them to a variety of odours, both food and non-food based, while showing them neutral images of random objects, so that over time subjects associated the images with the odours.
Using functional magnetic resonance imaging (fMRI), the researchers recorded activity in brain regions known to be involved in reward response from dopamine. They found that activity in these regions was higher in subjects injected with ghrelin, but only when responding to the images associated with food smells. This means that ghrelin is controlling the extent to which the brain associates reward with food odours.
Subjects also rated the pleasantness of the images associated with food odour, and the results showed that ghrelin both reduced the response time and increased the perceived pleasantness of food-associated images, but had no effect on their reaction to images associated with non-food odours.
People struggling with obesity often have abnormal reactivity to the food-related cues that are abundant in our environment, for example fast food advertising. This study shows that ghrelin may be a major factor in their heightened response to food cues. The brain regions identified have been linked to a neural endophenotype that confers vulnerability to obesity, suggesting a genetically-based hypersensitivity to food-associated images and smells.
"Obesity is becoming more common around the world and it's well known to cause health problems such as heart disease and diabetes," says Dr. Dagher. "This study describes the mechanism through which ghrelin makes people more vulnerable to hunger-causing stimuli, and the more we know about this, the easier it will be to develop therapies that counteract this effect."
https://www.sciencedaily.com/releases/2018/12/181212121907.htm