Study finds dopamine, biological clock link to snacking, overeating and obesity

Study finds dopamine, biological clock link to snacking, overeating and obesity

January 3, 2020

Science Daily/University of Virginia

A new study finds that the pleasure center of the brain and the brain's biological clock are linked, and that high-calorie foods -- which bring pleasure -- disrupt normal feeding schedules, resulting in overconsumption.

During the years 1976 through 1980, 15% of U.S. adults were obese. Today, about 40% of adults are obese. Another 33% are overweight.

Coinciding with this increase in weight are ever-rising rates of heart disease, diabetes, cancer and health complications caused by obesity, such as hypertension. Even Alzheimer's disease may be partly attributable to obesity and physical inactivity.

"The diet in the U.S. and other nations has changed dramatically in the last 50 years or so, with highly processed foods readily and cheaply available at any time of the day or night," Ali Güler, a professor of biology at the University of Virginia, said. "Many of these foods are high in sugars, carbohydrates and calories, which makes for an unhealthy diet when consumed regularly over many years."

In a study published Thursday in the journal Current Biology, Güler and his colleagues demonstrate that the pleasure center of the brain that produces the chemical dopamine, and the brain's separate biological clock that regulates daily physiological rhythms, are linked, and that high-calorie foods -- which bring pleasure -- disrupt normal feeding schedules, resulting in overconsumption. Using mice as study models, the researchers mimicked the 24/7 availability of a high-fat diet, and showed that anytime snacking eventually results in obesity and related health problems.

Güler's team found that mice fed a diet comparable to a wild diet in calories and fats maintained normal eating and exercise schedules and proper weight. But mice fed high-calorie diets laden with fats and sugars began "snacking" at all hours and became obese.

Additionally, so-called "knockout" mice that had their dopamine signaling disrupted -- meaning they didn't seek the rewarding pleasure of the high-fat diet -- maintained a normal eating schedule and did not become obese, even when presented with the 24/7 availability of high-calorie feeds.

"We've shown that dopamine signaling in the brain governs circadian biology and leads to consumption of energy-dense foods between meals and during odd hours," Güler said.

Other studies have shown, Güler said, that when mice feed on high-fat foods between meals or during what should be normal resting hours, the excess calories are stored as fat much more readily than the same number of calories consumed only during normal feeding periods. This eventually results in obesity and obesity-related diseases, such as diabetes.

Speaking of the modern human diet, Güler said, "The calories of a full meal may now be packed into a small volume, such as a brownie or a super-size soda. It is very easy for people to over-consume calories and gain excessive weight, often resulting in obesity and a lifetime of related health problems.

"Half of the diseases that affect humans are worsened by obesity. And this results in the need for more medical care and higher health care costs for individuals, and society."

Güler said the human body, through thousands of years of evolution, is hard-wired to consume as much food as possible as long as it's available. He said this comes from a long earlier history when people hunted or gathered food and had brief periods of plenty, such as after a kill, and then potentially lengthy periods of famine. Humans also were potential prey to large animals and so actively sought food during the day, and sheltered and rested at night.

"We evolved under pressures we no longer have," Güler said. "It is natural for our bodies as organisms to want to consume as much as possible, to store fat, because the body doesn't know when the next meal is coming.

"But, of course, food is now abundant, and our next meal is as close as the kitchen, or the nearest fast-food drive-through, or right here on our desk. Often, these foods are high in fats, sugars, and therefore calories, and that's why they taste good. It's easy to overconsume, and, over time, this takes a toll on our health."

Additionally, Güler said, prior to the advent of our electricity-powered society, people started the day at dawn, worked all day, often doing manual labor, and then went to sleep with the setting of the sun. Human activity, therefore, was synchronized to day and night. Today, we are working, playing, staying connected -- and eating -- day and night. This, Guler said, affects our body clocks, which were evolved to operate on a sleep-wake cycle timed to daytime activity, moderate eating and nighttime rest.

"This lights-on-all-the-time, eat-at-any-time lifestyle recasts eating patterns and affects how the body utilizes energy," he said. "It alters metabolism -- as our study shows -- and leads to obesity, which causes disease. We're learning that when we eat is just as important as how much we eat. A calorie is not just a calorie. Calories consumed between meals or at odd hours become stored as fat, and that is the recipe for poor health."

The National Institute of General Medical Sciences and University of Virginia Brain Institute funded the research.

https://www.sciencedaily.com/releases/2020/01/200103111717.htm

Comfort food leads to more weight gain during stress

April 25, 2019

Science Daily/Garvan Institute of Medical Research

It's no secret that overindulging on high-calorie foods can be detrimental to health, but it turns out that under stress, watching what you eat may be even more important. A team led by Professor Herbert Herzog, Head of the Eating Disorders laboratory at the Garvan Institute of Medical Research, discovered in an animal model that a high-calorie diet when combined with stress resulted in more weight gain than the same diet caused in a stress-free environment. The researchers revealed a molecular pathway in the brain, controlled by insulin, which drives the additional weight gain.

They publish their findings in the journal Cell Metabolism on 25 April 2019 (EST).

"This study indicates that we have to be much more conscious about what we're eating when we're stressed, to avoid a faster development of obesity," says Professor Herzog.

The brain's comfort food 'centre'

Some individuals eat less when they're stressed, but most will increase their food intake -- and crucially, the intake of calorie-dense food high in sugar and fat.

To understand what controls this 'stress eating', the Garvan researchers investigated different areas of the brain in mice. While food intake is mainly controlled by a part of the brain called the hypothalamus, another part of the brain -- the amygdala -- processes emotional responses, including anxiety.

"Our study showed that when stressed over an extended period and high calorie food was available, mice became obese more quickly than those that consumed the same high fat food in a stress-free environment," explains Dr Kenny Chi Kin Ip, lead author of the study.

At the centre of this weight gain, the scientists discovered, was a molecule called NPY, which the brain produces naturally in response to stress to stimulate eating in humans as well as mice.

"We discovered that when we switched off the production of NPY in the amygdala weight gain was reduced. Without NPY, the weight gain on a high-fat diet with stress was the same as weight gain in the stress-free environment," says Dr Ip. "This shows a clear link between stress, obesity and NPY."

A downward spiral to obesity

To understand what might control the NPY boost under stress, the scientists analysed the nerve cells that produced NPY in the amygdala and found they had receptors, or 'docking stations', for insulin -- one of the hormones which control our food intake.

Under normal conditions, the body produces insulin just after a meal, which helps cells absorb glucose from the blood and sends a 'stop eating' signal to the hypothalamus feeding centre of the brain.

In the study, the scientists discovered that chronic stress alone raised the blood insulin levels only slightly, but in combination with a high-calorie diet, the insulin levels were 10 times higher than mice that were stress-free and received a normal diet.

The study showed that these prolonged, high levels of insulin in the amygdala caused the nerve cells to become desensitised to insulin, which stopped them from detecting insulin altogether. In turn, these desensitised nerve cells boosted their NPY levels, which both promoted eating and reduced the bodies' normal response to burn energy through heat, the study showed.

"Our findings revealed a vicious cycle, where chronic, high insulin levels driven by stress and a high-calorie diet promoted more and more eating," explains Professor Herzog. "This really reinforced the idea that while it's bad to eat junk food, eating high-calorie foods under stress is a double whammy that drives obesity."

While insulin imbalance is at the centre of a number of diseases, the study indicates that insulin has more wide-spread effects in the brain than previously thought.

"We were surprised that insulin had such a significant impact on the amygdala," says Professor Herzog. "It's becoming more and more clear that insulin doesn't only impact peripheral regions of the body, but that it regulates functions in the brain. We're hoping to explore these effects further in future."

https://www.sciencedaily.com/releases/2019/04/190425143610.htm