Do you really have free will when it comes to diet? It's a troubling question at the heart of why so many people find it so difficult to stick to dieting.
To get the answer, one neuroscientist, Harvey J. Grill of the University of Pennsylvania, turned to the rats and asked what would happen if they removed all the brains other than the brain stem. The brainstem controls basic functions such as heart rate and breathing. However, the animals were unable to smell, could not see, and could not remember.
Do you know they burned enough calories?
To investigate, Dr. Grill drips liquid food into his mouth.
“When they reached the stop point, they allowed the food to be drained from their mouths,” he said.
Starting decades ago, these studies were the starting point for a series of studies that constantly surprised scientists and encouraged them to feel that perfect animals have nothing to do with consciousness. Scientists are more relevant as they are commonly referred to as GLP-1, as they confuse exactly how new drugs that cause weight loss, including ozempic, affect the brain's feeding control system.
The emerging stories do not explain why some people become obese and others are not. Instead, it provides clues as to what we start eating and when we stop.
Dr. Jeffrey Friedman, an obesity researcher at Rockefeller University in New York, said that while most of the research was rodents, it was against belief to think that humans are somehow different. Humans are the subject of billions of years of evolution, he said.
As they investigated how diet is controlled, researchers learned that their brains are steadily getting signals that suggest that they are clinically packed with food. The body needs a certain amount of calories, and these signals make sure the body gets them.
The process begins before the lab animal sucks a bite. Food can be exposed to the light that spurs them to predict whether many calories will be packed into the food. Neurons respond more strongly to foods like calorie-equipped peanut butter than low-calorie ones like mouse chow.
The next control point occurs when the animal tastes food. Neurons calculate calorie density again from signals sent from the mouth to the brainstem.
Finally, once food reaches the intestines, a new set of signals to the brain allows neurons to check their calorie content again.
And, in reality, as Zachary Knight, a neuroscientist at the University of California, San Francisco, learned, what the gut evaluates is the calorie content.
He saw this when three different foods were injected directly into the stomach of a mouse. One infusion was fatty food, the other was carbohydrate, and the third protein. Each infusion had the same number of calories.
In both cases, the message to the brain was the same. Neurons showed energy levels in the form of calories rather than in the source of calories.
When the brain determines that enough calories are being burned, the neurons send signals to stop feeding.
Dr. Knight said these findings surprised him. He always thought that the signal to stop eating would be “communication between the gut and the brain,” he said. There is a sense of fullness and a deliberate decision to stop eating.
Using that reasoning, some diets try to drink a large glass of water before a meal and fill it with low-calorie foods like celery.
However, these tricks didn't work for most people because they didn't explain how the brain controls diet. In fact, Dr. Knight discovered that mice do not even send satiety signals to the brain when only water is water.
It is true that people can decide to eat even when they are dressed, or not eat when they are trying to lose weight. And Dr. Grill said that he exerted control not only on the brain stem but also on the intact brain, but also on other areas of the brain.
But Dr. Friedman ultimately said that brain control usually negates a person's conscious decision about whether or not they feel the need to eat. He said, by analogy, you can hold your breath – but only for so long. And you can suppress the cough – but only until then.
Scott Sternson, a neuroscientist at the University of California, San Diego, agreed.
“We're excited to be able to help people get started,” said Dr. Sternson, co-founder of Penguin Bio, a startup that develops obesity treatments. People can decide whether to eat at the moment they are given them. But he adds, maintaining such control uses many mental resources.
“In the end, other things are being paid to the dominant automated processes,” he said.
When they investigated the brain's dietary control system, researchers were constantly surprised.
They learned about the rapid response of the brain to food sights, for example.
Neuroscientists discovered thousands of neurons in the hypothalamus deep inside the brain in mice and responded to starvation. But how are they regulated? They knew from previous studies that fasting turned on these starving neurons and that neuronal activity was low when animals were fully fed.
Their theory was that neurons were responding to fat storage in the body. If fat storage is low, for example, as occurs when an animal fasts – if the level of leptin, a hormone released from the fat, is also low. It will turn on hungry neurons. It was assumed that when animals eat, fat stores would be replenished, leptin levels increased, and neurons would be quieter.
The entire system was thought to respond slowly to the body's energy storage state.
However, three groups of researchers, led by Dr. Knight, Dr. Sternson and Mark Anderman of Beth Israel Deecones Medical Center, examined the instantaneous activity of starvation neurons.
They started with hungry mice. Their hungry neurons were being fired rapidly, signs that the animals needed food.
Surprising occurred when investigators showed animal food.
“Even before the first bite of food, those neurons stopped working,” Dr. Knight said. “Neurons were making predictions. Mice are looking at food. Mice predict how many calories they eat.”
The more calorie-rich foods you get, the more neurons are turned off.
“All three labs were shocked,” said Dr. Bradford B. Lowell, who worked with Andermann, Beth Israel Deaconess. “It was very unexpected.”
Dr. Lowell then asked what would happen if he intentionally turned off the hunger, even if the mice weren't able to eat much. Researchers can do this with genetic manipulations that mark neurons, and turn them on/off with drugs or blue light.
These mice do not eat for hours even if there is food in front of them.
Dr. Lowell and Dr. Sternson independently performed opposite experiments, turning on neurons in mice that had just eaten, the mice equivalent to Thanksgiving dinner. The animals were reclining and stuffed.
But Dr Anderman, who repeated the experiment, said “mice get up and eat another 10-15% of their body weight,” when he turned on the starving neurons. He added, “Neurons are saying, 'Focus on just food.'”
Researchers continue to be amazed at what they find. The layer of brain control ensures that diet is strictly regulated. And tips on new ways to develop drugs to control diet.
One piece of evidence was discovered by Amber Aradeff, a neuroscientist at the Monel Chemical Senses Center and the University of Pennsylvania. She recently discovered two separate groups of neurons in the brainstem that respond to GLP-1 obesity drugs.
One group of neurons informed that the animals were sufficient to eat. Other groups caused rodents that corresponded to nausea. Current obesity drugs have collided with both groups of neurons, she reports. She suggests that it may be possible to develop a drug that will hit satiety neurons rather than nauseous neurons.
Alexander Nectau at Columbia University has another surprising discovery. He identified a group of brainstem neurons that regulate the desired size of the diet and followed a bite of food. “I don't know how they're going to do that,” he said.
“I've been studying this brainstem area for 10 and a half years,” Dr. Nectow said.
He is now asking if neurons could become targets in a class of weight loss drugs that can stage GLP-1.
“That's really amazing,” Dr. Nectau said.
