Hungry? Your Stomach Really Does Have a Mind of Its Own
A group of Nestle SA researchers here are on an unusual mission: They hope to create new foods based on gut instinct.
Not the type of instinct one normally equates with intuitive decision-making, but the sophisticated processes that take place in our digestive tracts to let us know when we’re hungry. There, a collection of nerve cells work together and communicate much as the neurons in our brain do. It’s essentially an autonomous and self-governing second brain that we all carry in our belly.
I Am, Therefore I’m Hungry
The “gut brain,” formally known as the enteric nervous system, is made up of some 500 million nerve cells, as many as there are in a cat’s brain. They help to control muscular contractions in the gut as well as the secretions of glands and cells. And they help balance hunger and satiety, or the sense of being full, communicating those states to the big brain.
Nestle, one of the world’s largest food companies, hopes to develop new types of foods that, essentially, seek to trick the gut brain. The foods could make people feel full earlier, or stay full longer, in order to curb the desire to eat more. For example, cooking french fries in oil that gets digested more slowly than regular oil could confer a longer-lasting sense of satiety, researchers speculate.
“This means that people will report a sense of fullness more quickly,” says Heribert Watzke, a senior food scientist at Nestle. “That tells the big brain to stop eating.”
This avenue of food science, which is also being pursued by other food companies, could represent a fresh assault in the fight against flab. One in four Americans is obese, and obesity rates are also rising dramatically in parts of Europe, Asia and the Middle East. Although food companies have long tried to make effective fat-fighting food, their results have been modest.
Nestle and other food giants are now on a push to decipher the language of satiety—the complex signals our gut brain sends to the big brain—and use that knowledge to make better satiety-inducing foods, or foods that make you feel full longer. Nerve cells in the gut are located in the tissues lining the esophagus, stomach, small intestine and colon. Like the central nervous system, the gut brain makes use of neurotransmitters such as serotonin and dopamine.
Tracking the movement of food in a person’s gastrointestinal tract isn’t easy. So at a “digestion lab”—part of Nestle’s sprawling research and development center here—scientists use a million-dollar model of the human gut.
The machine is about the size of a large refrigerator. It has several compartments linked by valves, and it is carefully calibrated to the body’s temperature. The entire setup is controlled by a computer. The front is glass, allowing observers to watch as food travels through the system.
On a recent day, the “stomach” section at the top slowly squeezed and churned a salt solution, just like the real thing. The liquefied result then wended its way down the other tubes, representing other sections of the digestive tract. At each stage, tiny valves released the appropriate salt, bile and enzymes, which helped to digest the food.
The body is in a state of continual hunger—its default position. But several factors work to curtail the hunger instinct, such as the presence of food in the digestive tract, or the flow of nutrients in the blood. When these satiety factors dissipate, the body again demands food.
In the quest to balance hunger and satiety, the gut brain and big brain communicate via neural signals. When food enters the stomach, the stomach stretches, and the gut brain sends a neural message to the big brain. The gut brain also knows when there are nutrients in the gastrointestinal tract, stimulating the release of peptides into the blood and resulting in another message to the brain.
A peptide release is also part of the “ileal brake” mechanism. The ileum is the lower part of the small intestine. Fat penetrates there when there’s too much for the body to process, triggering an “I’m full” message to the big brain.
Nestle has run some early-stage experiments on foods using its artificial gut model. In a paper published in the journal Food Biophysics last year , Dr. Watzke and colleagues described one such experiment using olive oil. They first measured how long it took the artificial gut to digest olive oil at the natural rate. Then, they added a compound called monoglyceride, which formed a protective coat around the oil molecules, making it harder for the gut’s juices to break through and digest the oil.
The Nestle scientists monitored the oil’s progress as it gradually went through the system. They found it took eight times longer for the machine to “digest” the olive oil-monoglyceride combination compared with the olive oil alone. This resulted in more undigested oil reaching the small intestine. In the human body, this could lead to a stronger ileal brake signal of fullness to the big brain.
Food companies have been trying to make effective satiety-inducing foods for years, but with little success. Danone SA of France, for example, launched in the U.S. a nonfat yogurt “Light & Fit Crave Control,” whose combination of fiber and protein was intended to help people stave off hunger. But it was taken off the market in 2007 “because it wasn’t our best tasting product,” a spokesman says.
Food companies, including Unilever, have experimented with foods that activate the ileal brake. But Nestle researchers found that a food that only triggers the ileal brake mechanism likely won’t be enough to induce satiety, or win over a lot of consumers. “You’ve got undigested fat in your ileum, so it can end up making you feel queasy,” says Hilary Green, a spokeswoman for Nestle’s R&D center and a physiologist.
Who’s the Boss?
Even when we’re full, our big brain can overrule signals from the gut brain telling us to stop eating. Some messages that can cause us to eat even when we’re not hungry:
- Cultural or social expectations, such as ‘it’s dinnertime’
- The aroma or visual appeal of food
- Psychological compulsion such as ‘stress eating
Nestle is now pushing for a multi-faceted approach, one that targets several key neural signals sent by the gut brain and attacks the satiety problem in multiple ways at once. The Swiss company says it has a good understanding of the science and is now racing to make foods with the new technology. Nestle declined to say which foods its research might lead to, although Dr. Watzke says a hypothetical example could be a vegetable oil that could go in a dressing or be used for cooking.
Scientists say the gut brain reflects millions of years of evolution. The original nervous system possessed by the earliest life forms was a rudimentary gut brain that regulated digestion, they say.
Because higher animals needed more brain power in order to seek out food and sex, they eventually developed a second, big brain, allied to a central nervous system. At the same time, humans and other higher-end animals kept their enteric nervous system. Another shift likely occurred when humans learned to prepare food, specifically through cooking. When grains are ground, or leaves are cooked, they become more digestible, allowing more nutrients to get absorbed by the body.
“The brain in the gut has a complex language,” says Dr. Watzke. “We need to understand it properly” before we can make true satiety-inducing foods.