Why people like sugar so much

Allen Levine — of the Minnesota VA Medical Center and University of Minnesota — wonders why people like sugar so much.

He wonders how sugar affects our brains. Dr. Levine is trying to answer these questions by studying rats. He changes their diets and also injects them with chemicals that regulate eating.

Allen Levine: It’s tough to ask a rat how it feels. So, what we generally do is we look at their behavior. . . watch them for hours to see what kind of behavior they have. Are they moving more? Are they sleeping more? Are they grooming more?

Eating sucrose or table sugar does seem to produce complex changes in brain chemicals. But Levine wonders if those changes are unique to sugar.

Allen Levine: And when somebody eats something sweet, does it affect areas in a similar fashion to when they would take a drug that they get pleasure from, or other pleasant events in life — it could be gambling . . .

Or it could be drug use or sex. Levine is hoping to find out how these different activities are related. He plans to use brain imaging techniques — MRIs and PET scans — to see chemical changes in the human brain. By the way, Levine told us it’s still not completely understood why people like sugar so much — or what sugar does to us.

It’s still not understood why we like sugar so much and what it does to us. So you may wonder why you hear a new claim about sugar every day. Dr. Allen Levine said, “People don’t want to hear that we don’t know, so they’re looking for something, so scientists and media people will respond to it in that way, and they give data too early, is what happens.”

Dr. Levine’s current work consists of four parts:

1. Levine studies the naturally occurring neurochemicals that regulate an animal’s eating habits — such as endorphins (which scientists now called “endogenous opioids”) and “neuropeptide y.” Neuropeptides regulate food intake, blood pressure and anxiety. They’re also involved with a whole range of behaviors from sex to drug use. They help make us feel good when we eat and cause us to seek out nutritious foods. His team injects certain neurochemicals directly into certain regions of an animal’s brain — usually a rat’s brain. Then they look to see how the animal responds and what changes occur in its brain.
2. His team measures what changes happen in the brain when an animal eats a certain kind of diet. They give them high fat or high sugar diets to see what changes happen to the regulating chemicals in the brain. The brains are cut up later to identify what chemicals are there and in what quantities.
3. They also do behavioral studies — for example, “how hard will an animal work for certain kinds of food?”
4. They also study humans to see how easily they can detect sugar in their food. Then they block opioid receptors and see if that changes how people perceive those compounds.

Excerpts from interview with Dr. Levine:

Well it seems that we have some innate liking for it that we don’t necessarily exactly understand the mechanism behind it. But if you give sweet-tasting solutions to laboratory animals, or to human babies — to rat pups or humans — they show a preference for it. In a baby, of course, you’ll see a smile. So there are facial expressions that are linked with pleasure that one sees when sucrose is taken or glucose for example.

In many studies it’s been shown that drinking solutions of sweets or ingesting foods that are very high in sucrose there are changes in the brain that are not necessarily unique to that, but are than with other foods.

My area is trying to understand the neurochemistry of this — to understand what brain neuroregulators what compounds are involved in the rewarding properties of food.

It’s tough to ask a rat how it feels. So, what we generally do is we look at their behavior — watch them for hours to see what kind of behavior they have: are they moving more? Are they sleeping more? Are they grooming more? That type of thing.

So if we see a disruption in this pattern say this may not be normal feeding. So if I injected a compound into a rat’s brain, and they eat, but they don’t follow any of the behaviors when you look at them that look like normal eating , they may be eating for a different reason; it could just be a mechanical thing.

All the molecular biological techniques and the techniques that are used to identify specific areas of the brain that are involved have certainly helped us in laboratory animals. And in human studies, the thing that is going to help us is all the brain imaging studies that have been coming about, the functional MRI or the PET scans, those types of things where you can look for changes in …

We never really had a way to see what’s going on in the human brain. You know, as you said, you’re not going to inject into the brain of a human, you’re not going to cut it apart and look at parts of it. So we have to use imaging techniques. Those are the most exciting for human studies.

What we’d like to be able to do is see, at the first stage, what area of the brain is involved. Do a whole bunch of areas light up? Is it just one area that’s involved after consumption of one sweet substance, for example. And then you could do all sorts of manipulations and see if you could change that.

What parts of the brain are involved in reward in general? And when somebody eats something sweet, does it affect areas in a similar fashion to when they would take a drug that they get pleasure from, or other pleasant events in life — it could be gambling. You know, I’m not a rat, so I’m not going to be doing it. I’m interested in those areas of the brain that are regulating that type of reinforcing behavior — something you would work hard for to get.

Can you tell me about any setbacks, or frustrations in your research?

It’s frustrating when you’re developing these new molecular techniques when things just fail. totally fail. and you can’t figure out exactly what in the process went wrong so you spend lots of hours in the laboratory changing one or two particular solutions or the way you do things and you talk to other colleagues.

Something that’s been particularly rewarding in your scientific career

The most rewarding part is to have a hypothesis, to spend some time in the laboratory investigating that hypothesis, and to come forward with an answer, be it right or wrong, that you feel secure about. That’s the most satisfying part of this. It takes years before you believe something, if you’re a careful scientist. The one experiment isn’t going to do it. But when you’ve repeated it over and over, and then others also repeat it and they see the same thing, and it was your idea to begin with, that’s very exciting.