There’s a lot of confusion around sugar and sugar substitutes, their effect on our bodies and how much is too much. Kimber Stanhope, PhD, an associate researcher of molecular biosciences at UC Davis, addressed sugars as part of an expert panel on dietary science at the Association of Health Care Journalists annual conference last week. WebMD spoke to Stanhope on what research is uncovering about sugars and artificial sweeteners.

Q: What’s the difference between fructose and glucose?

A: Both glucose and fructose are sugars. My colleagues and I published a study that very clearly showed a marked difference between older, overweight people who consumed glucose-sweetened beverages and those who drank fructose-sweetened beverages.

For 10 weeks, the adults in the study got 25 percent of their daily calorie needs from either fructose-sweetened or glucose-sweetened beverages. Both groups gained the same amount of weight – about three and a quarter pounds. But those who drank the fructose-sweetened beverages turned more sugar into fat. They had increased levels of fats in their blood, increased insulin resistance, and they gained fat in the abdomen around the organs.

We saw none of these effects in the group that consumed glucose.

Q: Can we make better food and beverage choices based on this knowledge?

A: Our foods are sweetened with either high fructose corn syrup or sucrose. Those two sugars are combinations of both fructose and glucose.

Sucrose is 50 percent glucose and 50 percent fructose. High fructose corn syrup is usually, but not always, 55 percent fructose and 45 percent glucose. One study reported that some of the major soda brands had as much as 67 percent fructose. When a label says high fructose corn syrup, you really don’t know exactly how much of it is fructose and how much is glucose.

So I recommend reducing total sugar intake, whether that sugar comes from sucrose or from high fructose corn syrup.

Q: How much sugar can we safely have every day?

A: I hope I get to answer that question before I retire. The American Heart Association says it should be no more than about 5 percent of our daily calories. So a woman should only have 100 calories of added sugar per day – or 25 grams of sugar.

That’s two-thirds of a can of soda, and then no cookie, no cake, no brownie, no ice cream, no desserts. Definitely not a doughnut for breakfast, a granola bar for lunch, and dessert with dinner. Many of the sugar foods you will buy in the store will have far more than 25 grams of sugar in one serving.

But do we really need to go as low as the American Heart Association says? I would love to find out.

Q: What are the health impacts of too much sugar and how damaging is it?

A: Sugar starts a chain reaction of problems. Fructose and glucose leave the intestine and go straight to the liver. But there’s an enzyme that will shut off the metabolism of glucose if the liver doesn’t need any energy. Then glucose won’t even come into the liver. It just goes zipping right by to the brain, muscle, fat cells, and nerve cells. The rest of the body can use the energy from the glucose.

But the enzyme that controls fructose metabolism is always turned on. You drink a big gulp, and nearly all that fructose goes straight into the liver. Very little of it gets into the blood stream and to the brain, muscles and other parts of the body. Fructose overloads the liver, and the liver has to do something with it. Some gets turned into energy, but some of it is going to get turned into fat.

Then the liver is either going to store the fat or send some of it into the blood. As you continue to overwhelm your liver with sugar, the liver is going to do both. You’re going to have higher fat levels in the blood, and that’s going to increase your risk for cardiovascular disease. You’re also going to store more fat in the liver, and that’s going to cause insulin resistance, which is a risk factor for diabetes and a real problem for all metabolic functions.

With insulin resistance, it is likely that the liver turns even more sugar into fat. Then you’re going to get higher levels of liver fat. With higher levels of liver fat, you’re going to get more insulin resistance. It’s a vicious cycle. The liver does its best to keep everything in balance by sending some of that fat to the blood. Now the fat levels are higher in the blood, and that’s why we get metabolic syndrome, which is a cluster of conditions including high blood pressure, overweight – especially around the stomach — high blood sugar and high cholesterol. They all go hand in hand and make each other worse.

Q: Could this emerging knowledge about the differences between particular types of sugars have an impact on policy and regulations like we saw with trans fat?

A: Hopefully, we are already making progress on this. Current dietary guidelines set in 2010 say the upper level recommendation for sugar is 25 percent of your daily calories. I think we have a good amount of evidence that suggests nobody should be eating 25 percent of their daily calories as added sugar.

Now new guidelines could bring it down to 10 percent of daily calories. However, comments are still being made till May 9. … I think we’re going to have a new upper limit recommendation. It’s not as low as the American Heart Association’s, but it sure is an improvement over 25 percent.

Q: Can you give us any guidance on artificial sweeteners?

A: That is such a controversial question. In our experiments with fructose and glucose, our control group drank aspartame-sweetened beverages. I did not see a single negative effect. But can I guarantee that if you consume three aspartame-sweetened drinks a day for the next 10 or 20 years, that you will not have a single health consequence? No, and I don’t know what it will take before we know for sure.

Now if somebody came to me and said, ‘I love (soda). Is it better for me to drink the real (soda) or the aspartame-sweetened (soda)?’ I will tell them in a minute, drink the aspartame-sweetened (soda). Yes, it would be better to switch over to water, but if that’s not going to be the crutch they need to get off their sugar-sweetened beverage, then, for heaven’s sake, use the aspartame.

Q: What diet trends or myths drive you nuts and why? And which diets are actually on the right track?

A: We’re still arguing over what’s worse: a high-fat diet or a high-carb diet. When I say high-carb diet, I’m not talking about sugar. I’m talking a diet high in white bread or whole wheat bread, white rice or whole grain rice, brown rice, and so forth.

There is a huge divide among scientists as to which is the healthier diet. You hear a lot of people say, ‘I will never eat bananas because they have a very high glycemic index.’ I have a hard time with that.

I believe that a high-carb diet, especially the whole grain high-carb diet that is high in fruits and vegetables, is the healthiest way to eat. I would love to do the study to prove it. One tablespoon of oil has 100 calories. You can eat so much more food on the high-carb diet. I’m not interested in determining what works best for weight loss. I want to know what people should be eating when they’re living their regular lives. My personal hope is that the high-carb diet is the healthier diet than the high-fat diet. There is also the possibility that genetic differences mean some people thrive better on a high-carb diet, and some people may be so insulin sensitive that they have problems on the high-carb diet, even when it’s whole grains. That might be the answer, too.

As for diets that are on the right track, I could prescribe the Dash Diet to anybody that asked me. The Mediterranean Diet is super high in fruits and vegetables, and I like that concept, too.