What's good? What's bad? How much sugar is too much? Here's what the latest science says.

What's good? What's bad? How much sugar is too much? Here's what the latest science says.

On a steep, wet hillside near the equator, two hands place sugarcane stalks in shallow dirt trenches and cover them carefully with damp soil. Sprouts soon poke from the tropical ground in long, straight rows. After 12 to 18 months, the bumpy stalks grow as thick as a fireman's pole and as tall as a two-story house. Workers harvest the giant cane by hand and take it to the nearby sugar mill, where heavy metal rollers crush the stalks into a pulp and extract the sweet juice. Heat condenses the liquid into a syrup and the molasses is spun out.

Hard labor, primitive processing and months of waiting, all for one precious product: a small pile of sweet crystals, the last 17 percent of the original sugarcane plant, a substance commonly known as raw sugar, or sucrose.

The dance happens all over the tropical Earth. Sugarcane takes up only 16 percent of the world's total cultivated agricultural land, yet surprisingly is the world's biggest crop: 2.6 times more sugarcane is produced each year than wheat, 6.4 times more than soybeans. With this and all the sugar we extract from other plants, such as sugar beets (55 percent of the U.S.'s sugar comes from sugar beets), maple trees, corn and even coconuts, the amount of sugar produced has grown. Worldwide consumption of added sugar (that is, sugar not naturally found in food) has tripled over the last 50 years. And Americans now spend about 23 percent of our grocery dollars on processed foods and sweets-nearly double what we spent 20 years ago. Though the American Heart Association recommends women limit their added sugar to just 100 calories per day (6 teaspoons) and men to 150 calories a day (9 teaspoons), the average American now, consciously or not, eats 28 teaspoons of added sugars a day, or more than 90 pounds of sugar per year.

It doesn't take a medical genius to surmise that putting so much sugar in our bodies might not be a direct path to health nirvana. Most experts agree that we all eat far too much of it: rates of obesity have dramatically increased in the U.S. over the past 20 years, and studies have linked drinking large amounts of sugar-sweetened beverages to increased risk of obesity, especially in children.

But that's not news.

A new chapter in the history of sugar is now bursting open and it's causing many scientists to cringe, the public to pay attention and lots of folks to wonder whether this is just another false alarm. This new development in the sugar story is evangelized by one researcher in particular, a man who says there's a lot more to the health story than simply nutrient-empty calories from added sugar making us fat. The researcher, Robert Lustig, M.D., a pediatric endocrinologist at the University of California, San Francisco, states it like this, bluntly: "Fructose is a poison."

"High-fructose" corn syrup (HFCS), despite its name, and table sugar (sucrose) are both composed of two smaller sugar molecules, glucose and fructose, in roughly equal proportions. (HFCS and sucrose are virtually chemically equivalent, say most scientists and doctors.) The glucose part is fine, says Lustig; it's the body's preferred fuel, the type that smoothly runs the billions of cells in our body. But the fructose part "is a chronic poison," he says. "It doesn't kill you after one fructose meal, it kills you after 10,000. The problem is, every meal now is a fructose meal." HFCS is being added surreptitiously to processed foods. It has found its way into everything-from pretzels to ketchup.

Lustig says this mega-shot of fructose from added sugar uniquely gums up our inner workings and causes-in fact, is the primary cause of-metabolic syndrome, the constellation of disorders, including type 2 diabetes, cardiovascular disease and fatty liver disease, that are devastating our country. All of this happens, Lustig says, when we're consuming too many calories-and most Americans are eating 200 to 300 extra calories a day. He is quick to point out that he only means the fructose found in added sugar, the super-high levels of sucrose and HFCS we eat in processed foods and drinks (including fruit juices), not the lower levels found in fiber-rich whole fruit nor the sugars (lactose) found naturally in milk.

Lustig laid out his hypothesis in a 2009 lecture for the general public called "Sugar: The Bitter Truth" at UC, San Francisco. The university filmed the charismatic lecturer. The video was posted on YouTube; it went viral. In 2011, The New York Times Magazine published a piece by Gary Taubes admiring Lustig's theory. In 2012, 60 Minutes ran a segment on toxic sugar featuring Lustig. In December, Lustig will publish a book on nutrition, Fat Chance (Hudson Street Press), which includes his views on fructose.

Lustig presents a tempting, epic story of good versus evil, concluding in both his video and a recent commentary in the journal Nature that the government should regulate added sugar as it regulates alcohol. "Fructose is ethanol without the buzz," he says. And we are riveted: as of summer 2012, over 2.5 million people had sat down in front of their computers and watched Lustig's 90-minute lecture on fructose biochemistry, which he begins with a sort of arm-around-the-shoulder, conspiratorial tone: "I'm gonna tell you, tonight, a story." We crave a good narrative with real answers almost as much as we love sugar. But does the science actually support Lustig's theory?

The Science of Sugar

Tens of thousands of years ago, before two-liter sodas and oversized candy bars, our tongues rarely tasted sweetness. Sugar was extremely hard to come by. Honey had it (but it was protected by bees) and fruit contained it, enveloped in a fiber cage, but otherwise sweetness was a sensation few people experienced, and only in certain months of the year.

But because sugar provides safe calories (almost no plant that tastes sweet is poisonous), we evolved to crave it. Our brains are hard-wired to release a big shot of joy whenever we taste sweetness, by unleashing a chemical called dopamine that sparks our brain's pleasure center, a region called the nucleus accumbens. We also have a second way to make sure we are constantly on the lookout for this valuable energy: Even the thought of sugar makes us happy. The brain releases dopamine before we eat sugar, while we're seeking it out and as we anticipate placing it in our mouths. We have an ancient, always-on, deep-brain need to fill our stomachs with sweet calories.

Now, rubbing the magic lamp, we've finally gotten our genes' greatest wish: an endless supply of sugar. In the U.S., sucrose can be found all over the supermarket, but, more insidiously, ubiquitous HFCS is a cheap source of sweetness, a result of subsidies to corn farmers. "High-fructose corn syrup is evil, but it's not evil because it's metabolically evil; it's evil because it's economically evil," Lustig says in his YouTube video. Because it's so cheap it has found its way into nearly every processed food, including crackers, yogurt, tomato sauce, as well as cookies and sweetened beverages like sports drinks, juices, sodas.

But, Lustig says, the genie played a trick on us. Lustig explains the problem with fructose by explaining what happens when you put one of these processed goodies-say, a cracker-into your mouth (the details of this theory were mostly formulated through studies in animals): First, a bite. Then another bite. Sprinkles of cracker descend into your stomach and then to your small intestine, where enzymes dissect sucrose molecules into their constituent parts: glucose and fructose. (HFCS molecules are not bonded, thus the glucose and sucrose are already free.) Remember, glucose is the fuel of choice for our bodies; our cells use it or store it easily even when we eat it in high doses in processed food. Fructose, on the other hand, cannot by its very nature slip into our body's cells to make energy, so almost all of it slides down the portal vein into the liver, the toxin-processing organ, where it's dumped (and dumped again, as we eat more sweetened food).

What does our liver do with all this second-rate fructose fuel? It can't store it, so it tries to break it down into energy. But the cells' normal energy-generating cycle cannot possibly spin fast enough to process this mountain of fructose, so most of it meanders off into the liver in the form of citrate.

Too much citrate can hurt us. Citrate is the raw material for fat molecules called triglycerides. Excess triglycerides in the blood trigger cardiovascular disease, says Lustig. Some of the citrate also stays as fat droplets in the liver; a fatty liver triggers insulin resistance, which causes type 2 diabetes.

But it's not just the citrate. Lustig says that eating too much fructose can also spark inflammation in the liver, as well as increase blood-pressure-raising byproducts like uric acid.

Overall, eating too much fructose from added sugar is like using unleaded gasoline in a diesel engine: it makes bodies sputter and cough till they seize in a puff of smoke.

The Other Side of the Story

Lustig's idea sounds appealingly logical, but many experts don't buy his toxic-sugar theory. David Katz, M.D., M.P.H., is one such expert. He has written and spoken extensively on the subject. "That talk, what made it so viral was the extreme position," says Katz, director of the Yale University Prevention Research Center and an EatingWell advisor. "Vilifying a certain nutrient is a good-versus-evil worldview. It's easy to get people excited if you say the most extreme thing."

Though Lustig is a respected physician, he isn't a fructose researcher (he has only one original scientific paper on the subject, based on government-generated-not lab-generated-data). Most of his 90-plus published scientific papers focus on overweight children. And before his infamous lecture, only two mentioned fructose at all; since 2009, he's published six papers that mention fructose, mostly editorials, reviews and commentaries on his theory.

But he's not the only one to theorize that fructose is causing some of our modern health problems. In 2004, George Bray, M.D., at the Pennington Biomedical Research Center in Louisiana, and Barry Popkin, Ph.D., at the University of North Carolina at Chapel Hill, noticed that rising rates of obesity paralleled an increase in sugar consumption and they loosely attributed this to the harmful way our body metabolizes fructose. Other studies have since more strongly linked consuming sugar-sweetened beverages like sodas and juices with obesity, at least in children and adolescents, and for years researchers have been giving animals extremely high doses of fructose to create metabolic syndrome.

Why, then, is Lustig famous for the theory?

"Lustig takes a very evangelical and sensational approach to the data," says John Sievenpiper, M.D., Ph.D., a researcher at St. Michael's Hospital and McMaster University in Ontario who has analyzed many of the fructose studies; he comes to a conclusion that is the opposite of Lustig's. "He puts up these really wonderful, very seductive models. But, really, they're just hypotheses."

Hypotheses are unproven ideas that scientists can test, and many scientists have already tested whether consuming a lot of fructose alters the cholesterol and fats in the blood, the fats in the liver, blood pressure. Data from animal models, on which Lustig's hypothesis is firmly based, is clear: when animals consume very high levels of fructose, say, 60 percent of their calories, they do seem to have the symptoms of metabolic syndrome: high levels of triglycerides in their blood, high blood pressure, insulin resistance and weight gain.

But, say Sievenpiper and others, there are obvious problems with transposing animal experiments to human health: in animal studies, the researchers give the animals three times more than the highest amount of fructose most humans ever eat. Plus, animals process carbohydrates very differently from humans (their livers are naturally geared to make fat from carbohydrate).

In addition, human studies, at this point, don't even all point to the same answer. Supporting Lustig's theory are a few epidemiological studies (these studies follow large groups of people over time) that show increased health risks for people who frequently consume drinks high in sugars. The Nurses Health Study, one of the biggest epidemiological studies around, found that drinking a small glass of fruit juice daily (full of fructose) is associated with higher incidence of type 2 diabetes; daily consuming one (or more) sugar-sweetened beverages, which also contain a lot of fructose, raises risk of heart disease. The Framingham Heart Study showed that people who drank more than a can of soda a day were more likely to have metabolic syndrome.

Other epidemiological studies show a relationship that's tenuous at best between fructose and metabolic syndrome. The Women's Health Study found that risk of diabetes was no different in women who consumed the lowest amount of sucrose (about 6 1/2 teaspoons) versus those who consumed the most (about 14 teaspoons); the amount of fructose made no difference either. A 2010 scientific paper that reviewed all the epidemiological studies that have been published on the topic stated it like this: "epidemiological studies, at this stage, provide an incomplete, sometimes discordant appraisal of the relationship between fructose or sugar intake and metabolic/cardiovascular diseases."

In addition, short-term lab studies conducted in people-in which they are plucked from their daily lives and placed in a lab for a period of time-show that when we eat a very large percentage of our calories from pure fructose, we do have more triglycerides in our blood and more fat deposits in our liver and muscle, but our blood pressure and body weight don't rise compared to people who eat the same percentage of their calories from another carbohydrate. Though the trials are small (a dozen or two participants), they are the best we have right now.

In other words, these studies provide no clear answer yet to the question of whether fructose in added sugar is giving us metabolic syndrome.

Are We Overdosing?

Luckily for Lustig, Kimber Stanhope, Ph.D., and Peter Havel, D.V.M, Ph.D., have been busily conducting trials in their labs at the University of California, Davis. In one of their studies, overweight or obese people who spent 10 weeks drinking 25 percent of their calories from fructose drinks (versus a group drinking glucose) increased their post-meal triglycerides (a risk factor for heart disease) and decreased insulin sensitivity (a risk factor for type 2 diabetes).

Interestingly, they also found that drinking fructose caused the subjects to gain visceral fat, the kind of fat in the belly that's associated with metabolic syndrome; drinking glucose added fat, too, but here the fat was subcutaneous, the "safe" kind that has no established relationship with disease. Drinking fructose also enhanced the body's ability to convert carbohydrate into fat in the liver, which causes insulin resistance and type 2 diabetes.

Stanhope is in the middle of another big new trial in which, instead of giving subjects pure fructose (something no one drinks in the real world) as she has in earlier studies, she is giving folks what they can buy from convenience stores and vending machines: HFCS-sweetened drinks. She's also studying young, healthy people instead of obese people. The trial's first results (there's more to come) were just published and they, too, seem to support Lustig's theory: triglycerides and "bad" LDL cholesterol increased only in subjects who drank the fructose or HFCS, not glucose.

Still, the fructose doses used in most of Stanhope's studies are higher than most humans would normally consume. There's "no unequivocal evidence that fructose intake at moderate doses is directly related with adverse metabolic effects," said Luc Tappy, M.D., professor of physiology at the University of Lausanne and one of the world's premier fructose researchers, in a review. But Lustig thinks the higher doses in many of these trials just speeds up the inevitable. "It's completely dosage dependent. A little is fine. A lot is not. And that's true of every poison," says Lustig.

Many scientists, however, think that focusing public health on one vilified nutrient is the wrong tack to take. Such a strategy has backfired before: for example, doctors once told us all fat is bad, so manufacturers took it out of processed foods (and, interestingly, replaced it with sugar). Today, it's recommended we eat 20 to 35 percent of calories from fat-most of which should be the healthy, unsaturated kind.

"We certainly agree we should eat less sugar, but I think he's making a huge mistake from a public health perspective," says Katz. "We spent the last three decades doing exactly this: we thought just oat bran is good for us, so we put it in everything. Then we just needed to cut fat. Then it was carbs. So I can imagine we'll soon have a vast proliferation of sugar- or fructose-reduced junk food filled with some unhealthy substitute... I can't help but roll my eyes and ask, how many times do we have to get this wrong before we get it?"

And Tappy is concerned Lustig's public message is leaping ahead of the science: "So far, except for triglycerides, the data in the literature linking metabolic syndrome to fructose is pretty weak."

But Lustig counters that, with the U.S. losing $65 billion in worker productivity and spending $150 billion on medical care for health problems associated with metabolic syndrome each year, "Do we have to wait for those studies to be finished in humans before we can do anything about it? I would suggest that that would be way too late."

At the end of his YouTube lecture that sparked the sugar firestorm, the camera switches from generic blue PowerPoint slides to a gray-haired, gray-suited Robert Lustig. After 90 minutes of science, Lustig gives the audience some advice: drink only water or milk; exercise; eat your carbs with fiber (fruit's fiber slows the absorption of fructose so it never overwhelms your liver: "When God made the poison he packaged it with the antidote," says Lustig); wait 20 minutes before your second portion; use computers and TV for only as long as you exercise each day. It's all we need to avoid a deadly fructose fate, he says.

At the very end of his lecture, Lustig peers at his captive audience. He pauses a moment, and makes his final appeal. "I'm standing here today to recruit you in the war against bad food," he says. "And this [added sugar] is what's bad."

The storyteller closes his book. It's up to us to write the final chapter.

Contributing editor Rachael Moeller Gorman won a James Beard Award for her EatingWell article "Captain of the Happier Meal" (May/June 2010).

September/October 2012