What the doctor leading the charge against one of our biggest dietary enemies—sugar—wants you to know.
When you hear about a viral video on YouTube, you hardly expect it to feature a pediatric endocrinologist giving a biology lesson on high-sugar diets. But in the three years since the lecture "Sugar: The Bitter Truth," by Robert Lustig, MD, was uploaded to the site, it's had more than 2.9 million views and made Lustig, director of the University of California, San Francisco's Weight Assessment for Teen and Child Health Program, the pied piper of healthy eating. Now, in his new book, Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease, he explains why he believes the massive amounts of sugar and processed food we consume each day are making us not only fatter but sicker, too. Today's generation of American children may end up being the first with a shorter life expectancy than their parents, but the problem isn't confined to the young: Obesity-related conditions like type 2 diabetes and heart disease are now among the leading causes of preventable death in adults. We talked with the doctor about how our diet is harming us—and how we can take back our lives.
Q: Was there something particular that inspired you to spread the word about the dangers of sugar and processed food?
A: In 2003 a 6-year-old named Juan came into my clinic in California. He weighed 100 pounds—he was wider than he was tall. I asked his mother what he was eating and drinking, and among other things she said he consumed many glasses of orange juice every day—which she thought was healthy. But when you're drinking glass after glass of orange juice, you're getting a lot of sugar with no fiber to help limit its absorption. Having to explain to Juan's mom that eating fruit like oranges is good but drinking sugary juices in large quantities is bad made me realize that someone needed to dispel our food myths in a way people will understand.
Q: Roughly 80 percent of all packaged foods in the United States contain added sweeteners. Sugar is everywhere—is it all that bad?
A: The problem is "refined sugar"—that is, the stuff like high-fructose corn syrup and regular table sugar, made up of glucose and fructose—which has been stripped of any nutritional value. Processed food is full of refined sugar, and it has detrimental effects: The fructose in it gets turned into liver fat, which can prevent the liver from processing insulin properly. This may lead to insulin resistance and metabolic syndrome, which puts you at greater risk for type 2 diabetes, cardiovascular disease, and stroke.
Q: How did we get hooked on sugary foods to begin with?
A: We're biologically programmed to like sweets—our tongues and brains know that no food on the planet is both sweet and poisonous. It was a test for our hunting-and-gathering ancestors: If a food is sweet, it won't kill you. It's ironic because that's exactly what sugar is doing to us now.
Q: In your book, you say the widespread belief that "a calorie is a calorie" is one of the driving factors behind the obesity crisis. Why?
A: A calorie burned is a calorie burned, but the calories you eat don't all have the same impact on your body. Different foods can be either helpful or harmful depending on what they're made of and how much fiber they contain. Consider fats, for example. All fats release nine calories of energy per gram when burned, but omega-3 fatty acids can help lower your risk of heart disease, while trans fats may lead to heart disease and fatty liver disease. So one calorie of omega-3 is not equal to one calorie of trans fat. The same goes for proteins and carbs. It all depends on whether you're eating healthy or unhealthy forms of them.
Q: But isn't the bigger problem that we're simply eating more total calories than we were 30 years ago?
A: Not exactly. If you look at our fat intake as a percentage of total calories, it's actually decreased as the obesity pandemic has grown, largely because so much of our food these days is "low fat." Our protein consumption has stayed pretty level over time. But our fructose consumption has risen because of all the processed food we consume. When we eat a lot of sugar, liver fat accumulates and our body releases insulin to compensate. Higher insulin levels promote fat storage, which can lead to obesity and a host of other, potentially lethal, diseases.
Q: Why aren't our bodies better at regulating appetite?
A: Studies indicate that when we produce excess insulin as a result of our high-sugar diets, the insulin prevents leptin, a hormone that helps control appetite, from telling our brain that we've taken in enough energy. So in our head, we think we're hungry long after we're actually full. And we don't crave just any food—we go for the tasty stuff that's high in fat and sugar. It's a vicious cycle. Leptin resistance is what keeps people obese. Research suggests that this isn't about a leptin deficiency, because blood samples reveal that most obese people have plenty of it. The issue is that their leptin isn't working properly—if it were, they wouldn't be obese.
Q: Does stress eating play a part?
A: Yes. God knows I'm a stress eater! Researchers aren't sure excactly why the brain goes nuts for high-energy, dense food when we're stressed, but it does. So the more stressed out you are, the hungrier you get, and the more carb-heavy foods you eat—which in turn causes your insulin levels to rise even more. At the same time, the hormones released in response to stress direct your body to build up visceral fat, which you end up storing in the worst place possible: your belly.
Q: So what's the fix?
A: The obvious solution is to eat more fiber and less sugar, but exercise is important, too. It's not only the best stress buster there is—it's also something every single person can do to improve metabolic health, even if weight loss doesn't come along with it right away. For every molecule of sugar you absorb, you can either burn it, which doesn't require your body to make more insulin, or you can store it, in which case you need insulin. Burning it is the best option, and that's exactly what exercise does.
Q: What should we be eating?
A: Real food! That's it. If it came out of the ground, or it's from an animal that ate what came out of the ground, you're good to go. But if a human processed it in between, either something was added, usually sugar, or something was removed, most likely fiber and micronutrients like vitamins and minerals. The key for most people is reducing insulin, and to do that, you have to put back fiber into your diet and cut back on refined carbohydrates and sugar. If you're buying food that has a nutrition label, it's been processed. And if any form of sugar is one of the first three ingredients, consider it a dessert. When I was a kid, we had dessert once a week. Now we have it once a meal, and it's almost always processed. That's the problem.