- Your body breaks down carbohydrates in food into glucose — what we call blood sugar — as well as other sugars like sucrose, lactose, and fructose, to fuel the body and keep it running smoothly.
- Glucose is the body’s main energy source and can be burned as fuel (metabolized) by all organs in the body.
- As glucose floods the bloodstream, insulin spikes. Insulin is a naturally occurring hormone that helps our cells convert glucose into energy.
- Fructose, similar to glucose, has the same chemical compound but a different structure. Fructose can only be processed by the liver.
- Fructose occurs naturally in fruits and vegetables, but we’ve learned to extract it to create sweeteners like high-fructose corn syrup, which we add to soda and fruit-flavored drinks in high concentrations.
- Lactose is derived from dairy products, while sucrose is a combination of fructose and glucose.
Too much Sugar
But if there’s too much glucose in the body, insulin stores the excess in liver or muscle cells as glycogen, which can be broken down and used in the future. When there’s too much fructose, your liver also stores the excess for later, but this time as fat.
Added sugar leads to spikes and dips in insulin levels much like a roller coaster.
When blood sugar is chronically high, which leads to too much fat storage, the liver can get overloaded, contributing to fatty liver disease, increased risk of diabetes, and cardiovascular disease.
Good Insulin, Bad Insulin
Though it’s important to help fuel our cells or store energy sources for later, insulin isn’t always the good guy. Lustig says he realized insulin was “the bad guy in the story” in 1999. Conventional wisdom at the time said insulin regulates blood sugar, which is a good thing. But too much insulin, he learned, causes problems.
“Insulin, when it’s high, is basically depriving your heart, your liver, your muscles, your bones, your kidneys, your brain, your lean body mass, of energy,” he says. “Therefore, you have to eat more, and you feel lousy doing it.”
High Insulin Levels Are Dangerous
Chronically high insulin levels are dangerous. They’re associated with obesity, cholesterol abnormalities, and high blood pressure, a trifecta called metabolic syndrome. Ultimately, metabolic syndrome can lead to type 2 diabetes, heart disease, stroke, and even death.
In a study Lustig published in 2004 in the International Journal of Obesity, he found that when obese participants’ insulin levels were lowered with medicine, people had more energy and even started exercising spontaneously and voluntarily. “What we realized was that the gluttony and sloth that we were seeing in the obese population and the fact that everyone was getting obese was not the primary problem. It was a secondary problem from the biochemical rise in insulin. The insulin came first.”
And metabolic syndrome isn’t rare. The American Heart Association estimates that about 34 percent of adult Americans have the condition, mostly from consuming a fast-food diet (spicy chicken sandwich, please), maintaining a sedentary lifestyle (Netflix and chill, not a walk in the park), and eating too much sugar (Cokes for lunch and dinner).
People are Fatter, Sicker, and Dying Younger
Obesity, which is especially dire in Western countries, is now considered an all-out pandemic — people are fatter, sicker, and dying younger. Worldwide, obesity has tripled since 1975, and at least 2.8 million people die each year as a result of being overweight or obese.
“The vehicle is processed food,” Lustig says. “The payload is sugar, and it’s killing people just like any nuclear bomb would. It’s just slower.”
Thanks to Inverse for this great article about the work of one of our favorite researchers Robert Lustig.
To learn more read Is Sugar Toxic? Here’s the Actual Truth About the Sweet Substance