12 Common Questions About Sugar and Your Health — Answered

1) What is sugar?

Sugar is a carbohydrate, one of the three major dietary nutrients called macronutrients (the other two being fat and protein). Sugar is easy to vilify, but it’s a macronutrient for a reason — and our biological requirement for it demands nuanced understanding and respect.

Sugar is either a monosaccharide or a disaccharide. A monosaccharide, such as glucose, is the smallest unit of sugar. A disaccharide is a combination of two monosaccharides. Sucrose, commonly known as table sugar, is a disaccharide made up of glucose and fructose. It’s typically refined from sugarcane or sugar beets.

“Glucose is so essential that if you don’t eat it, your body turns other things into glucose just so you have it.”

Glucose fuels each one of the body’s approximately 30 trillion cells. “Glucose is so essential that if you don’t eat it, your body turns other things into glucose just so you have it,” says pediatric endocrinologist Robert Lustig, MD, MSL, author of Metabolical: The Lure and the Lies of Processed Food, Nutrition, and Modern Medicine.

Still, when it comes to table sugar, glucose is only half of the picture. The other half is fructose.

Until the 1960s, most of the fructose in the American diet came from fruit, which is why fructose is also called “fruit sugar.” Yet as the price of refining sugar rose, food makers turned to corn for a cheaper, sweeter alternative, and high-fructose corn syrup entered the marketplace for use mostly in sodas and ultraprocessed foods.

Unlike glucose, fructose plays no essential role in the body, Lustig says. And in high quantities, it can be addictive, contribute to cellular aging, and damage the liver. (More on fructose and the liver in question No. 3.)

3) What’s the impact of sugar on the liver?

Maintaining liver health may be among the best reasons to avoid excess fructose. Glucose can be metabolized by every cell, while fructose is processed only by the small intestine and the liver. So when large quantities of fructose hit the system, especially in the form of soda or energy drinks, the liver bears much of the burden.

In the short term, fructose depletes cellular energy and triggers the production of uric acid, a waste product that, in excess, can damage the kidneys and the heart. (For more on uric acid, visit “Uric Acid: A New Metric for Heart Health.”)

Over the long term, a diet high in fructose can contribute to liver complications. That’s because the liver turns excess fructose into fat, explains Lustig. Visceral liver fat may be exported to other parts of the body, where it can contribute to obesity, heart disease, and other metabolic conditions; it can also stay in the liver and contribute to a condition called nonalcoholic fatty liver disease. NAFLD can lead to an inflammatory condition called nonalcoholic steatohepatitis, which can culminate in cirrhosis and even liver failure.

Experts predict that more than half of all adults worldwide will have NAFLD by 2040 — and many believe this is at least partly due to the current high consumption of fructose. (For more on NAFLD, see “The Hidden Liver Crisis.”)

5) How does sugar influence mood?

To understand the impact of sugar on the brain, consider that the organ constitutes 2 percent of the body’s weight but burns 20 percent of its glucose.

“The brain takes up a huge percentage of blood sugar,” says Emmons. He adds that it relies so heavily on glucose because it can’t make energy from other sources, unlike other parts of the body.

Excess sugar consumption can lead to systemic inflammation anywhere in the body, which also affects how we feel. Inside the brain, systemic inflammation disrupts the ability of neurotransmitters to balance mood, he explains. (Our bodies need inflammation to fight off infection, but too much of it for too long can spur a wide range of illnesses. Learning to manage it effectively is key. See “How Chronic Inflammation Affects Your Health” for more.)

Especially important is the balance between glutamate, an activating neurotransmitter, and gamma-aminobutyric acid (GABA), a calming neurotransmitter. One reason people with sugar-fueled mood disorders often have too much brain activity — a cardinal sign of anxiety — may be because glutamate is driving the bus.

People also crave simple sugars when they are anxious, says nutritional psychiatrist Drew Ramsey, MD. “It’s easy to get into a maladaptive pattern with sugar because it’s so very pleasurable, and in nature, when something tastes sweet, it’s ripe and it’s usually safe,” he says. “And more than anything, our brain wants to feel safe.”

Growing evidence points to depression as an inflammatory disease, says Emmons. “That may be one of the reasons why antidepressants offer relief to so many people — they are in part anti-inflammatory.”

Numerous studies show a connection between high-sugar diets and depression risk. One of the most significant correlations was seen in a 2017 scientific trial. Researchers found that men who ate more than 67 grams of sugar a day were 23 percent more likely to be diagnosed with depression and other mental health challenges after five years than those who ate less than 40 grams a day. The authors suspected inflammation.

Growing evidence points to depression as an inflammatory disease, says Emmons. “That may be one of the reasons why antidepressants offer relief to so many people — they are in part anti-inflammatory.”

7) So, can I eat fruit?

Fruit contains fructose as well as fiber — and fiber is the game-changer. An essential nutrient, fiber moves food through the gut, signals feelings of fullness, and slows the body’s absorption of sugars.

Apples, for instance, have two kinds of fiber: soluble, which is jelly-like, and insoluble, which has more structure. Both types are important. (Insoluble fiber, soluble fiber, and prebiotic fiber are all essential to our health and well-being. Learn more at “The 3 Types of Dietary Fiber You Need.”)

Lustig compares insoluble fiber to a fishing net and soluble fiber to a coating of slippery kelp plugging the holes. “Together they form a barrier that prevents the fructose from touching the intestinal walls and being transported into the bloodstream.”

Fruit inches closer to the danger zone when it’s turned into fruit juice, which includes no fiber to slow the impact of its sugars. (Learn more about the importance of fiber at “Why You Need to Eat Fiber.”)

9) Where does added sugar hide?

Whole foods, like vege­tables and fruits, are a balanced package of micro- and macronutrients. The fiber in whole foods slows the absorption of their sugars, so generally speaking, whole foods on the sweeter end of the spectrum are not the problem.

Added sugars, on the other hand, most definitely are — in part because it’s not always easy to know where to find them, which makes it hard to know how much of them you’re eating.

Up to 75 percent of packaged foods contain sugars added during processing. For food manufacturers, these added sugars are a veritable Swiss Army knife. They create volume, retain moisture, extend shelf life, and enhance texture.

“Without added sugars, most processed foods would taste like cardboard,” says Schmidt.

The U.S. Food and Drug Admin­istration mandated in 2016 that ­nutrition-facts labels show added ­sugars. But because food makers now employ 262 names for sugar (here are 61 of those names), those added sugars are harder than ever to detect.

If a food manufacturer embeds a variety of sugars into foods as the fifth, sixth, seventh, and eighth ingredients, for example, sugar can easily add up to be the dominant ingredient without topping the list, Lustig says. Even savory foods like salsa, tomato sauce, and salad dressings often contain sugars (though often it’s to balance sour, salty, and spicy flavors).

Because food makers now employ 262 names for sugar, those added sugars are harder than ever to detect.

And then there are the beverages: Nearly half of the added sugars in the American diet are sipped, slurped, and gulped in the form of soft drinks, fruit drinks, sports drinks, and sweetened coffee and tea. (Here are seven “healthy” beverages — and how much sugar they actually contain.)

A meta-analysis published in 2023 looked at 85 studies on children and adults and found sugary beverages lead to weight gain. Researchers suspect it has to do with how the liver turns fructose into visceral fat. Soda sales are decreasing, but well over half of Americans still drink at least one a day.

“We, and especially our kids, are eating and drinking dessert all day long,” says Lustig.

11) Are artificial sweeteners better?

Though sugar alternatives might seem a safer bet, the research on their health implications suggests otherwise.

In 2023, the World Health Organization (WHO) released guidelines advising against using nonsugar sweeteners for weight control or to lower disease risk. The recommendation was based on a review of 283 studies showing that short-term use of the sweeteners could lead to a small reduction in body weight but have no benefit with regard to other sugar-induced health issues, such as elevated blood-glucose levels.

In July 2023, the WHO labeled aspartame a possible carcinogen. And in June 2024, xylitol, a rising star among sugar substitutes, made headlines when scientists discovered that people with the highest levels of xylitol in their blood plasma had a roughly 50 percent higher risk of experiencing a cardiovascular event over three years than people with the lowest levels.

Other studies have detected links between sugar alternatives and metabolic obesity, heart disease, and cancer.