10 Medical Studies That Prove Sugar is Bad for Us

Photo by John Kuczala

Photo by John Kuczala

What’s one of the first things we all learned about sugar when we were kids? That it would rot our teeth… especially if we didn’t whip out our toothbrushes just after we ate it. But the medical evidence on sugar consumption has advanced far beyond its impact on our teeth. We now know, for instance, that some sugars are natural and necessary, while others—particularly processed or added sugars—can spell trouble for our overall health.

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Startling research published in 2014 and 2016 showed the amount of added sugars consumed by the average American adult skyrocketed by more than 30% between 1977 and 2010. So, it’s clear we need to understand the various types of sugars in our foods and beverages and how they can affect our health. The fact is… we can’t totally avoid sugar. We need it! Glucose—a simple sugar—circulates in our blood stream and is found in every single cell of our body, where it provides the power cells need to multiply and function properly. But, since the sugars we eat aren’t nutritionally equal, here’s the skinny: no matter what food it’s in, sugar is comprised of the same two things, fructose and glucose. Common table sugar, also called sucrose, is equal parts fructose and glucose. And, most fruits are 40% to 55% fructose and 55% to 60% glucose.

Fructose is commonly added to many processed foods and drinks, but it’s only a nutritional standout in its natural form—whole fruit. Fructose doesn’t require a surge of insulin to be digested; therefore, the body has more time to use it for fuel before storing it as fat. On the other hand, glucose requires insulin to be used by cells, leaving us prone to blood sugar surges and drops that mess with energy levels and mood, as well as allowing sugar to be converted to fat more quickly.

 The focus of much research, as you’ll see, has been on sugar-sweetened beverages such as soda, energy drinks, and sports drinks because—according to Harvard Health—they’re the top sources of added sugar in the average American diet. Sugar itself isn’t the devil, but getting too much of it, especially from the wrong sources, might wreak havoc on our health. Here are 10 ways consuming added sugars, especially too much, can be harmful to your health.

1. Dangerous fats

In a 2013 review published in Advances in Nutrition, researchers looked at several trials, including many randomized controlled trials, in which drinking sugar-containing soft drinks or low- or no-calorie beverages was compared. Randomized controlled trials are considered the gold standard in terms of how to conduct clinical research. According to the researchers, either sucrose or fructose leads to a cascade of negative health effects, including increased triglyceride levels (ie, stored fat that’s bad news for heart health) and higher amounts of fat surrounding internal organs and muscles. Researchers noted, too, that consuming fructose also enhances the production of uric acid, which can trigger the painful joint condition gout. 

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2. Fatty liver disease    

The national rise in obesity and diabetes has been mirrored by an increase in non-alcoholic fatty liver disease (abbreviated as NAFLD), which is a chronic and dangerous problem characterized by too much fat stored in liver cells. The excess fat prevents the liver from working efficiently. Researchers, who published their work in the Journal of Hepatology in 2008, found that fructose consumption in patients with NAFLD was nearly 2- to 3-fold higher than a group of people without the disease of similar sex, age, and body mass index. People with NAFLD face issues ranging from chronic fatigue to swelling of the legs (edema) and abdomen (ascites) to end-stage liver failure.

3. Dying of heart disease  

In a 2014 review in JAMA Internal Medicine, researchers found a “significant relationship” between added sugar consumption and an increased risk of dying from cardiovascular disease. After nearly 43,000 adults were followed over an average period of nearly 15 years, researchers observed that people who consumed 10% to 25% of their calories from added sugar were 30% more likely to die from cardiovascular disease than those who ate less than 10% of their calories from added sugar. And, the death risk more than doubled for people who consumed more than 25% of their daily calories from added sugar.

4. Weight gain    

A once-controversial link between sugar-sweetened beverages and weight gain was reinforced in a 2013 meta-analysis published in the American Journal of Clinical Nutrition. Beyond individual randomized controlled trials, meta-analyses—where researchers combine and analyze data from multiple clinical trials—are considered the highest level of evidence possible on the clinical evidence hierarchy. In this one, researchers looked at 32 trials involving adults and children and found that sugar-sweetened drinks promoted weight gain in people of all ages. When children consumed fewer sugary drinks, less weight gain was observed.

5. High blood pressure  

In another meta-analysis of 6 studies involving more than 240,000 people, authors of a 2015 report in the American Journal of Clinical Nutrition found that the more sugar-sweetened drinks a person consumed, the higher their chances of developing high blood pressure (ie, hypertension), a major risk factor for heart disease and stroke. Compared to not consuming sugary beverages, drinking even 1 sugary beverage each day upped the odds of hypertension by 8.2%, researchers found.

Drinking even 1 sugary beverage each day upped the odds of hypertension by 8.2%, researchers found.”

6. Cardiovascular disease markers  

While large quantities of sugary drinks produce unfavorable effects on glucose and lipid metabolism in obese people, these effects occur even in normal-weight individuals. In a randomized controlled trial published in the American Journal of Clinical Nutrition in 2011, 29 healthy young men were assigned to drink sugar-sweetened beverages with high, moderate, or low amounts of fructose, glucose, or sucrose. Researchers found that consuming even small-to-moderate amounts of added sugar over a 3-week period negatively affected markers of heart disease risk, including the “bad” cholesterol known as low-density lipoprotein, fasting glucose levels, and systemic inflammation. 

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7. Type 2 diabetes   

Drinking sugary beverages may seem like main-lining sugar, but exactly how much does this practice increase the risk of developing type 2 diabetes, which affects nearly 1 in 10 Americans? In a 2004 JAMA publication, researchers tracked more than 91,000 young- and middle-aged women, who were diabetes-free at the start, over an 8-year period. They reported that women who consumed 1 or more soft drink each day carried an 83% higher risk of developing diabetes than women who drank less than 1 of these beverages per month. 

8. Stroke  

While much research has focused on cardiovascular conditions linked to added sugars, less has concentrated on sugar’s relationship to strokes, which affect nearly 800,000 Americans each year and are the third leading cause of death. But, a 2012 paper in the American Journal of Clinical Nutrition shed new light on this association. Researchers, who looked at data from 84,085 women over 28 years and 43,371 men over 22 years, found those who drank 1 or more sugar-sweetened beverages each day had a 16% higher risk of stroke than those who drank none.

9. Sugar addiction  

When we overeat sugary treats and later say we’re suffering from “sugar withdrawal,” it may not be so far from the truth. In research published in Neuroscience & Biobehavioral Reviews in 2008, scientists summarizing evidence of sugar dependence in rats pointed out that sugars release opioids and dopamine in the brain in a similar manner to addictive drugs. This phenomenon may translate into certain human conditions such as obesity or eating disorders, study authors said. 

10. Excess appetite  

Eating too much sugar can causes a naturally occurring hormone called leptin, which is made by fat cells and regulates appetite, to go awry. A 2008 paper in the American Journal of Physiology was the first to show that a high-fructose diet can lead to so-called “leptin resistance,” where chronically high levels of leptin fuel voracious eating even when we’ve already consumed enough to maintain proper nutrition. Skewed leptin levels, then, put us at risk for gaining extra pounds, especially when mixed with a high-fat, high-calorie diet.