Observational studies in humans have linked high added sugar and refined carbohydrate intake to many chronic diseases, including heart disease, cancer, diabetes, obesity and more.

Heart Disease

Several studies have found a strong link between consuming sugary drinks and an increased risk of heart disease ( 16 ).

A large study involving more than 75,000 women found that those who consumed a diet high in refined carbohydrates and sugar had up to a 98% greater risk of heart disease, compared to women with the lowest intake of refined carbs ( 17 ).

This is likely due to the impact of sugar consumption on heart disease risk factors, such as increased LDL cholesterol, increased blood pressure, obesity, insulin resistance and increased inflammatory markers ( 16 , 18 ).

Cancer

Several studies show people with high sugar intakes may be at a greater risk of developing cancer ( 19 , 20 , 21 , 22 ).

One study found that when mice were fed high-sugar diets, they developed breast cancer, which then spread to other parts of the body ( 3 ).

One study looking at the diets of over 35,000 women found that those who consumed the most sugary foods and drinks had double the risk of developing colon cancer, compared to those who consumed a diet with the least added sugar ( 20 ).

While more research is needed, it is thought that the increased risk of cancer may be due to the inflammatory effect of sugar. In the long-term, inflammation caused by sugar may damage DNA and body cells ( 23 ).

Some experts believe that chronically high insulin levels, which can result from consuming too much sugar, may also play a role in cancer development ( 24 ).

Diabetes

Studies link the increased consumption of added sugar to type 2 diabetes ( 25 , 26 , 27 , 28 ).

A large analysis including over 38,000 people found that just one serving of sugary drinks daily was associated with an 18% greater risk of developing type 2 diabetes ( 26 ).

Another study found that increasing corn syrup intake was strongly associated with diabetes. In contrast, fiber intake helped protect against the development of diabetes ( 27 ).

Obesity

Obesity is often referred to as a low-grade inflammatory disease. Eating too much added sugar is linked to weight gain and obesity ( 29 , 30 ).

Experts suggest that modern diets, which are often high in refined carbs and added sugar, can lead to an imbalance in gut bacteria. This may partly explain the development of obesity ( 9 ).

A review of 88 observational studies found that a higher intake of sugary soda was associated with greater calorie intake, higher body weight and lower intake of other important nutrients ( 31 ).

One study in mice found that a diet high in sugar counteracted the anti-inflammatory effects of fish oil and promoted obesity ( 4 ).

Other Diseases

A high intake of added sugar and refined carbs has been linked to the development of other diseases, such as liver disease, inflammatory bowel disease, mental decline, arthritis and others ( 2 , 32 , 33 , 34 ).

In particular, excess fructose consumption has been linked to non-alcoholic fatty liver disease. How this happens isn’t fully understood, but is thought to be due to a mix of increased gut permeability, bacterial overgrowth in the gut and ongoing low-grade inflammation ( 35 ).

However, evidence connecting sugar to health problems is mostly based on observational studies. Therefore, they cannot prove that sugar alone was the cause of these health problems ( 34 ).

Summary Observational studies have linked excess added sugar consumption to the development of several chronic diseases, such as diabetes, heart disease, obesity and cancer.