Understanding the Sugar and Diabetes Connection

The U.S. Centers for Disease Control and Prevention estimates that 38.4 million people in the United States—11.6% of the total population—have diabetes. The prevalence of diabetes has steadily increased over the past few decades, and several national and international organizations have published dietary guidelines that recommend limiting one’s daily intake of added sugars. Many people thus assume that sugar causes diabetes, and at first glance, this appears quite logical. But is it true?

To understand the relationship between sugar consumption and diabetes, we must first understand the basics of insulin. Insulin is an anabolic hormone produced by the pancreas that is needed to move glucose from the blood into cells. After a meal, blood glucose levels rise, stimulating the pancreas to release insulin. Insulin then notifies the cells to surface their glucose transporters, exposing them to the circulating blood glucose, which is subsequently taken into the cells.

There are two forms of diabetes mellitus: type 1 and type 2. Type 1 diabetes is an autoimmune condition caused by the destruction of insulin-producing cells in the pancreas. Type 2 diabetes occurs when the body becomes increasingly resistant to insulin; it is responsible for 90% to 95% of diabetes cases in the United States. The debate surrounding sugar intake is centered on its effects on the development of type 2 diabetes.

When tissues become resistant to the effects of insulin, glucose is unable to enter into cells and the levels of glucose in the blood rise. Elevated blood glucose, or hyperglycemia, is one of the hallmarks of diabetes. While the specifics of hyperglycemia are beyond the scope of this article, suffice it to say it has both short-term and long-term effects and contributes to much of the morbidity and mortality seen in people with diabetes (Lean and Te Morenga 2016).

Because dietary carbohydrates like sugar are broken down into glucose and various other monosaccharides, it seems that they should play some role in the development of diabetes. Indeed, carbohydrates, especially simple carbohydrates, do raise blood glucose levels more quickly than protein or fat. As was discussed earlier, though, it is the body’s inability to produce or respond to insulin that results in diabetes. What effect does sugar intake have on insulin?

Numerous studies have looked at this very issue. In a randomized clinical control trial published in 2014, a high-carbohydrate diet was not found to be associated with increased insulin resistance when compared with a low-carbohydrate diet. Notably, this study only ran for five weeks, so the effects of the diets on insulin resistance in the long term could not be seen (Sacks et al. 2014). Similarly, a Canadian study from 2021 looked at the association between added sugars versus naturally occurring sugars and cardiometabolic risk factors, including fasting blood glucose, fasting insulin levels, and insulin resistance (Bergeron et al. 2021). The study found that added sugars in drinks were associated with increased fasting insulin levels and insulin resistance. Naturally occurring sugars in drinks were also associated with increased fasting insulin levels but not with insulin resistance. Other sources of added and naturally occurring sugars showed no such associations with any of the metabolic risk factors analyzed (Bergeron et al. 2021).

Most studies have echoed these same findings. While there does appear to be a link between sugar-sweetened beverages and type 2 diabetes, how much of this association is due to the effect of sugar-sweetened beverages on adiposity is unclear (Lean and Te Morenga 2016, Lee et al. 2015). Moreover, this association has not been found with solid sugar sources, suggesting that sugar alone is not responsible for the increased risk (Yan et al. 2022, Bergeron et al. 2021).

In the end, we are left with a conglomeration of mostly observational studies suggesting that sugar intake does not cause diabetes. Keep in mind, however, that observational studies can only ever establish correlation, not causation, and that a diet high in sugar-sweetened beverages may increase one’s risk of obesity. Obesity, particularly abdominal obesity, is known to increase the risk of diabetes, albeit along with a plethora of other factors.ft