Does Sugar Cause Diabetes?

Patient Expert

For many decades, folk "wisdom" claimed that diabetes was caused by eating too much sugar.

There have always been curious ideas in the diabetic world. For instance, people with advanced diabetes excrete a lot of sugar in their urine, so one early diabetic diet prescribed eating nothing but candy, on the theory that because the patients were losing so much sugar in their urine, they should replace it with sugar in their diet.

Shortly after I was diagnosed, I had an idea of why people might think that eating sugar caused diabetes. For about 6 months previously, I had craved sugar. I think it was because my cells had trouble taking up sugar, so they made me want to eat more sugar. But in fact, I think it was the diabetes that made me want more sugar rather than eating more sugar that gave me diabetes.

If this were true, it's unlikely that friends and relatives would analyze the situation. They'd see someone eating a lot of sugar and then getting diabetes and they'd assume that the sugar had caused the diabetes.

One day the former owner of my house dropped in to visit and offered   me a big bag of peaches. I explained that I wasn't eating a lot of fruit because I had diabetes, and she said, "But you didn't eat a lot of sugar." An odd comment as she had no idea what I ate, but it confirmed that many people think that sugar causes diabetes.

Studies done in the 1980s in animals and humans showed that sugar had no effect on obesity, metabolism, or the development of diabetes in genetically prone individuals, according to one author of many of these studies, Richard S. Surwit. He said that it was only sugar in combination with fat that caused problems.

But now a new study suggests that sugar (either sucrose, "table sugar" or high-fructose corn syrup (HFCS), which has approximately the same composition) may be one cause of diabetes. Sucrose is half glucose and half fructose; HFCS has approximately the same composition. The "high" refers to comparison with regular corn syrup, which is almost all glucose. The full text of the study is also available online.

This is not a perfect study; it is not a randomized, double-blinded study in which you assign people at random to one of two treatment options and then follow them to see how they do. It wouldn't be ethical to tell thousands of people to eat a lot of sugar for 10 years or so to see if they developed more diabetes.

Instead, the researchers analyzed available data on the availability of sugar in 175 different countries and then used statistics to see if the availability of sugar was related to any health outcomes, including obesity and diabetes. Of course, availability is not the same thing as consumption, so the researchers had to estimate how much waste occurs in various countries. They said people in the United States waste more food than those in other countries.

The researchers found that diabetes was related to sugar availability, and this was independent of obesity. In other words, it's not just that sugar causes obesity and the obesity triggers diabetes in genetically predisposed people.   Because the data in many countries did not distinguish between type 1 and type 2 diabetes, the results cannot be limited to either group.

Their results showed that obesity is also related to diabetes, but the obesity simply adds to the effect of the sugar.

As noted above, this is not a perfect study, and the authors have discussed the strengths and limitations of their work. They point out that about 20% of obese people have normal insulin regulation and no signs of the metabolic syndrome; whereas up to 40% of normal-weight people do show signs of metabolic syndrome. Metabolic syndrome often progresses to type 2 diabetes. Clearly, obesity alone does not cause metabolic syndrome, it just increases your risk.

The authors controlled for many things, including other nutrients, total calories, sedentary behavior, rates of economic development, household income, urbanization, tobacco and alcohol use, and the percentage of the population over 65. One interesting control they did was a "Granger causality test," which looks at the order of things. If increased sugar availability occurred 10 years after diabetes rates increased, then it would be unlikely that the sugar caused the diabetes. But even the "causality test" doesn't prove causality. As they pointed out, Christmas usually follows the sending of Christmas cards (except in my house, where I may get the cards out in July), but Christmas cards don't cause Christmas.

However, they did find that the increase in sugar availability preceded the increase in diabetes, which is highly suggestive of causality.

The Internet is currently awash in blogposts on this topic, presenting different views. A blogpost in the N_ew York Times_ called "It's the Sugar, Folks," attracted more than 800 comments as of March 2. This topic is clearly of great interest.

What does this mean for us? Well, most people reading this already have diabetes and are probably working hard to control sugar intake. But how about our children and grandchildren?

This study suggests, although it doesn't prove, that trying to limit the sugar in their diet would be a good idea. Diabetes is partly genetic, so our families are at greater risk than normal, and any way we can prevent diabetes in them is good. The study found no difference between countries that use mostly sucrose and those that use HFCS, so switching from one to the other shouldn't make much difference.

The researchers found that the longer a population had been exposed to high sugar availability, the greater the diabetes rates. This means that even if you can limit your children's sugar intake for only the first 10 years of their life, you're still helping them.

The real problem is that food manufacturers put sugar in everything. Did you know there's even sugar in iodized salt? It's not enough to make a big difference, and they say it's necessary to bind the iodine. But it's symptomatic of the American food supply. There's sugar in chicken broth. There's sugar in tomato sauce. There's sugar in almost every processed food you can find.

There's even sugar in foods that don't mention sugar on the label, because it may be in small enough amounts that they are not required to mention it. Or it may be listed as a "flavoring." Or they may add sucrose plus HFCS plus dextrose (another name for glucose) plus levulose (another name for fructose) plus molasses, plus some other sugary syrup so the amount of each one is low. If they add enough different sugars, then none of them will be sufficient to require inclusion on the label, but you'll still be getting the sugars.

When everything you eat is sweet, you get accustomed to that taste and foods without sugars taste dull. That's why the manufacturers keep adding sugar.

The only way to avoid these hidden sugars is to avoid processed foods. Real foods can also contain sugar, of course, and many have been bred to be as sweet as possible (think sweet peas or very sweet apples or strawberries). We can't expect our nondiabetic children to avoid all sugar in their diet unless they eat a super-low-carb diet, which is difficult when they are children and their friends all get sweet treats. It's difficult for diabetic children too, but they know they have a reason to be careful with sweets.

Because this isn't a perfect study, the jury is still out on whether or not sugar really does cause diabetes. But it never hurts for people who want to avoid diabetes to be cautious and avoid as much sugar as they can. It certainly won't harm them.