by Marion Nestle
Mar 1 2013

Does sugar cause diabetes? Is a calorie a calorie?

I spent a lot of time last week talking to reporters about the widely publicized study in PloS One that correlates sugar and diabetes.

The study is based on an econometric model of data food availability and diabetes prevalence in many countries.  Such data are not particularly reliable, but the authors did the best they could with what they had.  They are quite forthcoming about the limitations of their model and the data on which it is based [see addition below].

Their principal conclusion: for every 150 kcal/person/day increase in sugar availability (about one can of soda/day), diabetes prevalence increases by about 1%.

Because no other dietary, weight, or behavioral factor shows this kind of effect in their model, it is tempting to interpret the study as demonstrating that sugar is a risk factor for diabetes independent of calorie intake or body weight.

I’m not so sure.  Take a look at the summary figures and decide for yourself.

Figure 1.  Relationship between obesity and worldwide prevalence of diabetes.

Figure 1 Relationship between obesity and diabetes prevalence rates worldwide.

Despite outliers, this figure shows an obvious and strong correlation between obesity and diabetes.  Compare this to Figure 2.

Figure 2.  Relationship of sugar availability to worldwide diabetes prevalence.

Figure 2 Adjusted association of sugar availability (kcal/person/day) with diabetes prevalence (% adults 20–79 years old).

The correlation here is much less obvious.  Without statistical tests, you could just as easily draw the line straight across the graph.  The statistical significance is much weaker than that in Figure 1.

This means that these data cannot easily distinguish between several possibilities:

(a) Calories –> Obesity –> Diabetes

(b) Sugar –> Diabetes

(c) Sugar –> Calories –> Obesity –> Diabetes

While waiting for science to clarify these distinctions, the bottom line is the same for all of them.

As I explained in yesterday’s post, everyone would be healthier eating less sugar.

Addition: The authors have posted detailed comments about their methods.

  • One problem with this post is that it mixes up two types of graphs in the study. The first graph is of “levels” of obesity and diabetes – the second graph is of “changes” in obesity and diabetes. The second is therefore saying a different thing that the first. if you plot change in obesity and change in diabetes you get a much weaker correlation. So the two plots should not be compared as they have been here. This is why we use statistical regression testing and why the full paper should be read.

  • johnny b

    while I am a diabetic and have read a lot about it..i have never read that sugar causes it..although my symptoms started while I was taken a blood pressure medicine that had a diuretic in it which caused me to have the incredible thirst symptom that most diabetics have before they even know their is a problem. I was taken off the med and the problem continued. I have since read that their are a few prescription drugs that can cause diabetes. Thast not to say all cases of it are caused by them, but it could be why its at epidemic proportions as many people are prescription drugs. Also..if you watch TV you probably have seen the lawyer adds claiming “if you”ve taken this drug and came down with diabetes, you could be entitled to compensation”…so that could be part of the reason so many of us have diabetes…we should also watch our diets and not eat any of the crap that they want to sell us and if you are diabetic or not… try to keep your glucose levels stable…your body burns fat best when they are kept in the 90’s

  • johnny b

    plain and simple…don’t make sugar or high fructose corn syrup a big part of your diet..

  • thomas C

    “..i have never read that sugar causes it..”
    Neither have I, and I’m beginning to think the myth of the myth is the myth. In today’s internet world, you’d have to be extremely clueless to think that. Just google it, the myth of the myth is extremely prima facie.