The Centers for Disease Control (CDC) currently estimates that a jaw-dropping 33 percent of US men, and 39 percent of US women, will develop diabetes at some point in their lives (1). Roughly one out of three people in this country will develop diabetes, and those who don't manage it effectively will suffer debilitating health consequences. Has the risk of developing diabetes always been so high, and if not, why is it increasing?
In the same issue of the Annals of Internal Medicine as the low-carb vs. low-fat study, appears another study that aims to partially address this question (2).
Menke and colleagues examined records of diabetes prevalence from the Centers for Disease Control's NHANES surveys. They identified cases of diabetes by either 1) self-report of a diabetes diagnosis, or 2) fasting plasma glucose of 7 mmol/L (126 mg/dL) or more.
Between the 1976-1980 and the 2007-2010 survey periods, the prevalence of diabetes in men increased from 4.7 to 11.2 percent, and among women it increased from 5.7 to 8.7 percent. In other words, the overall prevalence of diabetes has nearly doubled over the last 30 years.
The investigators then looked at a few physical and demographic characteristics to see how well they explained (mathematically speaking) the increase. Adjusting for age diminished the trend slightly-- since our mean age has increased over the last 30 years and age is a major risk factor for diabetes. Adjusting for population race/ethnicity changes had little impact on the trend.
However, the investigators found that adjusting for body mass index (BMI) and/or waist circumference greatly attenuated the trend, suggesting that the increase in diabetes prevalence is intimately linked to our expanding waistlines.
The story becomes a bit more complicated from here. Increasing BMI accounted for essentially all of the increase in diabetes prevalence in women, but in men it only accounted for some of it. There are apparently other unidentified factors in men, such as changes in physical activity and/or sedentary time, deteriorating sleep habits, or better diabetes diagnosis, that have played a role in the increase.
This study adds to a large body of evidence linking excess weight with diabetes risk. Here's a graph illustrating the relationship between BMI and the likelihood of developing diabetes over a 5-year period among US men (3):
People in the highest weight category had a 42 times higher diabetes risk than people in the lowest weight category. Body fatness is quite obviously a dominant risk factor for developing diabetes, even though lean people do sometimes develop diabetes*.
Obesity and diabetes risk are closely linked to one another, although there are other important risk factors, such as genetics, age, and inactivity. Even a modest degree of fat loss can greatly reduce the risk of developing diabetes among people who are overweight or obese (4).
* One confounding factor is that uncontrolled diabetes itself causes weight loss. People are sometimes diabetic for a while before receiving a diagnosis, such that they aren't as overweight by the time they're diagnosed. Often, that person was previously overweight or obese, and excess weight contributed to the development of their disease. This confounds the relationship between excess weight and diabetes. However, some people do develop diabetes without ever having excess body fat. This can be due to a combination of diet and lifestyle factors, age, and unlucky genetics.