All the way back in 1998, Reaven's group published a paper that should raise the eyebrows of anyone interested in cardiovascular health (1).
The study was relatively simple: first, they recruited 147 lean and overweight volunteers without diabetes or diagnosed cardiovascular disease. Then, they measured the volunteers' insulin sensitivity. While most studies of this nature indirectly estimate insulin sensitivity simply by using a formula based on fasting insulin and glucose measurements (HOMA-IR), which can be inaccurate, Reaven's group directly measured insulin sensitivity using a gold standard method**.
Next, they waited nearly 5 years and watched who developed cardiovascular disease over that period.
To analyze the results, they divided the volunteers into three equal-sized groups based on their degree of insulin resistance (inverse of sensitivity). Group I had the lowest level of insulin resistance, group II had an intermediate level, and group III had the highest level. The following graph illustrates the number of people who were diagnosed with cardiovascular disease, or suffered a cardiovascular event, in each group over the course of the study:
Clearly, if you care about your cardiovascular health, you should care about your insulin sensitivity.
People who were the least insulin resistant (group I) were also the leanest, exercised the most, had the lowest blood pressure, the lowest levels of LDL ("bad") cholesterol, and the highest levels of HDL ("good") cholesterol. Was insulin resistance really an important predictor of cardiovascular disease risk, or was it simply associated with other unhealthy characteristics? To answer this question, the research team analyzed the relationship between insulin resistance and cardiovascular disease risk while mathematically holding the other variables constant.
What this analysis showed is that insulin resistance was the strongest "independent predictor" of cardiovascular risk-- moreso than other established risk factors like LDL cholesterol. In fact, it was the only predictor that remained statistically significant. This shows that insulin resistance has major predictive value for cardiovascular disease risk, and it also raises the possibility that insulin resistance could be a powerful driver of cardiovascular disease. From the paper:
These data provide substantial support for the view that the presence of insulin resistance identifies a subset of the population who will develop CVD over a relatively short time period.Am I insulin resistant?
The test Reaven's group used to accurately measure insulin sensitivity is labor-intensive and it's only available for research purposes. Yet there are a few simple questions you can ask yourself that will give you a pretty good idea of whether or not you're insulin resistant.
- What's your body weight? If you're overweight, you may be insulin resistant. If you're obese, there's an 80-90 percent chance you're insulin resistant. If you're lean, that doesn't necessarily mean you're insulin sensitive, but the likelihood is higher.
- What's your body fat distribution? If you're moderately overweight but you carry your fat evenly all over your body, there's a good chance you're insulin sensitive. If you carry most of your fat in your abdominal region (belly), you're probably insulin resistant.
- How physically active are you? If you have a high level of physical activity and you aren't obese, you're probably insulin sensitive. If you're sedentary, particularly sedentary and overweight or obese, you're probably insulin resistant.
If you think you're insulin resistant, the fastest effective way to begin addressing the problem is to exercise regularly. Play basketball, swim, jog, hike, cycle, lift weights, walk-- it doesn't matter what activity you choose-- just get moving! Controlling your weight and eating a healthy, whole-food-based diet will also help over the long term.
* I would argue that leptin resistance is equally important.
** Insulin suppression test.