What determines whether or not an obese person is at increased risk for CVD? The more over- weight/obese the person, the more likely they are to be insulin-resistant and at increased risk of cardiovascular disease, but substantial numbers of overweight/obese individuals remain insulin-sensitive, and not all insulin- resistant persons are obese. The results in figure 4 compare daylong glucose, insulin and free fatty acid (FFA) concentrations in response to breakfast and lunch in 20 Insulin Resistant (IR) and 18 Insulin Sensitive (IS) obese individuals, matched for age, gender, BMI and WC (Waist Circumference). The most striking difference between IR & IS persons (both are equally obese) is the post-meal insulin spikes which represents the body's attempt to push the glucose into the cells that are resistant to insulin action.
Another issue Reaven pointed out is that measurements of BMI and WC (waist circumference) are very closely related, associated with IR to an identical degree, and CVD risk is increased primarily in those overweight/obese individuals who are also insulin-resistant. These conclusions are obviously at odds with the conventional wisdom that overweight/obesity is synonymous with insulin resistance, and the notion, codified by the ATP III and the IDF that abdominal obesity is the source of all metabolic evil.
From this study, I gained one insight which could be useful in clinical practice. According to Kraft, 2 hr post-glucose plasma insulin level >40mU/ml means insulin reistance/hyperinsulinemia and also prediabetic. In fig 4 of Reaven's paper, breakfast & lunch were provided at 8:00am & 12:00 noon respectively. 1 hr & even 2 hr post-meal plasma insulin levels exceeded 40 mU/mL both after breakfast & after dinner in insulin resistant obese persons (determined by mean SSPG of 227mg/dL). In contrast, insulin sensitive obese persons (determined by mean SSPG of 76 mg/dL) have post-meal plasma insulin levels below 40 mU/mL both after breakfast & after dinner. We can check 1 or 2 hr post-meal plasma insulin level in obese persons to see whether they are pre-diabetic or not. According to Kraft, many pre-diabetics (DM in situ as Kraft called them) that could be missed by standard OGTT can be detected by OGTT plus plasma insulin assay. However, giving patients 100g glucose load and checking insulin 2 hrs later is hard to perform in practice. This study provides evidence that post-meal insulin could be more practicable & pick up those who are at increased risk of CVD.