I wish to share with my readers an interesting study that the ZRT research team presented recently at the 7th Annual World Congress on Insulin Resistance in San Francisco and won a Bronze Award among appox. two hundred abstracts submitted for competition.
Postprandial insulin and triglyceride (Tg) levels have been suggested as potential clinical tools to help identify individuals at high risk of atherosclerosis and coronary heart disease. Published studies have used a variety of meal types. We investigated the effects of 5 different breakfast meals on postprandial insulin and triglyceride levels, to see if meal type elicited different responses and to help identify a suitable protocol for routine risk assessment.
Blood spots were obtained by finger stick from 19 healthy volunteers after a overnight fast and then 2 hours after eating each of 5 breakfast meals. At least 1 week elapsed between each test meal. After collecting blood spots on a filter paper, they were allowed to dry and stored at room temperature until analysis. 6-mm disks were punched from the dried blood spots into 96-well plates; insulin was assayed using modified serum ELISA assay kits after extraction with extraction buffer, and Tg were assayed using an enzymatic assay following extraction with methanol . The DBS assay correlates highly with simultaneous serum testing, demonstrated in a previously published study. The serum/DBS correlation coefficients for insulin and Tg in that study were r=.93 and r=.91 respectively.
For statistical analysis, insulin and Tg levels were categorized as either normal or abnormal; within the “normal” classification, they were further categorized into “optimal” or “non-optimal”. For insulin, values >15 µIU/mL were “abnormal” and >8 µIU/mL were “non-optimal”, while for Tg, >150 ng/mL was “abnormal” and >100 ng/mL “non-optimal”. Using a Wilcoxon paired sign test, outcomes for each meal were compared to all other meals.
Insulin levels at 2 hours showed a difference in response depending on meal composition. Postprandial insulin appears to correspond to overall carbohydrate content; more abnormal/non-optimal results were seen after meal 4 (highest carbohydrate content) and the fewest abnormal/non-optimal results were seen after meal 2 (lowest carbohydrate content), despite the fact that meal 2 had the highest fat content and the most overall calories. Sustained, higher than optimal insulin levels 2 hours after eating could represent an additional cardiometabolic risk factor, even in individuals whose fasting levels are normal. Dietary choices may therefore increase a person’s chances of postprandial dysmetabolism. In non-diabetics, high postprandial insulin levels are an independent risk factor for coronary artery disease.
Tg levels at 2 hours did not differ significantly between meals, although only about half the values seen were in the normal range. We know from the literature that Tg levels tend to peak around 4 hours postprandially, and in our subjects Tg was still rising after the 2 hour measurement. A 4-hour sample may have elicited a between-meal difference, but compliance issues with collecting a sample 4 hours after eating might preclude postprandial Tg as a routine clinical test.
Convenient, in-home collection of DBS offers a simple tool to research the phenomenon of postprandial dysmetabolism. Assessment of DBS insulin levels 2 hours after a meal may help identify risk in individuals whose fasting levels are normal, and can indicate whether routine dietary choices are exposing them to greater risk than necessary.
Following is the abstract of the study that was presented at the conference.
Insulin and triglyceride levels after different breakfast meal challenges – measurement in dried blood spots (DBS)
Sonia Kapur, Margaret Groves, David Zava, Sanjay Kapur
ZRT Laboratory, Beaverton, Oregon, USA.
The metabolic conditions that predispose individuals to atherosclerosis are thought to be a postprandial phenomenon, termed “postprandial dysmetabolism”. In non-diabetics, high postprandial insulin and triglycerides are independent risk factors for coronary artery disease and cardiovascular events.
Pre- and postprandial serum testing for insulin and triglycerides is inconvenient for patients and practitioners, limiting routine application of these tests and their use in large scale clinical studies.
We developed finger stick DBS tests for insulin and triglycerides that correlate highly with venous serum values (r=.93 and r=.91 respectively), and evaluated these analytes in DBS from 19 healthy volunteers after an overnight fast, before and 2 hours after eating 5 different breakfast meals.
Meals consisted of: 1) glazed donuts, fruit smoothie; 2) boiled eggs, sausages, 2% milk; 3) bagel, cream cheese, boiled egg, 2% milk; 4) pancakes, syrup, tea with cream/sugar; 5) oatmeal, almonds, apple, skim milk.
Postprandial insulin levels >8 µIU/mL were classified as “non-optimal” while >15 µIU/mL were “abnormal”; triglyceride levels >100 ng/mL were “non-optimal” and >150 ng/mL “abnormal”.
For insulin, meal 2 (lowest carbohydrate, highest protein) produced the best (fewer abnormal/non-optimal) postprandial results and meal 4 (highest carbohydrate, lowest protein) the worst (more abnormal/non-optimal) postprandial results. For triglycerides, no meal differed significantly from the others in the number of abnormal or non-optimal classifications.
The convenience of in-home collection and analyte stability offer much wider scale use of the DBS tests for routine clinical assessment and large scale epidemiological studies of postprandial dysmetabolism.