Chicken, Rice, Veggies & Oil and How Their Effects on Your Insulin & Glucose Levels Are 50% Off Those You'd Expect Based on the Calculated Glycemic Index of This Meal

The power of GI calculations is limited and even with meals as simple as the one in the picture, the calculated glycemic index can be ~50% off!

As a SuppVersity reader you've repeatedly read about macronutrient interactions, such as the insulin boosting effects of whey protein or dietary fat, studies that investigate the effects of the individual ingredients of a complete meal on the glycemic response healthy men and women, however, are scarce. Against that background the results of a recent study from the Clinical Nutrition Research Centre at the Singapore Institute for Clinical Sciences are of particular interest. After all, the Lijun Sun et al. (2014) determined the effect of co-ingesting a high-protein food (breast chicken), a fat (ground nut oil), a leafy vegetable or all three on the glycaemic and insulinaemic responses of white rice in healthy adults and did thus produce results that could be practically relevant for all of us - more relevant than inaccurately calculated GIs.
Before we get to the study results, though, let's briefly recap what the researchers actually did: Sun et al. recruited twelve healthy participants (six female and six male) by means of advertisements, flyers and personal communications.

"Before inclusion into the study, potential participants were briefed on all aspects of the experiment and were given the opportunity to ask questions. Following the securing of consent, a health assessment was performed which included anthropometric measurements and a health questionnaire (giving details of food allergies/intolerance, metabolic diseases, special dietary needs and smoking habits). Those who fulfilled all the inclusion criteria [body mass index 18.5–24.99 kg/m2; blood pressure (BP)—systolic BP between 110 and 120 mmHg and diastolic BP between 75 and 85 mmHg; age 21–50 years; fasting blood glucose, 4–6 mmol/L; not on prescription medication, non-smoking; no genetic or metabolic diseases) were enrolled into the study." (Sun. 2014)

In addition, the amount of regular physical activity was quantified and subjects who were partaking in competitive sports and endurance events were excluded. Eventually, the scientists ended up with a group of normal-weight men and women at the age of 21–34 years.

Table 1: Composition of the test meals, ACHO = available carbohydrates. Nutritional data were obtained from the manufacturers (Sun. 2014).

The subjects visited the laboratory 5 times (plus a baseline testing with a glucose solution). On each of these testing sessions, which were separated by at least one week, the subjects arrived at the laboratory between 7:30 and 8:30 after an overnight fast and received one of the five test meals from Table 1, which contained 194 g white of plain white rice,  254 g of white rice with fat, 294 g of plain white rice with chicken breast, 314g of white rice with vegetable and 474g of white rice with fat, chicken and vegetable, respectively.

Figure 1: Glucose levels expressed relative to the ingestion of 250g of glucose (Sun. 2014)

The values in Figure 1 are expressed relative to the glucose response to 250g of pure glucose, of which a brief glimpse at the data tells you that they produce higher peak and incremental area under the curve (iAUC, a measure for the glycemia over the whole testing period) levels than any of the meals. Statistical significant differences were yet observed only for rice with chicken breast, rice with vegetable, and rice with fat, chicken and vegetable - yet not for the plain rice and the rice + fat meal (the latter was to be expected based on the discussion in my previously referenced article "True or False? Adding Fat to A Carby Meal Lowers Insulin Response" | read more).

Significant differences for the insulin response were observed for the white rice + chicken meal, where the insulin response was significantly higher compared to the white rice only (+22%), as well as the rice with + vegetable meal, where the insulin response was significantly lower compared to the white rice only condition (-16%).

The combination of foods determines the GI of the meal

Based on the classic equation that's usually used to determine the glycemic index of a meal (Hätönen. 2011), Sun et al. calculated the predicted glycemic of the five test meals and compared it to the actual glycemic index (GI) that was calculated based on the measured glucose and insulin response of the subjects.

Figure 2: Predicted and measured glycemic index as well as measured insulinemic index of the meals (Sun. 2014)

As you can see in Figure 2, the comparison yields an unsurprising result. As it's usually the case, when simple equations are used to predict physiological effects, the real GI values were significantly different from the calculated ones and  - significantly lower, that is. Accordingly, the meal with the least impact on postprandial glycemia and a comparatively low insulinemic effect is the one containing rice, fat, chicken and veggies - in other words, the complete meal. 
References:

• Hätönen, Katja A., et al. "Protein and fat modify the glycaemic and insulinaemic responses to a mashed potato-based meal." British Journal of Nutrition 106.02 (2011): 248-253.
• Mah, Eunice, et al. "Postprandial hyperglycemia impairs vascular endothelial function in healthy men by inducing lipid peroxidation and increasing asymmetric dimethylarginine: arginine." The Journal of nutrition 141.11 (2011): 1961-1968. 
• Sun, Lijuan, et al. "Effect of chicken, fat and vegetable on glycaemia and insulinaemia to a white rice-based meal in healthy adults." European journal of nutrition (2014): 1-8.
• Wolever, T. M. S. "Is glycaemic index (GI) a valid measure of carbohydrate quality&quest." European journal of clinical nutrition 67.5 (2013): 522-531.