The continuous low dose insulin and glucose infusion test: a simplified and accurate method for the evaluation of insulin sensitivity and insulin secretion in population studies

Effects of Two Different Dietary Patterns on Inflammatory Markers, Advanced Glycation End Products and Lipids in Subjects without Type 2 Diabetes: A Randomised Crossover Study

Epidemiological studies suggest that consumption of red and processed meat and refined grains are associated with type 2 diabetes and metabolic syndrome and increased inflammatory and fibrinolytic markers. We hypothesised that a diet high in red and processed meat and refined grains (HMD) would increase inflammatory markers and advanced glycation end products (AGEs) compared with a diet high in dairy, whole grains, nuts and legumes (HWD). We performed a randomised crossover study of two four-week interventions in 51 participants without type 2 diabetes (15 men and 36 women aged 35.1 ± 15.6 years; body mass index: 27.7 ± 6.9 kg/m²). No baseline measurements were performed. Plasma fluorescent AGEs, carboxymethyllysine, glucose, insulin, lipids, hs-CRP, interleukin 6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) were analysed after four weeks on each diet. IL-6, hs-CRP, AGEs and carboxymethyllysine were not different between diets but PAI-1 was higher after the HMD than after HWD ((median and interquartile range) 158, 81 vs. 121, 53 ng/mL p < 0.001). PAI-1 on the HWD diet was inversely correlated with whole grains intake (p = 0.007). PAI-1 was inversely correlated with insulin sensitivity index (r = −0.45; p = 0.001) and positively correlated with serum total cholesterol (r = 0.35; p = 0.012) and serum triglyceride (r = 0.32; p = 0.021) on HMD. This trial was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12614000519651).

Differential Effects of Red Meat/Refined Grain Diet and Dairy/Chicken/Nuts/Whole Grain Diet on Glucose, Insulin and Triglyceride in a Randomized Crossover Study

Epidemiological studies suggest that a diet high in processed meat, with a high glycemic index is associated with an increased risk of type 2 diabetes. It is not clear if this is due to altered insulin sensitivity or an enhanced postprandial glucose. We aimed to compare the acute metabolic response of two different types of meals after ingestion of the matching diet for four weeks. The study was a randomized, crossover acute meal study. Volunteers consumed either a red meat/refined grain meal or a dairy/chicken/nuts/wholegrain meal after four weeks of the matching diet. After a three-week washout period and four weeks of the alternate diet, they consumed the matching meal. The diets differed with respect to both protein and carbohydrate sources. Blood samples were taken for 180 min for the measurement of glucose, insulin, C-peptide and triglyceride. Fifty-one participants (age: 35.1 ± 15.6 years; body mass index: 27.7 ± 6.9 kg/m², 17 with normal and 34 with impaired glucose tolerance) completed two meal tests. The area under the curve (p < 0.001) and incremental area under the curve (p = 0.001) for insulin was significantly higher after the red meat/refined grain diet than after the dairy/chicken/nuts/whole grain diet. There was an interaction between meal and glucose tolerance group (p < 0.05) in the area under the curve (AUC) and the incremental area under the curve (iAUC) of glucose; the red meat/refined grain diet increased glucose relative to the dairy/chicken/nuts/whole grain diet only in the normal group (+2.5 mmol/L/3 h). The red meat/refined grain diet increased glucose and insulin responses compared with the dairy/chicken/nuts/whole grain diet. This meal pattern would increase pancreatic stress long term and may account for the increased risk of type 2 diabetes with this diet.

Assessing the predictive accuracy of QUICKI as a surrogate index for insulin sensitivity using a calibration model

The quantitative insulin-sensitivity check index (QUICKI) has an excellent linear correlation with the glucose clamp index of insulin sensitivity (SI(Clamp)) that is better than that of many other surrogate indexes. However, correlation between a surrogate and reference standard may improve as variability between subjects in a cohort increases (i.e., with an increased range of values). Correlation may be excellent even when prediction of reference values by the surrogate is poor. Thus, it is important to evaluate the ability of QUICKI to accurately predict insulin sensitivity as determined by the reference glucose clamp method. In the present study, we used a calibration model to compare the ability of QUICKI and other simple surrogates to predict SI(Clamp). Predictive accuracy was evaluated by both root mean squared error of prediction as well as a more robust leave-one-out cross-validation-type root mean squared error of prediction (CVPE). Based on data from 116 glucose clamps obtained from nonobese, obese, type 2 diabetic, and hypertensive subjects, we found that QUICKI and log (homeostasis model assessment [HOMA]) were both excellent at predicting SI(Clamp) (CVPE = 1.45 and 1.51, respectively) and significantly better than HOMA, 1/HOMA, and fasting insulin (CVPE = 3.17, P < 0.001; 1.67, P < 0.02; and 2.85, P < 0.001, respectively). QUICKI and log(HOMA) also had the narrowest distribution of residuals (measured SI(Clamp) - predicted SI(Clamp)). In a subset of subjects (n = 78) who also underwent a frequently sampled intravenous glucose tolerance test with minimal model analysis, QUICKI was significantly better than the minimal model index of insulin sensitivity (SI(MM)) at predicting SI(Clamp) (CVPE = 1.54 vs. 1.98, P = 0.001). We conclude that QUICKI and log(HOMA) are among the most accurate surrogate indexes for determining insulin sensitivity in humans.

The effect of alcohol intake on insulin sensitivity in men: a randomized controlled trial

OBJECTIVE

Population data suggest that alcohol consumption may influence the risk of diabetes in a biphasic manner, but this has not been tested by any controlled interventions. The object of this study was to determine whether reducing alcohol intake in moderate-to-heavy drinkers (40-110 g/day) results in improvement in insulin sensitivity.

RESEARCH DESIGN AND METHODS

A 4-week run-in period where subjects maintained their usual drinking pattern was followed by randomization to a two-way cross-over intervention study. In each of two 4-week treatment interventions, subjects either substituted their usual alcohol intake with a 0.9% alcohol beer or maintained their usual alcohol intake. At the end of each 4-week period, insulin sensitivity as determined by the low-dose insulin glucose infusion test and the homeostasis model assessment (HOMA) score, and biomarkers of alcohol consumption (gamma-glutamyl transpeptidase [gamma-GT] and HDL cholesterol) were measured.

RESULTS

A total of 16 healthy men aged 51.0 +/- 2.7 (mean +/- SEM) years with a BMI of 26.4 +/- 0.61 kg/m(2) completed the study. There was a large reduction in alcohol intake (72.4 +/- 5.0 vs. 7.9 +/- 1.6 g/day, P < 0.001) and significant reductions in gamma-GT (geometric mean 24.4 units/l [95% CI 19.7-30.2] vs. 18.6 units/l [15.5-22.2], P < 0.01) and HDL cholesterol (1.36 +/- 0.07 vs. 1.13 +/- 0.07 mmol/l, P < 0.001). There was no effect of alcohol on insulin sensitivity index (ISI), fasting insulin, glucose, or HOMA score.

CONCLUSIONS

A substantial reduction in alcohol intake from 7.2 to 0.8 standard drinks per day in healthy men did not change insulin sensitivity as measured by ISI or HOMA score.

Effect of a high-protein, high-monounsaturated fat weight loss diet on glycemic control and lipid levels in type 2 diabetes

OBJECTIVE

To determine the effect of a high-protein (HP) weight loss diet compared with a lower-protein (LP) diet on fat and lean tissue and fasting and postprandial glucose and insulin concentrations.

RESEARCH DESIGN AND METHODS

Replacing dietary protein for carbohydrate (CHO) during energy restriction and weight loss has been effective in sparing lean mass and improving insulin sensitivity in obese subjects but has not been tested in subjects with type 2 diabetes. We compared an HP diet (28% protein, 42% CHO, 28% fat [8% saturated fatty acids, 12% monounsaturated fatty acids, 5% polyunsaturated fatty acids]) with an LP diet (16% protein, 55% CHO, 26% fat [8% saturated fatty acids, 11% monounsaturated fatty acids, 5% polyunsaturated fatty acids]) in 54 obese men and women with type 2 diabetes during 8 weeks of energy restriction (1,600 kcal) and 4 weeks of energy balance. Body composition was determined by dual-energy X-ray absorptiometry at weeks 0 and 12.

RESULTS

Overall, weight loss of 5.2 +/- 1.8 kg was achieved independently of diet composition. However, women on the HP diet lost significantly more total (5.3 vs. 2.8 kg, P=0.009) and abdominal (1.3 vs. 0.7 kg, P=0.006) fat compared with the women on the LP diet, whereas, in men, there was no difference in fat loss between diets (3.9 vs. 5.1 kg). Total lean mass decreased in all subjects independently of diet composition. LDL cholesterol reduction was significantly greater on the HP diet (5.7%) than on the LP diet (2.7%) (P < 0.01).

CONCLUSIONS

Both dietary patterns resulted in improvements in the cardiovascular disease (CVD) risk profile as a consequence of weight loss. However, the greater reductions in total and abdominal fat mass in women and greater LDL cholesterol reduction observed in both sexes on the HP diet suggest that it is a valid diet choice for reducing CVD risk in type 2 diabetes.