Diet & insulin resistance: a review & Asian Indian perspective

Insulin resistance is associated with type 2 diabetes mellitus (T2DM) and cardiovascular diseases (CVD). These abnormalities have been aggravated because of imbalanced and excess nutrition in developed countries, and rapid nutritional and lifestyle transition occurring in developing countries. This review presents evidence linking dietary nutrients with insulin resistance and its metabolic correlates, and also describes these issues from a Asian Indians and South Asian perspective. Despite possible influences from genetic and perinatal factors, diet and physical activity are likely to have greater and often overriding influence in pathogenesis of the insulin resistance, the metabolic syndrome, and T2DM. In animal studies, a link has been established between dietary nutrients and insulin resistance. However, in human studies evidence is not as strong as in animals. Data suggest that dietary omega-3 polyunsaturated fatty acids (PUFAs) improve lipid profile and may have beneficial effect on insulin resistance. Dietary saturated fatty acids intake is positively associated with insulin resistance. Also, low glycaemic index foods and whole grain intake decrease insulin resistance. Importantly, high carbohydrate diets increase plasma triglycerides, cause hyperinsulinaemia and decreases low-density lipoprotein cholesterol. Among micronutrients, high magnesium and calcium intake have been reported to decrease insulin resistance. High intake of dietary carbohydrate and omega-6 PUFAs, low intake of omega-3 PUFAs and fiber, and high omega -6/omega-3 PUFAs ratio have been reported in South Asians. Our recent investigations have shown that increased dietary omega-6 PUFAs and saturated fat intake are significantly associated with fasting hyperinsulinaemia and sub-clinical inflammation, respectively. Such imbalanced diets contribute to high prevalence of insulin resistance, the metabolic syndrome and T2DM in South Asians and Asian Indians.

A case-control study on insulin resistance, metabolic co-variates & prediction score in non-alcoholic fatty liver disease

BACKGROUND & OBJECTIVE

Asian Indians have a high prevalence of insulin resistance and the metabolic syndrome. Currently, non-alcoholic fatty liver disease (NAFLD) is considered to be an integral part of the metabolic syndrome with insulin resistance as a central pathogenic factor. We studied anthropometric parameters, insulin resistance and metabolic co-variates in subjects with NAFLD as compared to those without NAFLD, and also developed a prediction score for NAFLD.

METHODS

Thirty nine subjects with NAFLD and 82 controls were selected for the study after ultrasonography of 121 consecutive apparently healthy subjects. Anthropometric profile [body mass index (BMI), waist circumference (WC) etc,], lipid profile, hepatic aminotransferases, fasting blood glucose (FBG), insulin were recorded and value of homeostasis model assessment of insulin resistance (HOMA-IR) was analysed. Step-wise logistic regression analysis and area under the receiver operator curve (aROC) were analysed to arrive at a prediction score.

RESULTS

Overall, prevalence of NAFLD was 32.2 per cent and prevalence of metabolic syndrome was seen in 41 per cent among cases and 19.5 per cent in controls (P<0.01). Subjects with NAFLD had significantly higher values of BMI, WC, hip circumference, FBG, fasting insulin, total cholesterol and serum triglycerides. Step-wise logistic regression analysis showed odds ratio (OR) and 95 per cent confidence interval (CI) for BMI [ 4.3 (1.6, 11.3)], FBG [5.5 (1.5, 19.8)] and fasting insulin [ 2.4 (1.0, 5.8)] as independent predictors of NAFLD. The prediction score for NAFLD was; 1 (fasting insulin) +1.6 (BMI) + 1.9 (FBG) (sensitivity of 84.6%, specificity of 51.2% and aROC 76%).

INTERPRETATION & CONCLUSION

In this study, presence of NAFLD indicated close relationship with multiple features of metabolic syndrome. The prediction score developed could be used as a screening tool to predict NAFLD among Asian Indians in north India.

Consensus statement for diagnosis of obesity, abdominal obesity and the metabolic syndrome for Asian Indians and recommendations for physical activity, medical and surgical management

Asian Indians exhibit unique features of obesity; excess body fat, abdominal adiposity, increased subcutaneous and intra-abdominal fat, and deposition of fat in ectopic sites (liver, muscle, etc.). Obesity is a major driver for the widely prevalent metabolic syndrome and type 2 diabetes mellitus (T2DM) in Asian Indians in India and those residing in other countries. Based on percentage body fat and morbidity data, limits of normal BMI are narrower and lower in Asian Indians than in white Caucasians. In this consensus statement, we present revised guidelines for diagnosis of obesity, abdominal obesity, the metabolic syndrome, physical activity, and drug therapy and bariatric surgery for obesity in Asian Indians after consultations with experts from various regions of India belonging to the following medical disciplines; internal medicine, metabolic diseases, endocrinology, nutrition, cardiology, exercise physiology, sports medicine and bariatric surgery, and representing reputed medical institutions, hospitals, government funded research institutions, and policy making bodies. It is estimated that by application of these guidelines, additional 10-15% of Indian population would be labeled as overweight/obese and would require appropriate management. Application of these guidelines on countrywide basis is also likely to have a deceleration effect on the escalating problem of T2DM and cardiovascular disease. These guidelines could be revised in future as appropriate, after another large and countrywide consensus process. Till that time, these should be used by clinicians, researchers and policymakers dealing with obesity and related diseases.

Comparison of definitions of the metabolic syndrome in adult Asian Indians

OBJECTIVE

The optimum definition of the metabolic syndrome (MS) is not known. We compared international definitions of MS [recently proposed modified definition of National Cholesterol Education Programme, Adult Treatment Panel III (NCEP, ATP III) and International Diabetes Federation (IDF)] with two proposed candidate definitions in adult Asian Indians.

DESIGN

Data from three previous cross-sectional studies carried out in North India were analyzed.

SUBJECTS

The study included 2050 adult (mean age: 40 +/- 18 years) Asian Indian subjects residing two metropolitan cities.

MEASUREMENTS

Candidate definitions of MS were proposed by modifying the NCEP, ATP III and IDF definitions by including the following modified variables into two combinations (MS-ATP1 and MS-IDF1); waist circumference cut-off points as >90 cm in males and >80 cm in females, body mass index (BMI) cut-off point as >23 kg/m2, impaired fasting glucose (IFG) cut-off point >100 mg/dl and waist circumference as an obligatory criterion.

RESULTS

Maximum overall and gender-specific prevalence of the MS (49.2% overall; 41.4% in males; 55.3% in females) was observed using the definition which included modified cut-off points of WC (non-obligatory), BMI, and IFG (>100 mg/dl) in addition to other defining parameters. Compared to other definitions this proposed candidate definition maximally detected presence of MS in subjects with IFG and T2DM [Percentage prevalence: 78.1% (73.0-82.7) and 91.1% (84.2-95.6)]. Even in subjects without abdominal obesity, a high prevalence of other abnormal defining parameters of the metabolic syndrome; hypertension (> or = 130 or > or = 85 mmHg), 35.7%; BMI >23 kg/m2, 15.3%; hypertriglyceridemia (>150 mg/dl), 20.2% and low levels of HDL-C (<40 in males; <50 mg/dl in females), 55% were seen. Further, 10.5% of subjects who did not have abdominal obesity had presence of at least 3 risk variables of the metabolic syndrome. These data indicate that by making abdominal obesity a mandatory criterion would lead to missing of some cases of the metabolic syndrome.

CONCLUSION

By including BMI and making waist circumference as a non-obligatory criterion, more cases of the metabolic syndrome is detected. For Asian Indians, making waist circumference as mandatory variable in the definition of the metabolic syndrome would lead to non-inclusion of nearly 11% cases who would otherwise be diagnosed as metabolic syndrome according to modified NCEP, ATP III definition.

Waist circumference cutoff points and action levels for Asian Indians for identification of abdominal obesity

OBJECTIVE

To test the validity of internationally accepted waist circumference (WC) action levels for adult Asian Indians.

DESIGN

Analysis of data from multisite cross-sectional epidemiological studies in north India.

SUBJECTS

In all, 2050 adult subjects >18 years of age (883 male and 1167 female subjects).

MEASUREMENTS

Body mass index (BMI), WC, waist-to-hip circumference ratio, blood pressure, and fasting samples for blood glucose, total cholesterol, serum triglycerides, and high-density lipoprotein cholesterol.

RESULTS

In male subjects, a WC cutoff point of 78 cm (sensitivity 74.3%, specificity 68.0%), and in female subjects, a cutoff point of 72 cm (sensitivity 68.7%, specificity 71.8%) were appropriate in identifying those with at least one cardiovascular risk factor and for identifying those with a BMI >21 kg/m(2). WC levels of > or =90 and > or =80 cm for men and women, respectively, identified high odds ratio for cardiovascular risk factor(s) and BMI level of > or =25 kg/m(2). The current internationally accepted WC cutoff points (102 cm in men and 88 cm in women) showed lower sensitivity and lower correct classification as compared to the WC cutoff points generated in the present study.

CONCLUSION

We propose the following WC action levels for adult Asian Indians: action level 1: men, > or =78 cm, women, >/=72 cm; and action level 2: men, > or =90 cm, women, > or =80 cm.