Plasma glucose and insulin responses to starchy foods in Australian aborigines: a population now at high risk of diabetes

Starchy vegetable intake in the first trimester is associated with a higher risk of gestational diabetes mellitus: a prospective population-based study

OBJECTIVE

The purpose of this study was to evaluate the association between starchy vegetable consumption and subgroup consumption in the first trimester and the risk of gestational diabetes mellitus (GDM).

METHODS

A prospective study (n = 1444) was conducted in China. Dietary information was assessed by 24-hour dietary recalls for three days and then we calculated the consumption of total starchy vegetable and its subgroups, including (1) potato and (2) other starchy vegetable (pumpkin, lotus root, yam, taro, water chestnut, pea, and cowpea). GDM was diagnosed according to the results of 75-g two-hour oral glucose tolerance test (OGTT) at 24-28 weeks of gestation. A modified log-binomial regression was used to estimate RRs and 95% CIs of GDM risk.

RESULTS

Among the 1444 participants in our study, 520 were diagnosed with GDM. The adjusted RRs (95% CIs) for GDM from the lowest to the highest quartiles of total starchy vegetable consumption were 1.00 (reference), 1.29 (1.06, 1.57), 1.13 (0.93, 1.40), and 1.26 (1.02, 1.56), respectively; p for trend = .032. For potato, the RR of GDM risk was 1.32 for the highest potato intake quartile compared with the lowest quartile (95% CI 1.07-1.64, p for trend = .003). In addition, we did not observe an association between other starchy vegetable intakes and GDM risk.

CONCLUSIONS

A higher consumption of total starchy vegetables and potatoes in the first trimester is associated with a greater risk of GDM.

Diet-Induced Hyperinsulinemia as a Key Factor in the Etiology of Both Benign Prostatic Hyperplasia and Essential Hypertension?

Benign prostatic hyperplasia and hypertension are common age-related comorbidities. Although the etiology of benign prostatic hyperplasia (BPH) is still largely unresolved and poorly understood, a significant age-independent association was found between BPH and hypertension, indicating a common pathophysiological factor for both diseases. It has previously been suggested that the development of essential hypertension may be related to diet-induced hyperinsulinemia. This study follows the question, whether BPH may develop due to the same mechanism, thereby explaining the well-known comorbidity of these 2 disorders. The scientific evidence presented shows that BPH and hypertension share the same pathophysiological changes, with hyperinsulinemia as the driving force. It further shows that significant dietary changes during human history cause disruption of a finely tuned metabolic balance that has evolved over millions of years of evolution: high-insulinemic food, typical of current “Western” diets, has the potential to cause hyperinsulinemia and insulin resistance, as well as an abnormally increased activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system, alterations that play a pivotal role in the pathogenesis of BPH and hypertension.

The current state of Indigenous and Aboriginal women with diabetes in pregnancy: a systematic review

To undertake a systematic review of diabetes in pregnancy (DIP), determining prevalence and impact on maternal and child health outcomes for Indigenous and Aboriginal women.

METHOD

Electronic searches of MEDLINE, Embase, CINAHL, ERIC, DARE, CDSR, PsycINFO, Austhealth and HealthInfoNet were undertaken. Changes in diagnostic criteria for DIP and variability in methodology meant a qualitative synthesis of the data was undertaken.

RESULTS

From the 142 potential studies, 42 peer reviewed journal articles met the inclusion criteria. GDM prevalence in 65% of studies was greater for Indigenous and Aboriginal women than the comparison groups; Pacific Islander 8.1%, Canadian Aboriginal 11.5%, American Indian 7.9%, Australian Aboriginal 8.4% compared with 2-5% worldwide. Of studies reporting high birth weight (>4000 g) and DIP, 75% had a higher than expected prevalence, 86% had higher macrosomia prevalence and 63% had higher stillbirth rates. Studies with Alaskan, Australian Aboriginal and Pacific Islander women had GDM prevalence both greater and less than comparison groups.

CONCLUSION

Correcting the health disparity for Indigenous and Aboriginal women with DIP is a health priority. DIP prevalence is not the same for all Indigenous and Aboriginal women. Inconsistent study design without robust data is interfering with accurate prevalence of DIP. New international consensus guidelines provide opportunities for high quality studies of DIP for Indigenous and Aboriginal women.

The carnivore connection hypothesis: revisited

The "Carnivore Connection" hypothesizes that, during human evolution, a scarcity of dietary carbohydrate in diets with low plant : animal subsistence ratios led to insulin resistance providing a survival and reproductive advantage with selection of genes for insulin resistance. The selection pressure was relaxed at the beginning of the Agricultural Revolution when large quantities of cereals first entered human diets. The "Carnivore Connection" explains the high prevalence of intrinsic insulin resistance and type 2 diabetes in populations that transition rapidly from traditional diets with a low-glycemic load, to high-carbohydrate, high-glycemic index diets that characterize modern diets. Selection pressure has been relaxed longest in European populations, explaining a lower prevalence of insulin resistance and type 2 diabetes, despite recent exposure to famine and food scarcity. Increasing obesity and habitual consumption of high-glycemic-load diets worsens insulin resistance and increases the risk of type 2 diabetes in all populations.

Australian Aboriginal plant foods: a consideration of their nutritional composition and health implications

For at least 40–50 000 years, plants played an important but supplementary role in the animal-dominated diet of Australian Aboriginal (AA) hunter-gatherers. New knowledge of the nutrient composition and the special physiological effects of their foods provides another perspective in the current debate on the composition of the ‘prudent’ diet and the diet on which humans evolved. In the present paper we have calculated the average nutrient composition of over 800 Aboriginal plant foods (in total and by food group) and highlighted the differences between these and modern cultivated foods. The data enable us to calculate the absolute contribution of plant foods to total food and nutrient intake of traditional living AA. If plants provided 20–40% of the energy in the diet (the most likely range), then plants would have contributed 22–44g protein, 18–36g fat, 101–202g carbohydrate, 40–80g fibre and 90–180mg vitamin C in a 12500kJ (3000 kcal) diet. Since all the carbohydrate came from plant foods, the traditional AA diet would have been relatively low in carbohydrate (especially starch) but high in dietary fibre in comparison with current recommendations. Over half the carbohydrate could have been in the form of sugars derived from fruit and honey. The low glycaemic index of their carbohydrate foods, however, would generate a relatively low demand for insulin secretion and this characteristic may have protected AA from a genetic predisposition to insulin resistance and its consequences (non-insulin-dependent diabetes mellitus, coronary heart disease, obesity). The dietary pattern and active lifestyle of recent hunter-gatherers such as AA may be a reference standard for modem human nutrition and a model for defence against diseases of affluence.

Low-glycaemic diets and health: implications for obesity

The present review considers the background to terminology that relates foods, glycaemia and health, including ‘available carbohydrate’, ‘glycaemic index’ (GI), 'glycaemic glucose equivalent', 'glycaemic response index' and 'net carbohydrate', and concludes that central to each of these terms is 'glycaemic load' (GL). GL represents the acute increase in exposure of tissue to glucose determined by foods; it is expressed in ingested glucose equivalents (per 100 g fresh weight or per serving), and is regarded as independent of the state of glucose metabolism from normal to type 2 diabetes mellitus (T2DM). Ad libitum studies in overweight or obese adults and children show that low-GL diets are associated with marked weight benefits, loss of adiposity and reduced food intake. Weight benefits appear on low-glycaemic v. high-glycaemic available carbohydrates, unavailable v. available carbohydrates and protein v. available carbohydrate. Energy intake immediately after lowering of meal GL via carbohydrate exchanges is apparent only after a threshold cumulative intake of >2000 MJ. Various epidemiological and interventional studies are discussed. A relationship between GL and the development of T2DM and CHD is evident. Studies that at first seem conflicting are actually consistent when data are overlaid, such that diets with a GL of >120 glucose equivalents/d would appear to be inadvisable. Whereas certain studies might place GI as being slightly stronger than GL in relationto T2DM risk, this situation appears to be associated with observations in a lower range of GL or when the range of GI is too narrow for accuracy; nevertheless, authors emphasise the importance of GL. Among the studies reviewed, GL offers a better or stronger explanation than GI in various observations including body weight, T2DM in nurses, CHD, plasma triacylglycerols, HDL-cholesterol, high-sensitivity C-reactive protein and protein glycation. Where information is available, the associations between risk factors and GL are either similar or stronger in the overweight or obese, as judged by BMI, and apply to both body weight and blood risk factors. The implications tend to favour a long-term benefit of reducing GL, for which further study is necessary to eliminate any possibility of publication bias and to establish results in clinical trials with overweight and obese patients.

Pathogenesis and etiology of essential hypertension: role of dietary carbohydrate

The development of essential hypertension (EH) is proposed to be the result of a cascade of metabolic alterations, with high insulin levels/hyperinsulinemia and an abnormal reaction to the vasodilatory effect of insulin as the initiating factors. It is well established that insulin causes vasodilatation of peripheral resistance vessels. In normal subjects, this insulin-induced vasodilatation and decrease of the peripheral vascular resistance (PVR) is compensated by an SNS-mediated re-vasoconstriction in order to avoid hypotension, with the net effect of a slight decrease in blood pressure and no significant effect on peripheral vascular resistance. In contrast, in genetically predisposed subjects, prone to the development of essential hypertension, the insulin-induced vasodilatation is compensated by an increased heart rate and cardiac output (to avoid hypotension), mediated by an abnormal sympathetic overactivity, (characterised by high norepinephrine spillover rates and (frequently) a hyperdynamic circulation), while the PVR remains low during the early phase of developing EH. During the course of chronic hypertension, the SNS-overactivity leads to progressive trophic alterations of vessel walls, and structural and functional vascular remodeling, with narrowing of arterial resistance vessels and an increasing PVR. Vascular remodeling and lumen narrowing not only affect peripheral resistance vessels, but also kidney vessels. Narrowing and decreased distensibility of preglomerular kidney vessels lead to chronic activation of the Renin-Angiotensin-Aldosterone-System, with reinforcement and fixation of hypertension. High-glycemic index nutrition is suggested to play a key role in the etiology of hypertension: The chronic stimulus of pancreatic beta-cells due to high-glycemic index nutrition may cause cell hypertrophy and dysfunction, resulting in postprandial hyperinsulinemia, and -- in susceptible subjects -- the development of EH. Since significant evidence suggests that hyperinsulinemia also represents a key factor for the development of obesity, insulin resistance and the metabolic syndrome, the well-known common association of EH and these metabolic alterations becomes quite understandable.

High-complex carbohydrate or lente carbohydrate foods?

Current dietary guidelines of the American Diabetes Association emphasize the importance of minimizing risk factors for cardiovascular disease while maximizing diabetes control. Potential advantages are seen for increased monounsaturated fat intake, but only the quantity rather than the quality of the carbohydrate is considered important. However, review of the carbohydrate issue suggests that many cultures now at high risk of diabetes originally consumed starchy staples higher in fiber and with a lower glycemic index than eaten currently. Furthermore, diets high in cereal fiber have been associated with improved glycemic control, and low glycemic index diets resulted in reduction in glycosylated proteins in type 1 and 2 diabetes. Finally, large cohort studies have demonstrated beneficial effects of cereal fiber and low glycemic index carbohydrate foods in reducing the risk both for diabetes and cardiovascular disease. The effect of insoluble cereal fiber is not readily explained, but a low glycemic index may result from a slower rate of carbohydrate absorption. Increased meal frequency as a model for reducing the rate of carbohydrate absorption has been shown to reduce day-long glucose and insulin levels in type 2 diabetes and reduce serum lipids in nondiabetic subjects. Therefore, there appears to be a potential role for low glycemic index, high-cereal fiber foods for prevention and treatment of diabetes. Both the nature of the dietary fat and the carbohydrate should be considered as potentially modifiable factors that together with weight control and exercise may play a role in diabetes and cardiovascular disease prevention and treatment.

An evolutionary analysis of the aetiology and pathogenesis of juvenile-onset myopia

The available evidence suggests that both genes and environment play a crucial role in the development of juvenile-onset myopia. When the human visual system is examined from an evolutionary perspective, it becomes apparent that humans, living in the original environmental niche for which our species is genetically adapted (as hunter-gatherers), are either slightly hypermetropic or emmetropic and rarely develop myopia. Myopia occurs when novel environmental conditions associated with modern civilization are introduced into the hunter-gatherer lifestyle. The excessive near work of reading is most frequently cited as the main environmental stressor underlying the development of myopia. In this review we point out how a previously unrecognized diet-related malady (chronic hyperinsulinaemia) may play a key role in the pathogenesis of juvenile-onset myopia because of its interaction with hormonal regulation of vitreal chamber growth.

The carnivore connection: dietary carbohydrate in the evolution of NIDDM

We postulate a critical role for the quantity and quality of dietary carbohydrate in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM). Our primate ancestors ate a high-carbohydrate diet and the brain and reproductive tissues evolved a specific requirement for glucose as a source of fuel. But the Ice Ages which dominated the last two million years of human evolution brought a low-carbohydrate, high-protein diet. Certain metabolic adaptations were therefore necessary to accommodate the low glucose intake. Studies in both humans and experimental animals indicate that the adaptive (phenotypic) response to low-carbohydrate intake is insulin resistance. This provides the clue that insulin resistance is the mechanism for coping with a shortage of dietary glucose. We propose that the low-carbohydrate carnivorous diet would have disadvantaged reproduction in insulin-sensitive individuals and positively selected for individuals with insulin resistance. Natural selection would therefore result in a high proportion of people with genetically-determined insulin resistance. Other factors, such as geographic isolation, have contributed to further increases in the prevalence of the genotype in some population groups. Europeans may have a low incidence of diabetes because they were among the first to adopt agriculture and their diet has been high in carbohydrate for 10,000 years. The selection pressure for insulin resistance (i.e., a low-carbohydrate diet) was therefore relaxed much sooner in Caucasians than in other populations. Hence the prevalence of genes producing insulin resistance should be lower in the European population and any other group exposed to high-carbohydrate intake for a sufficiently long period of time.

Westernisation, insulin resistance and diabetes in Australian aborigines

OBJECTIVE

To examine the published data on the impact of westernisation on obesity, non-insulin dependent diabetes mellitus (NIDDM), and coronary heart disease (CHD) in Australian Aborigines.

DATA SOURCES

Fifty-five articles from Australian and international sources (primarily peer-reviewed journals) are cited.

STUDY SELECTION

Twenty-eight reports providing data on the diet, lifestyle, health and "lifestyle diseases" of Australian Aborigines before and after westernisation are included in this review. A further 27 articles on obesity, NIDDM, CHD, insulin resistance, and the impact of diet and exercise were used to help interpret the Aboriginal data.

DATA EXTRACTION

Information on dietary composition, anthropometry, disease and risk factor prevalence, and relevant biochemical measurements were used for comparative and interpretive purposes.

DATA SYNTHESIS

The traditional hunter-gatherer lifestyle of Australian Aborigines, characterised by high physical activity and a diet of low energy density (low fat, high fibre), promoted the maintenance of a very lean body weight and minimised insulin resistance. In contrast, for most Aborigines a Western lifestyle is characterised by reduced physical activity and an energy-dense diet (high in refined carbohydrate and fat) which promotes obesity and maximises insulin resistance. When they make the transition from their traditional hunter-gatherer lifestyle to a westernised lifestyle, Aborigines develop high prevalence rates for obesity (with an android pattern of fat distribution), non-insulin dependent diabetes, impaired glucose tolerance, hypertriglyceridaemia, hypertension and hyperinsulinaemia. The striking improvements in carbohydrate and lipid metabolism in diabetic and non-diabetic Aborigines after a temporary reversion to a traditional hunter-gatherer lifestyle highlight the potentially reversible nature of the detrimental effects of lifestyle change, particularly in young people who have not yet developed diabetes.

CONCLUSION

It is suggested that insulin resistance was important to the survival of Aborigines as hunter-gatherers, but is also the underlying metabolic characteristic predisposing them to obesity, NIDDM and CHD after westernisation. Intervention strategies to prevent chronic diseases related to insulin resistance should be directed at lifestyle modification. To be effective such programmes will have to be developed and implemented at the community level.

Cardiovascular disease risk factors in Australian aborigines

1. Aborigines from all over Australia develop unusually high prevalence rates for obesity, non-insulin dependent diabetes mellitus (NIDDM) and cardiovascular disease when they make the transition from their traditional hunter-gatherer lifestyle to a Westernized lifestyle. 2. There is no evidence that they experienced these diseases as hunter-gatherers. Data from the few extant traditionally orientated groups in very remote areas of northern Australia indicate that they were very lean (BMI less than 20 kg/m2), with low blood pressure, and that neither blood pressure nor BMI rose with age. 3. In addition, fasting glucose and cholesterol levels were low (usually below 4 mmol/L). However, in view of their extreme leanness and regular physical activity, fasting insulin and triglyceride levels were inappropriately elevated, suggestive of insulin resistance. 4. When Westernized diabetic Aborigines reverted temporarily to a traditional hunter-gatherer diet and lifestyle, all of the metabolic abnormalities of diabetes were greatly ameliorated (fasting glucose and triglyceride levels fell markedly and glucose tolerance and insulin secretion improved). In addition, they lost weight and there was a reduction in the major risk factors for cardiovascular disease (reduction in hypertriglyceridaemia and blood pressure, increase in bleeding time). 5. The hunter-gatherer lifestyle was associated with increased physical activity and a low-fat, high-fibre diet of low-energy density and high-nutrient density derived from very lean wild meat, and uncultivated vegetable foods. It has important therapeutic implications for the treatment and prevention of many of the chronic degenerative diseases of affluent Western societies.

Exocrine pancreatic dysfunction in malnourished Australian aboriginal children

Pancreatic exocrine dysfunction has been frequently recorded in protein-energy malnutrition in underdeveloped countries. In addition, the pancreas requires optimal nutrition for enzyme synthesis and potentially correctable pancreatic enzyme insufficiency may play a role in the continuation of protein-energy malnutrition. This problem has not been previously evaluated in Australian Aborigines. We have applied a screening test for pancreatic dysfunction (human immunoreactive trypsinogen [IRT] assay) to the study of 398 infants (6-36 months) admitted to the Alice Springs Hospital over a 20-month period. All infants were assessed by anthropometric measures and were assigned to three nutritional groups (normal, moderate or severely malnourished) and two growth groups (stunted or not stunted). Of the 198 infants who had at least a single serum cationic trypsinogen measurement taken, normal values for serum IRT (with confidence limits) were obtained from 57 children, who were normally nourished. IRT levels were significantly correlated with the degree of underweight but there was no correlation with the degree of stunting or age. Mean IRT levels for the moderate and severely underweight groups were significantly greater than the mean for the normal group (P less than 0.01). Seventeen children (8.6%) had trypsinogen levels in excess of the 95th percentile for the normally nourished group, reflecting acinar cell damage or ductal obstruction. We conclude that pancreatic dysfunction may be a common and important overlooked factor contributing to ongoing malnutrition and disease in malnourished Australian Aboriginal children.