Glycemic index and obesity

Although weight loss can be achieved by any means of energy restriction, current dietary guidelines have not prevented weight regain or population-level increases in obesity and overweight. Many high-carbohydrate, low-fat diets may be counterproductive to weight control because they markedly increase postprandial hyperglycemia and hyperinsulinemia. Many high-carbohydrate foods common to Western diets produce a high glycemic response [high-glycemic-index (GI) foods], promoting postprandial carbohydrate oxidation at the expense of fat oxidation, thus altering fuel partitioning in a way that may be conducive to body fat gain. In contrast, diets based on low-fat foods that produce a low glycemic response (low-GI foods) may enhance weight control because they promote satiety, minimize postprandial insulin secretion, and maintain insulin sensitivity. This hypothesis is supported by several intervention studies in humans in which energy-restricted diets based on low-GI foods produced greater weight loss than did equivalent diets based on high-GI foods. Long-term studies in animal models have also shown that diets based on high-GI starches promote weight gain, visceral adiposity, and higher concentrations of lipogenic enzymes than do isoenergetic, macronutrientcontrolled, low-GI-starch diets. In a study of healthy pregnant women, a high-GI diet was associated with greater weight at term than was a nutrient-balanced, low-GI diet. In a study of diet and complications of type 1 diabetes, the GI of the overall diet was an independent predictor of waist circumference in men. These findings provide the scientific rationale to justify randomized, controlled, multicenter intervention studies comparing the effects of conventional and low-GI diets on weight control.     

The optimal dietary fat to carbohydrate ratio to prevent obesity in the Japanese population: a review of the epidemiological, physiological and molecular evidence

The prevention of obesity, which leads to diabetes and other diseases, is a major concern for public health. There might be an optimal dietary fat to carbohydrate ratio for prevention and treatment of obesity. According to the Japanese Dietary Reference Intakes (RDA) for 2010, the optimal fat intake is 20-30% of energy for ages 1-29 y and 20-25% for ages 30 y and over. Upper boundary values of this recommendation were the median of the percentage of energy from dietary fat in Japanese. In a systematic review to estimate the optimal dietary fat to carbohydrate ratio, it was found that obese subjects with hyperinsulinemia (or insulin resistance) lost more weight on a mild low-carbohydrate (LC) (or low-glycemic load diet; 40% carbohydrate, 30-35% fat) than on a low-fat (LF) diet (55-60% carbohydrate, 20% fat), whereas those without hyperinsulinemia showed the opposite. In non-obese primarily insulin-sensitive subjects, decreasing fat rather than carbohydrate intake is generally more effective to prevent obesity. Physiological and molecular evidence supports this conclusion. Increased carbohydrate intake, especially in high-glycemic food, leads to postprandial hyperglycemia and hyperinsulinemia, which are exaggerated in obese insulin-resistant subjects. Even in an insulin-resistant state, insulin is able to stimulate fatty acid synthesis in liver, activate lipoprotein lipase, and prevent lipolysis in adipose tissues, which all facilitate adipose tissue enlargement. Optimal dietary fat to carbohydrate ratio may differ in populations depending on their prevalence for obesity. Because the prevalence of overweight/obesity in Japanese is low, a LF diet is recommended in the general population.     

A ketogenic diet favorably affects serum biomarkers for cardiovascular disease in normal-weight men

Very low-carbohydrate (ketogenic) diets are popular yet little is known regarding the effects on serum biomarkers for cardiovascular disease (CVD). This study examined the effects of a 6-wk ketogenic diet on fasting and postprandial serum biomarkers in 20 normal-weight, normolipidemic men. Twelve men switched from their habitual diet (17% protein, 47% carbohydrate and 32% fat) to a ketogenic diet (30% protein, 8% carbohydrate and 61% fat) and eight control subjects consumed their habitual diet for 6 wk. Fasting blood lipids, insulin, LDL particle size, oxidized LDL and postprandial triacylglycerol (TAG) and insulin responses to a fat-rich meal were determined before and after treatment. There were significant decreases in fasting serum TAG (-33%), postprandial lipemia after a fat-rich meal (-29%), and fasting serum insulin concentrations (-34%) after men consumed the ketogenic diet. Fasting serum total and LDL cholesterol and oxidized LDL were unaffected and HDL cholesterol tended to increase with the ketogenic diet (+11.5%; P = 0.066). In subjects with a predominance of small LDL particles pattern B, there were significant increases in mean and peak LDL particle diameter and the percentage of LDL-1 after the ketogenic diet. There were no significant changes in blood lipids in the control group. To our knowledge this is the first study to document the effects of a ketogenic diet on fasting and postprandial CVD biomarkers independent of weight loss. The results suggest that a short-term ketogenic diet does not have a deleterious effect on CVD risk profile and may improve the lipid disorders characteristic of atherogenic dyslipidemia.     

Carbohydrates--the good, the bad and the whole grain

Weight loss can be achieved by any means of energy restriction, but the challenge is to achieve sustainable weight loss and prevent weight 'creep' without increasing the risk of chronic disease. The modest success of low fat diets has prompted research on alternative dietary strategies including high protein diets and low glycemic index (GI) diets. Conventional high carbohydrate diets, even when based on whole grain foods, increase postprandial glycaemia and insulinemia and may compromise weight control via mechanisms relating to appetite stimulation, fuel partitioning and metabolic rate. This paper makes the case for the benefits of low glycemic index diets over higher protein diets. Both strategies are associated with lower postprandial glycemia and both are commonly labelled as 'low glycemic load' but the long-term health effects are likely to be different. There is now a large body of evidence comprising observational prospective cohort studies, randomised controlled trials and mechanistic experiments in animal models, that provides robust support for low GI carbohydrate diets in the prevention of obesity, diabetes and cardiovascular disease. While lower carbohydrate, higher protein diets also increase the rate of weight loss, cohort studies and meta-analyses of clinical trials suggest the potential for increased mortality.     

Dietary carbohydrates and insulin action in humans

The metabolic syndrome represents a vicious cycle whereby insulin resistance leads to compensatory hyperinsulinaemia, which maintains normal plasma glucose but may exacerbate insulin resistance. Excess insulin secretion may eventually reduce beta-cell function due to amyloid deposition, leading to raised blood glucose and further deterioration of beta-cell function and insulin sensitivity via glucose toxicity. Reducing postprandial glucose and insulin responses may be a way to interrupt this process, but there is disagreement about the dietary approach to achieve this. Glucose and insulin responses are determined primarily by the amount of carbohydrate consumed and its rate of absorption. Slowly absorbed, low glycaemic-index (GI) foods are associated with increased HDL cholesterol and reduced risk of type 2 diabetes. There is some evidence that low-GI foods improve insulin sensitivity in humans, although studies using established techniques (glucose clamp or frequently sampled intravenous glucose tolerance test) have not been done. Low carbohydrate diets have been suggested to be beneficial in the treatment of the metabolic syndrome because of reduced postprandial insulin. However, they may increase fasting glucose and impair oral glucose tolerance--effects which define carbohydrate intolerance. The effects of low carbohydrate diets on insulin sensitivity depend on what is used to replace the dietary carbohydrate, and the nature of the subjects studied. Dietary carbohydrates may affect insulin action, at least in part, via alterations in plasma free fatty acids. In normal subjects a high-carbohydrate/low-GI breakfast meal reduced free fatty acids by reducing the undershoot of plasma glucose, whereas low-carbohydrate breakfasts increased postprandial free fatty acids. It is unknown if these effects occur in insulin-resistant or diabetic subjects. Thus further work needs to be done before a firm conclusion can be drawn as to the optimal amount and type of dietary carbohydrate for the treatment of the metabolic syndrome.     

Alternatives for macronutrient intake and chronic disease: a comparison of the OmniHeart diets with popular diets and with dietary recommendations

BACKGROUND: Enhancements to current dietary advice to prevent chronic disease are of great clinical and public health importance. The OmniHeart Trial compared 3 diets designed to reduce cardiovascular disease (CVD) risk-one high in carbohydrate and 2 that replaced carbohydrate with either unsaturated fat or protein. The lower carbohydrate diets improved the CVD risk factors. Several popular diets claiming health benefits emphasize carbohydrate, fat, or protein or various combined approaches. OBJECTIVE: The objective of this study was to compare the macronutrient contents of the OmniHeart trial diets to those of several popular diets and to evaluate each diet for consistency with national health guidelines. DESIGN: The macronutrient contents of 7-d menu plans from the OmniHeart Study, Dietary Approaches to Stop Hypertension (DASH), Zone, Atkins, Mediterranean, South Beach, and Ornish diets were evaluated for consistency with the US Food and Nutrition Board's Acceptable Macronutrient Distribution Ranges (AMDRs) and with the dietary recommendations of several health organizations. RESULTS: The OmniHeart diets fulfilled the major AMDRs, but, of the popular diets, only the Zone diet did. The OmniHeart diets were generally consistent with national guidelines to prevent cancer, diabetes, and heart disease, whereas most popular diets had limitations for fulfilling one or more guidelines. CONCLUSIONS: Although the OmniHeart protein and unsaturated fat diets were superior to the carbohydrate diet in improving CVD risk, all 3 study diets were consistent with national guidelines to reduce chronic disease risk, which suggests that the guidelines might now be fine-tuned to optimize disease prevention. Popular diets vary in their nutritional adequacy and consistency with guidelines for risk reduction.     

Carbohydrate and fiber recommendations for individuals with diabetes: a quantitative assessment and meta-analysis of the evidence

To review international nutrition recommendations with a special emphasis on carbohydrate and fiber, analyze clinical trial information, and provide an evidence-based recommendation for medical nutrition therapy for individuals with diabetes. Relevant articles were identified by a thorough review of the literature and the data tabulated. Fixed-effects meta-analyses techniques were used to obtain mean estimates of changes in outcome measures in response to diet interventions. Most international organizations recommend that diabetic individuals achieve and maintain a desirable body weight with a body mass index of /=55%; protein, 12-16%; fat, <30%; and monounsaturated fat, 12-15%. The diet should provide 25-50 g/day of dietary fiber (15-25 g/1000 kcal). Glycemic index information should be incorporated into exchanges and teaching material.     

Dietary carbohydrates and insulin sensitivity

This review considers recent findings and ideas on the impact of dietary carbohydrates on insulin sensitivity in the context of the prevention of diabetes and cardiovascular disease. We assess the evidence for benefits in insulin sensitivity following high starch as distinct from high sucrose intakes when the diet is low in fat. We consider relationships between obesity, leptin and carbohydrate intake. We conclude that reducing the rate of carbohydrate digestion in the small bowel may be the key stage at which to intervene to reduce insulinaemia and so prevent downregulation of insulin receptors and insulin resistance.     

Optimal macronutrient balance.

There is at present a justifiable debate as to the optimum level of total dietary fat which will reduce the risk of obesity without an elevation of plasma triacylglycerol or a depression of plasma HDL-cholesterol. Total plasma cholesterol and LDL-cholesterol levels are lowered and risk of fatal myocardial infarction is lowered when either saturated or trans-unsaturated fatty acids are replaced isoenergetically by either monounsaturated or polyunsaturated fatty acids. The triacylglycerol-raising and HDL-lowering effects of low-fat high-carbohydrate diets can be overcome with low intakes of n-3 polyunsaturated fatty acids and moderate exercise. Whilst a reduction in dietary fat is being attained in many countries, the reduction is uniform across all fatty acids, leaving dietary fat composition unchanged. The ability of low-fat diets to reduce cholesterol and cause a fall in body weight is not influenced by the carbohydrate ratio starch: sugars in the diet. However, weight-gain susceptibility to high intakes of dietary fat and the plasma cholesterol responsiveness to diet are considerably influenced by common genetic polymorphisms.     

为糖尿病人用的肠内营养

Diabetes mellitus is a serious illness that affects over 140million people worldwide.It is estinated that by the year 2025,the worldwide incidence of diabetes will reach 300 million.The objectives of this presentation are:(1)To review some aspects of the pathophysiology of diabetes mellitus.(2)To review the current nutritional recommendations for diabetic ubduvudyaks.(3)To discuss relative effects om metabolic control of diets high in carbohydrate and diets reduced in carbohydrates and containg high levels of monounsaturated fatty acid(MUFA).(4)To discuss the need for specialized enteral formulas for diabetics requiring nutrition support.(5)To present the consensus guidelines for nutrition support of diabetics.Early diabnosis and treatment of diabetes can reduce the complications and consequently lower diabetes-related morbidity and mortality.Acute complications of diabetes include diabetic ketoacidosis and immune system dysfunction redulting in infections.Long-term complications of the disease include coronary artery disease,nephropathy.Two recently completed clinical trials,the Diabetes Control and Complication Trial and the United Kingdom Prospective Diabetes Study,have shown that tight glycemic control has positive effects on health outcomes in diabetic individuals.Optimal management of diabetes includes nutrition therapy.The American Diabetic Association has established guidelines for the proportion of dietary calories contributed from fat,carbohydrate and protein.The recommended distrigution is 10-20% of total calories as protein and the rest distributed bwtween fat and carbohydrates.There is no longer a linit placed on dietary fat,provided that sources of fat high in MUFA are used,and that saturated and polyunsaturated fatty acids are each linited to no more than 10 percent of total calories.Outcomes of clinical trials with vardicate that rapidly digested and absorbed carbohydrates in liquid enteral formulas result in poor metabolic control in patients with abnormal glucose tolerance or diabetes mellitus.Inclusion of fiber blone,in liquid formulas does not improve the glycemic response.Options for improving the metabolic response to liquid diets include the replacement of some carbohydrate with protein,MUFA or slowly digested carbohydrates with a low glycemic index.Studies conducted throughout the 1980's demonstrated that high carbohydrate liquid enteral formulas result in poor metabolic control in diabetic patients.These studies showed that reduced carbohydrate levels,increased dietary MUFA,and solid food could improve metabolic control and reduce risk factors for macrovascular disease.Garge A et al studied the effects of high carbohydrate solid food diets on glycemic control and serum lipoproteins in subjects with type 2 diabetes mellitus１.The subjects were randomly assigned to receive first one diet and then the other,each for 28 days,in a metabolic ward.The high-carbohydrate diet had 25 percent of calories from fat and 60 percent from carbohydrate.The high-monounsaturated-fat diet was 50 percent fat(33 percent of the total calories were from monounsaturated fatty acids)and 35 percent carbohydrate.As compared with the high-carbohydrate diet,the high-monounsaturated-fat diet resulted in lower mean plasma glucose levels and reduced insulin requirements;urinary glucose losses were higher for subjexts consuming the high-carbohydrate diet (table 1).As compared with the high carbohydrate diet,the high-monounsaturated-fat diet resulted in lower levels of plasma triglycerides and very-low-density lipoprotein cholesterol;they were lower by 25 and 35 percent,respectively.The high-MUFA-fat diet also resulted in higher levels of high-density lipoprotein choleterol.Levels of total cholesterol and low-density lipoprotein cholesterol did not differsignificantly between subjects on the two diets.These investigators concluded that partial replacemtn of complex carbohydrate with monounsaturated fatty acids in the diets of people with type 2 diabetes could improve glycemic control and levels of plasma triglycerides and HDL choleterol.It has the potential to reduce insulin requirements and improve the total cholesterol to HDL cholesterol ratio.In 1994,Garg A et al compared the long-term effects of high carbohydrate versus high MUFA fat diets on metabolic control in type 2 diabetes over the long-term3.Forty-two subjects with type 2 diabetes were rancomized to receive either a high-carbohydrate diet containing 55 percent of calories as carbohydrate and 30 percent as fat,or a high-monounsaturated-fat diet containing 40 percent of calories as carbohydrate and 45 percent as fat.These diets,prepared in metabolic kitchens,were the sole source of nutrition for subjexts for 6 weeks.To assess even longer-term effects,a subgroup of 21 subjects continued the diet they received second for an additional eight weeks.Four studies were conducted after Glucerna was commercialized.The purpose of the firest clinical trial by Peters AL et al was to determine which characteristics of formulas have the greatedst impact on the postprandial glycemic response;is the total amount of carbohydrate,the amount of simple versus complex carbohydrate,or the presence of fiber７? This study evaluated the blood glucose response to each of five commercially available products.As with earlier investigations by these investigators subjexts consumed 20 mL of the assigned formula every 15 minutes over a 4-hour time period.Results shoed the glucose response was significantly lower with Glucerna than with the high-carbohydrate test formulas(graph 3).Moreover,the glucose response for any given formula correlated with the total grams of carbohydrate in the formula,not with its fiber content.These investigators concluded that it is the amount of carbohydrate,versus the type,that appears to have the greatest effect on the glucose response.Also,a low-carbohydrate,high-fat product can produce an attenuated glusose response compared with products with higher carbohydrate content.The Committee to Advance Enteral Nutrition Therapy in Diabetes(CAENTD)represents a group of interntional experts dedicated to improving the quality of care for patients with diabetes who require enteral nutrition support through the development and implementation of a set of consensus guidelines.This group,along with other physicians,scientists and health care professionals,convened a symposium in March 1998 entitled“the Consensus Roundtable on Nutrition Support of Tube-Fed Ptients with Dabetes”.It was agreed that to achieve optimal plasma glucose and lipid levels,modifed enteral formulas that reflect current diabetes nutrition recommendations and provide for optimal postprandial glucose and lipid levels should be used.Replacing a portion of calories provided by carbohydrate with calories from fat sources high in monounsaturated fatty acids is an effective way to meet these objectives ofr patients with abnormal glucose tolerance. ……     

The effects of diet differing in fat, carbohydrate, and fiber on carbohydrate and lipid metabolism in type II diabetes

This study was designed to determine the effects of varying the proportions of carbohydrate, fiber, and fat on metabolic control in Type II diabetes. Ten men, aged 50 to 69 years, with Type II diabetes participated. Four isocaloric diets were consumed for 2 weeks each, with a break of 6 to 14 weeks between diets to ensure no carryover effects. Two of the diets were high in carbohydrate (63% to 65% energy) and low in fat (10% to 12% energy) but differed in their fiber contents (20 vs. 45 gm/day). The other two diets were low in carbohydrate (23% to 27% energy) with either a low or a high fat content (15% vs. 55% energy) and a high or normal protein content (62% vs. 18% energy). The composition of the subjects' usual diets in the week before each of the experimental diets did not vary significantly: carbohydrate 47% to 50% energy, protein 22% to 25% energy, fat 27% to 31% energy, and fiber 24 to 25 gm/day. A 75-gm oral glucose tolerance test and a 12-hour metabolic profile in response to 3 meals typical of the particular diet were conducted before and at the conclusion of each 2-week dietary period. The most significant improvements in metabolic control (as assessed by the effects of the diets on fasting glucose and on lipids, and on the glucose and insulin responses to oral glucose and the mixed meals) were obtained with the high-fiber, high-carbohydrate, low-fat diet and with the low-carbohydrate, high-protein, low-fat diet. Metabolic control was not significantly affected by the low-fiber, high-carbohydrate, low-fat diet, but it deteriorated significantly on the low-carbohydrate, high-fat diet. The results of this study confirmed the importance of high fiber and low fat in improving metabolic control in Type II diabetes. In conclusion, if high-carbohydrate, low-fat diets are to be recommended to patients with diabetes, it is essential that the type of carbohydrate recommended be unrefined and high in fiber.     

Strategies for healthy weight loss: from vitamin C to the glycemic response

America is experiencing a major obesity epidemic. The ramifications of this epidemic are immense since obesity is associated with chronic metabolic abnormalities such as insulin resistance, dyslipidemia, and heart disease. Reduced physical activity and/or increased energy intakes are important factors in this epidemic. Additionally, a genetic susceptibility to obesity is associated with gene polymorphisms affecting biochemical pathways that regulate fat oxidation, energy expenditure, or energy intake. However, these pathways are also impacted by specific foods and nutrients. Vitamin C status is inversely related to body mass. Individuals with adequate vitamin C status oxidize 30% more fat during a moderate exercise bout than individuals with low vitamin C status; thus, vitamin C depleted individuals may be more resistant to fat mass loss. Food choices can impact post-meal satiety and hunger. High-protein foods promote postprandial thermogenesis and greater satiety as compared to high-carbohydrate, low-fat foods; thus, diet regimens high in protein foods may improve diet compliance and diet effectiveness. Vinegar and peanut ingestion can reduce the glycemic effect of a meal, a phenomenon that has been related to satiety and reduced food consumption. Thus, the effectiveness of regular exercise and a prudent diet for weight loss may be enhanced by attention to specific diet details.     

Separate effects of reduced carbohydrate intake and weight loss on atherogenic dyslipidemia

BACKGROUND: Low-carbohydrate diets have been used to manage obesity and its metabolic consequences. OBJECTIVE: The objective was to study the effects of moderate carbohydrate restriction on atherogenic dyslipidemia before and after weight loss and in conjunction with a low or high dietary saturated fat intake. DESIGN: After 1 wk of consuming a basal diet, 178 men with a mean body mass index (in kg/m(2)) of 29.2 +/- 2.0 were randomly assigned to consume diets with carbohydrate contents of 54% (basal diet), 39%, or 26% of energy and with a low saturated fat content (7-9% of energy); a fourth group consumed a diet with 26% of energy as carbohydrate and 15% as saturated fat. After 3 wk, the mean weight loss (5.12 +/- 1.83 kg) was induced in all diet groups by a reduction of approximately 1000 kcal/d for 5 wk followed by 4 wk of weight stabilization. RESULTS: The 26%-carbohydrate, low-saturated-fat diet reduced triacylglycerol, apolipoprotein B, small LDL mass, and total:HDL cholesterol and increased LDL peak diameter. These changes were significantly different from those with the 54%-carbohydrate diet. After subsequent weight loss, the changes in all these variables were significantly greater and the reduction in LDL cholesterol was significantly greater with the 54%-carbohydrate diet than with the 26%-carbohydrate diet. With the 26%-carbohydrate diet, lipoprotein changes with the higher saturated fat intakes were not significantly different from those with the lower saturated fat intakes, except for LDL cholesterol, which decreased less with the higher saturated fat intake because of an increase in mass of large LDL. CONCLUSIONS: Moderate carbohydrate restriction and weight loss provide equivalent but nonadditive approaches to improving atherogenic dyslipidemia. Moreover, beneficial lipid changes resulting from a reduced carbohydrate intake were not significant after weight loss.     

A soybean peptide isolate diet promotes postprandial carbohydrate oxidation and energy expenditure in type II diabetic mice

The aim of the present study was to determine the effects of dietary proteins on the oxidation of dietary carbohydrate and lipids in type II diabetic mice. KK-A(y) strain mice were provided free access to a high fat diet (30% of energy as fat) for an initial 4-wk period to induce diabetes. To reduce body weight gain, the mice were subsequently fed restrictive isoenergetic and isonitrogenous diets (35% of energy as protein and 5% as fat) based on either casein or soy protein isolate hydrolysate (SPI-H) for 4 wk. To measure exogenous carbohydrate and lipid oxidation, the mice were fed a diet containing (13)C-glucose or (13)C-triolein while they were in a respiratory chamber for 72 h. Postprandial energy expenditure was higher in the SPI-H than in the casein group; this difference was due to an increase in postprandial exogenous and endogenous carbohydrate oxidation. There were no differences in 24-h energy expenditure between dietary groups. Oxidation of exogenous carbohydrate tended to be higher (P = 0.054) in the SPI-H group during the 24 h of measurement. Fecal excretion of (13)C-glucose was lower but the excretion of lipid was higher in mice fed the SPI-H diet than in casein-fed mice. These results indicate that in type II diabetic mice, dietary SPI-H not only inhibits the absorption of dietary lipids and increases the absorption of dietary carbohydrates but also augments postprandial energy expenditure, which is accompanied by a postprandial increase in oxidation of dietary carbohydrates.     

An isoenergetic very low carbohydrate diet improves serum HDL cholesterol and triacylglycerol concentrations,the total cholesterol to HDL cholesterol ratio and postprandial pipemic responses compared with a low fat diet in normal weight,normolipidemic women

Very low carbohydrate diets are popular, yet little is known about their effects on blood lipids and other cardiovascular disease risk factors. We reported previously that a very low carbohydrate diet favorably affected fasting and postprandial triacylglycerols, LDL subclasses and HDL cholesterol (HDL-C) in men but the effects in women are unclear. We compared the effects of a very low carbohydrate and a low fat diet on fasting lipids, postprandial lipemia and markers of inflammation in women. We conducted a balanced, randomized, two-period, crossover study in 10 healthy normolipidemic women who consumed both a low fat (<30% fat) and a very low carbohydrate (<10% carbohydrate) diet for 4 wk each. Two blood draws were performed on separate days at 0, 2 and 4 wk and an oral fat tolerance test was performed at baseline and after each diet period. Compared with the low fat diet, the very low carbohydrate diet increased (P 相似文献   

The 'carnivore connection'--evolutionary aspects of insulin resistance

Insulin resistance is common and is determined by physiological (aging, physical fitness), pathological (obesity) and genetic factors. The metabolic compensatory response to insulin resistance is hyperinsulinaemia, the primary purpose of which is to maintain normal glucose tolerance. The 'carnivore connection' postulates a critical role for the quantity of dietary protein and carbohydrate and the change in the glycaemic index of dietary carbohydrate in the evolution of insulin resistance and hyperinsulinaemia. Insulin resistance offered survival and reproductive advantages during the Ice Ages which dominated human evolution, during which a high-protein low-carbohydrate diet was consumed. Following the end of the last Ice Age and the advent of agriculture, dietary carbohydrate increased. Although this resulted in a sharp increase in the quantity of carbohydrate consumed, these traditional carbohydrate foods had a low glycaemic index and produced only modest increases in plasma insulin. The industrial revolution changed the quality of dietary carbohydrate. The milling of cereals made starch more digestible and postprandial glycaemic and insulin responses increased 2-3 fold compared with coarsely ground flour or whole grains. This combination of insulin resistance and hyperinsulinaemia is a common feature of many modern day diseases. Over the last 50 y the explosion of convenience and takeaway 'fast foods' has exposed most populations to caloric intakes far in excess of daily energy requirements and the resulting obesity has been a major factor in increasing the prevalence of insulin resistance.     

The role of carbohydrates in insulin resistance

Insulin resistance is a metabolic disorder that is increasing worldwide and is associated with some of the most common diseases affecting modern societies including diabetes, hypertension, obesity and coronary heart disease. Although pharmacologic approaches to managing insulin resistance are being advocated by some, public health approaches involving changes in diet and physical activity are attractive because of their lower cost and risk. We briefly summarize some new information on the mechanisms that mediate insulin's many biological actions and examine the effects of dietary carbohydrates on insulin sensitivity. Specifically, we summarize some of the information available on the effects of simple sugars, complex carbohydrates including fiber, slowly digested starch and the general concept of glycemic index. The available data support the idea that consumption of diets high in total carbohydrate does not adversely affect insulin sensitivity compared with high fat diets. Animal data suggest that simple sugars, in particular fructose, have adverse effects on insulin action, but adverse effects have not been shown conclusively in humans. Increased intake of dietary fiber appears to improve insulin action and may protect against the development of diabetes. The effects of diets with high or low glycemic index on insulin action are controversial at this time. For firm conclusions to be reached, future studies must be of reasonable duration, be in defined populations and compare the effects of relevant doses of nutrients on specific endpoints of insulin action.     

Changes in fat synthesis influenced by dietary macronutrient content

DE NOVO: lipogenesis is the biological process by which C2 precursors of acetyl-CoA are synthesized into fatty acids. In human subjects consuming diets higher in fat (> 30 % energy), lipogenesis is down regulated and extremely low; typically < 10 % of the fatty acids secreted by the liver. This percentage will increase when dietary fat is reduced and replaced by carbohydrate, although the extent of carbohydrate-induced lipogenesis is dependent on the type of carbohydrate (monosaccharide v. polysaccharide) and the form in which the carbohydrate is fed (liquid meals, solid less-processed food). Clearly, massive overconsumption of carbohydrate can also increase lipogenesis. A second related phenomenon that occurs when dietary fat is reduced is hypertriacylglycerolaemia. This rise in blood triacylglycerol concentration could be due to increased de novo lipogenesis or to reduced clearance of lipid from the blood. The present paper will review the metabolic mechanisms leading to the elevations in blood triacylglycerol concentration that occur with dietary fat reduction. Studies considered will be those investigating fatty acid synthesis in subjects chronically fed low-fat high-carbohydrate diets and studies in which data were obtained in both the fasted and fed states. Also summarized will be data from subjects who had consumed diets of different carbohydrate types, as well as the most recent data from postprandial studies investigating factors that affect the magnitude of the rise in blood lipids following a meal. Given the changing availability of carbohydrate in the food supply, it will be important to understand how the balance of fat and carbohydrate in the diet influences lipogenesis, and the relative contribution of the process of de novo lipogenesis to the escalating incidence of obesity observed around the world.     

Protein in optimal health: heart disease and type 2 diabetes

Diets with increased protein and reduced carbohydrates have been shown to improve body composition, lipid and lipoprotein profiles, and glycemic regulations associated with treatment of obesity and weight loss. Derived from these outcomes, high-protein, low-carbohydrate diets are also being examined for treatment of heart disease, metabolic syndrome, and type 2 diabetes. High-protein, low-carbohydrate diets have been found to have positive effects on reducing risk factors for heart disease, including reducing serum triacylglycerol, increasing HDL cholesterol, increasing LDL particle size, and reducing blood pressure. These diets appear particularly attractive for use with individuals exhibiting the atherogenic dyslipidemia of metabolic syndrome. High-protein, low-carbohydrate diets have also been investigated for treatment of type 2 diabetes with positive effects on glycemic regulation, including reducing fasting blood glucose, postprandial glucose and insulin responses, and the percentage of glycated hemoglobin. Specific effects of increasing protein compared with reducing carbohydrates have not been extensively investigated. Additional research is needed to determine specific levels of protein, carbohydrate, and fat for optimum health of individuals who differ in age, physical activity, and metabolic phenotypes.     

Strategies for Healthy Weight Loss: From Vitamin C to the Glycemic Response

Abstract America is experiencing a major obesity epidemic. The ramifications of this epidemic are immense since obesity is associated with chronic metabolic abnormalities such as insulin resistance, dyslipidemia, and heart disease. Reduced physical activity and/or increased energy intakes are important factors in this epidemic. Additionally, a genetic susceptibility to obesity is associated with gene polymorphisms affecting biochemical pathways that regulate fat oxidation, energy expenditure, or energy intake. However, these pathways are also impacted by specific foods and nutrients. Vitamin C status is inversely related to body mass. Individuals with adequate vitamin C status oxidize 30% more fat during a moderate exercise bout than individuals with low vitamin C status; thus, vitamin C depleted individuals may be more resistant to fat mass loss. Food choices can impact post-meal satiety and hunger. High-protein foods promote postprandial thermogenesis and greater satiety as compared to high-carbohydrate, low-fat foods; thus, diet regimens high in protein foods may improve diet compliance and diet effectiveness. Vinegar and peanut ingestion can reduce the glycemic effect of a meal, a phenomenon that has been related to satiety and reduced food consumption. Thus, the effectiveness of regular exercise and a prudent diet for weight loss may be enhanced by attention to specific diet details.