Carbohydrates, fat, and insulin action

Systematic Investigation of Ginkgo Biloba Leaves for Treating Cardio-cerebrovascular Diseases in an Animal Model

Globally, cardio-cerebrovascular diseases (CCVDs) are the leading cause of death, and thus the development of novel strategies for preventing and treating such diseases is in urgent need. Traditional Chinese medicine (TCM), used for thousands of years in Asia and other regions, has been proven effective in certain disorders. As a long-time medicinal herb in TCM, Ginkgo biloba leaves (GBLs), have been widely used to treat various diseases including CCVDs. However, the underlying molecular mechanisms of medicinal herbs in treating these diseases are still unclear. Presently, by incorporating pharmacokinetic prescreening, target fishing, and network analysis, an innovative systems-pharmacology platform was introduced to systematically decipher the pharmacological mechanism of action of GBLs for the treatment of CCVDs. The results show that GBLs exhibit a protective effect on CCVDs probably through regulating multiple pathways and hitting on multiple targets involved in several biological pathways. Our work successfully explains the mechanism of efficiency of GBLs for treating CCVDs and, meanwhile, demonstrates that GDJ, an injection generated from GBLs, could be used as a preventive or therapeutic agent in cerebral ischemia. The approach developed in this work offers a new paradigm for systematically understanding the action mechanisms of herb medicine, which will promote the development and application of TCM.

Body weight regulation and obesity: dietary strategies to improve the metabolic profile

This review discusses dietary strategies that may improve the metabolic profile and body weight regulation in obesity. Recent evidence demonstrated that long-term health effects seem to be more beneficial for low-glycemic index (GI) diets compared to high-protein diets. Still, these results need to be confirmed by other prospective cohort studies and long-term clinical trials, and the discrepancy between these study designs needs to be explored in more detail. Furthermore, the current literature is mixed with regard to the efficacy of increased meal frequency (or snacking) regimens in causing metabolic alterations, particularly in relation to body weight control. In conclusion, a growing body of evidence suggests that dietary strategies with the aim to reduce postprandial insulin response and increase fat oxidation, and that tend to restore metabolic flexibility, have a place in the prevention and treatment of obesity and associated metabolic disorders.

The effects of diet on circulating sex hormone levels in men

There is considerable epidemiological evidence that a Western-style diet may increase the risk of certain hormone-dependent conditions in men via its effects on hormone metabolism. Experimental evidence also suggests that dietary factors may exert subtle effects on hormone metabolism. Here we review the clinical and epidemiological evidence that diet is associated with circulating sex hormone levels in men. In comparison with factors such as age and BMI, nutrients do not appear to be strong determinants of sex hormone levels. Dietary intervention studies have not shown that a change in dietary fat and/or dietary fibre intake is associated with changes in circulating sex hormone concentrations over the short term. The data on the effects of dietary phyto-oestrogens on sex hormone levels in men are too limited for conclusions to be drawn. Observational studies between men from different dietary groups have shown that a vegan diet is associated with small but significant increases in sex-hormone-binding globulin and testosterone concentrations in comparison with meat-eaters. However, these studies have not demonstrated that variations in dietary composition have any long-term important effects on circulating bioavailable sex hormone levels in men. This lack of effect may be partly explained by the body's negative feedback mechanism, which balances out small changes in androgen metabolism in order to maintain a constant level of circulating bioavailable androgens. It appears, therefore, that future studies should look for dietary effects on the feedback mechanism itself, or on the metabolism of androgens within the target tissues.

Functional foods for dyslipidaemia and cardiovascular risk prevention

A food can be regarded as ‘functional’ if it can demonstrate a beneficial efficacy on one or more target functions in the body in a convincing way. Beyond adequate nutritional qualities, functional foods should either improve the state of health and wellbeing and/or reduce the risk of disease. Functional foods that are marketed with claims of heart disease reduction focus primarily on the major risk factors, i.e. cholesterol, diabetes and hypertension. Some of the most innovative products are designed to be enriched with ‘protective’ ingredients, believed to reduce risk. They may contain, for example, soluble fibre (from oat and psyllium), useful both for lowering cholesterol and blood pressure, or fructans, effective in diabetes. Phytosterols and stanols lower LDL-cholesterol in a dose-dependent manner. Soya protein is more hypocholesterolaemic in subjects with very high initial cholesterol and recent data indicate also favourable activities in the metabolic syndrome.n-3 Fatty acids appear to exert significant hypotriacylglycerolaemic effects, possibly partly responsible for their preventive activity. Dark chocolate is gaining much attention for its multifunctional activities, useful both for the prevention of dyslipidaemia as well as hypertension. Finally, consensus opinions about tea and coffee have not emerged yet, and the benefits of vitamin E, garlic, fenugreek and policosanols in the management of dyslipidaemia and prevention of arterial disease are still controversial.

Pathophysiology and aetiology of impaired fasting glycaemia and impaired glucose tolerance: does it matter for prevention and treatment of type 2 diabetes?

Prior to the development of type 2 diabetes, glucose levels increase into the prediabetic states of isolated impaired fasting glycaemia (i-IFG), isolated impaired glucose tolerance (i-IGT), or combined IFG/IGT. A better understanding of the aetiology and pathophysiology of the prediabetic states might give a basis for the development of individualised prevention and treatment strategies for type 2 diabetes. Several studies have examined mechanisms and potential aetiological factors leading to the development of the different prediabetic states. The pathophysiology of i-IFG seems to include the following key defects: reduced hepatic insulin sensitivity, stationary beta cell dysfunction and/or chronic low beta cell mass, altered glucagon-like peptide-1 secretion and inappropriately elevated glucagon secretion. Conversely, the prediabetic state i-IGT is characterised by reduced peripheral insulin sensitivity, near-normal hepatic insulin sensitivity, progressive loss of beta cell function, reduced secretion of glucose-dependent insulinotropic polypeptide and inappropriately elevated glucagon secretion. Individuals developing combined IFG/IGT exhibit severe defects in both peripheral and hepatic insulin sensitivity as well as a progressive loss of beta cell function. The aetiologies of i-IFG and i-IGT also seem to differ, with i-IFG being predominantly related to genetic factors, smoking and male sex, while i-IGT is predominantly related to physical inactivity, unhealthy diet and short stature. Since the transition from the prediabetic states to overt type 2 diabetes is characterised by a non-reversible vicious cycle that includes severe deleterious effects on glucose metabolism, there are good reasons to use the well-established aetiological and pathophysiological differences in i-IFG, i-IGT and IFG/IGT to design individualised preventive strategies.

Transcriptome profiling analysis reveals multiple modulatory effects of Ginkgo biloba extract in the liver of rats on a high-fat diet

Leaf extract of Ginkgo biloba (GBE) is increasingly used as a herbal medicine for the treatment of neurodegenerative, cardiovascular and cerebrovascular diseases. Several studies have demonstrated many protective effects of GBE in neurons, the endothelium and liver. In this study, we investigated the molecular mechanisms underlying the effects of GBE in disorders induced by long-term exposure to a high-fat diet (HFD). Rats were fed an HFD with or without the GBE product GBE50 for 19 weeks. We found that GBE50 reduced the development of fatty liver induced by an HFD and inhibited the commonly observed elevation of serum cholesterol and lactate dehydrogenase levels. Transcriptome profiling analysis showed that several genes were modulated by GBE50 in liver, including those involved in lipid metabolism, carbohydrate metabolism, vascular constriction, ion transportation, neuronal systems and drug metabolism. Notably, a number of genes coding for proteins involved in cholesterol metabolism were repressed, and some were upregulated. Fatty acid biosynthesis appeared to be repressed, whereas fatty acid metabolism appeared to be enhanced. In conclusion, using transcriptome profiling analysis, we demonstrated the molecular basis for the pleiotropic effects of GBE50, particularly those involved in lipid metabolism. This study provided new clues for further pharmacological study of GBEs.

Effects of high- and low-fat meals on the diurnal response of plasma lipid metabolite concentrations in healthy middle-aged volunteers

Three experiments were conducted in healthy middle-aged volunteers (six males and six females in Expt 1, six males and two females in Expt 2 and twelve males in Expt 3) with a mean BMI of 27 kg/m2to determine whether there is a difference between morning and afternoon dietary fat clearance and utilization, and to determine in what way the fat and starch contents of the meal influence postprandial blood lipid metabolites over 4·5 h. Over 4 days in Expt 1 each subject received isoenergetic, high-carbohydrate (L, 5·5 g mixed fat/meal) and moderately high-fat (M, 33 g mixed fat/meal) breakfasts and lunches, in three combinations (LL, MM, LM), or they fasted at breakfast time and received a high fat lunch (NM) in a randomized and balanced arrangement. Each evening a standard meal was given. The following effects were significant (P<0·05): plasma triacylglycerol (TAG) responses were greater following M meals; plasma TAG concentrations were greater in the afternoon than in the morning, following two meals of the same composition, although the postprandial incremental response was less following lunch than following breakfast and peak responses were reached much earlier than after breakfast; a low-fat breakfast, or fasting at breakfast time, delayed the peak TAG response to a M lunch. The plasma concentrations of non-esterified fatty acids (NEFA) and of free glycerol were higher in the afternoon following M meals at breakfast and lunch, especially in males. This response was reduced, by the L breakfast preceding the M lunch. Two M meals in succession lowered plasma HDL-cholesterol concentration. In Expt 2 each subject received a very low-fat (VL) breakfast, followed by a lunch of the same composition. Each of these meals was followed, 110 min from the start of eating, by an infusion of Intralipid 10% emulsion at the rate of 1 ml/kg body weight over 60 s. Clearance rates of Intralipid were faster in the afternoon than in the morning (P= 0·024). In Expt 3 twelve subjects were randomly allocated to either treatment MM or LM meal patterns, as given in Expt 1. These were given daily for a period of 17 d, during which the change in fasting plasma TAG concentration was similar in both treatments. On days 1, 16 and 17 responses were measured to the M lunch and to a glucose tolerance test (GTT), conducted 2 h 17 min after lunch. The post-lunch responses confirmed those found in Expt 1; but immediately following the glucose dose there was an abrupt increase in plasma TAG that was greater in treatment LM than in treatment MM (P= 0·025), whereas plasma NEFA concentration decreased rapidly in both treatments at that time (P = 0·00066)

Diet, obesity and diabetes: a current update

The prevalence of obesity has been increasing at a rapid rate over the last few decades. Although the primary defect can be attributed to an imbalance of energy intake over energy expenditure, the regulation of energy balance is now recognized to be complex. Adipose-tissue factors play a central role in the control of energy balance and whole-body fuel homoeostasis. The regulation of adipose-tissue function, in particular its secretion of adipokines, is impaired by increases in adipose mass associated with obesity, and with the development of insulin resistance and Type 2 diabetes. This review analyses adipose-regulated energy input and expenditure, together with the impact of dietary macronutrient composition on energy balance in relation to susceptibility to the development of obesity and Type 2 diabetes, and how these metabolic conditions may be exacerbated by the consequences of abnormal adipose function. By gaining a greater understanding of how energy balance is controlled in normal, and in obese and diabetic states, a more practical approach can be employed to prevent and better treat obesity and metabolic disorders.

Long-term intake of dietary fiber and decreased risk of cholecystectomy in women

BACKGROUND

Epidemiologic studies on the relationship between dietary fiber and gallstone disease are inconclusive, and the effects of different types of dietary fiber are not clear.

METHODS

We examined the association between long-term intake of dietary fiber as well as fiber from different sources and risk of cholecystectomy in a cohort of 69,778 women who were aged from 35 to 61 years in 1984 and had no history of gallstone disease. As part of the Nurses' Health Study, the women reported on questionnaires mailed to them every two years both their fiber intake and whether they had undergone cholecystectomy.

RESULTS

During 16 yr of follow-up, we documented 5,771 cases of cholecystectomy. After adjusting for age and other known or suspected risk factors in a multivariate model, compared with women in the lowest quintile of total dietary fiber intake, the relative risk of choleystectomy for those in the highest quintile was 0.87 (95% CI, 0.78-0.96, p for trend = 0.005). For a 5-g increase in total fiber intake, the multivariate relative risk was 0.94 (95% CI, 0.90-0.98). Insoluble fiber, taking soluble fiber into account in the multivariate model, was significantly associated with a reduced risk. The multivariate relative risk was 0.83 (95% CI, 0.73-0.94, p for trend = 0.009) for insoluble fiber, and was 1.01 (95% CI, 0.89-1.15, p for trend = 0.9) for soluble fiber, when extreme quintiles were compared. For a 5-g increase in intake, the relative risk was 0.90 (95% CI, 0.84-0.97) for insoluble fiber, and was 1.01 (95% CI, 0.83-1.23) for soluble fiber.

CONCLUSIONS

Our results suggest that increased long-term consumption of dietary fiber, particularly insoluble fiber, can reduce risk of cholecystectomy in women.

Sugars, energy metabolism, and body weight control

Obesity represents a major threat to health and quality of life. Although obesity has strong genetic determinants, it is generally accepted that it results from an imbalance between food intake and daily physical activity. Health guidelines have been focused on 3 particular lifestyle factors: increased levels of physical activity and reductions in the intakes of fat and sugars. The dietary guidelines, especially, are under debate. This review covers evidence from carefully controlled laboratory studies, clinical trials, studies in populations at high risk of developing obesity, and epidemiologic studies on the role of sugars, particularly sucrose, in the development of obesity. Although many environmental factors promote a positive energy balance, it is clear that the consumption of a low-carbohydrate, high-fat diet increases the likelihood of weight gain. The evidence related to carbohydrate, particularly sugars, and the type of food (solid or liquid) is less clear because the number of long-term ad libitum dietary intervention trials is very small. Data on sucrose intake in relation to metabolism and weight gain do not associate high consumption of sucrose with the prevalence of obesity. The evidence supports the current dietary guidelines for reducing fat intake. However, the effect of the carbohydrate source and class and of the form in which carbohydrate is consumed (solid or liquid) on body weight control requires further consideration.

Physiological validation of the concept of glycemic load in lean young adults

Dietary glycemic load, the mathematical product of the glycemic index (GI) of a food and its carbohydrate content, has been proposed as an indicator of the glucose response and insulin demand induced by a serving of food. To validate this concept in vivo, we tested the hypotheses that 1). portions of different foods with the same glycemic load produce similar glycemic responses; and 2). stepwise increases in glycemic load for a range of foods produce proportional increases in glycemia and insulinemia. In the first study, 10 healthy subjects consumed 10 different foods in random order in amounts calculated to have the same glycemic load as one slice of white bread. Capillary blood samples were taken at regular intervals over the next 2 h. The glycemic response as determined by area under the curve was not different from that of white bread for nine foods. However, lentils produced lower than predicted responses (P < 0.05). In the second study, another group of subjects was tested to determine the effects of increasing glycemic load using a balanced 5 x 5 Greco-Latin square design balanced for four variables: subject, dose, food and order. Two sets of five foods were consumed at five different glycemic loads (doses) equivalent to one, two, three, four and six slices of bread. Stepwise increases in glycemic load produced significant and predictable increases in both glycemia (P < 0.001) and insulinemia (P < 0.001). These findings support the concept of dietary glycemic load as a measure of overall glycemic response and insulin demand.

Maternal carbohydrate intake and pregnancy outcome

Experimental evidence indicates that the primary maternal environmental factor that regulates feto-placental growth is substrate delivery to the placental site, which is the product of maternal substrate levels and the rate of placental-bed blood flow. Thus, maternal factors which change either substrate level or flow alter feto-placental growth rate. The best-studied substrate in human pregnancy is glucose, and there is a direct relationship between maternal blood glucose levels and size at birth. Altering the type of carbohydrate eaten (high- v. low-glycaemic sources) changes postprandial glucose and insulin responses in both pregnant and non-pregnant women, and a consistent change in the type of carbohydrate eaten during pregnancy influences both the rate of feto-placental growth and maternal weight gain. Eating primarily high-glycaemic carbohydrate results in feto-placental overgrowth and excessive maternal weight gain, while intake of low-glycaemic carbohydrate produces infants with birth weights between the 25th and the 50th percentile and normal maternal weight gain. The calculated difference in energy retention with similar total energy intakes is of the order of 80,000 kJ. Preliminary information from subsequent metabolic studies indicates that the mechanisms involved include changes in: daily digestible energy requirements (i.e. metabolic efficiency), substrate utilization (glucose oxidation v. lipid oxidation), and insulin resistance and sensitivity. Thus, altering the source of maternal dietary carbohydrate may prove to be a valuable tool in the management of pregnancies at risk for anomalous feto-placental growth and for the prevention and/or treatment of obesity and insulin resistance in the non-pregnant state.

Risk of breast cancer in relation to anthropometry, blood pressure, blood lipids and glucose metabolism: a prospective study within the Malmö Preventive Project

Insulin resistance may be a risk factor for breast cancer, possibly through increased levels of oestrogens or insulin-like growth factor I. Insulin resistance has been associated with obesity, hypertension, dyslipidaemia and impaired glucose tolerance. We studied the relation of these factors to breast cancer risk in a prospective cohort study of 9738 women. Menopausal status was defined a priori, and 112 cases of invasive breast carcinoma occurred in women who were premenopausal at baseline and 157 cases in subjects who were peri/postmenopausal. Relative risks (RR) for breast cancer were calculated by Cox's proportional hazards analysis for different quartiles of height, weight, body mass index, blood pressure, pulse rate and serum levels of total cholesterol, triglycerides, fasting blood glucose and glucose at 120 min after an oral dose of glucose. Peri/postmenopausal women had a significantly increased age-adjusted relative risk of breast cancer associated with height (RR = 1.78 for the highest versus lowest quartile), and the RR was increased over quartiles of cholesterol levels (P-value for trend: 0.05). No other significant associations were found. Adjustments for potential confounding factors or restriction of the analysis to cases and person-years before 55 years of age (premenopausal women), or after 55 years (peri/postmenopausal women), did not change

Susceptibility of lean and obese Zucker rats to tumorigenesis induced by N-methyl-N-nitrosourea

To address the possible involvement of hyperinsulinemia in breast cancer development, we have examined the susceptibility of lean and obese Zucker rats to N-methyl-N-nitrosourea (MNU)-induced mammary cancer. Fifty-day-old female lean or obese Zucker rats received intraperitoneal (i.p.) injections of 37.5 or 20 mg/kg MNU, respectively. We showed in separate experiments that these doses produce similar levels of DNA methylation in the mammary epithelial cells of the lean and obese animals. Over the course of 29 weeks following MNU treatment, half of the lean rats developed carcinomas of the mammary gland, demonstrating that they are of intermediate susceptibility to mammary tumorigenesis. During this period, the obese rats developed hyperinsulinemia and insulin resistance as expected. Although palpable tumors developed at a similar rate in the lean and obese rats, only 10% of the obese animals developed mammary carcinomas. The obese rats, however, developed a high incidence (63.3%) of epidermal cysts that occurred mainly in the region of the mammary glands. A 13.3% incidence of colon carcinomas was also found in the obese rats. These results suggest that the development of hyperinsulinemia does not render the obese Zucker rats more susceptible to mammary gland carcinogenesis. Our observation of colon carcinomas in obese, but not lean rats, however, is consistent with evidence that hyperinsulinemia promotes colon cancer in rodents and humans.

Relations of insulin resistance and serum concentrations of estradiol and sex hormone-binding globulin to potential breast cancer risk factors

There is a hypothesis that hyperinsulinemia or insulin resistance may be a mediator for breast cancer risk factors. On the other hand, some, but not all, of the well-known risk factors of breast cancer have been associated with serum estrogen concentrations. We assessed the relationships of potential breast cancer risk factors to indicators of insulin resistance, fasting plasma insulin concentration and homeostasis model assessment insulin resistance (HOMA-R), in 88 postmenopausal Japanese women. We also examined whether insulin resistance would explain the association of breast cancer risk factors with serum estradiol and sex hormone-binding globulin (SHBG). Information on potential breast cancer risk factors, such as demographic characteristics, smoking and drinking habits, diet, exercise, menstrual and reproductive factors, was obtained by self-administered health questionnaire including a validated semiquantitative food frequency questionnaire. Body mass index (BMI) was significantly correlated with the ratio of estradiol to SHBG (Spearman r = 0.30, P = 0.0004), fasting plasma insulin (r = 0.45) and HOMA-R (r = 0.43, P = 0.0001) after controlling for age. The correlations were still significant between BMI and estradiol / SHBG ratio (r = 0.21, P = 0.047) after controlling for fasting plasma insulin and between BMI and fasting plasma insulin (r = 0.40, P = 0. 0001) as well as HOMA-R (r = 0.38, P = 0.0003) after controlling for estradiol / SHBG ratio. There is a possibility that effect of BMI on breast cancer risk is mediated by both insulin resistance and estrogen metabolism.

Effects of dietary restriction on insulin resistance in obese mice

In many cases, development of insulin resistance has been linked to obesity and may contribute to mechanism of aging. The role of diet, irrespective of degree of obesity, in modulating insulin resistance and development of age degeneration disease remains uncertain. Lowered blood glucose levels are commonly associated with diet restriction (DR), which is an intervention shown to successfully retard aging and age associated disease. The effects of DR on blood glucose and insulin resistance were measured in yellow obese (A(vy)/A), lean black (a/a) mice and in another common inbred strain (B6C3F1) (at three different ages). The yellow obese mice become diabetic as a result of an insulin receptor defect which is not clearly understood. Insulin responses and radioinsulin binding were assayed in yellow obese and lean black mice fed either ad libitum (AL) or DR diets (YAL, BAL, YDR and YAL, respectively) at four different circadian intervals. The B6C3F1 controls were fed either AL (CAL) or DR (CDR) and measures were made at six circadian stages and three different ages. Within 23 days, DR produced a significant loss in body weight and a time-dependent 22-55% reduction in basal blood glucose levels in the yellow obese mice. Additionally, exogenous insulin produced circadian stage dependent (at the time of food intake) reductions in blood glucose in the YDR animals that were not present in YAL animals. (125)I-Insulin binding in liver was increased nearly 2-fold in YDR and BDR mice during the time of day that animals were active and eating. (125)I-Insulin binding was two-fold-higher in CDR mice at 4, 12 and >24 months of age. Binding decreased as a function of age in both the CAL and CDR animals. However, even in the >24 month group the CDR animals were found to have levels of binding that were as high as those found in younger CAL liver. The mechanism of action appears to be through resolution of insulin resistance by modulating an insulin receptor defect.

Effects of insoluble and soluble dietary fiber on glycemic control in dogs with naturally occurring insulin-dependent diabetes mellitus

OBJECTIVE

To evaluate the effects of diets differing in type and quantity of fiber on glycemic control in dogs with naturally occurring insulin-dependent diabetes mellitus.

DESIGN

Prospective randomized crossover controlled trial.

ANIMALS

7 dogs with well-regulated naturally occurring insulin-dependent diabetes mellitus.

PROCEDURE

Dogs were fed 1 of 3 diets for 1 month each in 1 of 6 randomized diet sequences. Diets included a low-fiber diet (LF) and 2 high-fiber diets; 1 contained only insoluble fiber (HIF), and 1 contained soluble fiber in addition to insoluble fiber (HSF). Caloric intake was unchanged throughout the study. Glycemic control was assessed after each feeding trial by measuring serum fructosamine concentration and performing 5 serial measurements of blood glucose concentration every 2 hours after the morning feeding and insulin injection.

RESULTS

Significant differences were not detected in body weight, required insulin dosage, or albumin concentration among dogs fed the HIF, HSF, and LF diets. Mean and maximum blood glucose concentrations and area under the blood glucose curve were significantly lower in dogs fed the HIF diet, compared with values in the same dogs fed the HSF or LF diet. Fructosamine concentration was significantly lower in dogs fed the HIF or HSF diet, compared with values in the same dogs fed the LF diet.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs with naturally occurring insulin-dependent diabetes mellitus, a dry, high insoluble-fiber diet may aid in glycemic control.

Chromium homeostasis in patients with type II (NIDDM) diabetes

The purpose of this study was to assess chromium handling in non-insulin dependent diabetic patients (NIDDM) compared to healthy volunteers. Chromium handling was evaluated using fasting blood and second morning void urine samples from 93 NIDDM patients and 33 healthy volunteers. Significant differences in chromium homeostasis were seen between patients and controls. NIDDM patients had mean levels of plasma chromium around 33% lower and urine values almost 100% higher than those found in health. Healthy volunteers showed a significant negative correlation between fasting levels of plasma chromium and insulin. This was not evident in NIDDM patients. In the early years of onset of NIDDM, plasma chromium values were inversely correlated with plasma glucose. This was lost in patients with diabetes of more than 2 years duration. We suggest large losses of chromium over many years may exacerbate an already compromised chromium status in NIDDM patients and might contribute to the developing insulin resistance seen in patients with type 2 diabetes.

Breast cancer and the western diet: role of fatty acids and antioxidant vitamins

Epidemiological reports are inconsistent on the association between breast cancer risk and the dietary intake of either individual fatty acids or of antioxidant vitamins. It is postulated here that the inconsistencies are in part due to interactions between the two classes of nutrients at the level of the cell membrane, affecting their potential role in mammary carcinogenesis. In this review, the effects of specific dietary fatty acids and antioxidant vitamins on experimental mammary cancer systems are compared with reported epidemiological associations of the same agents with breast cancer risk in humans. An increased ratio of n-3 to n-6 polyunsaturated fatty acids (PUFAs) in the diet inhibits the growth of the rat mammary cancer model. There is also evidence that members of the n-3 PUFA series can inhibit the growth of human breast cancer cells both in vitro and in explants. Clinical trials of supplementary n-3 PUFAs in conjunction with a reduced fat intake have been proposed for breast cancer prevention. It is postulated that further dietary supplementation with vitamin E and a retinoid is likely to increase the effectiveness of such a diet. A study of this type allows better control of specific dietary components than prospective trials of dietary fat reduction which are presently under evaluation. In particular, it is suggested that studies focusing on a single nutrient often fail to recognise interactions with other nutrients.

Impaired ovulation and breast cancer risk

Conflicting results have been reported on the association between breast cancer risk and symptoms of luteal insufficiency, such as irregular or prolonged menstrual cycles and difficulty in becoming pregnant. Studies on the association between breast cancer risk and hormonal markers of impaired ovulation have also yielded conflicting results. Inadequate allowance for body mass and fat distribution may lead to inconsistent results when assessing the association between luteal insufficiency in premenopausal women and breast cancer risk. Ovulatory function is impaired by obesity, especially if it is predominantly abdominal in distribution. The Western diet and lifestyle favour early manifestation of hyperinsulinaemic insulin resistance in genetically-predisposed women. It is commonly associated with obesity which is predominantly abdominal in distribution. In a subset of premenopausal women, the concomitants of hyperinsulinaemia may impair maturation of ovarian follicles by a direct effect of insulin or insulin-like growth factors on ovarian tissue. Even when women are ovulating regularly, obesity may be associated with luteal insufficiency as shown by decreased levels of progestins or other changes in the sex steroid profile. Insulin resistance is likely to be involved and might explain the weak reduction in breast cancer risk associated with overweight in premenopausal Western women, in contrast with the increased risk widely reported in obese post menopausal women.

Diurnal trends in responses of blood plasma concentrations of glucose, insulin, and C-peptide following high- and low-fat meals and their relation to fat metabolism in healthy middle-aged volunteers

An experiment was conducted in twelve healthy middle-aged volunteers, six of each sex, with a mean BMI of 27 kg/m2 to detect differences between morning and afternoon in postprandial blood glucose, insulin and C-peptide concentrations. These responses were measured following the consumption of isoenergetic meals that were high or low in fat content, at breakfast and at lunch. Over 4 d each subject received the high-carbohydrate (L, 5.5 g mixed fat/meal) and moderately high-fat (M, 33 g mixed fat/meal) breakfasts and lunches, in three combinations (LL, MM, LM), or they fasted at breakfast time and received a moderately high-fat lunch (NM), in three Latin squares. Each evening a standard meal was given. Plasma glucose, insulin and C-peptide responses were greater following L than M meals and within both MM and LL treatments insulin and C-peptide responses were greater following breakfast than following lunch. The incremental C-peptide response to a fatty lunch following a fast at breakfast time (NM) was similar to that to a fatty breakfast, but the incremental insulin response for the same comparison was marginally lower at lunch (P = 0.06). The relationship of C-peptide and insulin concentrations was assessed. Plasma glucose response to a fatty lunch was increased by a fatty breakfast. The relationships of these metabolic events with fat metabolism are discussed.

Selected medical conditions and risk of breast cancer

Several diseases are known or suspected to be associated with altered levels of hormones and growth factors that may influence breast cancer risk. To elucidate this possibility, we studied the relationship between 23 medical conditions or procedures and breast cancer risk by means of data from a multicentric case-control study conducted between 1991 and 1994 in six Italian areas. The study included 2569 histologically confirmed incident cases of breast cancer (median age 55 years, range 23-74 years) and 2588 control women (median age 56 years, range 20-74 years) admitted to the same hospitals as cases for a variety of acute conditions unrelated to known or suspected risk factors for breast cancer. After allowance for education, parity and body mass index, elevated odds ratios (ORs) emerged for history of diabetes mellitus in post-menopausal women (OR = 1.5, 95% CI 1.1-2.0), hypertension in pregnancy (OR = 1.8, 95% CI 1.0-3.4) and breast nodules (OR = 1.3, 95% CI 1.0-1.7). Risk decreases were associated with ovarian ablation for ovarian cysts (OR = 0.5, 95% CI 0.3-0.7) and with thyroid nodules (OR = 0.7, 95% CI 0.5-0.9) but not with the combination of any type of benign thyroid disease. While most examined conditions seemed unrelated to breast cancer risk, the association with late-onset diabetes is of special interest as it suggests a role of hyperinsulinaemia and insulin resistance in breast cancer promotion. It also points to preventive lifestyle modifications.

Nutrition and breast cancer risk: can an effect via insulin resistance be demonstrated?

It is postulated that the metabolic/endocrine concomitants of insulin resistance resulting from high animal fat intake and weight gain after the age of 30 could be contributing to the increasing incidence of postmenopausal breast cancer and recent changes in its biologic characteristics. Case/control studies have shown that hyperinsulinaemia and abdominal obesity, which are recognized as markers of insulin resistance, are risk markers for postmenopausal breast cancer also. Excess weight gain linked to high dietary intake of saturated fat is thought to be a major cause of insulin resistance. The hypothesis is compatible with the "breast tissue age" model for breast cancer risk. Biological evidence suggests that the concomitants of insulin resistance may stimulate growth activity in existing breast cancer also. The hypothesis that nutritional factors which favour hyperinsulinaemia may also favour breast cancer growth can be tested. Restriction of dietary fat and high intake of fibre and complex carbohydrate have been shown to normalise insulin levels in a proportion of subjects with hyperinsulinaemia. Restriction of dietary fat intake has also been shown to reduce bioavailable oestrogen levels in healthy postmenopausal women. A randomised trial of a low fat, high fibre, high complex carbohydrate regimen is proposed as adjuvant treatment following primary surgery in postmenopausal women with early breast cancer. A cancer preventive or delaying ability can be assessed by comparing the incidence of contralateral second breast cancer and the metastasis rate in the diet and control groups. Insulin levels, abdominal obesity, and body mass should be monitored although normalisation of insulin levels need not necessarily involve decrease in body mass.

Physical activity, nutrition, and chronic disease

Epidemiologic, animal, clinical, and metabolic studies demonstrate the independent roles of physical activity and nutrition in the prevention and treatment of several chronic diseases. Fewer data are available to describe the synergistic effects of exercise and diet, and questions remain as to whether and how these two lifestyle factors work together to promote health and prevent disease. This paper briefly reviews many of the known effects of physical activity and nutrition on the prevention and treatment of coronary heart disease, non-insulin-dependent diabetes mellitus, obesity, and osteoporosis as well as how exercise and diet may work together. A discussion of how to increase physical activity levels and how to improve dietary intake also is included. Finally, current exercise and dietary recommendations are summarized, as are directions for future research.

Beneficial effect of a moderately energy-restricted diet on fibrinolytic factors in non-obese men

Impaired fibrinolytic activity has been reported in the elderly and is thought to play a role in the etiology of cardiovascular disease, one of the leading causes of death in most Western countries. Since restriction of energy intake has been demonstrated to act beneficially on the aging process in a variety of species, we studied the effect of a 10-week moderately energy-restricted (ER) regimen (80% of habitual) on plasminogen activator inhibitor (PAI) activity, PAI-1 antigen, tissue plasminogen activator (tPA) activity, and tPA antigen in non-obese, middle-aged men. Moreover, the relationship between these fibrinolytic markers and glucose tolerance was investigated. Weight loss in the ER group (n = 16) was considerable (-7.4 +/- 1.7 kg, P < .001). Subjects in the control group (n = 8) also lost some weight (-2.1 +/- 1.5 kg, P < .01). Fasting glucose levels decreased in the ER group (-0.31 +/- 0.48 mmol/L, P < .05), which was correlated with the extent of weight loss (P < .01). Baseline insulin levels at 2 hours after an oral glucose load correlated with baseline PAI activity (P < .001) and PAI-1 antigen levels (P < .001). PAI activity decreased in the ER group (-2.94 +/- 2.90 IU/mL, P < .001), particularly in subjects with a high baseline PAI activity (> 9 IU/mL). Furthermore, energy restriction led to decreased PAI-1 antigen concentration (P < .05), a nonsignificant increase in tPA activity, and a decrease in tPA antigen concentration (P < .001). All these changes were more clear in subjects with a high baseline PAI activity. These results suggest that 10 weeks of moderate energy- restriction has a profibrinolytic effect in non-obese, middle-aged men, at least in subjects with higher baseline PAI activity (> 9 IU/mL). Moreover, in line with the suggestion that high PAI activity goes together with insulin resistance, a relationship between insulin concentration after a glucose load and PAI activity was found.

Dietary factors in the aetiology of diabetes

Quite different nutrition-related environmental factors influence the development of type 1 insulin-dependent diabetes (IDDM) and type 2 non-insulin-dependent diabetes (NIDDM). IDDM is characterized by progressive beta-cell destruction which leads to complete insulin deficiency; at the time of diagnosis 80-90% of beta cells have been destroyed. In children there is epidemiological evidence that high intake of nitrites and N-nitroso compounds, early introduction of cow's milk to the diet and short duration or absence of breastfeeding increase the risk of IDDM. Studies in experimental animals suggest that cow's milk and soy proteins may be diabetogenic. There is current interest in the effects of free radical scavengers, particularly niacin and natural and synthetic antioxidants on the incidence of IDDM. These findings from ecological, animal, and human case-control studies remain to be evaluated in prospective cohort studies covering infancy and childhood and finally in human intervention trials. NIDDM is characterized by insulin resistance which is complicated by impaired insulin secretion at the time of appearance of hyperglycaemia and clinical diabetes. Its preclinical development is insidious and poorly defined, and there is little direct evidence that the same factors which influence metabolic control in clinical diabetes also affect the preclinical development of the disorder. Obesity, particularly of the abdominal type, is common in people who develop NIDDM, and weight control by appropriate diet and physical activity is probably the most important measure for preventing NIDDM. High (saturated) fat intake seems to be associated with insulin resistance, obesity and increased risk of NIDDM, and diets high in carbohydrate seem to protect from glucose intolerance and diabetes, mainly owing to their high fibre content.