摘要:

Although plant sterols (phytosterols) were chemically described in 1922, their biological role in human and animal health has been underestimated. Their ability to control cholesterol plasma levels in hypercholesterolimic patients was first described in 1983 when the structure of phytosterols implied that they could, by steric hindrance, inhibit the absorption of cholesterol from our diets. This has led to the development of functional foods containing high contents of these plant molecules or their esters as cholesterol controlling foods. Over the last 15 years, however, several reports have appeared in the literature indicating that phytosterols have some immunological activity as highlighted in animal models of inflammation or even inin-vitroandin-vivomodels of cancer (colorectal and breast cancer). These findings were paralleled by epidemiological studies correlating the reduced risk of numerous diseases and the dietary intake of phytosterols. It is only in the last 10 years, however, that their direct immune modulatory activity on human lymphocytes has been proven and the mechanism of action in cancer cells has been elucidated. The use of phytosterols as supportive therapies in certain chronic conditions has been tested under clinical trial conditions. This review presents a summary of thein-vitroandin-vivostudies published to date.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Inflammation causes a decrease in serum retinol and carotenoids as a consequence of the acute phase response of the organism. Under normal conditions both the acute phase response and the alterations in dynamics of retinol and carotenoids are transient. For both retinoids and carotenoids the adaptive benefit or the principal mechanism causing this decrease are not clear. Because nutritional deficiency results in a similar decrease of these nutritional biomarkers, it is necessary to be able to differentiate between inflammation or nutrition deficiency as the cause. This is of importance with regard to the supplementation of both critically ill patients and populations with a high infection load. The review covers several very recent publications shedding new light on and expanding our knowledge of the interaction between inflammation and the decrease in serum retinol and carotenoids.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

The K vitamins, a group of napthoquinones, are required for the carboxylation of a limited number of proteins including the bone matrix protein osteocalcin. Vitamin K1(phylloquinone) and vitamin K2(menaquinones), differ regarding food source (green vegetables and fermented products, respectively), bioavailabilty and intermediate metabolism. Epidemiological studies provide evidence for an association between a low vitamin K intake and an enhanced osteoporotic fracture risk. Doses of vitamin K1up to 15 times the current recommended dietary allowance have successfully been used to reduce the percentage of undercarboxylated osteocalcin in the circulation. Studies demonstrating clear beneficial effects on bone health, however, are still lacking. In contrast, therapy with very high pharmacological doses of the vitamin K2menatetrenone has impressively been used to prevent further bone mineral loss and fracture risk in osteoporotic patients.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Adult male and female humans have clear differences in muscle mass and there is mounting evidence that substrate metabolism differs between genders. These facts suggest that there are gender differences in protein metabolism between males and females. Studies utilizing stable isotopically labeled amino acids show little indication that whole body protein synthesis or breakdown is different between genders. There is evidence that leucine oxidation may be different, both at rest and during exercise, but this evidence is not unequivocal and more, properly controlled studies need to be undertaken to clarify this controversy. Muscle hypertrophy results from positive net muscle protein balance, thus, adult males must have greater net muscle protein synthesis than females, at least at some point in development. Although there is a paucity of data, no gender differences in the basal level net muscle protein balance have been found. It is possible that there are small differences that cannot be distinguished with current methods due to small sample sizes and the sensitivity of the methods. It is more likely, however, that sex hormones contribute to the clear differences in musculature by influencing muscle protein metabolism, especially during puberty. Testosterone increases muscle protein synthesis and net muscle protein balance, resulting in increased muscle mass. Males and females have similar amounts of testosterone until puberty, then testosterone levels increase much more dramatically in males, as does muscle mass. Furthermore, although no evidence exists in humans, in-vitro and rat data suggest that ovarian hormones inhibit muscle protein synthesis. Whereas solid conclusions are difficult to make given the paucity of studies focusing on gender differences in human protein metabolism, it seems that the sex hormones may play an important role. Certainly, more studies need to be conducted to ascertain what gender differences in whole body and muscle protein metabolism exist and how these differences result in different phylogenetic characteristics.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Women generally have a higher percentage of body fat than men. Also, women store more fat in the gluteal-femoral region, whereas men store more fat in the visceral (abdominal) depot. This review focuses on differences in regional fatty acid storage, mobilization and oxidation that may contribute to gender-related differences in body fat distribution. There are pronounced regional differences in the regulation of regional fatty acid metabolism between men and women. Firstly, there is evidence thatin vivo, catecholamine mediated leg free fatty acid release is lower in women than in men, whereas free fatty acid release from the upper body depots is comparable. These data correspond to in-vitro adipose tissue biopsy data, which indicate a more pronounced difference in catecholamine mediated lipolysis between upper body and lower body fat depots in women than in men. Secondly, free fatty acid release by the upper body subcutaneous fat depots is higher in men than in women, indicating a higher resistance to the antilipolytic effect of meal ingestion in the upper body fat depots in men. Thirdly, there are indications that basal fat oxidation (adjusted for fat free mass) is lower in females as compared to males, thereby contributing to a higher fat storage in women. Finally, postprandial fat storage may be higher in subcutaneous adipose tissue in women than in men, whereas storage in visceral adipose tissue has been hypothesized to be higher in men. All the above differences may play a role in the variation in net regional fat storage between men and women, but the number of in-vivo studies on gender-related differences in fatty acid metabolism is very limited and most findings require confirmation. Furthermore, there is abundant evidence that the proportion of energy derived from fat during exercise is higher in women than in men. With respect to total body fat, this finding seems counterintuitive, as percentage body fat is increased in women. Further studies are necessary to investigate the significance of differences in exercise-induced fat oxidation on 24-h fat balance.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

This brief review examines the influence of aging on skeletal muscle mass and strength and specifically highlights sex-related differences. It is well established that aging is associated with a significant decline in muscle strength that becomes functionally important by the seventh decade of life. Age-related strength losses are mainly secondary to decline in skeletal muscle mass in men and women. While women may experience earlier strength losses than men, overall, age associated decreases in strength are similar when controlling for muscle mass. Although men may experience greater losses of total muscle mass, recent evidence, however, points toward greater declines in muscle quality in older women. The implications and potential mechanisms for these differences are discussed.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Recent evidence suggests that oestrogen and sex may influence the degree of disruption and post-damage inflammatory response seen in skeletal muscle. Evidence primarily from animal models suggests that oestrogen may be able to attenuate muscle disruption and attenuate or delay muscle leukocyte infiltration after contraction-induced and ischaemia-reperfusion-induced damage. Several potential mechanisms for this effect are discussed, along with the potential for oestrogen to influence the ultimate rate of skeletal muscle recovery from damage.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Growing evidence suggests that the ovarian hormones have major effects on lipid and carbohydrate metabolism, and may also play a major role in up-stream molecular signaling mechanisms for regulating substrate metabolism. It appears that the absence of estrogen can impair glucose uptake during exercise. In contrast, progesterone not only impairs contraction-mediated glucose uptake when solely administered, but impairs glucose uptake when physiological concentrations of both estrogen and progesterone are administered. Likewise, progesterone administered to rodents for 14 days decreases glucose transporter (GLUT) 4 protein content in skeletal muscle and adipose tissue. Furthermore removing the ovaries decreases the activity of key oxidative enzymes while estrogen treatment restores the activity of these enzymes. It appears, therefore, that estrogen increases the metabolic capacity for both carbohydrate and lipid metabolism, perhaps increasing the overall metabolic flexibility of skeletal muscle. Conversely, progesterone negates both these effects, and could therefore result in a state of relative metabolic inflexibility, similar to that observed in the metabolic syndrome.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

During submaximal endurance exercise, women oxidize more lipid and less carbohydrate as metabolic substrates than men. This is reflected in a lower glycogen utilization in skeletal muscle and lower hepatic glucose production for women compared with men. These latter observations may explain the lower leucine oxidation observed during endurance exercise in women. Animal and preliminary human study evidence suggests that 17-β-estradiol may be a major determinant of the sex dimorphic response in carbohydrate metabolism during exercise. From a practical standpoint, it appears necessary for women to increase their dietary energy intake (and percentage derived from carbohydrates) for four days before a sporting event in order to supercompensate muscle glycogen concentrations. Sex differences in carbohydrate metabolism may have future implications for the care of patients with diabetes and inborn errors of lipid metabolism.

ISSN:1363-1950    

出版商:OVID    

年代:2001

数据来源: OVID