3848 MENSTRUAL CYCLE: NUTRITIONAL ASPECTS
reported to provide an opportunity for greatly improving the performance and productivity of fermentation. Ultrafiltration is also used for the production of high-quality water suitable for pharmaceutical and biotechnology purposes. The most efficient removal of pyrogens, bacteria, and particulates at low energy are the main advantages of ultrafiltration over other water treatment techniques. (See Water Supplies: Water Treatment.)
Other Applications 0053
Other useful applications of ultrafiltration in the food industry include production of concentrates and isolates from soya, sunflower, and cotton seeds; removal of glucose from egg white and its partial concentration prior to drying; refining of sugar solutions; fractionation and concentration of gelatin, and many more. See also: Beers: Chemistry of Brewing; Cheeses: Types of Cheese; Chemistry of Gel Formation; Drying: Spray Drying; Effluents from Food Processing: Composition and Analysis; Milk: Dietary Importance; Starter Cultures; Vinegar; Water Supplies: Water Treatment; Whey and Whey Powders: Production and Uses; Wines: Production of Table Wines; Production of Sparkling Wines
Further Reading Cheryan M (1986) Ultrafiltration Handbook. Lancaster, PA, Technomic. Cheryan M (1998) Ultra-filtration and Micro-filtration Handbook. Lancaster, PA: Technomic.
EI-Shibiny S, Shahein NM and Sheikh M (1996) Preparation and functional properties of ultrafiltered milk protein isolates. Bulletin of International Dairy Federation 311: 28–30. Fukumoto, LR, Delaquis P and Girard B (1998) Microfiltration and ultrafiltration ceramic membrane for apple juice clarification. Journal of Food Science 63: 845–850. Gauthier SF and Pouliot Y (1996) Use of ultra-filtration for the preparation of enzymatic hydrolysates from milk proteins. Bulletin of International Dairy Federation 311: 31–32. Glover FA (1985) Ultrafiltration and Reverse Osmosis for the Dairy Industry. Technical Bulletin no. 5. Reading, NIRD. Horton BS (1997) Whatever happened to the ultrafiltration of milk? Australian Journal of Dairy Technology 52(1): 47–49. Kosikowski FV (1986) New cheese making process utilising ultra-filtration. Food Technology 40(6): 71–77. Lelievre J and Lawrence RC (1988) Manufacture of cheese from milk concentrated by ultra-filtration: a review. Journal of Dairy Research 55: 373–392. Novak A (1996) Application of membrane filtration in the production of milk protein concentrates. Bulletin of International Dairy Federation 311: 26–27. Pal D and Cheryan M (1987) Membrane technology in dairy industry. Part II. Ultrafiltration. Indian Dairyman 39(8): 373–392. Puhan Z (1996) Protein standardization. Bulletin of International Dairy Federation 311: 4–6. Renner E and Abd El-Salam MH (1991) Application of Ultra-filtration in Dairy Industry. Barking: Elsevier. Vasiljevic T and Jelen P (1999) Temperature effect on behaviour of minerals during ultrafiltration of skimmilk and acid whey. Milchwissenchaft 54(5): 243–246.
See Vitamin K: Properties and Determination; Physiology
MENSTRUAL CYCLE: NUTRITIONAL ASPECTS F Ford, University of Sheffield, Sheffield, UK Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
be reviewed, together with the influences of: body weight, body fat, dietary restraint, dietary fat and energy intake, lignans, isoflavones, vegetarianism, and PCB residues on the menstrual cycle.
The effects of dietary intake on the menstrual cycle have been the subjects of a great deal of research, but many aspects are still poorly understood. The relationship between nutritional status and menarche will
Nutritional Status and Menarche Some research shows that girls who experience early menstruation reach their mature height sooner than girls who experience late menarche (the onset of
MENSTRUAL CYCLE: NUTRITIONAL ASPECTS
menstrual periods). In one study, girls who ate primarily protein foods were shown to reach menarche sooner, and girls who eat primarily carbohydrates reached menarche later. However, in other studies of all the dietary variables analyzed, only energy intake was related to age at menarche. In a longitudinal study, girls who consumed more (energy-adjusted) animal protein and less vegetable protein at ages 3–5 years had an earlier menarche, and girls aged 1–2 years with higher dietary fat intakes and girls aged 6–8 years with higher animal protein intakes became adolescents with earlier peak growth. Controlling for body size, girls who consumed more calories and animal protein 2 years before peak growth had a higher peak growth velocity. These findings may have implications regarding adult diseases whose risks are associated with adolescent growth and development factors.
Body Weight and the Menstrual Cycle 0003
It is well established that starvation and emaciation are almost invariably associated with amenorrhea (lack of menstrual periods), the most profound disturbance of the menstrual cycle. The work of Frisch in the USA identified the link between body composition and ovulation in the human female. She suggested that fat must comprise at least 22% of body weight for the maintenance of ovulatory cycles and also observed that in normal postpubertal women, fat is about 28% of body weight. It is well recognized that the relationship is to the fat content of the body rather than absolute body weight. Trained athletes of average or above average body weight may have a very low body fat content and may be oligo- or amenorrheic. Frisch observed that amongst trained athletes who became fit after a normal menarche, 60% continued regular cycles, but 40% had irregular cycles and presumably associated subfertility. Eating disorders such as anorexia nervosa and bulimia nervosa are also causes of oligo- or amenorrhea. In anorexia nervosa, amenorrhea and failure to maintain a body weight within 15% of that expected are both diagnostic criteria. However, many women engage in pathologic dieting behaviors without meeting the current diagnostic criteria for anorexia or bulimia nervosa. Clinical eating disorders are only the most extreme form of pathologic eating attitudes and behaviors that are present in many young women. Specific food choices and nutrient intakes may be associated with altered gonadal hormone status of these dieters. Extreme weight loss is not a prerequisite for menstrual cycle disturbances because dieting can induce
missed cycles before substantial weight loss occurs. Even a very short-term (i.e., 4-day) acute energy shortage can interfere with luteinizing hormone pulsatility and thereby affect cycle function. In humans, dieting with minor or moderate weight loss has been shown to cause menstrual cycle disturbances or may be a risk factor for the development of reproductive dysfunction in normal weight healthy women. Cognitive factors may also be associated with the stability of the menstrual cycle. One such factor is cognitive dietary restraint, the perception that food intake is constantly being limited in an effort to control body weight. Menstrual differences between women with high and low restraint scores were detected in a number of studies. One study found that women with high restraint scores had significantly shorter cycle lengths, shorter lutealphase lengths, and lower mean luteal-phase progesterone concentrations. In a group of women with a wide range of physical activity levels who were initially confirmed to ovulate normally, it was found that the luteal-phase length was shorter, without alteration of cycle length, in women with high restraint scores. Cycle disturbances are associated with obesity as well as with energy shortages. A high prevalence of obesity among amenorrheic women was reported many years ago, and anovulatory cycles appear to be more common in obese women. Weight loss in obese women results in improved ovulation and pregnancy rates. It has been suggested that high androstenedione concentrations observed in obese women may activate the conversion of estradiol to estrone in adipose tissue. Estrone in turn may trigger higher luteinizing hormone concentrations, leading to ovarian hyperstimulation, thus increasing testosterone concentrations, resulting in anovulatory cycles. The Nurses Health Study in the USA has also produced some interesting information about the relative risk of menstrual cycle irregularity not only in the underweight but also in the overweight woman. For women with a body mass index (BMI) below 20, at the age of 18 years, ovulatory infertility was found with a relative risk of about 1.2 compared to women with a BMI of 20–25. Interestingly, however, the relative risk of ovulatory infertility was 1.5 in those with a BMI of 28 and more than 2 in the obese group with a BMI above 30. About half of the risk is associated with polycystic ovarian syndrome, in which ovulatory infertility and obesity coexist, but there is still a doubling in relative risk of ovulatory infertility in women with a BMI above 30 who do not have ultrasonically detectable polycystic ovaries.
3850 MENSTRUAL CYCLE: NUTRITIONAL ASPECTS
Energy Intake and the Menstrual Cycle 0008
The biological regulation of appetite is currently an important topic in nutrition, because of its relationship with the increasing burden of obesity. Cyclical fluctuations in food intake occur in women across the menstrual cycle, with a periovulatory nadir and a peak in the luteal phase. These alterations in food intake, in response to ovarian steroid hormone changes, may be more than 2.5 MJ per day, with the mean reported changes shown in 19 separate studies of 1.0 MJ per day. Hormonally induced fluctuations in food intake could, therefore, contribute to energy imbalance and consequent weight gain. The regulation of food intake by menstrual cycle hormones suggests that it is essential to consider the phase of the menstrual cycle in studies of nutrient intake performed in women.
Vegetarian Women and the Menstrual Cycle 0009
The question of whether menstrual disturbances are more common in vegetarian than in nonvegetarian women in complex. Three general mechanisms that could contribute to menstrual disturbances that may differ between vegetarians and nonvegetarians include energy imbalances associated with body-weight disturbances or exercise, psychosocial and cognitive factors, and dietary components. Although results from several cross-sectional studies suggest that clinical menstrual disturbances may be more common in vegetarians, a prospective study that controlled for many potential confounders found that subclinical disturbances were less common in weight-stable, healthy vegetarian women. Because the sample studied may not be representative of all vegetarian women, however, these results cannot be generalized. Population studies are needed to draw definitive conclusions.
Effects of Exercise on the Menstrual Cycle 0010
Several prospective studies have shown that menstrual function does not change with exercise, provided that increases in activity are gradual, and body weight is maintained. This suggests that adequate energy availability may be a key factor in maintaining normal hormonal function with exercise. A study was conducted to determine whether rigorous exercise training adversely affects ovarian hormone levels and bone health in cyclically menstruating trained runners. Results indicated that lower estrogen production, especially during the early
follicular phase, but not progesterone, was associated with a lower whole body calcium per kilogram of soft lean tissue and probably bone mineral density.
Dietary Components and the Menstrual Cycle Research suggests that concentrations of ovarian hormones or their metabolites may be lower at various points in the menstrual cycle in women consuming diets high in fiber, low in fat, or both. This is consistent with cross-sectional studies reporting inverse associations between hormone concentrations and fiber intake, direct associations between hormone concentrations and fat intake, and lower serum estrogen concentrations with a faster intestinal transit. It also corroborates the lower estradiol and progesterone concentrations observed in women 2 years after being randomly assigned to a low-fat, high-carbohydrate diet for a study in breast cancer risk reduction. However, the data must be interpreted cautiously because many experimental studies were conducted over only one or two menstrual cycles, and other data suggest that changes observed acutely may not persist over time. In addition, some subjects were free-living and others were housed in metabolic wards, which could affect the menstrual cycle differently. Studies have been conducted to explore the effects of two classes of phytoestrogens, lignans and isoflavones. One study examined the effects of flaxseed powder, which is high in lignan precursors, in 18 women with normal ovulatory cycles using a randomized, crossover design. Each women followed her usual omnivorous, low-fiber diet for three cycles and then followed her usual diet supplemented with flaxseed powder for another three cycles. The last two cycles of each dietary period were compared. During flaxseed supplementation, luteal-phase lengths were significantly longer, and the ratio of progesterone to estradiol during the luteal phase was higher. Moreover, no anovulatory cycles occurred during flaxseed supplementation, but three anovulatory cycles occurred during the control diet period. In another study, the effects of isoflavones were examined in six women with regular ovulatory cycles. It was found that diets containing 60 g of soy protein per day (with 45 mg of isoflavones) significantly increased follicular-phase length compared with control diets. Subsequently, they showed that a soybean product from which the isoflavones had been extracted had no effect on the cycle. Thus, lignans and isoflavones, two different classes of phytochemicals, appeared to have different effects: flaxseed lignans increased luteal-phase length and did not affect follicular-phase length, whereas soybean isoflavones
MENSTRUAL CYCLE: NUTRITIONAL ASPECTS
increased follicular-phase length but did not influence luteal-phase length. Previous studies have suggested that high soybean intakes are associated with lower concentrations of serum cholesterol and may be related to decreased rates of coronary artery disease, cancer, and osteoporosis. One of the postulated mechanisms of these effects is that soy products, particularly the isoflavones in soy, act through changes in endogenous hormonal balance. Isoflavones significantly improved the lipid profile across the menstrual cycle in normocholesterolemic, premenopausal women. Although of small magnitude, these effects could contribute to a lower risk of developing coronary heart disease in healthy women who consume soy over many years.
Relationship Between Diet, Menstrual Hormones, and Breast Cancer 0016
There is compelling evidence linking ovarian hormonal activity to breast cancer risk. Since the mid-1980s, dietary fat intervention studies have been conducted to investigate the effect of fat intake on endogenous estrogen levels. A meta-analysis of dietary fat intervention studies that investigated serum estradiol levels reviewed the nature of the evidence provided by prospective analytic studies of fat consumption and breast cancer risk. Results indicated that dietary fat reduction can result in a lowering of serum estradiol levels and suggest that a low-fat highcarbohydrate diet may reduce the risk of breast cancer by reducing exposure to ovarian hormones that are a stimulus to cell division in the breast. Intake of soybean protein is associated with a reduced risk of breast cancer in a case-control study. It has also been demonstrated to increase menstrual cycle length in an experimental setting. Most epidemiological studies of the relationship between alcohol consumption and breast cancer risk over the past decade have shown that persons who consume a moderate amount of alcohol are at 40–100% greater risk of breast cancer than those who do not consume alcohol. Dose–response effects have been observed, but no causal relationship has been established. However, it has also been shown that alcohol consumption in premenopausal women is associated with increases in total estrogen levels and amount of bioavailable estrogens. This may help to explain the relationship between the risk of breast cancer and alcohol intake.
Dietary Contaminants and the Menstrual Cycle 0019
Highly contaminated Lake Ontario sport fish represent an important human dietary exposure to
polychlorinated biphenyls (PCBs) and other toxic contaminants that may disrupt endocrine pathways. In one study, women anglers were interviewed by telephone to determine menstrual cycle length and fish consumption in order to calculate a PCB exposure index. Multiple regression analyses identified significant cycle-length reductions with consumption of more than one fish meal per month and a moderate/ high estimated PCB index. Women who consumed contaminated fish for 7 years or more also had shorter cycles.
Menstrual Cycle and Iron-deficiency Anemia Menorrhagia (heavy menstrual bleeding) is a benign yet debilitating social and health condition. The widely accepted clinical definition of menorrhagia is blood loss of 80 ml or more per period. This figure is derived from population studies that have shown that the average blood loss is between 30 and 40 ml, and 90% of women have blood losses of less than 80 ml. Excessive menstrual bleeding is the commonest cause of iron deficiency in the UK, affecting 20–25% of the fertile female population. Menorrhagia is a common problem accounting for 12% of all gynecological referral in the UK.
Conclusion The evidence presented above appears primarily to show associations between dietary factors and the menstrual cycle rather than causation. What does, however, seem clear is that the relationship between normal ovarian hormone function and diet is complex and needs further evaluation from prospective rather than epidemiological research studies. See also: Anemia (Anaemia): Iron-deficiency Anemia; Anorexia Nervosa; Bulimia Nervosa; Exercise: Metabolic Requirements; Obesity: Etiology and Diagnosis; Vegetarian Diets
Further Reading Barnard ND, Scialli AR, Bertron P, Hurlock D, Edmonds K and Talev L (2000) Effectiveness of a low-fat vegetarian diet in altering serum lipids in healthy premenopausal women. Randomized Controlled Trial. American Journal of Cardiology 85(8): 969–972. Barr SI (1999) Vegetarianism and menstrual cycle disturbances: is there an association? American Journal of Clinical Nutrition 70 (3 supplement): 549S–554S. Boyd NF, Lockwood GA, Greenberg CV, Martin LJ and Tritchler DL (1997) Effects of a low-fat high-carbohydrate diet on plasma sex hormones in premenopausal women:
3852 MERCURY/Properties and Determination results from a randomized controlled trial. Canadian Diet and Breast Cancer Prevention Study Group. British Journal of Cancer 76(1): 127–135. Bruinsma K and Taren DL (1999) Chocolate: food or drug? Journal of the American Dietetic Association 99(10): 1249–1256. Campbell WS, Franz C, Kahle L and Taylor PR (1996) Relation of energy, fat, and fiber intakes to plasma concentrations of estrogens and androgens in premenopausal women. American Journal of Clinical Nutrition 64(1): 25–31. Doll H, Brown S, Thurston A and Vessey M (1989) Pyridoxine (vitamin B6) and the premenstrual syndrome: a randomized crossover trial. Journal of the Royal College of General Practitioners 39(326): 364–368. Eck LH, Klesges RC, Meyers AW, Slawson DL and Winders SA (1997) Changes in food consumption and body weight associated with smoking cessation across menstrual cycle phase. Addictive Behaviors 22(6): 775–782. Frisch RE (1994) The right weight: body fat, menarche and fertility. Proceedings of the Nutrition Society 53(1): 113–129. Gendall KA, Bulik CM, Joyce PR, McIntosh VV and Carter FA (2000) Menstrual cycle irregularity in bulimia nervosa. Associated factors and changes with treatment. Journal of Psychosomatic Research 49(6): 409–415.
Jones DY, Judd JT, Taylor PR, Campbell WS and Nair PP (1987) Influence of dietary fat on menstrual cycle and menses length. Human Nutrition – Clinical Nutrition 41(5): 341–345. Kato I, Toniolo P, Koenig KL et al. (1999) Epidemiologic correlates with menstrual cycle length in middle aged women. European Journal of Epidemiology 15(9): 809–814. Lu LJ, Anderson KE, Grady JJ, Kohen F and Nagamani M (2000) Decreased ovarian hormones during a soya diet: implications for breast cancer prevention. Cancer Research 60(15): 4112–4121. McLean JA, Barr SI and Prior JC (2001) Cognitive dietary restraint is associated with higher urinary cortisol excretion in healthy premenopausal women. American Journal of Clinical Nutrition 73(1): 7–12. Mendola P, Buck GM, Sever LE, Zielezny M and Vena JE (1997) Consumption of PCB-contaminated freshwater fish and shortened menstrual cycle length. American Journal of Epidemiology 146(11): 955–960. Norman RJ and Clark AM (1998) Obesity and reproductive disorders: a review. Reproduction, Fertility, & Development 10(1): 55–63. Thys-Jacobs S (2000) Micronutrients and the premenstrual syndrome: the case for calcium. Journal of the American College of Nutrition 19(2): 220–227.
MERCURY Contents Properties and Determination Toxicology
Properties and Determination C J Cappon, Cappon Associates, Henrietta, NY, USA This article is reproduced from Encyclopaedia of Food Science, Food Technology and Nutrition, Copyright 1993, Academic Press.
Mercury is probably the most ubiquitous heavy metal in the environment, resulting from natural geological activity and industrial pollution. Although it is extremely useful, it is also highly toxic, depending on its specific chemical form. The hazards of mercury and its compounds have been long known and of much concern. Its history as an occupational hazard has been linked to its elemental and divalent ionic – inorganic – forms, mostly due to volatility and skin
contact. However, there has been much recent concern for widespread environmental contamination from organic mercury species, namely the alkylmercuries – methyl, ethyl-, and phenylmercury. Alkylmercury poisoning has been almost exclusively linked to methylmercury pollution of waterways and aquatic food sources, specifically in Japan, Sweden, and Canada. This has initiated several comprehensive worldwide analytical surveys of foods to assess human mercury intake levels and potential adverse health effects. It has also highlighted the critical need for more accurate and reliable mercury analytical methods for a variety of materials. Most modern methods involve mercury speciation separation schemes. This article discusses the environmental sources and toxicological impact of mercury in food, with special emphasis on analytical speciation