Human Feeding Studies Research Articles

Nut consumption, lipids, and risk of a coronary event

In the past many have avoided nuts because of their high fat content. The Dietary Approaches to Stop Hypertension diet, however, recommends regular consumption of this food along with seeds and dried beans (4-5 servings per week) as part of a diet to control hypertension. Nuts are nutrient-dense and most of their fat is unsaturated. They are also perhaps the best natural source of vitamin E and are relatively concentrated repositories of dietary fibre, magnesium, potassium and arginine, which is the dietary precursor of nitric oxide. Human feeding studies have demonstrated reductions of 8-12% in low-density lipoprotein (LDL) cholesterol when almonds and walnuts are substituted for more traditional fats. Other studies show that macadamias and hazelnuts appear at least as beneficial as fats in commonly recommended diets. Whether the daily consumption of modest quantities of nuts may promote obesity is not known with certainty, but preliminary data suggest that this is unlikely. Four of the best and largest cohort studies in nutritional epidemiology have now reported that eating nuts frequently is associated with a decreased risk of coronary heart disease in the order of 30-50%. The findings are very consistent in subgroup analyses and unlikely to be due to confounding. Possible mechanisms include reduction in LDL cholesterol, the antioxidant actions of vitamin E, and the effects on the endothelium and platelet function of higher levels of nitric oxide. Although nuts may account for a relatively small percentage of dietary kilojules, the potential interacting effects of these factors on disease risk may be considerable.

A QUANTITATIVE RISK ASSESSMENT FOR BACILLUS CEREUS EMETIC DISEASE ASSOCIATED WITH THE CONSUMPTION OF CHINESE‐STYLE RICE

A quantitative microbial risk assessment (QMRA) was undertaken to model the risk of the Bacillus cereus emetic foodborne disease syndrome associated with the consumption of contaminated Chinese-style boiled or fried rice. Using Monte Carlo simulation, exposure variables were modeled for four different food storage scenarios, including holding at room temperature (20C), under optimal growth conditions (30C) under legal holding conditions (60C), and over a range of holding temperatures. Because human or animal feeding studies are not available for the B. cereus emetic syndrome, epidemiological data was substituted for more conventional dose-response data. Exposure and dose-response assessments were combined, predicting a cumulative estimate for the risk of emetic illness associated with the consumption of B. cereus-contaminated Chinese-style rice of 2.13 x 10(-3), 5.50 x 10(-2), 6.80 x 10(-2), and 6.11 x 10(-3) for the 60, 20, 30C, and overall handling scenarios, respectively. The QMRA revealed that the risk of illness was highly correlated with temperature abuse of cooked rice.

The optimal ratio of fat-to-carbohydrate in the diet.

A major issue in human nutrition is the optimal relation of carbohydrate-to-fat in the diet. According to some investigators, a high proportion of fat energy to total energy favors the development of several chronic diseases. Among these are obesity, coronary heart disease, diabetes, and cancer. The theory that a high proportion of fat relative to other nutrients promotes the development of obesity is founded on research with experimental animals and in human population surveys. This theory has been difficult to prove in prospective feeding studies in humans; therefore it remains a contentious issue. Regarding coronary heart disease, little evidence supports a claim that a high proportion of dietary fat predisposes to disease. On the other hand, strong evidence bolsters the claim that certain fatty acids raise the risk for coronary heart disease. These include saturated fatty acids and trans fatty acids, both of which raise serum cholesterol levels. In contrast, neither monounsaturated nor polyunsaturated fatty acids raise serum cholesterol levels and seemingly pose little risk for coronary disease. The relationship between dietary fat and type 2 diabetes is tied largely to the issue of obesity, because obesity is a major cause of diabetes. Although animal studies and epidemiological studies have implicated dietary fat as a factor in cancer, recent prospective epidemiological data in humans have cast doubt on the possibility of a strong relationship. In summary, clear evidence points to the need to reduce intakes of saturated and trans fatty acids in the diet. Beyond this change, a balanced ratio of unsaturated fatty acids to carbohydrate leading to fat intake of approximately 30% of total energy seems appropriate for the American public.

Nut consumption, lipids, and risk of a coronary event.

In the past, many have avoided nuts because of their high fat content. The Dietary Approaches to Stop Hypertension (DASH) diet, however, recommends regular consumption of this food along with seeds and dried beans (4-5 servings per week) as part of a diet to control hypertension. Nuts are nutrient-dense and most of their fat is unsaturated. They are also perhaps the best natural source of vitamin E and are relatively concentrated repositories of dietary fiber, magnesium, potassium, and arginine, the dietary precursor of nitric oxide. Human feeding studies have demonstrated reductions of 8-12% in low-density lipoprotein (LDL) cholesterol when almonds and walnuts are substituted for more traditional fats. Other studies show that macadamias and hazelnuts appear at least as beneficial as fats in commonly recommended diets. Whether consuming modest quantities of nuts daily may promote weight gain is not known with certainty, but preliminary data suggest that this is unlikely. Four of the best and largest cohort studies in nutritional epidemiology have now reported that eating nuts frequently is associated with a decreased risk of coronary heart disease of the order of 30-50%. The findings are very consistent in subgroup analyses and unlikely to be due to confounding. Possible mechanisms include reduction in LDL cholesterol, the antioxidant actions of vitamin E, and the effects on the endothelium and platelet function of higher levels of nitric oxide. Although nuts may account for a relatively small percentage of dietary calories, the potential interacting effects of these factors on disease risk may be considerable.

Metals and micronutrients – food safety issues

Of all the elements, the most important to consider in terms of food-chain contamination are arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb) and selenium (Se). Where soils are enriched in these elements, it is usually through the agricultural, industrial or urban activities of man, except for Se where high concentrations in soil are often derived from high-Se parent rock materials. The propensity for plants to accumulate and translocate these contaminants to edible and harvested parts depends largely on soil and climatic factors, plant genotype and agronomic management. Elevated As intake, especially of inorganic As, is most likely to arise from high-As drinking water than from ingestion of food. Cadmium and Se are of the greatest concern in terms of terrestrial food-chain contamination, with the former element receiving most attention. Worldwide, the probability of insufficient Se in the human diet exceeds that of toxicity, with deficiency usually associated with monotonous vegetarian diets in areas with Se-deficient soils. Excessive human intake of Cd is of concern as this element accumulates over a lifetime in the body, with impairment of kidney function being the main adverse effect. Cadmium inputs to soil in fertilizer, biosolids, soil amendments and atmospheric deposition often exceed outputs in crops and drainage waters, so that Cd concentrations in many agricultural soils are slowly increasing. However, evidence for increases in Cd concentrations in crops over time is contentious, as is the evidence for human health problems due to low-level Cd contamination of the food chain. Adverse health effects due to Cd intake have been manifest only in situations of gross soil contamination, with a predominantly rice-based diet, where soil–plant and plant–human transfer of Cd would have been enhanced. Human feeding studies have indicated that food Cd bioavailability is dependent on Fe nutrition, and animal studies have indicated that Zn, Ca, P and other elements and food constituents (e.g. fiber, phytate) affect Cd bioavailability. While plant breeding and agronomic management can minimize soil–plant transfer of Cd, and maximize concentrations of antagonists to Cd assimilation in humans, it remains important that inputs of this metal to soil be minimized.

Influence of soybean processing, habitual diet, and soy dose on urinary isoflavonoid excretion

In an attempt to explain the wide individual variation seen in urinary isoflavonoid phytoestrogen excretion, we conducted a series of 3 human feeding studies: a large crosssectional study of equol production in humans with a soy challenge, a comparison of phytoestrogen metabolism when subjects consumed fermented and unfermented soy products, and a dose-response study of urinary isoflavonoid excretion at the low end of soy consumption. All studies were conducted in young, healthy humans. Urinary isoflavonoids were measured by isotope-dilution gas chromatography–mass spectrometry. Similar to results from other studies, 35% of screened subjects (30 men and 30 women) excreted equol (> 2000 nmol/d). In women, equol excretion was associated with higher intake of dietary fiber and carbohydrate. Fermentation of soy decreased the isoflavone content of the product fed but increased the urinary isoflavonoid recovery, suggesting that fermentation increases availability of isoflavones in soy. When soy-protein powder was fed at 0, 5, 10, and 20 g/d (0–36 mg isoflavones), there was a linear dose response of urinary isoflavonoid excretion to soy consumption that did not differ between subjects with high and low equol excretion. These results suggest that equol excretion may be related to the fermentable carbohydrate content of the diet; additional study is needed. Processing of soy affects isoflavone metabolism and must be considered in recommending exposure to isoflavones from soyfoods. Although optimal isoflavone exposure for disease protection has not been determined, urinary isoflavonoid excretion appears linear at low-to-moderate soy consumption.

Diet Design for a Multicenter Controlled Feeding Trial: The DELTA Program

Objective To describe the process and results of diet standardization, diet validation, and monitoring of diet composition, which were key components of protocol 1 of Dietary Effects on Lipoproteins and Thrombogenic Activity (DELTA-1), the initial protocol in a program of multicenter human feeding studies designed to evaluate the effects of amount and type of fat on lipoproteins and hemostasis parameters in various demographic groups. Design DELTA-1 was based on a randomized, blinded, crossover experimental design. Three diets were fed for 8 weeks to 103 healthy men and women aged 22 to 67 years at 4 field centers. Diet A, an average American diet, was designed to provide 37% of energy from fat, 16% of energy from saturated fatty acids (SFAs); diet B (step 1 diet) was designed to provide 30% of energy from fat, 9% of energy from SFA; and diet C (low SFA diet) was designed to provide 26% of energy from fat, 5% of energy from SFA. Key features of diet standardization included central procurement of fat-containing foods, inclusion of standard ingredients, precision weighing of foods—especially sources of fat and cholesterol—and use of standardized written procedures. Setting For menu validation, a set of 12 menus for each diet was prepared in duplicate and chemically assayed. For monitoring of diet composition during the study, an 8-day diet cycle (6 weekday and 2 weekend menus) was sampled by every field center twice during each of 3 feeding periods. Statistical analyses Means (±standard error) were calculated and compared with target nutrient specifications. Results DELTA-1 was able to provide a standardized diet that met nutrient specifications across 4 field centers over 24 weeks of participant feeding spanning a total of 8 months. Applications Prestudy chemical validation of menus and continuous sampling and assay of diets throughout the study are essential to standardize experimental diets and to ensure that nutrient target goals are met and maintained throughout a controlled multicenter feeding study. J Am Diet Assoc. 1998;98:766–776.

Topics in microbial risk assessment: dynamic flow tree process.

Microbial risk assessment is emerging as a new discipline in risk assessment. A systematic approach to microbial risk assessment is presented that employs data analysis for developing parsimonious models and accounts formally for the variability and uncertainty of model inputs using analysis of variance and Monte Carlo simulation. The purpose of the paper is to raise and examine issues in conducting microbial risk assessments. The enteric pathogen Escherichia coli O157:H7 was selected as an example for this study due to its significance to public health. The framework for our work is consistent with the risk assessment components described by the National Research Council in 1983 (hazard identification; exposure assessment; dose-response assessment; and risk characterization). Exposure assessment focuses on hamburgers, cooked a range of temperatures from rare to well done, the latter typical for fast food restaurants. Features of the model include predictive microbiology components that account for random stochastic growth and death of organisms in hamburger. For dose-response modeling, Shigella data from human feeding studies were used as a surrogate for E. coli O157:H7. Risks were calculated using a threshold model and an alternative nonthreshold model. The 95% probability intervals for risk of illness for product cooked to a given internal temperature spanned five orders of magnitude for these models. The existence of even a small threshold has a dramatic impact on the estimated risk.

Cadmium Burden of Men and Women Who Report Regular Consumption of Confectionery Sunflower Kernels Containing a Natural Abundance of Cadmium

Because of inherent genetic and physiological characteristics, the natural concentration of cadmium in the kernels of sunflowers grown in uncontaminated soils of the northern Great Plains region of the United States is higher than in most other grains. We tested the hypothesis that a habitual consumption of sunflower kernels will increase the body burden and health effects of cadmium in humans. Sixty-six men and women who reported consuming various amounts of sunflower kernels were recruited and divided by sex and kernel consumption: those who consumed less than or equal to 1 ounce(oz)/week and those who consumed more than 1 oz/week. Cadmium intake was assessed by calculation from 7-day food diaries, cadmium burden by whole blood cadmium, red blood cell (RBC) cadmium and urine cadmium concentrations, and health effects by urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) activity and beta2-microglobulin (beta2MG). The results showed that high intakes of sunflower kernels (>1 oz/day) significantly increased the intake of cadmium (p<0.004). However, the amount of cadmium in whole blood or RBCs was not affected by cadmium intake. Urinary excretion of cadmium also was not affected by cadmium intake. Urine NAG activity and the amount of urinary beta2MG were significantly elevated in the urine of high sunflower kernel consumers when the values were expressed on a urine volume basis (p<0.03), but not when expressed on a creatinine basis (p>0.05). Because normal ranges for the excretion of these protein markers have not been established, it was not possible to determine if these elevated values were meaningful. However, given the knowledge that habitual consumption of sunflower kernels with natural cadmium concentrations higher than most other food products will increase the average intake of dietary cadmium, the potential exists for an increased body burden of cadmium. Controlled feeding studies in humans should be pursued in order to determine if the body burden does indeed increase and, if so, is it a cause for concern.

Use of Epidemiologic and Food Survey Data To Estimate a Purposefully Conservative Dose-Response Relationship for Listeria monocytogenes Levels and Incidence of Listeriosis

The development of effective quantitative microbial risk-assessment models for foodborne pathogens depends on the availability of data on the consumers' exposure to a biological agent and the dose-response relationship that relates levels of the biological agent ingested with frequency of infection or disease. Information on the latter has historically been acquired from human volunteer feeding studies. However, such studies are not feasible for pathogens that either have a significant risk of being life threatening or for which morbidity is primarily associated with high-risk populations (i.e., immunocompromised persons). For these pathogens, it is proposed that purposefully conservative dose-response relationships can be estimated on the basis of combining available epidemiologic data with food-survey data for a ready-to-eat product. As an example, data on the incidence of listeriosis in Germany were combined with data on the levels of Listeria monocytogenes in smoked fish to generate a dose-response curve for this foodborne pathogen.

Assessment of the dose-response relationship of Campylobacter jejuni

Mathematical relations describing the risk of infection after exposure to enteropathogens are important tools for the evaluation of the potential health risk from exposure via food and water. A quantitative description of the dose-response relation for Campylobacter jejuni with the Beta-Poisson model was fitted to experimental data of infection with Campylobacter jejuni (as determined by shedding of C. jejuni) obtained in human feeding studies performed by Black et al. (1988). The maximum likelihood estimates for the Beta-Poisson model parameters based on these data are: \\ ̂ ga = 0.145 and \\ ̂ gb = 7.59. The fit of the model on the experimental data was good: the difference between the likelihood obtained with the Beta-Poisson model and the maximum possible likelihood was not significant. The occurrence of symptoms of intestinal illness did not follow a similar dose-related trend. Overall, 22% of the infected volunteers developed symptoms (diarrhea, fever). The highest illness-to-infection ratio was found at an intermediate dose (9 × 10 4). The dose-response relation and the illness-to-infection ratio appeared to differ between different C. jejuni isolates. The dose-response relation derived from feeding studies with a single isolate should therefore be considered indicative. The absence of experimental data in the low dose range resulted in a relatively large confidence interval at low doses. However, in cases where the dose-response relation has been applied so far to estimate the health risk of exposure to C. jejuni in water, the uncertainty in the dose-response relation was insignificant compared to the uncertainty in the exposure estimate.

Nutritional aspects of breast cancer.

Nutrition, in its broadest sense, plays a clear role in breast cancer, identified through its relationship to such known risk factors as rate of growth and development, age at menarche, adult height, postmenopausal body weight, and fat distribution. The relative importance of daily diet is hotly debated. There is no agreement on the relative importance of nutrition's effect, the responsible food groups and nutrients, nor the age or ages at which it can be influential. Evidence linking breast cancer and diet comes from human ecologic and observational studies as well as a body of experimental feeding studies in rats and mice. The population studies, including increasing numbers of migrant studies, and the animal experiments suggest that high-fat diets promote breast cancer, particularly among older women. Studies that compare diets of persons with and without breast cancer and those that record breast cancer incidence among women with different dietary histories have been inconclusive enough as to warrant randomized intervention trials. Recognition of differences between the risk factors for premenopausal and postmenopausal women and increasing insight into the ages at which known risk factors exert their influence have helped in the design of these trials. Human feeding studies and the trials themselves are identifying metabolic changes and their biomarkers as well as biomarkers for changes in fat and nutrient intakes. The Women's Health Initiative Dietary Modification Trial was designed to show whether a sustained (9-year) low-fat, high-fruit-and-vegetable eating pattern will lower the incidence of breast cancer among women who will be between ages 59 and 88 when the trial ends, the time of peak incidence. Meanwhile, the Women's Intervention Nutrition Study will learn in approximately 5 years whether a low-fat, adjuvant eating pattern will improve the prognoses of postmenopausal women with early and moderate stage breast cancer and whether tamoxifen should be used as at least part of their treatment. The results of these trials will have important applications for both public health and the provision of medical care.

Genetic marking of Lactococcus lactis shows its survival in the human gastrointestinal tract.

A human feeding study was performed with Lactococcus lactis TC165.5, which is genetically marked by insertion of the sucrose-nisin conjugative transposon Tn5276 and chromosomal resistance to rifampin and streptomycin. The fate of strain TC165.5 and its nucleic acids was monitored by conventional plating methods and by molecular detection techniques based on specific PCR amplification of the nisin (nisA) gene from DNA extracted from human feces. A method was developed for the efficient extraction of microbial DNA from human feces. The results show that a fraction of viable cells of L. lactis TC165.5 survived passage through the human gastrointestinal tract. Only cells that passed within 3 days of ingestion could be recovered from the feces of the volunteers, and they accounted for approximately 1% of the total number of cells consumed. The presence of nisA in DNA extracted from feces could be detected up to 4 days, when viable cells were no longer present.

Quantitative Risk Assessment for Viral Contamination of Shellfish and Coastal Waters

Human pathogenic viruses have been detected from approved shellfish harvesting waters based on the fecal coliform indicator. Until recently it was difficult to assess viral contamination and the potential impact on public health. Risk assessment is a valuable tool which can be used to estimate adverse effects associated with microbial hazards. This report describes the use of quantitative risk assessment for evaluating potential human health impacts associated with exposure to viral contamination of shellfish. The four fundamental steps used in a formal risk assessment are described within and include i) Hazard identification, ii) Dose-response determination, iii) Exposure assessment, and iv) Risk characterization. Dose-response models developed from human feeding studies were used to evaluate the risk of infection from contaminated shellfish. Of 58 pooled samples, 19% were found to be positive for viruses. Using an echovirus-12 probability model, the individual risk was determined for consumption of 60 g of raw shellfish. Individual risks ranged from 2.2 × 10−4 to 3.5 × 10−2. These data suggest that individuals consuming raw shellfish from approved waters in the United States may have on the average a 1 in 100 chance of becoming infected with an enteric virus. Using the rotavirus model which represents a more infectious virus, the risk rose to 5 in 10. The potential for use of a risk assessment approach for developing priorities and strategies for control of disease is immense. Epidemiological data have demonstrated the significance of shellfish-associated viral disease and, although limited, appropriate virus occurrence data are available. Additional information on virus occurrence and exposure is needed, and then scientific risk assessment can be used to better assure the safety of seafood.

Modulation of lipid derived mediators by polyunsaturated fatty acids

Cell stimulation by a number of agonists triggers the formation of products of lipid hydrolysis, which act either as intracellular mediators of signal transduction or as modulators of cell-cell interactions. This process is mediated by the activation of hydrolytic enzymes, the phospholipases (PLase), especially the A 2 and C, acting on cell phospholipids (PL). Among the major products being formed, the following: a) the inositol phosphates (IP), especially IP 3, and diacylglycerols (DAG) generated intracellularly from phosphoinositides through PLase C, b) the eicosanoids, the arachidonic acid (AA) metabolites produced through combined PLase A 2 and (cyclo- and lip-) oxygenase activities, and released from cells, c) the ether lipid PAF, derived from alkylacyl phosphatidylcholine through PLase A 2, have attracted the attention of investigators for their important biological roles. Interest has also been recently developed towards products of sphingolipid hydrolysis, sphingosine and ceramide, which are generated by various cell types after stimulation, and exert biological activities. Cell glycerophospholipids are rich in long-chain polyunsaturated fatty acids (PUFA) of the n-6, namely AA 20:4 n-6, and n-3, mainly docosahexaenoic acid (DHA) 22:6, series. These compounds are differentially distributed among the various PL classes and their levels in cells are modulated through the intake with the diet of either the 18-C fatty acids (FA), precursors, linoleic 18:2 n-6, and, alpha-linolenic 18:3 n-3, respectively-followed by conversion to their long-chain PUFA derivatives, or through the intake of the preformed compounds. Levels of the long-chain PUFA in membranes can also be modulated in cultured cells, through manipulation of the supply with the growth medium. The incorporation of exogenous FA in cell lipids, in this type of study, however, follows patterns which are different from those observed in vivo after dietary manipulations. The levels of long chain n-6 and n-3 PUFA in cell phosphoglycerides modulate the generation of lipid derived mediators, in various types of cells, after in vitro stimulation. These effects can be ascribed to various mechanisms: 1. 1. Changes in eicosanoid production as a consequence of: a) changes in the levels of AA, the major precursor of these compounds, b) accumulation of long-chain PUFA of the n-3 series, which act as precursors (e.g. eicosapentaenoic acid (EPA), 20:5) of eicosanoids with biological activities different from those of the products derived from AA, or inhibitors (EPA) and/or modulators (DHA) of the AA oxygenases. 2. 2. Changes in the stimulated formation of other products of PL hydrolysis, such as the IP and PAF, possibly as a consequence of a modified micro-environment of the PLases, or as a consequence of modified eicosanoid production. The fomation of other mediators, such as the cytokines, in specialized cells, is also affected by changes of cell PUFA, possibly as an additional consequence of altered eicosanoid formation. In this presentation, examples of changes of cell n-6 and n-3 PUFA, obtained in circulating cells (e.g. platelets, leukocytes) through feeding studies in animals and humans, or induced in cultured cells after FA supplementation, will be presented and discussed, in relation to the effects on the production of eicosanoids and other lipid derived mediators.

Mineral balances in humans as affected by fructose, high fructose corn syrup and sucrose

The utilization of selected minerals when sugars were supplemented to basal diets was investigated in two separate, laboratory-controlled human feeding studies. Fructose-fed subjects had higher fecal excretions of iron and magnesium than did subjects fed sucrose. Apparent iron, magnesium, calcium, and zinc balances tended to be less positive during the fructose feeding period as compared to balances during the sucrose feeding period. Conversely, high fructose corn syrup (HFCS) did not affect the mineral balances when compared to sucrose feeding. Subjects fed fructose experienced diarrhea which possibly decreased absorption of minerals and thus increased fecal mineral losses. No such adverse effects were noticed when HFCS was fed.

Use of Risk Assessment for Development of Microbial Standards

A single-hit exponential model and a β-distributed “infectivity probability” model were used to evaluate the potential health risks from drinking water containing low levels of protozoan cysts and viruses, respectively. The models were based on dose response curves developed from human feeding studies and assumed consumption of 2 L/day. The US EPA has suggested that one infection/10,000/year is an acceptable risk for infectious agents acquired through potable water. Based on this risk, acceptable levels of viruses and cysts were determined using the probability models. Thus poliovirus and rotavirus levels should not be more than 0.1 and 0.3 pfu/100L respectively per day. Giardia levels should be below 0.2 cysts/100L. To achieve a 1:10,000 annual risk, the geometric average should not exceed 10−3 organisms/100L. As monitoring treated water for these levels would be difficult, source waters may be monitored. Geometric averages of 1-100 organisms/100L require 3-5 logs of treatment reduction to achieve the 1:10,000 risk. The risk models for viruses and protozoa can be used to evaluate the occurrence of pathogens in source water and determine the appropriate treatment needed to obtain specific levels of safety for drinking water.

Risk assessment and control of waterborne giardiasis.

Waterborne giardiasis has been increasing in the United States with 95 outbreaks reported over the last 25 years. The Safe Drinking Water Act has mandated control of this pathogen. A risk assessment model was developed to estimate risk of infection after exposure to treated waters containing varying levels of Giardia cysts. The model was defined by a dose-response curve developed from human feeding studies for Giardia and assumed 2L of water consumption per day. Data on concentrations and distribution of the organism in source waters were used to assess exposure after varying reductions achieved through treatment. In surveys reporting prevalence and levels of Giardia cyst contamination, average levels of cysts in surface waters ranged from 0.33 to 104/100L; from pristine watersheds (protected from all human activity) 0.6 to 5/100L. Yearly risks were 4.8 x 10(-3) for systems using polluted waters and 1.3 x 10(-4) for pristine waters with a 10(-3) treatment reduction. Public Health officials will need to work with the water industry to ensure a risk of less than 1/10,000 for source waters with 0.7 to 70 cysts per 100 liters through treatment achieving reduction of 10(-3) to 10(-5), respectively, of Giardia cysts.

Endogenous labeling of bovine milk with the stable isotope 44Ca 1,2

Calcium endogenous to bovine milk was biosyntheticallylabeled by intravenous injection of calcium highly enriched in 44Ca to a single lactating dairy cow. Approximately 63% of a 4 g dose was recovered in the milk in 56.5 h. The milk was homogenized, pasteurized and then stored at −70°C after processing. A 300% enrichment of 44Ca in the first postdose milking was sufficient for use in human feeding studies currently underway.

REGULATORY SIGNIFICANCE OF AEROMONAS IN FOODS

ABSTRACTAeromonas hydrophila and other Aeromonas spp. are commonly found in fresh water and in foods. Although their isolation from stools of persons with diarrhea has implicated them as a cause of diarrheal disease, these microbes have failed to produce disease, even at very high doses, in voluntary human feeding studies. The presence of A. hydrophila in foods destined for cancer patients is certainly contraindicated, but at present Aeromonas spp. should be considered putative causes of acute gastroenteritis in normal persons. However, regulatory action based on health concerns seems insupportable at this time.