Sorbitol intolerance: an unappreciated cause of functional gastrointestinal complaints

Sorbitol, a polyalcohol sugar, is the sweetener in most "sugar-free" products and may produce an osmotic diarrhea if ingested in large amounts (20-50 g). Whether or not smaller amounts of ingested sorbitol may be associated with other symptoms characteristic of carbohydrate malabsorption has not been determined. Using breath hydrogen analysis, the absorption of 5, 10, and 20 g of sorbitol was studied in 7 healthy volunteers. In a majority of subjects, ingestion of as little as 5 g sorbitol was associated with a significant increase in breath hydrogen concentration. Most subjects experienced mild gastrointestinal distress (gas, bloating) after 10 g and severe symptoms (cramps, diarrhea) after 20 g. These data suggest that the evaluation of patients with "functional" gastrointestinal complaints should include careful inquiry into the use of products containing sorbitol.     

Diet selection improves morphine's antinociceptive actions in rats with streptozotocin-induced diabetes.

Following the administration of the diabetogenic drug streptozotocin, rats selecting their diet from separate sources of macronutrients (e.g., proteins, fats, and carbohydrates) demonstrated less severe symptoms of diabetes than did rats fed ground Purina chow or a composite diet containing the same nutrient sources as found in the self-selection diet but in the proportions found in chow. After the induction of diabetes, rats selecting their own diet ate and drank less, weighed more, and had more adipose tissue and lower blood glucose levels than did rats consuming chow or the composite diet. In addition, rats choosing their diet were more sensitive to morphine's pain-relieving properties than were rats in the other 2 dietary groups. Rats given the self-selecting diet consumed more protein and fat and less carbohydrate than did those eating a single diet. Data suggest that rats must select their diet preceding and following the induction of diabetes for amelioration of diabetic symptoms to occur. These results indicate that diet can contribute to the severity of diabetes and could be used as an adjunct to standard treatment of the disease. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of the pathogenesis of flatulence and abdominal cramps in patients with lactose malabsorption

Aim of this study was to assess whether the interindividual differences in the development of flatulence and cramps in patients with lactose malabsorption are due to the quantity of malabsorbed lactose or gas accumulation, or if accelerated intestinal transit or increased perception of gas might play a role. Hydrogen breath tests were performed in 43 patients with lactose malabsorption after ingestion of 50 g lactose and, on a separate day, 25 g lactulose. The unabsorbed amount of lactose, small bowel transit time and colonic hydrogen accumulation were assessed in patients who did and did not develop flatulence and cramps after ingestion of lactose. The unabsorbed amount of lactose, small bowel transit time and volume and rate of colonic hydrogen accumulation were the same in patients who did or did not have symptoms after lactose. Patients with flatulence and cramps had a significantly longer time interval between the onset of the increase and peak breath hydrogen concentration (p < 0.05) and a significant correlation between the time of occurrence of peak symptoms and the time of peak breath hydrogen concentration (r = 0.75, p < 0.001). Our data suggest that subjective symptoms of lactose intolerance are not due to the amount of malabsorbed lactose or to the volume or rate of gas accumulation per se, but are related to increased perception of gas.     

Fecal bile acids and neutral sterols in patients with familial polyposis

Fecal neutral steroids and bile acids were measured in patients with familial polyposis, family controls who are immediate relatives of patients, and controls other than relatives. All subjects were consuming a mixed Western diet at the time of collection of stool specimens. Although the total fecal neutral sterol concentrations were not different between the groups, the patients with familial polyposis excreted a high amount of cholesterol and low levels of coprostanol and coprostanone compared with other groups. Patients with familial polyposis excreted levels of total bile acids in their feces comparable to those excreted by controls; lithocholic acid excretion was decreased in patients with familial polyposis. These findings suggest that analysis of stools for cholesterol and its metabolites be useful in screening the siblings of polyposis families for latent disease.     

The relation of passage of gas an abdominal bloating to colonic gas production

OBJECTIVE: To determine the relation of gas passage and abdominal bloating to the production of gas in the colon. DESIGN: Randomized, double-blind, crossover study of gaseous symptoms during a 1-week period. SETTING: A Veterans Affairs medical center. PARTICIPANTS: 25 healthy medical center employees. INTERVENTION: Participants' diets were supplemented with either a placebo (10 g of lactulose, a nonabsorbable sugar), psyllium (a fermentable fiber), or methylcellulose (a nonfermentable fiber). MEASUREMENTS: All participants were polled for gaseous symptoms (including number of gas passages, impression of increased rectal gas, and abdominal bloating), and five were examined for breath hydrogen excretion. RESULTS: Participants passed gas 10 +/- 5.0 times per day (mean +/- SD) during the placebo period. A significant increase in gas passages (to 19 +/- 12 times per day) and a subjective impression of increased rectal gas were reported with lactulose but not with either of the two fiber preparations. Breath hydrogen excretion, an indicator of hydrogen production in the colon, did not increase after ingestion of either of the fibers. However, a statistically significant (P < 0.05) increase in feelings of abdominal bloating (which the participants perceived as excessive gas in the bowel) was reported with both fiber preparations and with lactulose. CONCLUSIONS: The physician should distinguish between excessive gas (which indicates excessive gas production) and feelings of bloating (which are usually unrelated to excessive gas production). Treatment of the former consists of limiting the supply of fermentable material to the colonic bacteria. Symptoms of bloating usually indicate the irritable bowel syndrome, and therapy should be directed accordingly.     

Elevated serum tryptase levels in a patient with protracted anaphylaxis

BACKGROUND: Anaphylactic reactions usually occur seconds to minutes after exposure to the relevant antigen. Late onset, biphasic, and protracted anaphylaxis also occur. The incidence of prolonged responses is unknown, but may be common. In all nonfood-related cases, levels of tryptase were not measured during protracted episodes. Tryptase has been shown to be a useful specific indicator of mast cell involvement in anaphylaxis. OBJECTIVE: To determine whether mast cell activation, as demonstrated by elevated serum tryptase concentrations, can occur in protracted anaphylaxis. METHODS: Case report; serum tryptase concentrations were measured by radioimmunoassay. RESULTS: A 33-year-old white man developed hives three days prior to admission. The next day, vomiting, abdominal cramps and bloating, lower lip swelling, wheezing, and a feeling of tightness over his throat and chest were experienced. The gastrointestinal symptoms continued until his hospital admission. One day prior to admission, he developed transient lightheadedness. On admission he had generalized urticaria and abdominal tenderness. Blood pressure of 115/58 mm/Hg rose to 180/60 and heart rate fell from 107/min to 90/min following 2.2 L of intravenous fluids. Serum tryptase levels were elevated at 7.2 ng/mL and 5.1 ng/mL on the first and second hospital days (fourth and fifth days of symptoms). Serum tryptase was < 1.0 ng/mL 5 months later. CONCLUSIONS: The elevated serum tryptase levels at 96 and 120 hours following the onset of symptoms strongly suggest that continued mast cell degranulation can occur during protracted anaphylaxis. This strengthens the argument that mast cell activation is important in the pathophysiology of protracted anaphylaxis.     

CombiDOCK: structure-based combinatorial docking and library design

BACKGROUND: Pathogen-negative diarrhea is common in HIV infection and has been associated with clinical symptoms, histopathology, HIV expression, CD4+ lymphocyte depletion, cytokine mRNA expression, and apoptosis of lamina propria mononuclear cells. OBJECTIVES AND METHODS: To examine the short-term (7-day) effects of treatment with combination antiretroviral therapies upon gastrointestinal symptoms and rectal mucosa in 15 HIV-infected subjects. RESULTS: Treatment was associated with significant decreases in the perception of abdominal bloating and cramps. Similar declines in RNA burden and rises in CD4+ lymphocyte counts were found in blood and mucosa. Treatment was also associated with a fall in the number of lamina propria mononuclear cells undergoing apoptosis by in situ labeling, a change that correlated with the change in mucosal viral burden. CONCLUSIONS: Peripheral blood and mucosal compartments are equally responsive to effective antiretroviral therapies. The detection of significant changes within 7 days of starting antiviral therapy implies that intestinal dysfunction may be a direct result of local HIV infection.     

Vegetables, fruits, and legumes: effect on urinary isoflavonoid phytoestrogen and lignan excretion

OBJECTIVE: To compare the effect of vegetable, fruit, and legume consumption on urinary isoflavonoid phytoestrogen and lignan excretion. DESIGN: After 4 days of data collection, during which subjects consumed their habitual diets, subjects were randomly placed on four 9-day controlled experimental diets with each subject receiving each diet in a random order. SUBJECTS: Seven men and three women, aged 20 to 35 years, were recruited from the University of Minnesota Twin Cities community. INTERVENTIONS: All subjects consumed four experimental diets in an assigned random order: a controlled basal diet, a legume/allium diet (containing garbanzo beans, garlic, and onions), and diets low or high in vegetables and fruits (containing apples, pears, potatoes, and carrots). MAIN OUTCOME MEASURES: Urine samples that were collected while subjects consumed their habitual diets and during the last 3 days of each feeding period were analyzed for isoflavonoid and lignan content using isotope dilution gas chromatography-mass spectrometry. STATISTICAL ANALYSIS PERFORMED: The effect of vegetable and fruit intake on urinary isoflavonoid and lignan excretion was analyzed using the general linear model procedure. Post hoc comparisons were made using Duncan's multiple range test. RESULTS: Subjects excreted more of the lignan enterodiol on the high vegetable/fruit diet compared with the basal and legume/allium diets (P = .03); more of the isoflavonoids O-desmethylangolensin (O-DMA), genistein, and sum of isoflavonoids on the legume/allium diet compared with the other controlled diets (P < .05); and more of the isoflavan equol on the basal and legume/allium diets compared with the high vegetable/fruit diet (P < .01). Subjects who excreted higher levels of equol on the basal and legume/allium diets also consumed more of the milk-based pudding provided as part of the controlled diets. CONCLUSIONS: Urinary lignan and isoflavonoid excretion changed in response to alterations in vegetable, fruit, and legume intake under controlled dietary conditions.     

Vagotomy produces learned food aversions in the rat.

Two experiments, each with 28 female Long-Evans rats, examined whether some of the depression in food intake observed in rats with vagotomy could be due to the development of aversions to the foods eaten after surgery. In Exp I, significant aversions developed to the specific novel diet consumed after vagotomy, results indicating that the symptoms associated with vagotomy (hypophagia, weight loss, discomfort) can serve as effective UCSs in the acquisition of learned food aversions. Exp II compared vagotomized Ss consuming familiar laboratory chow with those consuming a novel diet. In contrast to the novel diets, learned aversions to the familiar chow did not develop and hypophagia was less persistent and severe. It is concluded that learned food aversions can contribute to the appetite and weight loss exhibited by vagotomized animals. Consideration of the conditions under which these aversions arise after vagotomy surgery may allow for the design of studies so as to minimize the aversions and thereby separate these nonspecific effects from direct regulatory deficits produced by vagotomy. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exposure to elevated levels of dietary fat attenuates psychostimulant reward and mesolimbic dopamine turnover in the rat.

Recent studies indicate that decreased central dopamine is associated with diet-induced obesity in humans and in animal models. In the current study, the authors assessed the hypothesis that diet-induced obesity reduces mesolimbic dopamine function. Specifically, the authors compared dopamine turnover in this region between rats fed a high-fat diet and those consuming a standard low-fat diet. The authors also assessed behavioral consequences of diet-induced obesity by testing the response of these animals in a conditioned place paradigm using amphetamine as a reinforcer and in an operant conditioning paradigm using sucrose reinforcement. Results demonstrate that animals consuming a high-fat diet, independent of the development of obesity, exhibit decreased dopamine turnover in the mesolimbic system, reduced preference for an amphetamine cue, and attenuated operant responding for sucrose. The authors also observed that diet-induced obesity with a high-fat diet attenuated mesolimbic dopamine turnover in the nucleus accumbens. These data are consistent with recent hypotheses that the hormonal signals derived from adipose tissue regulate the activity of central nervous system structures involved in reward and motivation, which may have implications for the treatment of obesity and/or addiction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Maintenance of elevated lead levels in drinking water from occasional use and potential impact on blood leads in children

The variation in lead concentration was measured by thermal ionisation mass spectrometry isotope dilution in household tap water throughout the day when the plumbing system was not fully flushed. After collection of an initial 125-ml water sample containing 119 micrograms/l and a 2-l sample, 125-ml samples were collected at hourly intervals for 8 h. The concentrations in the hourly samples remained in the range 35-52 micrograms/l compared with 1.7 micrograms/l for fully flushed water. High precision lead isotopic measurements showed that approximately 50% of the lead in these water samples derives from the tap 'housing' compared with the overall household system. A health risk assessment was performed employing the US Environmental Protection Agency Integrated Exposure Uptake Biokinetic Model. Predicted blood lead levels in infants only exceeded the 'levels of concern' of 10 micrograms/dl when 100% of the water consumed contained 100 micrograms Pb/1. It would appear that unless the infant consumed 100% of first flush water at lead concentrations of approximately 100 micrograms/l, the blood lead would not exceed the recommended 'level of concern'. However, if more than 0.51 was consumed in drinks and formulae using first flush water, then the blood lead could easily exceed the recommended level. Likewise, a pregnant mother could be at risk of consuming considerably more than the 0.51/day first flush water of the concentrations measured, or throughout the day, if the system were not fully flushed.     

A high sucrose diet decreases the mechanical strength of bones in growing rats

High sucrose diets alter mineral metabolism in humans and animals. We examined the effect of a high sucrose diet on bone growth, composition and mechanical strength in growing rats. Weanling Wistar rats received a high sucrose (43 g/100 g) diet (9 males, 11 females). In the control diet (8 males, 8 females), sucrose was replaced with potato starch, providing an equal energy value. At the onset of the experiment, bones were marked by tetracycline. After 5 wk, the tibias and femurs were weighed, and maximum breaking strengths were determined. Tibias were cut at the tibia-fibular junction; the widths of the bone at the start of the experiment, the periosteal bone formation during the experiment, the widths of the medullary cavity and the final bone width were determined from tetracycline lines. Bone ash weight, Ca and P contents were determined. The breaking strengths of both bones were significantly lower in the sucrose-fed groups of both sexes. In females, the weight of both bones and the final width of the tibias were significantly lower in the sucrose-fed group. The Ca concentration in both bones and the P concentration in tibias were significantly lower in the sucrose-fed group. It was concluded that the metabolic interference induced by sucrose was the reason for the differences. The alterations were more pronounced in females, but independent of body weight.     

Reproducibility of breath hydrogen concentration measurements in dogs after change of diet

OBJECTIVE: To assess reproducibility of breath hydrogen (H2) concentration measurements in dogs on 3 consecutive days after introduction of a new diet. ANIMALS: 10 healthy colony-source dogs. Procedure Dogs were fed a commercial pet food for a minimum of 10 days before introduction of a high-carbohydrate commercial diet. Expired breath samples were collected at baseline and every 90 minutes for 18 hours on the first 3 days after introduction of the new diet. The area under the curve (AUC) for breath H2 concentration versus time on days 1, 2, and 3 were compared by use of repeated-measures ANOVA. RESULTS: The (AUC) did not differ significantly among test days 1, 2, and 3. CONCLUSIONS: Expired breath H2 concentration in dogs indicated good reproducibility during the first 3 days after introduction of a new diet. CLINICAL RELEVANCE: It is not necessary to provide a period for adaptation to a test diet prior to performing breath H2 tests in dogs.     

Fat substitutes promote weight gain in rats consuming high-fat diets.

The use of food products designed to mimic the sensory properties of sweet and fat while providing fewer calories has been promoted as a method for reducing food intake and body weight. However, such products may interfere with a learned relationship between the sensory properties of food and the caloric consequences of consuming those foods. In the present experiment, we examined whether use of the fat substitute, olestra, affect energy balance by comparing the effects of consuming high-fat, high-calorie potato chips to the effects of consuming potato chips that sometimes signaled high calories (using high-fat potato chips) and that sometimes signaled lower calories (using nonfat potato chips manufactured with the fat substitute olestra). Food intake, body weight gain and adiposity were greater for rats that consumed both the high-calorie chips and the low-calorie chips with olestra compared to rats that consumed consuming only the high-calorie chips, but only if animals were also consuming a chow diet that was high in fat and calories. However, rats previously exposed to both the high- and low-calorie chips exhibited increased body weight gain, food intake and adiposity when they were subsequently provided with a high fat, high calorie chow diet suggesting that experience with the chips containing olestra affected the ability to predict high calories based on the sensory properties of fat. These results extend the generality of previous findings that interfering with a predictive relationship between sensory properties of foods and calories may contribute to dysregulation of energy balance, overweight and obesity. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A comparison of in vivo and in vitro strain with posterior fixed partial dentures

Formulated diets associated with a high risk (HR) or low risk (LR) for colon cancer were used to assess the effect of diet on putative metabolic biomarkers in human flora-associated rats: The HR diet was high in fat and sucrose and low in calcium and fiber; the LR diet was low in fat and high in starch, calcium, and fiber. The nutrient-to-energy ratio and energy intake were the same for both diets. Body and liver weights were significantly higher in animals fed the HR diet, possibly due to greater energy availability from fat. Cecal weights were significantly higher in animals fed the LR diet, presumably due to a bulking effect of the fiber and increased bacterial biomass. The HR diet significantly altered cecal bacterial enzyme activity: beta-glucuronidase activity increased 2.5-fold, and beta-glucosidase activity was halved. Ammonia production and the bacterial metabolism of 2-amino-3-methyl-7H-imidazo[4,5-f] quinoline (IQ) to 7-hydroxy-IQ (7OHIQ) were significantly higher in animals fed the HR diet. The HR diet, which contained factors common to diets consumed throughout the Western world, increased beta-glucuronidase activity, elevated cecal ammonia concentrations, and enhanced the genotoxic risk from 7OHIQ formation, three putative metabolic biomarkers of colorectal cancer. The significance of the reduction in beta-glucosidase is unclear.     

Lactose maldigestion is not an impediment to the intake of 1500 mg calcium daily as dairy products

BACKGROUND: A National Institutes of Health consensus conference concluded that a daily calcium intake of 1500 mg reduces the severity of osteoporosis. Because dairy products are the main natural source of dietary calcium, a diet providing 1500 mg Ca must contain large quantities of dairy products. However, it is widely believed that the lactose content of these products will not be tolerated by persons with lactose maldigestion (approximately 30% of the adult US population). OBJECTIVE: We evaluated the symptoms of lactose maldigestion and digestion when the diet was supplemented with dairy products providing 1300 mg Ca/d. DESIGN: Sixty-two women (31 with lactose maldigestion and 31 without) were studied in a double-blind, randomized protocol. Symptoms were compared during 1-wk periods when the diet was supplemented with 480 mL (2 cups) milk, 56 g cheese, and 240 mL yogurt provided as conventional products (34 g lactose/d) or as lactose-hydrolyzed products (2 g lactose/d). RESULTS: Women who digested lactose reported no significant difference in symptoms between the 2 treatment periods. Women with lactose maldigestion reported significantly increased flatus frequency and subjective impression of rectal gas during the period of high lactose intake; however, bloating, abdominal pain, diarrhea, and the global perception of overall symptom severity were not significantly different between the 2 treatment periods. CONCLUSION: The symptoms resulting from lactose maldigestion are not a major impediment to the ingestion of a dairy-rich diet supplying approximately 1500 mg Ca/d.     

Development of data-based semi-quantitative food frequency questionnaire for dietary studies in middle-aged Japanese

BACKGROUND: We designed a data-based semi-quantitative food frequency questionnaire to clarify the relationship between food intake and lifestyle-related diseases among middle-aged Japanese. METHODS: A total of 351 middle-aged individuals were recruited to a one-day weighed diet record survey in 1994. In all, 586 foods were consumed. Intake of 31 nutrients including energy, protein, fat, carbohydrate, vitamins, minerals and dietary fiber by food was computed by multiplying the weight of food consumed by its nutrient content. First, 252 foods with up to 90 cumulative % contribution to nutrient intake were selected. Of these, foods having apparently the same/similar nutrient content were combined into 206 foods by research dietitians. Next, 183 foods with up to 0.90 cumulative multiple regression coefficient and 90 cumulative % contribution were chosen. At this stage an additional food grouping was made. RESULTS: Finally, 102 foods/recipes were included in the questionnaire: rice (2 items), bread and noodles (11), eggs, milk and dairy products (10), soybean, soybean products and other beans (7), meat including beef, pork and chicken (12), fish (5), other fish, shellfish and fish products (10), green-yellow vegetables (8), other vegetables and mushrooms (7), edible roots (2), seaweeds (3), seeds (2), fruits (8), beverages (7) and confectioneries (8). The frequencies were classified into eight categories. Portion size was calculated for the respective foods largely from the one-day weighed diet record. CONCLUSIONS: The developed semi-quantitative food frequency questionnaire substantially covered the intake of 31 nutrients and may be competent to rank middle-aged Japanese efficiently.     

13C]octanoic acid breath test for non-invasive assessment of gastric emptying in diabetic patients: validation and relationship to gastric symptoms and cardiovascular autonomic function

Since there is a need for a widely applicable non-invasive test to assess gastric emptying in diabetic patients, we evaluated the sensitivity, specificity, and reproducibility of the [13C]octanoic acid breath test as compared with scintigraphy. Moreover, we examined the relationship between the breath test indices and gastric symptoms, cardiovascular autonomic function, and metabolic parameters. Forty healthy control subjects and 34 diabetic patients were studied. Three indices of gastric emptying, assessed by the breath test, were computed: half-emptying time (t1/2breath), gastric emptying coefficient (GEC), and lag phase. Furthermore, the half-emptying time, measured by scintigraphy (t1/2scint), was calculated and gastric symptoms and cardiovascular autonomic neuropathy (CAN) were scored. The coefficients of variation of day-to-day reproducibility in 10 healthy subjects were 29.6% for t1/2breath, 7.4% for GEC, and 46.5% for lag phase. An abnormal delay for t1/2scint (> 100 min) or t1/2breath (> 200 min) was noted in 12 patients. Based on the results for t1/2scint, the sensitivity of t1/2breath and GEC was 75% and the specificity was 86%. Both t1/2breath (rs = 0.523; p < 0.05) and GEC (r2 = -0.594; p < 0.05) were significantly associated with the gastric symptom score. A significant relationship to the CAN score was demonstrated for t1/2breath (rs = 0.448; p < 0.05), GEC (rs = -0.467; p < 0.05), and t1/2scint (rs = 0.602; p < 0.05). There were no significant associations of the breath test indices with the blood glucose levels during the test, HbA1c, age, and duration of diabetes. In patients with abnormal t1/2scint (n = 12) not only was t1/2breath significantly prolonged and GEC reduced, but also the scores of CAN and gastric symptoms were significantly increased as compared with those who had a normal t1/2scint (n = 22). We conclude that the [13C]octanoic acid breath test represents a suitable measure of delayed gastric emptying in diabetic patients which is associated with the severity of gastric symptoms and CAN but not affected by the blood glucose level.     

Raising milk energy content retards gastric emptying of lactose in lactose-intolerant humans with little effect on lactose digestion

Lactose digestion improves when the energy content of a meal is raised, perhaps due to delayed gastric emptying; however, this has not been demonstrated directly. It is not known whether lactose-intolerant subjects should consume full-fat or high energy milk instead of half-skimmed milk. In this study, breath 13CO2 and hydrogen (H2) measurements were combined to assess simultaneously the effect of increasing milk energy content on gastric emptying, digestion, and tolerance of lactose. On two separate days, 11 adult lactose maldigesters ingested, in the fasting state, a single dose of 710 kJ half-skimmed milk or 1970 kJ high energy milk. Both contained 18 g lactose and were supplemented with 100 mg 13C-glycine for breath 13CO2 measurement. For 6 h after milk ingestion, samples of expired breath were collected, and subjects scored their symptoms on a four-grade questionnaire. Gastric emptying was measured from excretion of breath 13CO2. The mean gastric emptying half-time was significantly longer after ingestion of high energy milk than after half-skimmed milk (84 +/- 4 vs. 64 +/- 4 min, P = 0.004). The mean area under the breath H2 excretion curve measured for 6 h was 330 +/- 61 microL/L after subjects consumed high energy milk vs. 470 +/- 82 microL/L after they consumed half-skimmed milk (P = 0.07). Mean symptom scores did not differ after ingestion of the two milks, but only two subjects experienced disturbing symptoms after high energy milk ingestion compared with five subjects after ingestion of half-skimmed milk (P = 0.56). Although ingestion of high energy milk delayed the gastric emptying of lactose for significantly longer than the ingestion of half-skimmed milk (P < 0.01), it did not lead to significant improvement in symptoms and reflected only a trend toward improved lactose digestion (P = 0.07), as measured by the area under the breath H2 excretion curve. These results indicate that it is not beneficial for most lactose-intolerant subjects to replace consumption of half-skimmed milk by milk with a higher energy content.     

Influence of carbon source on nitrate removal by nitrate-tolerant Klebsiella oxytoca CECT 4460 in batch and chemostat cultures

The nitrate-tolerant organism Klebsiella oxytoca CECT 4460 tolerates nitrate at concentrations up to 1 M and is used to treat wastewater with high nitrate loads in industrial wastewater treatment plants. We studied the influence of the C source (glycerol or sucrose or both) on the growth rate and the efficiency of nitrate removal under laboratory conditions. With sucrose as the sole C source the maximum specific growth rate was 0.3 h-1, whereas with glycerol it was 0.45 h-1. In batch cultures K. oxytoca cells grown on sucrose or glycerol were able to immediately use sucrose as a sole C source, suggesting that sucrose uptake and metabolism were constitutive. In contrast, glycerol uptake occurred preferentially in glycerol-grown cells. Independent of the preculture conditions, when sucrose and glycerol were added simultaneously to batch cultures, the sucrose was used first, and once the supply of sucrose was exhausted, the glycerol was consumed. Utilization of nitrate as an N source occurred without nitrite or ammonium accumulation when glycerol was used, but nitrite accumulated when sucrose was used. In chemostat cultures K. oxytoca CECT 4460 efficiently removed nitrate without accumulation of nitrate or ammonium when sucrose, glycerol, or mixtures of these two C sources were used. The growth yields and the efficiencies of C and N utilization were determined at different growth rates in chemostat cultures. Regardless of the C source, yield carbon (YC) ranged between 1.3 and 1.0 g (dry weight) per g of sucrose C or glycerol C consumed. Regardless of the specific growth rate and the C source, yield nitrogen (YN) ranged from 17.2 to 12.5 g (dry weight) per g of nitrate N consumed. In contrast to batch cultures, in continuous cultures glycerol and sucrose were utilized simultaneously, although the specific rate of sucrose consumption was higher than the specific rate of glycerol consumption. In continuous cultures double-nutrient-limited growth appeared with respect to the C/N ratio of the feed medium and the dilution rate, so that for a C/N ratio between 10 and 30 and a growth rate of 0.1 h-1 the process led to simultaneous and efficient removal of the C and N sources used. At a growth rate of 0.2 h-1 the zone of double limitation was between 8 and 11. This suggests that the regimen of double limitation is influenced by the C/N ratio and the growth rate. The results of these experiments were validated by pulse assays.