Lothar D. J. Kuijper

Omnivory and food web dynamics

Abstract Intraguild predation is a trophic interaction in which two consumers compete for one resource and where one of the consumer species may also feed on its competitor. The intraguild predator’s diet follows from the relative strength of its interactions with its potential prey. Current view holds that weak interactions between species promote the stability of food webs. To the contrary, nutrient enrichment is predicted to destabilize ecosystems. We present a theoretical analysis of the interplay between intraguild predation and nutrient enrichment in a Marr-Pirt chemostat model of a microbial food web. We perform a two-dimensional bifurcation analysis along a gradient of allochtonous nutrient levels and a gradient of one out of two biologically plausible strategies to explore the spectrum of the intraguild predator’s foraging interactions. Both strategies show that intraguild predation may • stabilize food chains; • eliminate chaos, predicted by food chain models; • give rise to multiple stable states; • be favored in systems with low turn-over rates, where the intraguild predator has a low interaction strength and a low yield on the basal resource.

The Effect of Sugar-Free Versus Sugar-Sweetened Beverages on Satiety, Liking and Wanting: An 18 Month Randomized Double-Blind Trial in Children

Background Substituting sugar-free for sugar-sweetened beverages reduces weight gain. A possible explanation is that sugar-containing and sugar-free beverages cause the same degree of satiety. However, this has not been tested in long-term trials. Methods We randomized 203 children aged 7-11 years to receive 250 mL per day of an artificially sweetened sugar-free beverage or a similarly looking and tasting sugar-sweetened beverage. We measured satiety on a 5-point scale by questionnaire at 0, 6, 12 and 18 months. We calculated the change in satiety from before intake to 1 minute after intake and 15 minutes after intake. We then calculated the odds ratio that satiety increased by 1 point in the sugar-group versus the sugar-free group. We also investigated how much the children liked and wanted the beverages. Results 146 children or 72% completed the study. We found no statistically significant difference in satiety between the sugar-free and sugar-sweetened group; the adjusted odds ratio for a 1 point increase in satiety in the sugar group versus the sugar-free group was 0.77 at 1 minute (95% confidence interval, 0.46 to 1.29), and 1.44 at 15 minutes after intake (95% CI, 0.86 to 2.40). The sugar-group liked and wanted their beverage slightly more than the sugar-free group, adjusted odds ratio 1.63 (95% CI 1.05 to 2.54) and 1.65 (95% CI 1.07 to 2.55), respectively. Conclusions Sugar-sweetened and sugar-free beverages produced similar satiety. Therefore when children are given sugar-free instead of sugar-containing drinks they might not make up the missing calories from other sources. This may explain our previous observation that children in the sugar-free group accumulated less body fat than those in the sugar group. Trial Registration ClinicalTrials.gov NCT00893529 http://clinicaltrials.gov/show/NCT00893529

Effect of sugar-sweetened beverages on body weight in children: design and baseline characteristics of the Double-blind, Randomized INtervention study in Kids☆

BACKGROUND Intake of sugar-sweetened beverages is associated with overweight in observational studies. A possible explanation is that liquid sugars do not satiate and that their intake is not compensated by reduced caloric intake from other foods. However, evidence from intervention studies for this hypothesis is inconclusive because previous studies were not blinded. Hence results may have been influenced by expectations and behavioral cues rather than by physiological mechanisms. METHODS We designed the Double-blind, Randomized INtervention study in Kids (DRINK) to examine the effect on body weight of covertly replacing sugar-sweetened by sugar-free beverages. Children were only eligible if they habitually drank sugar-sweetened beverages. We recruited 642 healthy children (mean age 8.2, range 4.8-11.9). We designed, tested and produced custom-made beverages containing 10% sugar and sugar-free beverages with the same sweet taste and look. Children receive one 250 mL can of study beverage daily for 18 months. We perform body measurements at 0, 6, 12 and 18 months. The primary outcome is the z-score of BMI for age. The maximum predicted difference in this score between groups is 0.72, which corresponds with a difference in body weight of 2.3 kg. DISCUSSION The double-blind design eliminates behavioral factors that affect body weight. If children gain less body fat when drinking sugar-free than when drinking sugar-sweetened beverages that would show that liquid sugar indeed bypasses biological satiation mechanisms. It would also suggest that a reduction in liquid sugars could decrease body fat more effectively than reduction of other calorie sources.

Cross-Sectional Growth References and Implications for the Development of an International Growth Standard for School-Aged Children and Adolescents

Normative data are needed to create a reference that indicates optimal development of weight in relation to height and age, particularly in the face of the unfolding obesity epidemic. The body-mass index (BMI) has some serious limitations: it is a relatively poor predictor of current and future fatness. Currently, however, there are few available alternatives, with the possible exception of waist circumference or skinfolds. The use of cross-sectional references to construct a BMI-reference curve is problematic when there are period and cohort effects. Ideally, a reference would be based on longitudinal data in populations with little underweight, overweight, and obesity. In the meantime cross-sectional data in appropriate populations could be used to construct BMI percentiles linking BMI values at age 5 to those at age 18 (or 21) that would correspond with adult BMI values reflecting optimal health (e.g., that would correspond to adult BMI values between 21 and 23 kg/m2).

Distribution of macro- and micronutrient intakes in relation to the meal pattern of third- and fourth-grade schoolchildren in the city of Quetzaltenango, Guatemala.

OBJECTIVE Our objective was to assess the distribution of energy, macro- and micronutrient intakes by meal (breakfast, lunch, dinner and combined snacks) in a cross-sectional sample of schoolchildren. DESIGN Cross-sectional dietary survey in schoolchildren. SETTING Twelve private and public schools in the urban setting of Quetzaltenango, Guatemala. SUBJECTS A total of 449 schoolchildren (from higher and lower socio-economic strata) were enrolled in the study. METHODS Each child completed a single, pictorial 24 h prospective diary and a face-to-face interview to check completeness and estimate portion sizes. Estimated daily intakes were examined by mealtime as: (i) absolute intakes; (ii) relative nutrient distribution; and (iii) critical micronutrient density (i.e. nutrient density in relation to the WHO Recommended Nutrient Intakes/median age-specific Guatemalan energy requirements). RESULTS The daily distribution of energy intake was 24% at breakfast, 30% at lunch, 23% at dinner and 23% among snacks. Lunch was also the leading meal for macronutrients, providing 35% of proteins, 27% of fat and 30% of carbohydrate. The distribution of selected micronutrients did not follow the pattern of energy, insofar as lunch provided relatively more vitamin C and Zn, whereas breakfast led in terms of vitamins A and D, thiamin, riboflavin, folate, Ca and Fe. CONCLUSIONS Meal-specific distribution of energy, macro- and micronutrients provides a unique and little used perspective for evaluation of childrens habitual intake, and may provide guidance to strategies to improve dietary balance in an era of coexisting energy overnutrition and micronutrient inadequacy.

Ready-to-eat cereals are key sources of selected micronutrients among schoolchildren from public and private elementary schools in Quetzaltenango, Guatemala.

This cross-sectional dietary survey aimed to assess the consumption and relative nutrient contribution of ready-to-eat cereals (RTEC) among schoolchildren from 2 social classes in an urban center in the Guatemalan province of Quetzaltenango. A total of 449 24-hour dietary records were collected using a pictorial workbook registry method among third- and fourth-grade schoolchildren. The sample population was divided between low-income, public school attendants (n = 219) and students from higher-income private institutions (n = 230). We described the contribution of RTEC to estimated total energy; carbohydrates; protein; fat; vitamins A, C, and D; thiamin; riboflavin; folate; calcium; iron; and zinc over the 24-hour interval of registry. Approximately 41% of the subjects mentioned RTEC at least once in their 24-hour record; 93% of these at breakfast time. From the 7 RTEC varieties reported, 4 were presweetened. Estimated cereal consumption was significantly higher among private school participants (P < .001). The RTEC contributed 2.4% of estimated total energy across the whole sample and 3.6% of total carbohydrate; iron intake from RTEC was 21% of total, whereas less than 1% of calcium intake came from this source. Among the subgroup of cereal consumers, RTEC accounted for more than 40% of their daily recommendation intake for iron, vitamin C, thiamin, and riboflavin. The RTEC consumers had significantly higher intakes for all nutrients except carbohydrate and riboflavin as compared with nonconsumers. This study demonstrates the importance of RTEC as a key source of several selected micronutrients to schoolchildrens diet in this setting.

Impact of masked replacement of sugar-sweetened with sugar-free beverages on body weight increases with initial BMI: secondary analysis of data from an 18 month double–blind trial in children

Background Substituting sugar-free for sugar-sweetened beverages reduces weight gain. This effect may be more pronounced in children with a high body mass index (BMI) because their sensing of kilocalories might be compromised. We investigated the impact of sugar-free versus sugary drinks separately in children with a higher and a lower initial BMI z score, and predicted caloric intakes and degree of compensation in the two groups. Methods and Findings This is a secondary, explorative analysis of our double-blind randomized controlled trial (RCT) which showed that replacement of one 250-mL sugary drink per day by a sugar—free drink for 18 months significantly reduced weight gain. In the 477 children who completed the trial, mean initial weights were close to the Dutch average. Only 16% were overweight and 3% obese. Weight changes were expressed as BMI z-score, i.e. as standard deviations of the BMI distribution per age and sex group. We designated the 239 children with an initial BMI z-score below the median as ‘lower BMI’ and the 238 children above the median as ‘higher BMI’. The difference in caloric intake from experimental beverages between treatments was 86 kcal/day both in the lower and in the higher BMI group. We used a multiple linear regression and the coefficient of the interaction term (initial BMI group times treatment), indicated whether children with a lower BMI responded differently from children with a higher BMI. Statistical significance was defined as p ≤ 0.05. Relative to the sugar sweetened beverage, consumption of the sugar—free beverage for 18 months reduced the BMI z-score by 0.05 SD units within the lower BMI group and by 0.21 SD within the higher BMI group. Body weight gain was reduced by 0.62 kg in the lower BMI group and by 1.53 kg in the higher BMI group. Thus the treatment reduced the BMI z-score by 0.16 SD units more in the higher BMI group than in the lower BMI group (p = 0.04; 95% CI -0.31 to -0.01). The impact of the intervention on body weight gain differed by 0.90 kg between BMI groups (p = 0.09; 95% CI -1.95 to 0.14). In addition, we used a physiologically-based model of growth and energy balance to estimate the degree to which children had compensated for the covertly removed sugar kilocalories by increasing their intake of other foods. The model predicts that children with a lower BMI had compensated 65% (95% CI 28 to 102) of the covertly removed sugar kilocalories, whereas children with a higher BMI compensated only 13% (95% CI -37 to 63). Conclusions The children with a BMI above the median might have a reduced tendency to compensate for changes in caloric intake. Differences in these subconscious compensatory mechanisms may be an important cause of differences in the tendency to gain weight. If further research bears this out, cutting down on the intake of sugar-sweetened drinks may benefit a large proportion of children, especially those who show a tendency to become overweight. Trial Registration ClinicalTrials.gov NCT00893529

Experiences of HIV-Positive Adolescents and Young Adults in Care in Soweto, South Africa

The authors of this qualitative study explored clinic experiences of adolescents and young adults (AYAs) attending HIV treatment at the Perinatal HIV Research Unit, Soweto, South Africa. Focus group discussions were conducted with 18 AYAs to elicit perspectives about the clinic and the staff, ideas for improvements, and opinions about clinic transfer. Three themes emerged: preference for personalized patient–provider relationships, suggestions for clinic improvements, and negative perceptions of transfers to community clinics. The findings provide insight into building youth-friendly HIV treatment services. Further research is needed to understand if negative perceptions of transfers to community clinics will translate into poor retention.