Sodium and potassium intake and blood pressure.

Sodium and potassium intakes were increased in normotensive volunteers to assess the effects on their blood pressures. An approximately threefold increase in sodium intake for eight days had no effect on the blood pressures of seven volunteers, while a two-stage increase in potassium intake, by about 40% for eight days and a further 55% for 14 days, had no effect on the blood pressures of 21 volunteers. Renal electrolyte excretions and the blood pressures of all 28 subjects showed no statistically significant correlations between either sodium or potassium excretion and blood pressure. A weak negative correlation was found between the sodium: potassium ratio and systolic pressure. The small reductions in sodium intake and increases in potassium intake that might be achieved through propaganda and changes in food processing are unlikely to lower mean blood pressure in Western societies.     

Social information, social feeding, and competition in group-living goats (Capra hircus)

There are both benefits (e.g., social information) and costs(e.g., intraspecific competition) for individuals foraging ingroups. To ascertain how group-foraging goats (Capra hircus)deal with these trade-offs, we asked 1) do goats use socialinformation to make foraging decisions and 2) how do they adjusttheir intake rate in light of having attracted by other groupmembers? To establish whether goats use social information,we recorded their initial choice of different quality food patcheswhen they were ignorant of patch quality and when they couldobserve others foraging. After determining that goats use socialinformation, we recorded intake rates while they fed alone andin the presence of potential competitors. Intake rate increasedas the number of competitors increased. Interestingly, lonegoats achieved an intake rate that was higher than when onecompetitor was present but similar to when two or more competitorswere present. Faster intake rates may allow herbivores to ingesta larger portion of the available food before competing groupmembers arrive at the patch. This however, does not explainthe high intake rates achieved when the goats were alone. Weprovide 2 potential explanations: 1) faster intake rates area response to greater risk incurred by lone individuals, theloss of social information, and the fear of being left behindby the group and 2) when foraging alone, intake rate is no longera trade-off between reducing competition and acquiring socialinformation. Thus, individuals are able to feed close to theirmaximum rate.     

The effects of dietary nitrogen to water-soluble carbohydrate ratio on isotopic fractionation and partitioning of nitrogen in non-lactating sheep

The main objective of this study was to investigate the relationship between partitioning and isotopic fractionation of nitrogen (N) in sheep consuming diets with varying ratios of N to water-soluble carbohydrate (WSC). Six non-lactating sheep were offered a constant dry matter (DM) allowance with one of three ratios of dietary N/WSC, achieved by adding sucrose and urea to lucerne pellets. A replicated 3 dietary treatments (Low, Medium and High N/WSC) × 3 (collection periods) and a Latin square design was used, with two sheep assigned to each treatment in each period. Feed, faeces, urine, plasma, wool, muscle and liver samples were collected and analysed for ¹⁵N concentration. Nitrogen intake and outputs in faeces and urine were measured for each sheep using 6-day total collections. Blood urea N (BUN) and urinary excretion of purine derivative were also measured. Treatment effects were tested using general ANOVA; the relationships between measured variables were analysed by linear regression. BUN and N intake increased by 46% and 35%, respectively, when N/WSC increased 2.5-fold. However, no indication of change in microbial protein synthesis was detected. Results indicated effects of dietary treatments on urinary N/faecal N, faecal N/N intake and retained N/N intake. In addition, the linear relationships between plasma δ¹⁵N and urinary N/N intake and muscle δ¹⁵N and retained N/N intake based on individual measurements showed the potential of using N isotopic fractionation as an easy-to-use indicator of N partitioning when N supply exceeds that required to match energy supply in the diet.     

Growth and feed utilization by F4 human growth hormone transgenic carp fed diets with different protein levels

The F₄ generation of human growth hormone (hGH) transgenic red common carp Cyprinus carpio had significantly higher growth rates than the non-transgenic controls. Protein and energy intakes were significantly higher in the transgenic carp than in the controls fed the 20% protein diet, but were not different between the two strains fed diets with 30 and 40% protein. Faecal protein loss, as a proportion of protein intake, was significantly lower in the transgenics than in the controls fed diets with 20 and 30% protein, but was not different between the two strains fed diet with 40% protein. Faecal energy loss, as a proportion of energy intake, was significantly lower in the transgenics than in the controls fed diet with 20% protein, but was not different between the two strains fed diets with 30 and 40% protein. Recovered protein, as a proportion of protein intake, was significantly higher in the transgenics than in the controls fed all diets, whereas recovered energy was significantly higher in the transgenic fish fed the 40% protein diet. For fish fed each diet, the transgenics had significantly higher body contents of dry matter and protein, but lower contents of lipid than the controls. It was concluded that transgenics were more efficient in utilizing dietary protein than the controls. At a lower dietary protein level, transgenics achieved higher growth rates mainly by increasing feed intake; at higher levels of dietary protein, transgenics achieved higher growth rates mainly through a higher energy conversion efficiency.     

A causal analysis of diet composition in free ranging cattle in reed-dominated vegetation

Summary Theoretical and observed diets of free-ranging yearling cattle in an area of reed-dominated vegetation were related to constraints inherent to ruminants (rumination time as reflected in the zone of acceptable crude fibre content of the ration; rumen fill) and in more general terms, to requirements for minerals (Na, Ca, Mg, P), for protein and for metabolisable energy in order to balance the growth rate achieved by experimental animals. Theoretical diets in spring were mainly limited by feeding time; theoretical diets in summer and autumn were mainly limited by rumen capacity. The high proteinto-energy ratio in the forage species caused protein intake to exceed the animals' demands. Mineral intake was in excess of requirements except for sodium. Yearling cattle in our study area maximized their energy intake, with feeding time, rumen capacity and crude fibre content of the forage as important constraints.     

Can grazing sheep compensate for a daily foraging time constraint?

1. Theoretical studies of large herbivore foraging assume that total daily grazing time is a key constraint on daily intake and diet choice. We experimentally tested this assumption and investigated the effects of food availability on the ability of grazing sheep to compensate for restriction of available daily grazing time.
2. Foraging behaviour, intake and diet digestibility by sheep, were measured on grass pastures in a replicated 2 × 2 factorial experiment, in which overnight access to pasture was varied (restricted overnight and continuous access) on two sward heights (5·5 and 3·0 cm), representing high and low food availability.
3. Regardless of food availability, the overnight-restricted sheep fed for almost all of the available grazing time by grazing for fewer, longer foraging bouts, but still had much shorter total daily grazing time than the continuous access sheep.
4. In response to overnight penning, the sheep had a significantly higher instantaneous rate of intake achieved mainly via larger bites. The continuous access sheep were hence not maximizing their short-term rate of intake, whilst grazing according to the daily schedule considered normal for sheep.
5. The behavioural responses to overnight food restriction were able to counteract the reduction in daily grazing time only where food availability was high. In contrast on short swards overnight grazing restriction led to a reduction in total daily intake. We suggest that the interactions between the factors considered as constraints on foraging behaviour of herbivores are, as yet, only poorly quantified.     

Diet switching in a generalist mammalian folivore: fundamental to maximising intake

Generalist mammalian herbivores exploit a diverse diet. A generalised feeding strategy utilises a mixed diet to obtain a range of nutrients and to reduce the detoxication load of similar groups of plant secondary metabolites (PSMs). There is limited research investigating how mammalian herbivores achieve this dietary mixing in their daily foraging activities. We investigated the patterns of, and behaviours associated with, dietary mixing in a generalist mammalian folivore, the common brushtail possum (Trichosurus vulpecula). Possums were offered foliage of two eucalypt species (Eucalyptus globulus and E. regnans) as either (a) Full choice: both species offered for 8 h; (b) Restricted choice: both species offered for 2×2 h blocks; (c) G–R no choice: E. globulus offered for the first 4 h, E. regnans offered for next 4 h; and (d) R–G no choice: E. regnans offered for first 4 h, E. globulus offered for next 4 h. We hypothesised that possums would maximise intake on the Full choice diet, where time availability was greatest in combination with a choice of foliage. We also hypothesised that diet switching, defined as the frequency of changing between food types while feeding, would play a fundamental role in maximising intake. Possums achieved maximum intake on the Full choice diet and minimum intake on the No choice diets. Although intake was similar between the Restricted choice and No choice diets, possums achieved this intake in half the amount of time when able to switch regularly between foliage on the Restricted choice diet. We conclude that a generalist herbivore’s ability to effectively switch diets when foraging is fundamental to maximising intake. Hence, the degree of plant heterogeneity in an environment, and the spatial scale at which it occurs, may affect an herbivore’s foraging decisions and, ultimately, influence its foraging efficiency.     

Peripheral Serotonin: a New Player in Systemic Energy Homeostasis

Whole body energy balance is achieved through the coordinated regulation of energy intake and energy expenditure in various tissues including liver, muscle and adipose tissues. A positive energy imbalance by excessive energy intake or insufficient energy expenditure results in obesity and related metabolic diseases. Although there have been many obesity treatment trials aimed at the reduction of energy intake, these strategies have achieved only limited success because of their associated adverse effects. An ancient neurotransmitter, serotonin is among those traditional pharmacological targets for anti-obesity treatment because it exhibits strong anorectic effect in the brain. However, recent studies suggest the new functions of peripheral serotonin in energy homeostasis ranging from the endocrine regulation by gut-derived serotonin to the autocrine/paracrine regulation by adipocyte-derived serotonin. Here, we discuss the role of serotonin in the regulation of energy homeostasis and introduce peripheral serotonin as a possible target for anti-obesity treatment.     

The Obesity Epidemic: A Consequence of Reduced Energy Expenditure and the Uncoupling of Energy Intake?

Obesity prevalence has increased, and increased energy intake or decreased physical activity are the two most obvious contributing factors. The percentage of Americans engaging in exercise has been stable over the past few decades, but decreases in occupation‐related energy expenditure are sufficient to partially explain increased obesity prevalence. Further, the contribution of energy intake and energy expenditure to the obesity epidemic is complicated because they are not independent—they are influenced by each other. For example, Mayer found that low activity levels were marked by higher body weight and higher “unregulated” energy intake levels. Conversely, higher activity levels were marked by lower body weight and energy intake that matched energy expenditure. Consistent with Mayer, we propose that because most Americans have low levels of occupation‐related activity, they do not benefit from the regulation of energy intake achieved at higher activity levels, resulting in weight gain due to energy intake exceeding energy expenditure.     

Effect of dietary lysine on muscle protein turnover in growing chickens.

Day-old male chickens were fed ad libitum isoenergetic diets containing 20% crude protein but differing in their lysine content (from 6.5 up to 11.3 g/kg). At 3 weeks of age, protein fractional synthesis rates in the pectoralis major muscle were determined using a large dose injection of 120 mumol per kg body weight of L-[4-3H] phenylalanine. Protein gain in the pectoralis major was measured between 19 and 23 days of age. Protein breakdown was obtained by calculating the difference between protein synthesis and deposition. Weight gain varied curvilinearly with dietary lysine intake and was maximum for 11.3 g lysine/kg of diet. In birds fed an adequate lysine intake (10.1-11.3 g/kg) protein fractional synthesis and breakdown rates were 23.6-25.9 and 17.8-19.8%/d respectively. Increasing lysine supplementation in the diet resulted in an impairment of protein fractional breakdown rates. By contrast, protein fractional synthesis rates remained unchanged owing mainly to an improvement in the synthesis efficiency (kRNA), until birds were fed an adequate lysine intake. These data suggest that the growth rate reduction of chickens fed lysine deficient diets was due to alterations in both rates of protein synthesis and breakdown in skeletal muscle. A maximum protein deposition is achieved when kRNA was optimal, ie for a dietary lysine content of about 9 g/kg, a value close to the requirement.     

Shorebird predation of horseshoe crab eggs in Delaware Bay: species contrasts and availability constraints

1. Functional responses -- the relationship between resource intake rate and resource abundance -- are widely used in explaining predator-prey interactions yet many studies indicate that resource availability is crucial in dictating intake rates. 2. For time-stressed migrant birds refuelling at passage sites, correct decisions concerning patch use are crucial as they determine fattening rates and an individual's future survival and reproduction. Measuring availability alongside abundance is essential if spatial and temporal patterns of foraging are to be explained. 3. A suite of shorebird species stage in Delaware Bay where they consume horseshoe crab Limulus polyphemus eggs. Several factors including spawning activity and weather give rise to marked spatial and temporal variation in the abundance and availability of eggs. We undertook field experiments to determine and contrast the intake rates of shorebird species pecking for surface and probing for buried eggs. 4. Whether eggs were presented on the sand surface or buried, we demonstrate strong aggregative responses and rapid depletion (up to 80%). Depletion was greater at deeper depths when more eggs were present. No consistent give-up densities were found. Type II functional responses were found for surface eggs and buried eggs, with peck success twice as high in the former. Maximum intake rates of surface eggs were up to 83% higher than those of buried eggs. 5. Caution is needed when applying functional responses predicted on the basis of morphology. Our expectation of a positive relationship between body size and intake rate was not fully supported. The smallest species, semipalmated sandpiper, had the lowest intake rate but the largest species, red knot, achieved only the same intake rate as the mid-sized dunlin. 6. These functional responses indicate that probing is rarely more profitable than pecking. Currently, few beaches provide egg densities sufficient for efficient probing. Areas where eggs are deposited on the sand surface are critical for successful foraging and ongoing migration. This may be especially true for red knot, which have higher energetic demands owing to their larger body size yet appear to have depressed intake rates because they consume smaller prey than their body size should permit.     

Comparative diurnal and nocturnal foraging behaviour and energy intake of premigratory Grey Plovers Pluvialis squatarola and Whimbrels Numenius phaeopus in South Africa

Estimates of the energy budgets of nonbreeding waders (Charadrii) have frequently been hampered by ignorance of the birds' nocturnal activities. During the premigratory period (March), Grey Plovers Pluvialis squatarola and Whimbrels Numenius phaeopus at the Zwartkops estuary, South Africa, foraged throughout the nocturnal as well as the diurnal low-tide period. Although both species continued to forage visually at night, they exhibited behavioural changes to compensate for the reduced visibility. Both species foraged more slowly at night, taking fewer steps per minute, and Grey Plovers paused for longer to search for prey. Prey items were sighted from shorter distances at night than during the day. Energy intake rates, however, did not differ significantly by day and night for either species, and both achieved over 40% of their daily low-tide period intake at night. The energy intake rates and total daily intake of Grey Plovers, which fed exclusively on the study area, exceeded allometrically predicted values.     

The feeding height preferences of two goat breeds fed Grewia occidentalis L. (Tiliaceae) in the Eastern Cape,South Africa

Nguni goats and Boer goats, which are farmed together in the savannas of the Eastern Cape Province, depend on the same feed resources. The feeding height intake rates and preferences of one of their most preferred browse species, Grewia occidentalis L. (Tiliaceae), were studied in order to indirectly determine resource partitioning between these goat breeds on the basis of feeding height. The two hypotheses tested were that taller Boer goats feed at higher levels than do Nguni goats and that both breeds have feeding height preferences that are related to differences in intake rates. Four individuals of each breed were fed branches attached to a height foraging board. The two breeds showed no particular height preference in either season. Bite rates varied with feeding height, while bite sizes and intake rates increased with feeding height. Boer goats had lower bite rates compared to Nguni goats, although both breeds achieved similar bite sizes and intake rates. Bites sizes and intake rates for both breeds were higher in summer than in winter, possibly because more browse biomass was available per branch in summer than in winter since G. occidentalis is deciduous. There was no evidence to support that feeding height preference was related to differences in intake rates. It is concluded that Boer goats may compete for forage resources during times of resource limitation. Thus, Nguni goats might be a more favourable breed in semi-arid savannas because of their smaller body-size and, therefore, absolute nutrient requirements as well as their better reproductive performance compared to Boer goats.     

Quantitative therapeutic plan for the treatment of obesity and a simple method for estimating appropriate caloric intake by using previous rate of weight loss

We have formulated an equation for the calculation of the caloric intake in a reducing diet that is suited to individual obese patients. We have designed a system in which the weight loss achieved after the intake of a fixed number of calories over a given period is used as a basis for the next weight-reducing plan for a given patient. We devised the formula Y = X - 1000 (b2/a2-b1/a1) for calculating the daily caloric intake (Y). X is the previous caloric intake; b1 is achieved weight loss (kg) in the previous period (a1 weeks); and b2 is the planned reduction in weight in the subsequent target period (a2 weeks).     

Functional implications of omnivory for dietary nutrient balance

Captive experiments have shown that many species regulate their macronutrient (i.e. protein, lipid and carbohydrate) intake by selecting complementary food types, but the relationships between foraging strategies in the wild and nutrient regulation remain poorly understood. Using the pine marten as a model species, we collated available data from the literature to investigate effects of seasonal and geographic variation in diet on dietary macronutrient balance. Our analysis showed that despite a high variety of foods comprising the diet, typical of a generalist predator, the macronutrient energy ratios of pine martens were limited to a range of 50–55% of protein, 38–42% of lipids and 5–10% of carbohydrates. This broad annual stabilisation of macronutrient ratios was achieved by using alternative animal foods to compensate for the high fluctuation of particular prey items, and sourcing non‐protein energy (carbohydrates and fats) from plant‐derived foods, particularly fruits. Macronutrient balance varied seasonally, with higher carbohydrate intake in summer–autumn, due to opportunistic fruit consumption, and higher protein intake in winter–spring. In terms of their proportional dietary carbohydrate intake the pine marten's nutritional strategy fell between that of true carnivores (e.g. the wolf) and more omnivorous feeders (e.g. the European badger). However, in terms of energy contributed by protein pine martens are equivalent to obligate carnivores such as the wolf and domesticated cat, and different to some omnivorous carnivores such as the domesticated dog and grizzly bears.     

Systematic review of dietary intervention trials to lower blood total cholesterol in free-living subjects

Objectives: To estimate the efficacy of dietary advice to lower blood total cholesterol concentration in free-living subjects and to investigate the efficacy of different dietary recommendations. Design: Systematic overview of 19 randomised controlled trials including 28 comparisons. Subjects: Free-living subjects. Interventions: Individualised dietary advice to modify fat intake. Main outcome measure: Percentage difference in blood total cholesterol concentration between the intervention and control groups. Results: The percentage reduction in blood total cholesterol attributable to dietary advice after at least six months of intervention was 5.3% (95% confidence interval 4.7% to 5.9%). Including both short and long duration studies, the effect was 8.5% at 3 months and 5.5% at 12 months. Diets equivalent to the step 2 diet of the American Heart Association were of similar efficacy to diets that aimed to lower total fat intake or to raise the polyunsaturated to saturated fatty acid ratio. These diets were moderately more effective than the step 1 diet of the American Heart Association (6.1% v 3.0% reduction in blood total cholesterol concentration; P<0.0001). On the basis of reported food intake, the targets for dietary change were seldom achieved. The observed reductions in blood total cholesterol concentrations in the individual trials were consistent with those predicted from dietary intake on the basis of the Keys equation. Conclusions: Individualised dietary advice for reducing cholesterol concentration is modestly effective in free-living subjects. More intensive diets achieve a greater reduction in serum cholesterol concentration. Failure to comply fully with dietary recommendations is the likely explanation for this limited efficacy.

Key messages

• Results from metabolic ward studies suggest that dietary change can reduce blood cholesterol concentrations by up to 15%
• In free-living subjects the standard step 1 diet of the American Heart Association lowers cholesterol concentration by about 3%, and about another 3% can be achieved with more intensive diets
• Difficulties in complying with the prescribed dietary change explain the failure to achieve the expected reductions in cholesterol concentrations
• It is important to be realistic about the reductions in cardiovascular risk that can be achieved by individual dietary counselling

     

Randomized controlled trial of dietary intervention: association between level of urinary phenolics and anti-mutagenicity

We have undertaken a randomized trial to confirm the ability of a class of phenolics, flavonoids, to increase urinary anti-mutagenicity in smokers. Ninety heavy smokers were recruited and randomly assigned to three groups, who were given three different diets. One diet was rich in flavonoids, but not based on supplementation ('flavonoid'), one was a normal iso-caloric diet with an adequate administration of fruit and vegetables ('normal'), and one was based on supplementation of flavonoids in the form of green tea and soy products ('supplement'). The urinary anti-mutagenicity-as inhibiting effect of the urinary extracts on the mutations induced by MeIQx-was measured in Salmonella typhimurium YG1024 in the presence of liver S9 from male Sprague-Dawley rats treated with Aroclor 1254. The amount of total phenolics in the urinary extracts was measured by use of spectrometric analysis. We found that important dietary modifications can be achieved through special recipes and instructions given by a cook during an intensive course. The intervention was focused on increasing the flavonoid intake, and it was successful in that respect. In fact, differences in flavonoid intake were appreciated mainly between the first group (normal diet) and the other two (flavonoid-rich and supplemented diet), suggesting that dietary modification can be as effective as supplementation. However, both urinary anti-mutagenicity and the amounts of urinary phenolics did not change as a consequence of the trial. These results suggest that only a small fraction of urinary phenolics is influenced by dietary changes in the intake of flavonoids, and that most urinary anti-mutagens and phenolics are metabolites of dietary flavonoids, whose formation is more affected by the activity and diversity of bacterial flora in the colon than by the quantity and type of intake. A strong correlation was found between urinary phenolics and anti-mutagenicity in all the groups involved in the trial. Such correlation was not explained by dietary variables.     

Foraging effort, food intake, fat deposition and puberty in female mice

A novel caging system was used to study the interrelationships between foraging effort, food intake, growth and sexual maturation of peripubertal female mice. Females housed in these cages were forced to work (forage) at various intensities in order to obtain food pellets. It is argued that this is a biologically more meaningful approach to understanding the energetics of sexual development than the traditional approach of simple underfeeding. Female mice exhibited a cascade of developmental adjustments and deficits when challenged to forage harder for less food. The functions most sensitive to increased foraging effort were sexual development and growth in body length; growth in body weight was intermediate and fat deposition was least sensitive of all. The relative insensitivity of fat deposition to higher foraging costs suggests a strategy for survival during the postweaning dispersal movements of the wild ancestors of the laboratory mouse. Finally, regression analyses suggested that heavier females who had less than average body fat and higher than average food intake achieved their pubertal ovulation most rapidly.     

Simultaneous estimation of daily weight and feed intake curves for growing pigs by random regression

In this study, random regression models were used to estimate covariance functions between feed intake and BW in boars from the two breeds: the Norwegian Landrace and the Norwegian Duroc. In total, 1476 animals of the Norwegian Landrace breed and 1300 animals of the Norwegian Duroc breed had registrations on daily feed intake and growth from 54 to 180 days of age. Random regressions on the Legendre polynomials of age were used to describe genetic and permanent environmental curves in BW (up to the second order) and feed intake (up to the first order) for both the breeds. Heritabilities on BW increased over time for the Landrace (0.18 to 0.24), but were approximately constant for the Duroc (0.33 to 0.35). Average heritabilities for feed intake were approximately the same in both the breeds (0.09 to 0.11), and the estimates decreased over time, most pronounced in Duroc. On the basis of the current data, daily feed intake was seemingly controlled by the same genetic factors throughout the test period for Duroc; however, for Landrace, genetic correlations between test days decreased with increasing distance in time. For BW, the genetic correlations between test days were in general high, and did not go below 0.8 for any of the two breeds in this study. For both feed intake and BW, permanent environmental correlations between start and end of the test were reduced with increasing difference in days, most pronounced in Duroc. This study indicates that weight of the animal at the end of the test was more closely genetically correlated to feed intake of earlier periods compared with later periods of growth for both the breeds. This may be explained by the fact that BW is the cumulative growth of an individual, which is likely to be heavily affected by the feed intake during the most intense growth period.     

Selective decrease in protein intake following brain serotonin depletion.

The effect of reduced brain serotonin concentration achieved with drugs or raphé lesions on the control of protein intake and energy intake by young rats was examined. All rats were provided an oppurtunity to select from 15% and 55% casein diets provided simultaneously in two food cups. Systemic parachlorphenylalanine, central 5, 7-dihydroxytryptamine or mid-brain raphé lesions reduced by 20–30% the amount of protein consumed from these two diets over a two week study period. Across these same groups total energy intake was not different from the control groups. This decrease in the proportion of dietary energy selected as protein by the treated self-selecting rats was associated with the reduction observed in brain serotonin and its major metabolite, 5-hydroxyindole acetic acid at the completion of the feeding period. These findings support previous work implicating brain serotonin metabolism in the selective control of protein intake.