Macronutrient Self-selection Research Articles

Food limitation and starvation independently affect predator macronutrient selection.

Predators are often food limited in their habitat, and some are limited by specific macronutrients (protein, lipid or carbohydrate). It is unresolved, however, to what extent and in what way food and macronutrient limitation are connected. Using a carabid beetle (Nebria brevicollis), we compared macronutrient self-selection of the animals three times: immediately after collection in the field, after being fed to satiation and nutritional balance and after a subsequent period of starvation. Both sexes were food and females lipid limited in the field; after 7-21 days of starvation both sexes increased proportional carbohydrate intake significantly. Thus, starvation created a nutrient deficit that was different from what the animals had experienced in the field. We conclude that while macronutrient limitation in nature may be influenced by hunger due to food limitation, this is not its main determinant. A nutritional imbalance of available food may override this effect.

Macronutrient intake of dogs, self-selecting diets varying in composition offered ad libitum.

The diet of the domestic dog has changed significantly from that of its wolf ancestor, with to date only two studies having examined macronutrient self-selection in dogs. Whilst the first focused solely on protein intake, determining an intake of 30% metabolisable energy (ME), the second investigated dietary protein, fat and carbohydrate (PFC), indicating an intake ratio of 30:63:7% by energy. This study's aim was to further elucidate macronutrient intake by providing greater macronutrient range, energy content, and to investigate over a longer duration than previous studies. Fifteen adult dogs were given access to three wet diets providing 500% of daily ME, twice daily over 10days. The diets were nutritionally complete and formulated using the same four ingredients in different proportions to supply high levels of protein (58% ME), fat (86% ME) or carbohydrate (54% ME). Overall fat and carbohydrate consumption significantly declined from 6,382 to 917kcals per day (p<0.001) and 553 to 214kcalsday-1 (p<.01) respectively. Protein intake, however, remained constant over the study and ranged from 4,786 to 4,156kcalsday-1 . Such results impacted on percentage total energy intake, with fat decreasing from 68% to 52% (p<.001) and protein increasing from 29% to 44% (p<.01). Our findings suggest that dogs still possess a "feast or famine" mentality, wherein energy dense fat is prioritised over protein initially. With continued feeding over 10days, a transition to a more balanced energy contribution from both macronutrients is evident. The study also shows that given the option, dogs do not select carbohydrate to be a significant portion of the diet. The health implications of such dietary selection are of interest.

Daily self-feeding activity rhythms and dietary self-selection of pirarucu (Arapaima gigas)

Daily feeding rhythms and the ability of pirarucu (Arapaima gigas) to compose a balanced diet through macronutrient self-selection were evaluated. Twelve fish (1573.3±74.4g) were distributed in six tanks of 250l, two fish per tank. First, three experimental diets were prepared using an incomplete mixture of macronutrients (75%protein/25%carbohydrate-PC, 75%protein/25%fat-PF and 10% protein/45%fat/45%carbohydrate-PFC). These diets were provided to fish through a self-feeding system connected to a computer to record feeding activity. After this procedure, fish were challenged with a 50% protein dilution (diets: PC50 and PF50). The results showed that pirarucu exhibited a strict diurnal feeding pattern with 95.4% of daily feeding activity observed in the daytime. Fish selected 56.3% P, 24.2% C, 19.5% F, and consumed 150–151kJ/kg BW/day of energy. After protein dilution, fish sustained energy intake by increasing the consumption of PC50 and PF50 to maintain the target protein intake of the previous stage. When fish were protein-restricted, they failed to sustain previous energy intake. These findings can be used to design feeding regimes and for formulating aquafeed for pirarucu. Statement of relevanceThe use of an automatic feeder system activated by the fish could allow the animal to feed at their preferred time and hence reduces waste and improve the intake. Studies that consider the fish preference as a guide in designing diets can provide data on mechanisms of nutrient intake regulation for the development of aquafeeds for new species with potential for aquaculture.

A study on macronutrient self-selection after acute aerobic exercise in college females.

[Purpose] This study was conducted to determine whether acute aerobic exercise (climbing) is associated with changes in the dietary intake pattern. [Subjects and Methods] Food intake and physical activity data for 15 female college students were sampled for 3 days and categorized according to routine activity or high-intensity activity such as hiking. Nutrient intake based on the data was analyzed using a nutrition program. [Results] Carbohydrate and protein intake was significantly decreased after exercise compared to before acute aerobic exercise, but lipid intake showed no significant difference. Calorie intake was significantly decreased after exercise compared to before exercise; however, calorie consumption was significantly increased after exercise. [Conclusion] Aerobic exercise causes a decrease in total calories by inducing reduction in carbohydrate and protein intake. Therefore, aerobic exercise is very important for weight (body fat) control since it causes positive changes in the food intake pattern in female students.

A test of “nutritional wisdom” in perch (Perca fluviatilis) by self-selection of encapsulated macronutrients

Developing optimal diets based on fish macronutrient requirements is an expensive and laborious task requiring years of research. However, many species of fish can compose a species-specific optimal diet from single source macronutrients in capsules through self-selection. Eurasian perch is a species in which commercial culture is still in development and determination of whether this species can self-select its own diet is still unknown. Twenty-four individually held Eurasian perch (Perca fluviatilis) were trained to eat capsules of three different colours (purple, yellow and white) filled with a commercial diet. The fish exhibited a pronounced preference for the purple capsules. After training, capsules of each colour were then filled with either of three pure macronutrients to subvert the colour bias. There was still a preference of purple capsules which decreased with time. The resulting self-selection of macronutrients showed a significant lower selection of capsules with carbohydrates (17%) but no significant difference between fat (45%) and protein (38%). This self-selected proportion of macronutrients deviates from the recommended diet for farmed perch; 62% protein, 26% carbohydrates and 12% fat. The self-selected mean energy level with commercial feed in the capsules (133.0±10.6kJkgBW−1day−1) filled with the commercial diet was significantly lower than when the capsules were filled with macronutrients (197.0±24.1kJkgBW−1day−1). The perch actively selected against carbohydrates and reduced the number of capsules eaten when offered macronutrients, although not sufficient to keep daily energy intake at a constant level compared to the commercial diet. This result together with the preference for a specific colour implies that self-selection of diet composition may not be a suitable tool for the feed optimization of perch.

Use of self-feeders to evaluate macronutrient self-selection and energy intake regulation in Nile tilapia

Our objective was to evaluate the capacity of Nile tilapia ( Oreochrmis niloticus) to self-select the most nutritious foods when offered with other foods. The fish were offered pairs of macronutrients (protein + carbohydrate, PC; protein + fat, PF; carbohydrate + fat, CF) in three self-feeders and subjected to different challenges: i) the relative position of the self-feeders was changed, ii) the protein content was reduced by 50%, and iii) protein was withdrawn. In the experiment, 90 males (142.0 ± 18.0 g) were kept in 6 tanks (150 l each) and their daily macronutrient intake was calculated. Regardless of the self-feeder position, fish composed a diet containing 41.7% P, 34.8% C and 23.5% F, and a relatively stable energy content of around 187.0 kJ/kg BW/day. When the protein-containing diets (PC and PF) were diluted by 50%, fish increased their food intake to compensate for the energy dilution and thus sustain the dietary composition (42.6% P, 33.3% C and 23.2% F). Finally, when PC and PF were removed, fish maintained the energy intake at around 178.2 kJ/kg BW/day. These results indicate that tilapia can adapt to protein dilution/removal to sustain its energy intake, making it a useful model for dietary selection and nutritional studies.

The effects of macronutrient self‐selection and sucrose form on energy intake, body composition, and aspects of the metabolic syndrome in rats

The effects of macronutrient self‐selection and sucrose form on energy intake, percent body fat, insulin tolerance, and fasting serum triacylglycerol (TG) were determined in young adult male Sprague Dawley rats over 21 days. In experiment one, 24 rats were weight matched to control (chow), sucrose (chow and 30% sucrose solution), or choice (chow, 30% sucrose solution, and lard) diets. Energy intake of sucrose rats was 25% chow and 75% sucrose while energy intake of choice rats was 27% chow, 32% sucrose, and 41% lard. Energy intake, body weight gain, and percent body fat were higher in the sucrose (1872±31 kcal/21d, 44±5 g/21d, 9.4±0.7%) and choice (1894±45 kcal/21d, 50±6 g/21d, 11.2±0.7%) rats than controls (1260±31 kcal/21d, 11±4 g/21d, 5.2±0.4%). Choice rats were less insulin sensitive than control or sucrose animals. TG were higher in sucrose (105±4 mg/dL) than control (58±4 mg/dL) or choice (75±9 mg/dL) rats. In experiment two, 16 rats were weight matched to either a 20% protein, 35.5% sucrose, 34.5% starch, and 10% fat diet or a 20% protein, 70% sucrose, and 10% fat diet. There were no differences in energy intake, body weight gain, percent body fat, insulin sensitivity, or fasting TG after 21 days. Thus, liquid, but not solid dietary sucrose promotes obesity. Macronutrient self‐selection influences the development of specific aspects of the metabolic syndrome independent of adiposity.Support: NIH R01 DK53903

Effects of chewing gum on specific macronutrient and total caloric intake in an afternoon snack

Hetherington and Boyland (2007) have reported that gum chewing in the afternoon after lunch produced a significant reduction in subsequent snack intake, compared to the control condition. The objective of the present study was to verify this observation and to assess specific macronutrient intake and total caloric intake after having chewed gum as compared with intake in the control, no‐gum condition. After consuming a standard lunch, subjects chewed gum for 15 minutes hourly for 3 hours and then were tested in a modified version of our Macronutrient Self‐Selection Paradigm (MSSP). The MSSP consisted of 12 snack foods in which macronutrient content was varied significantly and systematically in a 2 (Fat factor: High Fat and Low Fat) X 2 (Carbohydrate Factor: High Sugar and High Complex Carbohydrate) design. Results showed that, in the gum condition, subjects specifically decreased their caloric intake of high‐sugar, snack foods in comparison with their intake in the no‐gum condition. Intake of the other foods presented in the MSSP did not differ between the two conditions. These results suggest that chewing gum may be effective in the control of intake of sweet snacks and thereby would be useful in weight management. Funding provided by a research grant from the Wrigley Science Institute.

Macronutrient self-selection in Solea senegalensis fed macronutrient diets and challenged with dietary protein dilutions

Macronutrient self-selection and responses to dietary protein dilution were investigated in Senegalese sole, a flatfish species of interest for Mediterranean aquaculture. Eight groups of six sole were distributed among 75-l tanks and allowed to feed on three experimental diets composed of pure macronutrients: PC (75% crude protein and 25% carbohydrate), PF (75% crude protein and 25% crude fat) and PFC (10% crude protein, 45% crude fat and 45% carbohydrate). Choosing from the above diets, the sole selected a diet containing 68.0% crude protein, 15.7% crude fat and 16.3% carbohydrate. When the PF diet was diluted 50% with cellulose, the fish increased their feed intake to sustain the energy intake (5.0 kJ/kg BW/day). Their selection of fat remained unchanged, while carbohydrate selection significantly increased by 36% and protein selection slightly decreased by 11%. When both PC and PF were diluted 50% with cellulose, the sole increased their feed intake again to sustain their energy intake (5.2 kJ/kg BW/day). The sole sustained their fat intake, significantly increased their carbohydrate selection by 33%, and significantly decreased their protein selection by 18% compared with the initial situation. These results indicated that Senegalese sole can select from unevenly balanced diets to compose a protein-rich balanced (target) diet, reflecting their carnivorous feeding behaviour. In addition, sole tried to compensate dietary dilutions in order to regulate energy intake by altering their feed intake level and the relative proportions of macronutrients selected.

Effect of Chronic Treatment with Clomipramine on Food Intake, Macronutrient Selection and Body Weight Gain in Rats

Long-term treatment with clomipramine (CMI), a tricyclic antidepressant, induces food craving and body weight gain in patients. The present study investigated the effects of chronic treatment with CMI on total food intake, macronutrient selection, and body weight gain in rats. Male Wistar rats were maintained on a dietary self-selection regime with separate sources of protein, fat and carbohydrate. Animals received i.p. injections of CMI (0, 3, 10, 30 mg/kg) during 27 consecutive days. Food consumption and body weight were recorded daily and results were calculated as average of three consecutive days, namely during pre-treatment (3 d before pharmacological treatment), treatment (7th-9th; 16th-18th and 25th-27th days), and post-treatment (28th-33rd days). Results showed that CMI (30 mg/kg) significantly decreased energy intake during all treatment period, an effect that was related to a decrease in both carbohydrate-rich diet intake and body weight gain. At dose of 3 mg/kg CMI increased the total energy intake in the 16th-18th days, suggesting an apparent biphasic effect of chronic treatment with CMI on caloric intake. Chronic administration with CMI (27 d) did not alter protein-rich or fat-rich diet consumption. The main result of this study indicated that chronic treatment with CMI decreases rather than increase food consumption and body weight gain in rats exposed to a macronutrient self-selection procedure.

Macronutrient selection through post-ingestive signals in sharpsnout seabream fed gelatine capsules and challenged with protein dilution

Sharpsnout seabream ability for macronutrient self-selection was studied using gelatine capsules containing pure macronutrients. In particular, the existence of non-oropharyngeal chemosensory pathways involved on protein (P), fat (F) and carbohydrate (CH) selection, as well as sharpsnout seabream response to dietary protein dilution were investigated. In a sequence of experimental phases, sharpsnout seabream were fed a pelleted complete diet, an encapsulated complete diet or a combination of separately encapsulated pure macronutrients. In order to induce associative learning, capsules containing a given macronutrient were paired with a particular colour. The animals composed a diet containing 62.7% P, 21.3% CH and 16.0% F, in terms of macronutrient percentage intake, and this selection pattern was maintained throughout all experimental phases. In a second experiment, individually kept sharpsnout seabream were challenged with protein dilution. After protein capsules were diluted (from 91.9% P to 56.3% P) with cellulose, the animals increased their protein intake to compensate for dilution in such a way that their energy intake was not significantly modified (17.4 kJ/100 g BW vs. 17.6 kJ/100 g BW after dilution). These results show that sharpsnout seabream feeding on encapsulated diets are able to select and maintain a particular diet composition, as well as sustain their energy intake, without using the diet's oropharyngeal chemosensory properties. Moreover, they were also able to maintain their protein intake after dilution, which highlights the importance of this macronutrient in this omnivorous species.

Fetal programming of appetite by exposure to a maternal low-protein diet in the rat

Undernutrition in fetal life programmes risk of obesity and the metabolic syndrome in adult life. Rat studies indicate that exposure to a maternal low-protein diet throughout fetal life establishes a preference for high-fat foods. The present study aimed to assess the effect of low protein exposure during discrete 7-day periods of gestation upon feeding behaviour (full gestation 22 days). Pregnant rats were fed control or low-protein diet, with low-protein feeding targeted at day 0--7 (LP Early), day 8--14 (LP Mid) or day 15--22 (LP Late) of gestation. At 12 weeks of age, offspring were placed on a macronutrient self-selection regimen. Prenatal protein restriction programmed feeding behaviour in female, but not male, offspring. Among females, all low-protein exposed groups consumed less fat than the control group (P<0.05). Male offspring showed no changes in feeding behaviour. In males and females fed a low-fat chow diet, there were metabolic differences between the groups. LP Early and LP Late males had greater hepatic glycogen stores than control animals. There were no differences in the size of abdominal fat depots in either male or female rats exposed to low-protein diet at any point in gestation. The data suggest that programming of feeding behaviour is likely to be gender-specific and dependent upon the timing of nutrient insult in fetal life. This work may have implications for the development of the metabolic syndrome.

Self-selected macronutrient diet affects energy and glucose metabolism in brown fat-ablated mice.

Obese transgenic UCP-DTA mice have largely ablated brown adipose tissue and develop obesity and diabetes, which are highly susceptible to a high-fat diet. We investigated macronutrient self-selection and its effect on development of obesity, diabetes, and energy homeostasis in UCP-DTA mice. UCP-DTA and wild-type littermates were fed a semisynthetic macronutrient choice diet (CD) ad libitum from weaning until 17 weeks. Energy homeostasis was assessed by measurement of food intake, food digestibility, body composition, and energy expenditure. Diabetes was assessed by blood glucose measurements and insulin tolerance test. Wild-type and UCP-DTA mice showed a high fat preference and increased energy digestion on CD compared with a low-fat standard diet. On CD, wild-type mice accumulated less body fat (16.9%) than UCP-DTA (32.6%) mice, although they had a higher overall energy intake. Compared with wild-type mice, resting metabolic rate was reduced in UCP-DTA mice irrespective of diet. UCP-DTA mice progressively decreased their carbohydrate intake, resulting in an almost complete avoidance of carbohydrate. UCP-DTA mice developed severe insulin resistance but showed decreased fed and fasted blood glucose on CD. In contrast to wild-type mice, UCP-DTA mice were not able to reduce their weight gain efficiency on CD. This suggests that, because of the high fat preference of the background strain and the increased metabolic efficiency, brown adipose tissue-deficient mice still develop obesity and insulin resistance on a macronutrient CD even when decreasing overall energy intake. Through the avoidance of carbohydrates, however, they are able to maintain normoglycemia.

Mice bearing Acads mutation display altered postingestive but not 5-s orosensory response to dietary fat.

A previous survey of mouse inbred strains revealed a wide range in self-selected fat intake, from 26 to 83% of energy. The BALB/cByJ strain selected a lower percentage of fat intake (36%) than all other strains tested except for the CAST/Ei. BALB/cByJ mice are deficient in the short-chain acyl-CoA dehydrogenase (SCAD) enzyme due to a spontaneous mutation in Acads. We hypothesized that this deficiency would alter fat appetite and used three behavioral test paradigms to compare the response of BALB/cByKz. Acads -/- and BALB/cByKz. Acads +/+ mice to fat stimuli. First, during 10-day exposure to a macronutrient self-selection diet, Acads -/- mice consumed proportionately less fat and more carbohydrate than Acads +/+ mice, yet total energy intake was similar between strains. Next, in 48-h two-bottle preference tests, Acads +/+ mice displayed a preference for 50% corn oil, but Acads -/- mice did not. Finally, in brief-access taste tests employing successive 5-s presentations of corn oil in an ascending concentration series ending with 50%, there were no effects of strain on total licks, indicating that Acads does not alter acute orosensory response to this fat stimulus. With 15-s presentations, however, the Acads +/+ mice licked more of the 50% oil than Acads -/-, suggesting orosensory effects related to the increased exposure time. In contrast to corn oil, there were no strain differences in licking response to sucrose solution in either the two-bottle or brief-access taste tests. The observation that SCAD-deficient mice display altered postingestive responses to dietary fat provides further evidence for the metabolic control of feeding.

Patterns of food intake and self-selection of macronutrients in rats during short-term deprivation of dietary zinc

Although it has been known for more than 50 years that zinc (Zn) deficiency regularly and consistently causes anorexia in many animal species, the basic mechanism(s) that cause this phenomenon still remain(s) an enigma. The following studies describe feeding behavior in the early stages of zinc deficiency in the rat model. In one experiment, we used computerized feeding monitors that measured the intake of individual rats at 10-min intervals over 24-hr periods. Male rats were acclimated to the cages and fed a Zn-adequate egg-white-based diet, or a similar diet with <1.0 mg Zn/kg. Food intake was monitored for seven, consecutive 24-hr periods. The 24-hr food intake pattern of the Zn-deprived rats did not differ from the controls; they simply ate less food, mainly during the night hours, with no differences between groups during the day. Although Zn-deprived rats ate less food than controls, the percentage of total diet consumed during night and day did not differ between groups. In another experiment, we simultaneously offered male rats three isocaloric diets with different macronutrient compositions and with or without adequate Zn, and measured the amount of each diet selected during seven, 24-hr periods. The three diets contained either 57% protein from egg white, 30% fat from soybean oil, or 80% carbohydrate from a combination of starch, hydrolyzed starch, and sucrose. For the first four days on experiment, rats selected similar amounts of each diet. Then the Zn-deprived rats began to select only 50% as much of the protein diet as the controls. Similar results were obtained when the data were expressed on the basis of each macronutrient as a percentage of the total diet selected. Zn-deprived rats selected a diet that contained 8% protein, 73% carbohydrate, and 6% fat while the Zn-adequate rats selected 12% protein, 69% carbohydrate, and 6% fat. Fat intake was not affected by Zn-deprivation. The results confirm our previous findings, and are discussed in terms of Zn-deprivation blunting the pathways of signal transduction that involve the peptide hormones known to affect food intake regulation.

Macronutrient selection through postingestive signals in sea bass fed on gelatine capsules

The role of the food orosensory properties on protein (P), fat (F) and carbohydrate (CH) self-selection was investigated in fish fed gelatine capsules containing pure macronutrients. A total of 40 sea bass (39.6±6.2 g initial body weight) distributed in eight 75-l tanks were used. In a sequence of experimental phases, sea bass were fed a pelleted complete diet, an encapsulated complete diet or a combination of separately encapsulated pure macronutrients. In order to induce associative learning, capsules containing a given macronutrient were paired with a particular colour. Our results demonstrate that fish are able to regulate food intake, so as to balance their energy intake, when they are fed a complete encapsulated diet and, therefore, without using the orosensory properties of the diet. Moreover, sea bass learn to discriminate and select among colour-coded, pure macronutrient capsules to compose a complete and balanced diet using colour as the only external cue. The composition of selected diet was 55% P, 23% CH and 22% F in terms of macronutrient percentage. The diet orosensory properties do not seem to be necessary to regulate macronutrient intake either, suggesting that an associative learning between capsule colour and content can be established through monitoring of macronutrient intake by postingestive and/or postabsorptive mechanisms. These results provide the first insight into energy and macronutrient self-selection by fish fed on gelatine capsules containing separate macronutrients.

Macronutrient self-selection in European sea bass in response to dietary protein or fat restriction

Because European sea bass (Dicentrarchus labrax L.) has strictly carnivorous feeding habits, protein and fat are the most important dietary components. In this paper we study the effect of restricted availability of protein and fat on the feeding behaviour and macronutrient selection. To this end, five groups of 20 sea bass with a body weight of 100.0 ± 20.1 g (mean ± SD) were raised in five circular 450-L tanks. Each group could choose among three self-feeders (experiment 1 and 2), each containing a different, incomplete, diet: P + CH (55.4% protein, 18.5% carbohydrate, DM diet), P + F (55.4% protein, 18.5% fat) or F + CH (36.9% fat, 36.9% carbohydrate) or between two self-feeders (experiment 3), each containing protein (100%) or carbohydrate–fat (52.7% and 47.3% respectively). In experiments 1 and 2, sea bass selected a diet consisting of 65.3% digestible energy (DE) protein, 26.2% DE fat and 8.4% DE carbohydrate. The composition of the self-selected diet did not differ when sea bass selected between the two diets in experiment 3. When fish were deprived of protein for two weeks, or deprived of fat for three weeks, they were unable to sustain their previous energy intake. This phenomenon was particularly evident during protein fasting, with the intake of fat and carbohydrate being negligible. During the first 2–3 days, after each fasting period, sea bass showed hyperphagic behaviour, but restricted availability of specific nutrients did not trigger any subsequent increased intake of these specific macronutrients. In conclusion, although sea bass were able to self-compose a nutritionally balanced diet from three or two incomplete diets, no specific hunger was elicited after two weeks of protein fasting or three weeks of fat fasting.

Effect of water temperature and short-term fasting on macronutrient self-selection by common carp (Cyprinus carpio)

Abstract The influence of water temperature (17 and 25 °C) and a period of fasting on the self-selection of macronutrients were examined in common carp held on a 12:12-h light/dark cycle. Eight replicate groups of juvenile carp (ca. 15 g body weight at 17 °C and 25 g at 25 °C) were fed with three test diets [high-protein (HP), high-fat (HF) and high-carbohydrate (HC) diets] by individual self-feeders for 3 weeks, followed by a 2-week period of fasting and then 3 weeks of refeeding. At 17 °C, the carp initially selected the HP and HF diets [HP/HF/HC (%)=38:40:22], whereas at 25 °C, the carp selected the HP diet over the others (55:21:24). After fasting, the carp tended to increase their demand for the HF diet at 17 °C and for the HC diet at 25 °C, but the overall self-selection of the test diets did not differ markedly from that prior to fasting. Carp held at 17 °C had higher relative whole body fat content and plasma triglyceride concentration; the latter decreased markedly during fasting. These results suggest that water temperature influences the macronutrient selection by carp: a relatively high demand for both protein and fat at 17 °C and for protein at 25 °C. Two weeks of fasting, however, did not markedly alter their macronutrient selection.

Influence of decreasing water temperature and shortening of the light phase on macronutrient self-selection by rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio

SUMMARY: Macronutrient self-selection patterns in rainbow trout and common carp, which were maintained in groups, were examined when both water temperature and duration of light phase gradually decreased. Three semipurified macronutrient diets composed mainly of protein (casein and gelatin; crude protein (CP) = 65%), fat (pollock oil and soybean oil; crude fat (CF) = 38%), or digestible carbohydrate (dextrin and gelatinized starch; crude starch (CS) = 57%) were offered to five groups of trout (20 fish/group, 51 g/fish) and carp (15 fish/group, 36 g/fish) using three self-feeders. A standard diet (ST) containing the three macronutrients at an appropriate ratio (CP = 47%, CF = 14%, CS = 25%) was also offered to three groups each by a single self-feeder. After an initial 3 weeks of experiencing a long photoperiod (14 h light : 10 h dark cycle) and high water temperature (trout, 17°C; carp, 25°C), the light phase and temperature were gradually decreased in the following 3 weeks to 10 h light : 14 h dark, and 8°C for trout and 13°C for carp, and feeding was continued for a further 3 weeks under low temperature and short photoperiod conditions. Growth and protein utilization parameters between the ST diet self-fed groups and macronutrient diet self-selection groups were not different (P > 0.05) for both trout and carp. Trout preferred the high-protein diet (HP) to the high-fat and the high-carbohydrate diets (P < 0.05) regardless of the changes in water temperature and photoperiod. Carp also preferred the HP diet (P < 0.01) under the high temperature and long photoperiod conditions; however, this preference gradually disappeared with lower temperatures and shorter photoperiods. These results suggest that the most appropriate macronutrient ratios in carp diets change with environmental conditions.

Effect of short-term fasting on macronutrient self-selection in sea bass

The influence of two different fasting periods on macronutrient self-selection during refeeding was studied in sea bass. Twelve groups of three sea bass were kept under laboratory conditions with a 12:12 light–dark cycle and at 22.5°C. Each aquarium was provided with three self-feeders containing three different diets made up of two macronutrients: protein–fat, protein–carbohydrate, and carbohydrate–fat. The fish were allowed to acclimatise to the diets and laboratory conditions in 4 weeks, during which they selected a baseline diet of 51% protein, 16.5% carbohydrate, and 32.5% fat, in terms of digestible energy. The fish were then deprived of food for 6 days, after which they were permitted to refeed. When food demands stabilised, they were subjected to total food deprivation for another 2 weeks. The total energy demanded from all the macronutrients increased significantly during the first day after both fasting periods. The proportion of macronutrient self-selection after fasting periods remained unchanged in respect to the baseline, except for protein energy which remained high in the two first days of refeeding after the second fasting period (the 51% of total demanded energy from protein during the baseline period rising to 60%). In short, after two short fasting periods of different length, sea bass showed a compensatory ingestion of energy, with a slightly increased demand from protein after the longest fasting period.