Substrate oxidation during exercise in the rat cannot fully account for training-induced changes in macronutrients selection

What does self-selection of dietary proteins in rats tell us about protein requirements and body weight control?

Omnivores are able to correctly select adequate amounts of macronutrients from natural foods as well as purified macronutrients. In the rat model, the selected protein levels are often well above the requirements estimated from the nitrogen balance. These high intake levels were initially interpreted as reflecting poor control of protein intake, but the selected levels were later found to be precisely controlled for changes in dietary protein quality and adjusted for cold, exercise, pregnancy, lactation, age, etc. and therefore met physiological requirements. Several authors have also suggested that instead of a given level of protein intake, rodents regulate a ratio of protein to dietary carbohydrates in order to achieve metabolic benefits such as reduced insulin levels, improved blood glucose control, and, in the long term, reduced weight and fat gain. The objective of this review was to analyze the most significant results of studies carried out on rats and mice since the beginning of the 20th century, to consider what these results can bring us to interpret the current causes of the obesity pandemic and to anticipate the possible consequences of policies aimed at reducing the contribution of animal proteins in the human diet.

The Physiology of Exercise in Free-Living Vertebrates: What Can We Learn from Current Model Systems?

SYNOPSIS

Many behaviors crucial for survival and reproductive success in free-living animals, including migration, foraging, and escaping from predators, involve elevated levels of physical activity. However, although there has been considerable interest in the physiological and biomechanical mechanisms that underpin individual variation in exercise performance, to date, much work on the physiology of exercise has been conducted in laboratory settings that are often quite removed from the animal's ecology. Here we review current, laboratory-based model systems for exercise (wind or swim tunnels for migration studies in birds and fishes, manipulation of exercise associated with non-migratory activity in birds, locomotion in lizards, and wheel running in rodents) to identify common physiological markers of individual variation in exercise capacity and/or costs of increased activity. Secondly, we consider how physiological responses to exercise might be influenced by (1) the nature of the activity (i.e., voluntary or involuntary, intensity, and duration), and (2) resource acquisition and food availability, in the context of routine activities in free-living animals. Finally, we consider evidence that the physiological effects of experimentally-elevated activity directly affect components of fitness such as reproduction and survival. We suggest that developing more ecologically realistic laboratory systems, incorporating resource-acquisition, functional studies across multiple physiological systems, and a life-history framework, with reproduction and survival end-points, will help reveal the mechanisms underlying the consequences of exercise, and will complement studies in free-living animals taking advantage of new developments in wildlife-tracking.

Low-level laser therapy (LLLT) combined with swimming training improved the lipid profile in rats fed with high-fat diet

Obesity and associated dyslipidemia is the fastest growing health problem throughout the world. The combination of exercise and low-level laser therapy (LLLT) could be a new approach to the treatment of obesity and associated disease. In this work, the effects of LLLT associated with exercises on the lipid metabolism in regular and high-fat diet rats were verified. We used 64 rats divided in eight groups with eight rats each, designed: SC, sedentary chow diet; SCL, sedentary chow diet laser, TC, trained chow diet; TCL, trained chow diet laser; SH, sedentary high-fat diet; SHL, sedentary high-fat diet laser; TH, trained high-fat diet; and THL, trained high-fat diet laser. The exercise used was swimming during 8 weeks/90 min daily and LLLT (GA-Al-As, 830 nm) dose of 4.7 J/point and total energy 9.4 J per animal, applied to both gastrocnemius muscles after exercise. We analyzed biochemical parameters, percentage of fat, hepatic and muscular glycogen and relative mass of tissue, and weight percentage gain. The statistical test used was ANOVA, with post hoc Tukey-Kramer for multiple analysis between groups, and the significant level was p < 0.001, p < 0.01, and p < 0.05. LLLT decreased the total cholesterol (p < 0.05), triglycerides (p < 0.01), low-density lipoprotein cholesterol (p < 0.05), and relative mass of fat tissue (p < 0.05), suggesting increased metabolic activity and altered lipid pathways. The combination of exercise and LLLT increased the benefits of exercise alone. However, LLLT without exercise tended to increase body weight and fat content. LLLT may be a valuable addition to a regimen of diet and exercise for weight reduction and dyslipidemic control.

Efeitos de dois tipos de treinamento de natação sobre a adiposidade e o perfil lipídico de ratos obesos exógenos

OBJETIVO: Investigar os efeitos do exercício de natação intermitente em relação ao exercício contínuo e ao sedentarismo, em ratos Wistar, após o desenvolvimento de obesidade exógena pela administração de uma dieta hiperlipídica palatável sobre: evolução do peso corporal, ingestão alimentar, adiposidade, percentual de gordura dos tecidos e perfil lipídico. MÉTODOS: Foram utilizados ratos adultos, mantidos em gaiolas individuais, com livre acesso a água e comida. O protocolo experimental incluiu: 1) desenvolvimento da obesidade exógena (3 semanas), os animais foram divididos em: P: sedentários alimentados com dieta padrão Primor® (n=8) e H: sedentários alimentados com dieta hiperlipídica (n=32); 2) tratamentos (8 semanas subseqüentes), os animais (n=24) passaram a receber dieta padrão e foram divididos em: sedentário; treinado contínuo e treinado intermitente. Treinamentos (5x semana): Contínuo (90 minutos/dia) e Intermitente (3x30min/dia). Os animais foram submetidos à eutanásia (3 e 8 semanas), sendo coletados os tecidos adiposos, o fígado e o sangue. Foram determinados a adiposidade e o percentual de gordura dos tecidos adiposos e do fígado, o ganho de peso corporal, o consumo alimentar e o perfil lipídico. RESULTADOS: A dieta hiperlipídica aumentou a adiposidade, o percentual de gordura acumulada no fígado e desenvolveu dislipidemias. A troca de dieta e os dois tipos de treinamento foram capazes de reverter o quadro de obesidade exógena. Contudo, o exercício intermitente foi mais eficiente na redução da adiposidade e de ganho de peso. CONCLUSÃO: Associados à dieta balanceada, os treinamentos aplicados neste estudo poderiam ser utilizados como estratégia no controle de peso e de dislipidemias, tanto em modelos experimentais quanto em seres humanos.

Efficiency of intermittent exercise on adiposity and fatty liver in rats fed with high-fat diet

OBJECTIVE

This study aimed to examine and compare the effects of continuous or intermittent exercises on adiposity and fatty liver in rats fed with high-fat diet.

METHODS AND PROCEDURES

Wistar rats were divided according to diet composition-chow diet (C) or high-fat diet (H)-and kinds of exercise-sedentary (S), continuous (CE), or intermittent (IE) exercises. The CE group swam 90 min/day, and the IE group swam 3 x 30 min/day (at 4-h intervals between sessions); both groups exercised 5 days/week during 8 weeks. Body weight and food intake were recorded daily. Lipogenesis rate in vivo was determined by the incorporation of (3)H(2)O into saponified lipids in retroperitoneal (RET), epididymal (EPI), and visceral (VIS) white adipose tissues, brown adipose tissue (BAT), liver (L), and gastrocnemius muscle (GAST) using the gravimetric method. Total cholesterol, high-density lipoprotein (HDL)-cholesterol, and triacylglycerol (TG) were analyzed.

RESULTS

The major finding of this study is that IE was more efficient than CE in reducing the adverse effects of high-fat diet and sedentarism. There was an improvement in the lipid profile and a reduction in food intake, body weight gain, visceral and central adiposity, and fatty liver, contributing to the control of obesity and other comorbidities, including nonalcoholic fat liver diseases.

DISCUSSION

Earlier studies have discussed the effects of diet consumption on adiposity and their relation to chronic diseases and obesity. This study discusses the effects of high-fat diet consumption and the different kinds of exercise on weight gain, adiposity, fatty liver, and lipid profile in rats. The results may depend on the exercise, time of each session, age, gender, and experimental period.

Fat-depleted CLA-treated mice enter torpor after a short period of fasting

Resting energy expenditure (Resting-EE), EE with treadmill exercise, and post-prandial thermogenesis were continuously monitored by indirect calorimetry during a 24 h recording session in control (CT) and CLA-treated (CLA) (1% CLA in the food, by weight) C57Bl/6 male mice. After 15 days of CLA treatment, the fat content of CLA mice had fallen to 20% of that in CT mice. CLA mice were able to face the energy challenge of exercise but used less lipid than CT mice. Resting-EE values fell during the post-exercise period. The thermogenic response to a calibrated test meal given 5 h after the run abolished the differences in EE and substrate oxidation between CT and CLA mice. However, 2.5 h after ingestion of the test meal onward, CT mice gradually increased their lipid oxidation to sustain resting-EE levels. In contrast, CLA mice did not increase their lipid oxidation and their resting-EE levels fell significantly until they entered into torpor. Blood leptin was low but similar in CT and CLA-treated mice suggesting that leptin is not critical to induce torpor. We suggest that the durable inhibition of lipid oxidation in fasting CLA mice was an adaptive behaviour devoted at sparing the residual adipose deposits.

Rats free to select between pure protein and a fat-carbohydrate mix ingest high-protein mixed meals during the dark period and protein meals during the light period

Rats that are allowed to select their diets [dietary self- selection (DSS)] often ingest >30% of their daily energy in the form of protein. Such an intake may seem unhealthy, but the consistency of this choice suggests that it is motivated by physiologic drives. To gain a clearer understanding of how protein selection is structured during DSS, we adapted 12 rats to a standard diet (14% Protein) and then allowed them to choose between two diets, i.e., total milk protein (P) and a mix of carbohydrates and lipids (FC). The protein intake during DSS rose above 40%; assuming an intermeal interval of 10 min, 70% of the energy intake occurred with meals that included both P and FC, with the sequence of FC followed by P preferred to the sequence of P followed by FC (70 vs. 30%, P < 0.001). In addition, energy intake during the light period was reduced to only 10% of the daily energy intake [vs. 30% with the control P14 diet or a with a high-protein diet (50%)], and 90% of the intake was in the form of pure protein meals. In complementary studies, we verified that the high protein intake also occurred when rats were offered casein and whey and was not due to the high palatability of the milk protein. We conclude that a specific feeding pattern accompanies high protein intake in rats allowed DSS. The mechanisms underlying this behavior and its potential beneficial/adverse consequences over the long term still must be clarified.

A preexercise alpha-lactalbumin-enriched whey protein meal preserves lipid oxidation and decreases adiposity in rats

The composition of the preexercise food intake is known to affect substrate utilization during exercise and thus can affect long-term changes in body weight and composition. These parameters were measured in male rats exercised 2 h daily over 5 wk, either in the fasting state or 1 h after they ingested a meal enriched with glucose (Glc), whole milk protein (WMP), or alpha-lactalbumin-enriched whey protein (CPalphaL). Compared with fasting, the Glc meal increased glucose oxidation and decreased lipid oxidation during and after exercise. In contrast, the WMP and CPalphaL meals preserved lipid oxidation and increased protein oxidation, the CPalphaL meal increasing protein oxidation more than the WMP meal. At the end of the study, body weight was larger in the WMP-, Glc-, and CPalphaL-fed rats than in the fasted ones. This resulted from an increased fat mass in the WMP and Glc rats and to an increased lean body mass, particularly muscles, in the CPalphaL rats. We conclude that the potential of the CPalphaL meal to preserve lipid oxidation and to rapidly deliver amino acids for use during exercise improved the efficiency of exercise training to decrease adiposity.

A CLA mixture prevents body triglyceride accumulation without affecting energy expenditure in Syrian hamsters

We examined the effects of feeding conjugated linoleic acids (CLA) to adult male hamsters on several components of energy metabolism and body composition. Hamsters (n = 54) were assigned for 6-8 wk to one of three diets: 1) a standard diet (in percentage energy: lipids, 33, carbohydrates, 49, and proteins, 18); 2) to the standard diet augmented with the 9c,11t-isomer of CLA to 1.6% of energy (R group); or 3) the standard diet augmented with the 9c,11t-isomer and the 10t,12c-CLA isomer to 3.2 (1.6 + 1.6) % of energy (CLA mix group). (15)N uniformly labeled milk-protein was included in the diet to measure the incorporation of dietary protein into liver and muscle. Basal metabolic rate, thermogenic response to feeding and energy expenditure during spontaneous activity or during an exercise at approximately 60% of VO(2max) were measured. Carnitine palmitoyltransferase-I (CPT-I), leptin, insulin and triiodothyronine concentrations, as well as the in vivo overall adiposity changes were also determined. After 6 wk, the whole-body triglyceride content determined in vivo by NMR was significantly higher in the R group than in the control and CLA mix groups. The CLA mix group differed from the others in the lack of body triglyceride accumulation between d 21 and d 45 of the study, and the appearance of a slight insulin-resistance (homeostatic model assessment index, P < 0.05). Paradoxically, the lack of effect on whole-body lipid oxidation was associated with a greater CPT-I-specific activity in tissues of both CLA-fed groups (P < 0.05). No other major effects of CLA feeding were detected. In conclusion, CLA supplementation in hamsters did not affect adipose weight or the components of energy expenditure despite a theoretically higher capacity of red muscle to oxidize lipids. Only a CLA mixture prevented whole-body triglyceride accumulation over time.

Body weight, body composition, and energy metabolism in lean and obese Zucker rats fed soybean oil or butter

BACKGROUND

Dietary fat composition is thought to affect body weight regulation independent of the amount of fat ingested.

OBJECTIVE

We analyzed the feeding behavior, body weight gain, body composition, and energy metabolism in lean and obese rats fed a diet in which fat was in the form of either butter or soybean oil.

DESIGN

Ten lean (Fa/?) and 10 obese (fa/fa) adult Zucker rats were divided into 4 groups according to a 2 x 2 experimental design. They were fed a normally balanced diet over 11 wk in which 30% of energy was either soybean oil or butter. Food intake, body weight gain, and body composition were measured. Indirect calorimetry was used to study energy metabolism at rest and in relation to feeding and activity.

RESULTS

Food intake increased similarly in lean and obese rats after butter feeding. Body weight gain increased in obese rats and decreased in lean rats after butter feeding. Body weight gain in obese rats was due mainly to an increase in the weight of lean tissues besides muscle, whereas adiposity and distribution of fat between the various pads did not change. Resting metabolic rates and postprandial lipid oxidation increased in butter-fed obese rats. Lipid oxidation during exercise was not significantly different between obese and lean rats. Fat oxidation increased in butter-fed lean rats during treadmill running at moderate intensity.

CONCLUSIONS

In obese rats, basal metabolism and postprandial lipid oxidation increased during butter feeding, which appeared to prevent fat accumulation in the long term. In lean rats, butter feeding favored lipid utilization by working muscles, an observation that deserves further investigation in terms of endurance and performance.

The effect of repeated episodes of dietary restriction and refeeding on systolic blood pressure and food intake in exercise-trained normotensive rats

OBJECTIVE

To explore the effects of weight cycling and exercise on blood pressure and macronutrient intake in Sprague-Dawley rats.

RESEARCH METHODS AND PROCEDURES

Female Sprague-Dawley rats (n = 62; 5 months old) were assigned to an ad libitum (Con) or weight-cycled (Cyc) group. They were either sedentary (Con-Sed and Cyc-Sed) or exercise-trained (Con-Ex and Cyc-Ex) on a motorized treadmill (20 m/minute; 60 minutes/day; 6 days/week). The Cyc groups underwent 2 cycles of 3 weeks of 60% food restriction followed by 5 weeks of ad libitum refeeding using a macronutrient self-selection diet. Body mass and food intake were analyzed weekly. Systolic blood pressure (SBP) was measured at baseline and during the first and fifth weeks of each refeeding.

RESULTS

For both cycling periods, SBP was elevated in Cyc vs. Con groups at Week 1 of refeeding, but was similar among groups by Week 5 of refeeding. Both Con groups had greater total energy intake than the Cyc groups for both cycling periods (Cycle 1: 2882.2 +/- 75.1, Con-Sed; 2916.1 +/- 67.1, Con-Ex; 2692.2 +/- 58.7, Cyc-Sed; and 2780.5 +/- 52.4 kcal, Cyc-Ex) (Cycle 2: 2815.8 +/- 75.1, Con-Sed; 2938.8 +/- 49.4, Con-Ex; 2577.1 +/- 60.5, Cyc-Sed; and 2643.5 +/- 65.9 kcal, Cyc-Ex). Relative fat intake (percentage of total kcal/week) was significantly less for Con-Ex and Cyc-Ex than Con-Sed and Cyc-Sed throughout both refeeding periods.

DISCUSSION

Weight cycling failed to produce significant sustained effects on SBP, body mass, or food intake. Exercise training, irrespective of diet, lowered dietary fat intake.

Physical activity and preference for selected macronutrients

OBJECTIVE

The impact of physical exercise on macronutrient preferences was examined with a perspective to improve preventive and therapeutic strategies of obesity.

DESIGN

The literature was reviewed pertaining to the acute effects of physical activity and the short-term and chronic effects of exercise training on macronutrient preferences.

RESULTS

The presently available literature does not permit to establish a consensus regarding the impact of physical activity, be it acute or long-term, on macronutrient selection. However, one observation stands out and that is the fact that dietary fat intake needs to be controlled in order for exercise to produce a negative energy and fat balance.

CONCLUSION

Because active individuals do not systematically choose foods that are low in fat content, it is important to provide nutritional guidelines in a context where physical activity aims at reducing or better controlling body weight.