Opportunities for Consistent and Holistic Metrics to Support Food Systems Transformation: A Summary of a Symposium Presented at Nutrition 2023.

There is an urgent need for global food systems transformation to realize a future where planetary health reaches its full potential. Paramount to this vision is the ability of stakeholders across sectors to understand how foods and dietary patterns impact food systems inclusive of all domains of sustainability-environmental, nutrition/health, economic and social. This article is a synopsis of presentations by 3 food systems experts to share the latest science in a session entitled "How do you measure sustainability? Opportunities for consistent and holistic metrics to support food systems transformation" at the American Society for Nutrition's 2023 annual conference. As summarized here, global population data showing widespread malnutrition underscore the important role of dietary diversity through a balance of plant- and animal-source foods to achieve nutritionally adequate diets and reduce risk of noncommunicable diseases. Yet, recent international audits of countries, companies, and organizations and their sustainability targets largely demonstrate an underrepresentation of robust nutrition/health metrics to support public nutrition and health progress. Addressing limitations in diet-sustainability modeling systems provides a viable opportunity to accurately reflect the important contributions and trade-offs of diets across all domains of sustainability to ultimately support evidence-based decision making in advancing healthy food systems.

Assessment of Beverage Trends and Replacing Nondairy Caloric Beverages with Milk at Meals across Childhood Improves Intake of Key Nutrients at Risk of Inadequate Consumption: An NHANES Modeling Study.

Background: Milk is a key source of important nutrients including the nutrients of public health concern. However, most Americans do not meet current (dairy) United States Department of Agriculture (USDA) dietary guideline recommendations, and the intake has been declining. Objective: The aim of this study was to investigate milk and beverage intake trends and nutrient intakes from these products in United States children aged 6-18 y and to model the effect of isocaloric substitution of nondairy beverages with milk. Methods: Data from National Health and Nutrition Examination Survey (NHANES) 2001-2018 for children age 6-8 (N = 4696), 9-13 (N = 8117) and 14-18 y (N = 8514) were used with milk and other beverage intakes determined from the first 24-h in-person dietary recall. Nutrient intake was determined using the NHANES cycle-specific total nutrient intake files. Nutrient modeling was performed by isocaloric substitution with milk of all nondairy beverages consumed during lunch and dinner meals combined. Sample-weighted analyses were performed using SAS 9.4. Results: Between ages 6-8 and 14-18 y, daily intake of milk and flavored milk decreased by 10% and 62%, respectively, while daily intake of caloric beverages excluding milk increased by 96%. Daily intake from caloric beverages and milk combined decreased for fiber, protein, fat, saturated fat, calcium, magnesium, potassium, vitamin A, and vitamin D and increased for energy, carbohydrates, added sugars, and folate between ages 6-8 y and 14-18 y. Isocaloric substitution of all caloric nondairy beverages at meals with milk (using nutrient contribution of USDA milk, not further specified (NFS)) resulted in increases in protein, fat, saturated fat, calcium, magnesium, potassium, sodium, vitamin A, folate, vitamin B12, and vitamin D and decreases in carbohydrate, fiber, and added sugar. Conclusion: These findings provide additional evidence to support dietary recommendations for milk, and efforts should be made on behalf of leading health professionals and childhood meal programs to highlight milk as a beverage of choice in children and adolescents.

Perspective: The Benefits of Including Flavored Milk in Healthy Dietary Patterns.

The Dietary Guidelines for Americans recommend two-and-a-half cup equivalents of low-fat and fat-free dairy foods per day for children 4-8 y and 3 cup equivalents per day for adolescents aged 9-18 and adults. Currently, the Dietary Guidelines for Americans recognizes 4 nutrients as being of public concern because of suboptimal levels in the diet. These include calcium, dietary fiber, potassium, and vitamin D. In the American diet, dairy foods are leading contributors of calcium, vitamin D, and potassium. Milk, because of its unique nutrient package that provides shortfall nutrients to the diets of children and adolescents, remains an underpinning of dietary recommendations and is included with school meals. Despite this, milk consumption is declining, and >80% of Americans do not meet recommendations for dairy. Data indicate that children and adolescents who consume flavored milk are more likely to consume more dairy and adhere to healthier overall dietary patterns. Flavored milk, however, receives more scrutiny than plain milk because of its contribution of added sugar and calories to the diet and concerns over childhood obesity. Therefore, the purpose of this narrative review is to describe trends in beverage consumption in children and adolescents aged 5-18 y and highlight the science that has examined the impact of including flavored milk in overall healthy dietary patterns within this population.

Association of Dietary Protein Intake and Grip Strength Among Adults Aged 19+ Years: NHANES 2011-2014 Analysis.

Background: Research on the role of protein in the diet has evolved beyond a focus on quantity to include the impact of its quality and distribution across meal times in an effort to optimize dietary protein recommendations. Objective: To determine the association of dietary protein amount, type, and intake pattern with grip strength in adults. Design: Data from the National Health and Nutrition Examination Survey (NHANES) 2011-2014 for adults 19 + years (N = 9,214) were used with exclusions for pregnant and lactating women. Intakes of dietary total protein (TP), animal protein (AP, including dairy), plant protein (PP), and leucine (Leu) were determined using day 1 24 h dietary recall data after adjusting for the complex sample design of NHANES. Regression analyses were used to assess the association of dietary protein and leucine intake quartiles, and whether consuming > 20 g of dietary protein at one or more meals was related to grip strength with adjustment for age, gender, and ethnicity. Results: Mean intake of TP among adults aged 19 + years was 83.6 ± 0.5 g/day, and 2/3rd of this was from animal sources (including dairy). Grip strength increased (p < 0.05) with increasing quartiles of TP, AP, PP, and leucine among all adults 19 + years (ß = 1.340.19, 1.27 ± 0.19, 0.76 ± 0.20, and 1.33 ± 0.23, respectively), 19-50 years (ß = 1.14 ± 0.27, 1.06 ± 0.25, 0.77 ± 0.30, and 1.18 ± 0.27, respectively), and 51 + years (ß = 0.95 ± 0.26, 1.08 ± 0.27, and 1.05 ± 0.27, respectively, for TP, AP, and Leu); however, the increase was more pronounced for AP than PP. Grip strength also increased (p < 0.05) with increasing the number of meal occasions containing > 20 g of dietary protein (ß = 1.50 ± 0.20, 1.41 ± 0.25, and 0.91 ± 0.37 for 19+, 19-50, and 51 + years, respectively), and significant increases were detected for two meals compared to zero meals. Conclusion: Dietary protein quantity, quality, and distribution should be considered collectively when looking to optimize protein intake to support muscle strength and function.

Growth and Development of Preschool Children (12-60 Months): A Review of the Effect of Dairy Intake.

Undernutrition in young children is a global health issue. The ability to meet energy and nutrient needs during this critical stage of development is necessary, not only to achieve physical and mental potential but also socio-economic achievement later in life. Given ongoing discussions regarding optimization of dietary patterns to support achievement of the Sustainable Development Goals established by the United Nations, it is important to identify foods/food groups that have shown efficacy in reducing the negative impacts of undernutrition in young children. This narrative review addresses the impact of dairy intake, with a focus on linear growth, cognitive development and weight gain in early childhood (12-60 months). The impact of country economic status is also examined, to help elucidate regional specific recommendations and/or future research needs. Overall, the body of research addressing this age group is somewhat limited. Based on the data available, there is a positive association between dairy intake and linear growth. The impact of milk or dairy products on cognitive development is less clear due to a lack of evidence and is a gap in the literature that should be addressed. Regarding the impact on body weight, the majority of evidence suggests there is either no association or an inverse association between milk intake by preschool children on overweight and obesity later in life. This evidence is exclusively in high income countries, however, so additional work in lower income countries may be warranted.

Level of dietary protein intake affects glucose turnover in endurance-trained men.

BACKGROUND: To examine the effects of higher-protein diets on endogenous glucose metabolism in healthy, physically active adults, glucose turnover was assessed in five endurance-trained men (age 21.3 ± 0.3 y, VO2peak 70.6 ± 0.1 mL kg-1 min-1) who consumed dietary protein intakes spanning the current dietary reference intakes. FINDINGS: Using a randomized, crossover design, volunteers consumed 4 week eucaloric diets providing either a low (0.8 g kg-1 d-1; LP), moderate (1.8 g kg-1 d-1; MP), or high (3.6 g kg-1 d-1; HP) level of dietary protein. Glucose turnover (Ra, glucose rate of appearance; and Rd glucose rate of disappearance) was assessed under fasted, resting conditions using primed, constant infusions of [6,6-2H2] glucose. Glucose Ra and Rd (mg kg-1 min-1) were higher for MP (2.8 ± 0.1 and 2.7 ± 0.1) compared to HP (2.4 ± 0.1 and 2.3 ± 0.2, P < 0.05) and LP (2.3 ± 0.1 and 2.2 ± 0.1, P < 0.01) diets. Glucose levels (mmol/L) were not different (P > 0.05) between LP (4.6 ± 0.1), MP (4.8 ± 0.1), and HP (4.7 ± 0.1) diets. CONCLUSIONS: Level of protein consumption influenced resting glucose turnover in endurance athletes in a state of energy balance with a higher rate of turnover noted for a protein intake of 1.8 g kg-1 d-1. Findings suggest that consumption of protein in excess of the recommended dietary allowance but within the current acceptable macronutrient distribution range may contribute to the regulation of blood glucose when carbohydrate intake is reduced by serving as a gluconeogenic substrate in endurance-trained men.

Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis.

BACKGROUND: The effects of essential amino acid (EAA) supplementation during moderate steady state (ie, endurance) exercise on postexercise skeletal muscle metabolism are not well described, and the potential role of supplemental leucine on muscle protein synthesis (MPS) and associated molecular responses remains to be elucidated. OBJECTIVE: This randomized crossover study examined whether EAA supplementation with 2 different concentrations of leucine affected post-steady state exercise MPS, whole-body protein turnover, and mammalian target of rapamycin 1 (mTORC1) intracellular signaling. DESIGN: Eight adults completed 2 separate bouts of cycle ergometry [60 min, 60% VO(2)peak (peak oxygen uptake)]. Isonitrogenous (10 g EAA) drinks with different leucine contents [leucine-enriched (l)-EAA, 3.5 g leucine; EAA, 1.87 g leucine] were consumed during exercise. MPS and whole-body protein turnover were determined by using primed continuous infusions of [(2)H(5)]phenylalanine and [1-(13)C]leucine. Multiplex and immunoblot analyses were used to quantify mTORC1 signaling. RESULTS: MPS was 33% greater (P < 0.05) after consumption of L-EAA (0.08 ± 0.01%/h) than after consumption of EAA (0.06 ± 0.01%/h). Whole-body protein breakdown and synthesis were lower (P < 0.05) and oxidation was greater (P < 0.05) after consumption of L-EAA than after consumption of EAA. Regardless of dietary treatment, multiplex analysis indicated that Akt and mammalian target of rapamycin phosphorylation were increased (P < 0.05) 30 min after exercise. Immunoblot analysis indicated that phosphorylation of ribosomal protein S6 and extracellular-signal regulated protein kinase increased (P < 0.05) and phosphorylation of eukaryotic elongation factor 2 decreased (P < 0.05) after exercise but was not affected by dietary treatment. CONCLUSION: These findings suggest that increasing the concentration of leucine in an EAA supplement consumed during steady state exercise elicits a greater MPS response during recovery. This trial is registered at clinicaltrials.gov as NCT01366924.

High protein diet maintains glucose production during exercise-induced energy deficit: a controlled trial.

BACKGROUND: Inadequate energy intake induces changes in endogenous glucose production (GP) to preserve muscle mass. Whether addition provision of dietary protein modulates GP response to energy deficit is unclear. The objective was to determine whether exercise-induced energy deficit effects on glucose metabolism are mitigated by increased dietary protein. METHODS: Nineteen men ([mean ± SD] 23 ± 2 y, VO2peak 59 ± 5 ml·kg-1·min-1) were divided into three groups, two consuming moderate (MP; 0.9 g protein kg-1 d-1), and one high (HP; 1.8 g protein kg-1 d-1) protein diets (55% energy from carbohydrate) for 11 days. Following 4 days of energy balance (D1-4), energy expenditure was increased for 7 days (D5-12) in all groups. Energy intake was unchanged in two, creating a 1000 kcal d-1 deficit (DEF-MP, DEF-HP; n = 6, both groups), whereas energy balance was maintained in the third (BAL-MP, n = 7). Biochemical markers of substrate metabolism were measured during fasting rest on D4 and D12, as were GP and contribution of gluconeogenesis to endogenous glucose production (fgng) using 4-h primed, continuous infusions of [6,6-2H2]glucose (dilution-method) and [2-13C]glycerol (MIDA technique). Glycogen breakdown (GB) was derived from GP and fgng. RESULTS: Plasma ß-hydroxybutyrate levels increased, and plasma glucose and insulin declined from D4 to D12, regardless of group. DEF-MP experienced decreased plasma GP from D4 to D12 ([mean change ± SD] 0.24 ± 0.24 mg·kg-1·min-1), due to reduced GB from D4 (1.40 ± 0.28 mg·kg-1·min-1) to D12 (1.16 ± 0.17 mg·kg-1·min-1), P < 0.05. Conversely, BAL-MP and DEF-HP sustained GP from D4 to D12 ([mean change ± SD] 0.1 ± 0.5 and 0.0 ± 0.2 mg·kg-1·min-1, respectively) by maintaining GB. CONCLUSION: Exercise-induced energy deficit decreased GP and additional dietary protein mitigated that effect.

Dairy components and risk factors for cardiometabolic syndrome: recent evidence and opportunities for future research.

Cardiometabolic syndrome (CMS), a cluster of metabolic abnormalities that increases the risk of cardiovascular disease (CVD) and type 2 diabetes, affects over one-third of American adults and accounts for billions of dollars in health care costs annually. Current evidence indicates an inverse association between consumption of dairy foods and risk of CMS and its related disease outcomes. Although the specific mechanism(s) underlying the beneficial effects of dairy consumption on the development of CMS, CVD, and type 2 diabetes have not been fully elucidated, there is evidence that specific components within dairy such as milkfat, vitamin D, calcium, magnesium, potassium, and whey proteins may be individually or collectively involved. Specifically, each of these dairy components has been implicated as having a neutral or beneficial effect on one or more elements of CMS, including the serum lipid profile, blood pressure, fasting glucose, and body composition. Although several mechanisms have been identified by which components in dairy may beneficially affect symptoms associated with CMS, further research is required to better understand how dairy and its components may contribute to metabolic health. The purpose of this review is to present the mechanisms by which specific dairy components modulate risk factors for CMS and identify opportunities for future research.

Molecular responses to moderate endurance exercise in skeletal muscle.

This study examined alterations in skeletal-muscle growth and atrophy-related molecular events after a single bout of moderate-intensity endurance exercise. Muscle biopsies were obtained from 10 men (23 ± 1 yr, body mass 80 ± 2 kg, and VO(2peak) 45 ± 1 ml x kg⁻¹ x min⁻¹) immediately (0 hr) and 3 hr after a 60-min bout of cycle exercise (60% +/- 5% VO(2peak)). Corresponding muscle biopsies were also obtained under resting conditions. The phosphorylation status of insulin/IGF-PI3K molecular-signaling proteins, ubiquitin-proteasome-related gene expression, FOXO transcription factors, and myogenic regulatory factors in muscle samples was analyzed using multiplex analysis, Western blotting, and quantitative real-time polymerase chain reaction (qRT-PCR). A condition-time interaction was observed for Akt phosphorylation (p < .05) with multiplexing. Regardless of endurance exercise, Akt phosphorylation decreased and ERK phosphorylation increased at 3 hr compared with 0 hr (p < .05). Levels of p70(S6K) phosphorylation were 110% greater (p < .05) at 3 hr than at 0 hr using Western blots. MuRF mRNA expression postexercise increased; levels were 4.7- and 5.7-fold greater (p < .05) at 0 hr and 3 hr, respectively, than at rest with qRT-PCR. Atrogin mRNA expression was up-regulated 3.2-fold 3 hr postexercise compared with rest. These findings demonstrate modest changes in the molecular responses to moderate endurance exercise in the absence of nutrition. This study provides the groundwork for future investigations designed to optimize the metabolic conditions necessary to positively influence the cellular mechanisms specific to skeletal-muscle protein turnover during recovery from endurance exercise.

Aerobic fitness does not modulate protein metabolism in response to increased exercise: a controlled trial.

BACKGROUND: A sudden increase in exercise and energy expenditure is associated with an increase in protein turnover and nitrogen excretion. This study examined how a sudden increase in exercise-induced energy expenditure affected whole body protein metabolism and nitrogen balance in people of differing levels of aerobic fitness. We hypothesized that alterations in whole-body protein turnover would be attenuated, and nitrogen balance would be preserved, in individual with higher levels of aerobic fitness. METHODS: Eleven men, categorized as either having a lower (LOW-FIT; n = 5) or higher (FIT; n = 6) aerobic fitness level, completed a 4-d baseline period (BL) of an energy balance diet while maintaining usual physical activity level, followed by a 7-d intervention consisting of 1,000 kcal·d⁻¹ increased energy expenditure via exercise (50-65% VO2peak). All volunteers consumed 0.9 g protein.kg⁻¹·d⁻¹ and total energy intake was adjusted to maintain energy balance throughout the 11-d study. Mean nitrogen balance (NBAL) was determined for BL, days 5-8 (EX1), and days 9-11 (EX2). Whole-body protein turnover was derived from phenylalanine and tyrosine kinetics assessed while fasting at rest on days 4, 7, and 12 using a priming dose of L-[ring-¹5N]tyrosine and a 4-h primed, continuous infusion of L-[¹5N]phenylalanine and L-[ring-²H4]tyrosine. RESULTS: A significant main effect of time indicated that NBAL increased over the course of the intervention; however, a group-by-time interaction was not observed. Although FIT demonstrated a lower net protein oxidation and higher net protein balance compared to LOW-FIT, neither the effect of time nor a group-by-time interaction was significant for Phe flux, net protein oxidation, or derived whole-body protein synthesis and net protein balance. CONCLUSION: The absence of significant group-by-time interactions in protein metabolism (i.e., NBAL and whole-body protein turnover) between LOW-FIT and FIT males suggest that aerobic fitness level does not modulate protein "sparing" in response to an unaccustomed increase in energy expenditure.

Habitual consumption of eggs does not alter the beneficial effects of endurance training on plasma lipids and lipoprotein metabolism in untrained men and women.

Changes in plasma lipid and apolipoprotein profiles were evaluated in 12 healthy, unfit subjects (VO(2peak) 39.1+/-2.8 ml.kg(-1).min(-1); 5 women, 7 men) at baseline and following endurance exercise training. The exercise protocol consisted of a 6-week endurance exercise training program (4-5 days week(-1); 60 min.session(-1); > or =65% HR(max)). Subjects were randomly assigned to consume an egg- (n=6; 12 eggs.week(-1)) or no-egg (n=6; 0 eggs.week(-1))-based, eucaloric, standardized diet for 8 weeks. Both diets were macronutrient balanced [60% carbohydrate, 30% fat, 10% protein (0.8 g.kg(-1).day(-1))] and individually designed for weight maintenance. Plasma lipids were measured twice within the same week at baseline and following exercise training. At baseline, subjects were normolipidemic with values of 163.9+/-41.8, 84.8+/-36.7, 60.6+/-15.4 and 93.1+/-52 mg dl(-1) for total cholesterol, LDL cholesterol and HDL cholesterol and triglyceride concentrations, respectively. A two-way ANOVA was used to analyze diet and exercise effects and interactions. In both groups, endurance exercise training resulted in a significant 10% increase in HDL-C (P<.05), a 19% decrease in Apo B concentrations (P<.05) and reductions in plasma CETP activity (P<.05). Plasma LDL-C decreased by 21% (P=.06). No main effects of diet or interactions with plasma lipids or Apo B concentrations were observed. These data demonstrate that endurance training improved the plasma lipid profiles of previously unfit, normolipidemic subjects independent of dietary cholesterol intake from eggs.

Increased protein maintains nitrogen balance during exercise-induced energy deficit.

PURPOSE: This study examined how a high-protein diet affected nitrogen balance and protein turnover during an exercise-induced energy deficit. METHODS: Twenty-two men completed a 4-d (D1-4) baseline period (BL) of an energy balance diet while maintaining usual physical activity level, followed by 7 d (D5-11) of 1000 kcal.d increased energy expenditure via exercise (50-65% V O2peak). One group consumed 0.9 g of protein per kilogram per day and maintained energy balance throughout the 11-d intervention (BAL, N = 8). The other two groups consumed their BL energy intake throughout the 11 days, resulting in a 7-d, 1000-kcal.d energy deficit. These groups consumed either 0.9 g of protein per kilogram per day (DEF, N = 7) or 1.8 g of protein per kilogram per day (DEF-HP, N = 7). Mean nitrogen balance (NB), calculated per kilogram of fat-free mass (FFM), was determined for BL, days 5-8 (EX1), and days 9-11 (EX2). Whole-body protein turnover was derived from phenylalanine and tyrosine kinetics assessed while fasting at rest on days 4, 7, and 12, using a priming dose of L-[ring-N]tyrosine and a 4-h, primed, continuous infusion of L-[N]phenylalanine and L-[ring-H4]tyrosine. RESULTS: DEF experienced a decrease in NB from BL to EX 1 that was maintained in EX 2. No changes in NB occurred for BAL or DEF-HP over time. No within- or between-group differences were found over time for Phe flux (Qp), conversion rate of Phe to Tyr (Qpt), or the derived protein synthesis value (Sp). CONCLUSION: Increased dietary protein maintained NB during exercise-induced energy deficit, but this did not impact resting whole-body protein turnover.

Gender impacts the post-exercise substrate and endocrine response in trained runners.

BACKGROUND: Although several studies have investigated gender differences in the substrate and endocrine responses during and following endurance exercise, few have studied sex differences during a more prolonged recovery period post endurance exercise. The purpose of this study was to compare and characterize the endocrine and substrate profiles of trained male and female adult runners during the three-and-a-half hour recovery period from an endurance run. METHODS: After consuming a euenergetic diet (1.8 g.kg-1.d-1 protein, 26% fat, 58% carbohydrates, 42.8 +/- 1.2 kcal/kg body weight) for 8 days, blood was collected from trained male (n = 6, 21 yrs, 70 kg, 180 cm, 9% body fat, VO(2peak) 78.0 +/- 3.4 mL.kg FFM-1.min-1) and female (n = 6, 23 y, 66 kg, 170 cm, 29% body fat, VO(2peak) 71.6 +/- 4.5 mL.kg FFM-1.min-1) endurance runners at rest and during recovery from a 75 min run at 70% VO(2peak). Circulating levels of glucose, lactate, free fatty acids (FFAs), insulin, cortisol, growth hormone (GH), and free insulin-like growth factor I (IGF-I) were measured. RESULTS: During the recovery period, females experienced increases in glucose, lactate and insulin while no changes were noted in men (P < 0.05). Males experienced increases in GH and decreases in IGF-I levels respectively (P < 0.05) while no changes were observed in females. FFA levels increased during recovery from endurance exercise, but changes were not different between genders. CONCLUSION: These data further document gender differences in substrate and endocrine changes during a prolonged recovery period following endurance exercise. Future studies are needed to evaluate the effect of differing diets and nutritional supplements on these gender-specific post-exercise substrate and endocrine differences.

Energy flux, more so than energy balance, protein intake, or fitness level, influences insulin-like growth factor-I system responses during 7 days of increased physical activity.

The purpose of this study was to determine the impact of dietary factors and exercise-associated factors on the response of IGF-I and its binding proteins (IGFBPs) during a period of increased physical activity. Twenty-nine men completed a 4-day (days 1-4) baseline period of a controlled energy balanced diet while maintaining their normal physical activity level followed by 7 days (days 5-11) of a 1,000 kcal/day increase in physical activity above their normal activity levels. Two subject groups, one sedentary (Sed, mean Vo(2peak): 39 mlxkg(-1)xmin(-1), n = 7) and one fit (FIT1, mean Vo(2peak): 56 ml.kg(-1)xmin(-1), n = 8) increased energy intake to maintain energy balance throughout the 7-day intervention. In two other fit subject groups (FIT2, n = 7 and FIT3, n = 7), energy intake remained at baseline resulting in a 1,000 kcal/day exercise-induced energy deficit. Of these, FIT2 received an adequate protein diet (0.9 g/kg), and FIT3 received a high-protein diet (1.8 g/kg). For all four groups, IGF-I, IGFBP-3, and the acid labile subunit (ALS) were significantly decreased by day 11 (27 +/- 4%, 10 +/- 2%, and 19 +/- 4%, respectively) and IGFBP-2 significantly increased by 49 +/- 21% following day 3. IGFBP-1 significantly increased only in the two negative energy balance groups, FIT2 (38 +/- 6%) and FIT3 (46 +/- 8%). Differences in initial fitness level and dietary protein intake did not alter the IGF-I system response to an acute increase in physical activity. Decreases in IGF-I were observed during a moderate increase in physical activity despite maintaining energy balance, suggesting that currently unexplained exercise-associated mechanisms, such as increased energy flux, regulate IGF-I independent of energy deficit.

Postexercise whole-body protein turnover response to three levels of protein intake.

PURPOSE: This investigation examined the effect of variations in protein intake on whole-body protein turnover (WBPTO) after exercise in endurance-trained males. METHODS: Five male runners (21.3 +/- 0.3 yr, 179 +/- 2 cm, 70.6 +/- 0.1 kg, 8.7 +/- 0.4% body fat, 70.6 +/- 0.1 VO2peak) participated in a randomized, crossover-design diet intervention, where they consumed either a low- (0.8 g.kg(-1); LP), moderate- (1.8 g.kg(-1); MP), or high-protein (3.6 g.kg(-1); HP) diet for 4 wk. WBPTO (Ra, leucine rate of appearance; NOLD, nonoxidative leucine disposal; and Ox, leucine oxidation) were assessed after a 75-min run at 70% VO2peak after each diet-intervention period. RESULTS: Leucine Ra (indicator of protein breakdown) and leucine Ox were greater on the HP diet than on the LP diet (Ra, 123.4 +/- 6.9 vs 97.9 +/- 6.0 micromol.kg(-1).h(-1); Ox, 23.9 +/- 0.5 vs 17.0 +/- 0.8 micromol.kg(-1).h(-1), P < 0.05). No differences were noted in NOLD (an indicator of protein synthesis) across diets. Plasma branched chain amino acids (BCAA) at rest were greater for MP and HP than for LP, and nonessential amino acids (NEAA) were greater for LP than MP at rest and greater than MP and HP after exercise. CONCLUSION: Findings from this study show that variations in protein intake can alter plasma amino acid levels and modulate rates of WBPTO after exercise. Additionally, a lower protein intake was associated with decreased rates of WBPTO after exercise.

Level of dietary protein impacts whole body protein turnover in trained males at rest.

The current investigation examined the effect of variations in protein intake on Whole body protein turnover (WBPTO) at rest in endurance-trained males. Whole body protein turnover is influenced by both diet and exercise. Whether endurance athletes require more protein than the non-exerciser remains equivocal. Five male runners (21.3 +/- 0.3 years, 179 +/- 2 cm, 70.6 +/- 0.1 kg, 8.7% +/- 0.4% body fat, 70.6 +/- 0.1 VO(2)max) participated in a randomized, crossover design diet intervention where they consumed either a low-protein (LP; 0.8 g/kg), moderate-protein (MP; 1.8 g/kg), or high-protein (HP; 3.6 g/kg) diet for 3 weeks. Whole body protein turnover (Ra, leucine rate of appearance; NOLD, nonoxidative leucine disposal; and Ox, leucine oxidation), nitrogen balance, and substrate oxidation were assessed at rest following each dietary intervention period. The HP diet increased leucine Ra (indicator of protein breakdown; 136.7 +/- 9.3, 129.1 +/- 7.4, and 107.8 +/- 3.1 micromol/[kg . h] for HP, MP, and LP diets, respectively) and leucine Ox (31.0 +/- 3.6, 26.2 +/- 4.3, and 18.3 +/- 0.6 micromol/[kg . h] for HP, MP, and LP diets, respectively) compared with LP diet (P < .05). No differences were noted in nonoxidative leucine disposal (an indicator of protein synthesis) across diets. Nitrogen balance was greater for HP diet than for MP and LP diets (10.2 +/- 0.7, 1.8 +/- 0.6, and -0.3 +/- 0.5 for HP, MP, and LP diets, respectively). Protein oxidation increased with increasing protein intake (54% +/- 6%, 25% +/- 1%, and 14% +/- 2% for HP, MP, and LP diets, respectively). Findings from this study show that variations in protein intake can modulate WBPTO and that protein intake approximating the current recommended dietary allowance was not sufficient to achieve nitrogen balance in the endurance-trained males in this investigation. Our results suggest that a protein intake of 1.2 g/kg or 10% of total energy intake is needed to achieve a positive nitrogen balance. This is not a concern for most endurance athletes who routinely consume protein at or above this level.

Effects of dietary protein intake on indexes of hydration.

This study aims to characterize the relationship between increased protein intake and hydration indexes. Five men participated in a 12-week, randomized, crossover, controlled diet intervention study. Subjects consumed eucaloric diets containing 3.6 (high protein), 1.8 (moderate protein), and 0.8 (low protein) g/kg/day of protein for 4 weeks each. Energy intakes were based on requirements established relative to resting energy expenditure and activity at baseline. Assessments included blood urea nitrogen, plasma osmolality, urine-specific gravity, and estimates of fluid balance. Repeated-measures analyses of variance and paired t tests were used to determine effects of treatment and time. Fluid intake and fluid balance were unaffected. Blood urea nitrogen was higher for high protein vs low protein and vs moderate protein, and urine-specific gravity was higher for high protein vs moderate protein. Baseline plasma osmolality was greater for high protein vs low protein and vs moderate protein. The effect of increasing dietary protein on fluid status was minimal.

Aerobic exercise training increases skeletal muscle protein turnover in healthy adults at rest.

The effect of a 4-wk aerobic exercise training program (30-45 min, 3-5 d/wk, >or=65% maximal heart rate) on mixed skeletal muscle protein fractional synthetic rate (FSR), fractional breakdown rate (FBR), and net protein balance (FSR - FBR) (NET) was examined in 8 healthy, previously unfit men and women [21.0+/- 0.4 y, 163.7+/- 4.4 cm, 75.6+/- 5.7 kg, 33.5+/- 4.1% body fat, VO(2 peak) 38.6+/- 2.3 mL/(kg.min)] fed eucaloric diets providing 0.85 g protein/(kg.d) for the 6-wk study. Measurements were made at baseline after 2 wk of diet intervention only, and after 4 wk of aerobic exercise training and diet intervention. Primed continuous infusions of ring-[(2)H(5)]-phenylalanine (2 micromol/kg; 0.05 micromol/(kg.min) and [(15)N]-phenylalanine (2 micromol/kg; 0.05 micromol/(kg.min) were used to assess skeletal muscle protein turnover at rest via the precursor-product method. Endurance training improved cardiovascular fitness, with a significant increase in VO(2 peak) (P<0.01) and a significant decrease in running time on a standard course (P<0.01). There were o significant changes in body mass or composition. There was a significant increase in FSR (0.077+/- 0.007 vs. 0.089+/- 0.006%/h, P<0.05) and decrease in NET (FSR - FBR) (-0.023 +/-0.004 vs. -0.072 +/- 0.012%/h, P < 0.05); FBR tended to increase (0.105+/- 0.014 vs. 0.143+/- 0.018%/h; P=0.06) after training. Findings show that aerobic training for 4 wk increases skeletal muscle protein turnover in previously unfit subjects.

Aerobic exercise training decreases leucine oxidation at rest in healthy adults.

Both exercise and dietary protein intake affect whole-body protein turnover (WBPTO). Few studies have investigated the effect of aerobic exercise training on WBPTO [leucine rate of appearance (Ra), oxidation (Ox), and nonoxidative leucine disposal (NOLD)] in untrained individuals consuming a specified level of protein. This study examined the effect of aerobic exercise training on WBPTO in untrained men and women during a controlled diet intervention providing 0.88 g protein/(kg . d). After a 2-wk adaptation to the study diet, 7 subjects [3 men, 4 women; 76.1 +/- 5.8 kg, 164.7 +/- 4.4 cm, 30.7 +/- 4.5% body fat, 39.1 +/- 2.8 VO(2max) (maximal oxygen uptake) mL/(kg . min)] participated in 4 wk of aerobic exercise training (running and walking 4-5 times/wk at 65-85% maximal heart rate). WBPTO (determined via constant infusion of 1-[(13)C] leucine), nitrogen balance, and body composition were determined at baseline and after 4 wk of training. Nitrogen balance (-1.0 +/- 0.7 vs. 0.9 +/- 1.1 g N/24 h, P = 0.03) improved with exercise training, whereas body mass and composition did not change. Leucine Ra did not change, Ox decreased [18 +/- 2 to 15 +/- 2 micromol/(kg . h), P