Wayne W. Campbell

Higher Protein Intake Preserves Lean Mass and Satiety with Weight Loss in Pre-obese and Obese Women

Objective: To examine the effects of dietary protein and obesity classification on energy‐restriction‐induced changes in weight, body composition, appetite, mood, and cardiovascular and kidney health.

Is the Optimal Level of Protein Intake for Older Adults Greater Than the Recommended Dietary Allowance

BACKGROUND Protein is a macronutrient essential for growth, muscle function, immunity and overall tissue homeostasis. Suboptimal protein intake can significantly impact physical function and overall health in older adults. METHODS This article reviews the literature on the recommendations for protein intake in older adults in light of the new evidence linking protein intake with sarcopenia and physical function. Challenges and opportunities for optimal protein nutrition in older persons are discussed. RESULTS Recent metabolic and epidemiological studies suggest that the current recommendations of protein intake may not be adequate for maintenance of physical function and optimal health in older adults. Methodological limitations and novel concepts in protein nutrition are also discussed. CONCLUSION We conclude that new research and novel research methodologies are necessary to establish the protein needs and optimal patterns of protein intake for older persons.

Dietary Protein and Resistance Training Effects on Muscle and Body Composition in Older Persons

The regular performance of resistance exercises and the habitual ingestion of adequate amounts of dietary protein from high-quality sources are two important ways for older persons to slow the progression of and treat sarcopenia, the age-related loss of skeletal muscle mass and function. Resistance training can help older people gain muscle strength, hypertrophy muscle, and increase whole body fat-free mass. It can also help frail elderly people improve balance and physical functioning capabilities. Inadequate protein intake will cause adverse metabolic and physiological accommodation responses that include the loss of fat-free mass and muscle strength and size. Findings from controlled feeding studies show that older persons retain the capacity to metabolically adjust to lower protein intakes by increasing the efficiency of nitrogen retention and amino acid utilization. However, they also suggest that the recommended dietary allowance of 0.8 g protein · kg−1 · d−1 might not be sufficient to prevent subtle accommodations and blunt desired changes in body composition and muscle size with resistance training. Most of the limited research suggests that resistance training-induced improvements in body composition, muscle strength and size, and physical functioning are not enhanced when older people who habitually consume adequate protein (modestly above the RDA) increase their protein intake by either increasing the ingestion of higher-protein foods or consuming protein-enriched nutritional supplements.

Effects of Food Form and Timing of Ingestion on Appetite and Energy Intake in Lean Young Adults and in Young Adults with Obesity

OBJECTIVE Overweight and obesity have been attributed to increased eating frequency and the size of eating events. This study explored the influence of the timing of eating events and food form on appetite and daily energy intake. DESIGN Crossover, clinical intervention where participants consumed 300-kcal loads of a solid (apple), semisolid (apple sauce), and beverage (apple juice) at a meal or 2 hours later (snack). SUBJECTS Twenty normal-weight (body mass index 22.6+/-1.8) and 20 obese (body mass index 32.3+/-1.5) adults. There were 10 men and 10 women within each body mass index group. MEASUREMENTS On six occasions, participants reported to the laboratory at their customary midday mealtime. Appetite questionnaires and motor skills tests were completed upon arrival and at 30-minute intervals for the 2 hours participants were in the laboratory and at 30-minute intervals for 4 hours after leaving the laboratory. Diet recalls were collected the next day. Data were collected between January 2006 and March 2007. RESULTS Whether consumed with a meal or alone as a snack, the beverage elicited the weakest appetitive response, the solid food form elicited the strongest appetitive response and the semisolid response was intermediate. The appetite shift was greatest for the solid food when consumed as a snack. The interval between test food consumption and the first spontaneous eating event >100 kcal was shortest for the beverage. No significant treatment effects were observed for test day energy intake or between lean individuals and individuals with obesity. CONCLUSIONS Based on the appetitive findings, consumption of an energy-yielding beverage either with a meal or as a snack poses a greater risk for promoting positive energy than macronutrient-matched semisolid or solid foods consumed at these times.

Comparison of self-reported, measured, metabolizable energy intake with total energy expenditure in overweight teens

BACKGROUND The accuracy of dietary energy assessment tools is critical to understanding the role of diet in the increasing rate of obesity. OBJECTIVES The purposes of our study in overweight adolescent boys and girls were 1) to assess the energy reporting bias of diet records against the referent of total energy expenditure (TEE) and 2) to compare the methods of determining energy needs by using measured metabolizable energy intake (MEI) and TEE. DESIGN Twenty girls [12-15 y, body mass index (in kg/m2) = 33.0 +/- 5] and 14 boys (12-14 y, body mass index = 27.4 +/- 4) participated in 2- to 3-wk metabolic balance studies. TEE was measured by using doubly labeled water (TEE(DLW)), and MEI was measured by bomb calorimetry of composite daily diet, urine, and fecal collections. Food records were collected before each study. RESULTS Food records underreported TEE(DLW) by 35 +/- 20%. Underreporting of energy intake was correlated with all macronutrient intake concentrations (g or kcal) (P < 0.0001). A multiple regression model showed that 86.4% of the variance in underreporting error was explained by dietary fat (g), BMI, and sex. The intrasubject CV was 3.9% for TEE(DLW) and 9.9% for MEI. MEI for weight stability (MEI(wtstb)) averaged 99 +/- 11% of TEE. CONCLUSIONS The increased underreporting of dietary intake with increasing body weight in teens may explain in part previous reports noting that there has been an increased incidence of obesity, although energy intakes have not appeared to increase. MEI(wtstb) and TEE(DLW) gave similar estimates of energy needs. This trial was registered at clinicaltrials.gov as NCT 00592137.

Meal triacylglycerol profile modulates postprandial absorption of carotenoids in humans

SCOPE Dietary lipids are considered to be primary potentiators of carotenoid absorption, yet the amount and source required to optimize bioavailability has not been systematically evaluated. The objective of this study was to examine the impact of both amount and source of triacylglycerols on postprandial absorption of carotenoids from vegetable salads. METHODS AND RESULTS Healthy subjects (n = 29) were randomized using a Latin square design (3 × 3) and consumed three identical salads with 3, 8, or 20 g of canola oil, soybean oil, or butter. Blood was collected from 0-10 h and triacylglycerol-rich fractions (TRLs) were isolated by ultracentrifugation. Carotenoid contents of TRL fractions were analyzed by HPLC-DAD. Considering all lipid sources, 20 g of lipid promoted higher absorption compared to 3 and 8 g for all carotenoid species (p < 0.05), except for α-carotene (p = 0.07). The source of lipid had less impact on the absorption of carotenoids than amount of lipid. Pooling results from all lipid amounts, monounsaturated fatty acid rich canola oil trended toward enhancing absorption of lutein and α-carotene compared to saturated fatty acid rich butter (p = 0.06 and p = 0.08, respectively). CONCLUSION While both amount and source of co-consumed lipid affect carotenoid bioavailability from vegetables, amount appears to exert a stronger effect.

The Effect of Eating Frequency on Appetite Control and Food Intake: Brief Synopsis of Controlled Feeding Studies

Increased eating frequency is postulated to increase metabolism, reduce hunger, improve glucose and insulin control, and reduce body weight, making it an enticing dietary strategy for weight loss and/or the maintenance of a healthy body weight. Because past research has primarily focused on the effects of eating frequency on changes in energy expenditure and body weight, limited data exist surrounding the impact of eating frequency on appetite control and energy intake. We provide a brief review of the controlled-feeding studies that primarily targeted the appetitive, hormonal, and food intake responses potentially altered with eating frequency. The 3 meal/d pattern served as the reference for defining increased or reduced eating frequency. In general, increased eating frequency led to lower peaks (P < 0.05) in perceived appetite, satiety, glucose, insulin, ghrelin, and PYY responses compared with reduced eating frequency. However, when examining these responses over the course of the day (i.e. using area under the curve assessments), no differences in any of these outcomes were observed. The rate of gastric emptying also appears to be unaltered with increased eating frequency. Subsequent food intake was examined in several studies with conflicting results. Regarding the effect of reduced eating frequency, several studies indicate significant increases in perceived appetite and reductions in perceived satiety when 1 or 2 meals were eliminated from the daily diet. Taken together, these findings suggest that increased eating frequency (>3 eating occasions/d) has minimal, if any, impact on appetite control and food intake, whereas reduced eating frequency(<3 eating occasions/d) negatively effects appetite control.

Dietary protein adequacy and lower body versus whole body resistive training in older humans

This study assessed the effects of long‐term consumption of the United States Recommended Dietary Allowance (RDA) for protein by older people who were sedentary or performed resistive training (RT) on body composition, skeletal muscle size and protein metabolism, and if the number of muscle groups trained influenced the muscle hypertrophy response to RT. Twelve men and 17 women (age range 54–78 years) completed this 14 week controlled diet and exercise study. Throughout the study, each subject completely consumed daily euenergetic menus that provided the RDA of 0.8 g protein kg−1 day−1. From study weeks 3–14 (weeks RT1‐RT12), 10 subjects (four men, six women) performed whole body RT (WBRT), nine subjects (four men, five women) performed lower body RT (LBRT) and 10 subjects (four men, six women) remained sedentary (SED). Both the LBRT and WBRT groups performed knee extension and flexion exercises, and the WBRT group also performed chest press and arm pull exercises (three sets per exercise at 80 % of one repetition maximum, 3 days per week for 12 weeks). From week 2 (baseline) to week RT12, muscle strength increased in muscle groups trained in the LBRT and WBRT groups, and was not changed in the SED group. From baseline to week RT12, whole body muscle mass and protein‐mineral mass were not changed, fat‐free mass (P= 0.004) and total body water (P= 0.013) were decreased, and percentage body fat was increased (P= 0.011) in these weight‐stable older people, independent of group assignment. The RT‐induced increases in mid‐thigh muscle area (from computed tomography scans) were comparable in the LBRT and WBRT groups (2.13 ± 1.26 cm2 and 2.17 ± 1.24 cm2, respectively), and were different from those in the SED group, which lost muscle area (‐1.74 ± 0.57 cm2; group‐by‐time P < 0.05). From baseline to week RT12, 24 h urinary total nitrogen excretion decreased (P < 0.001), nitrogen balance shifted from near equilibrium to positive, whole body leucine oxidation (from the infusion of L‐[13C]leucine) decreased (P < 0.05) and net (postabsorptive vs. postprandial) leucine balance (P < 0.05) increased from near equilibrium to positive, with no differences in responses over time among the three groups. In conclusion, the number of muscle groups trained did not influence whole body protein metabolism or RT‐induced muscle hypertrophy in older people. Most of these data are consistent with a successful adaptation to the RDA for protein. However, research should continue to question whether the decreases in fat‐free mass and total body water observed in all subjects, and the decrease in mid‐thigh muscle area in the SED group, are physiological accommodations, and whether the RDA for protein might be marginally inadequate for older people to maintain skeletal muscle.

The influence of higher protein intake and greater eating frequency on appetite control in overweight and obese men.

The purpose of this study was to determine the effects of dietary protein intake and eating frequency on perceived appetite, satiety, and hormonal responses in overweight/obese men. Thirteen men (age 51 ± 4 years; BMI 31.3 ± 0.8 kg/m2) consumed eucaloric diets containing normal protein (79 ± 2 g protein/day; 14% of energy intake as protein) or higher protein (138 ± 3 g protein/day; 25% of energy intake as protein) equally divided among three eating occasions (3‐EO; every 4 h) or six eating occasions (6‐EO; every 2 h) on four separate days in randomized order. Hunger, fullness, plasma glucose, and hormonal responses were assessed throughout 11 h. No protein × eating frequency interactions were observed for any of the outcomes. Independent of eating frequency, higher protein led to greater daily fullness (P < 0.05) and peptide YY (PYY) concentrations (P < 0.05). In contrast, higher protein led to greater daily ghrelin concentrations (P < 0.05) vs. normal protein. Protein quantity did not influence daily hunger, glucose, or insulin concentrations. Independent of dietary protein, 6‐EO led to lower daily fullness (P < 0.05) and PYY concentrations (P < 0.05). The 6‐EO also led to lower glucose (P < 0.05) and insulin concentrations (P < 0.05) vs. 3‐EO. Although the hunger‐related perceived sensations and hormonal responses were conflicting, the fullness‐related responses were consistently greater with higher protein intake but lower with increased eating frequency. Collectively, these data suggest that higher protein intake promotes satiety and challenge the concept that increasing the number of eating occasions enhances satiety in overweight and obese men.

Food form and portion size affect postprandial appetite sensations and hormonal responses in healthy, nonobese, older adults.

Data are limited concerning the dietary factors that influence appetite control in older adults. This study examined the effects of food form and portion size on appetite in 43 older adults (age: 72 ± 1 years; BMI: 25.6 ± 0.3 kg/m2). Subjects were assigned to groups based on portion size of the test meal (12.5% (n = 18) vs. 25% (n = 25) of estimated energy need). Subjects randomly consumed, on two separate days, the respective solid or beverage test meal. Appetite sensations and hormonal responses were measured over 4 h. Main effects of food form (P < 0.05) and/or portion size (P < 0.05) were observed for each appetite sensation. Postprandial hunger and desire to eat were greater following beverage vs. solid meal (between 12.5% vs. 25%), whereas fullness was lower after beverage vs. solid meal (P < 0.05). Main effects of food form and/or portion size were observed for glucose, insulin, and ghrelin. Postprandial glucose and insulin concentrations were lower after beverage vs. solid meal (between 12.5% vs. 25%; all comparisons, P < 0.05) whereas beverage meal led to greater 4‐h ghrelin vs. solid meal (P = 0.09). No main effects were observed for glucagon‐like peptide‐1 (GLP‐1) or cholecystokinin (CCK). When adjusting for age, food form remained significant for postprandial hunger and fullness; portion size remained significant for postprandial glucose. Greater hunger and reduced satiety with accompanying glucose, insulin, and ghrelin following the beverage vs. solid meals, and to some extent, in smaller vs. larger portions suggest that appetite control is influenced by food form and portion size in older adults. These findings may enhance the development of appropriate dietary strategies that help to regulate energy balance.