TABLE 2.
Suggested outcome measures and recommendations for their use in future dietary protein-related research (listed alphabetically by domain).
| Outcome measures | Effect of dietary protein | Recommendations |
|---|---|---|
| Cardiometabolic | ||
| Blood Lipids (for example, TC, LDL, HDL, and TG) | = | Control for confounding effects of the food matrix, particularly fat and carbohydrate amount and type |
| Blood pressure | ↑, = | Determine whether protein source and food matrix affect observed changes |
| Insulin sensitivity | ↑, =, ↓ | Control for confounding effects of weight loss/gain and assess efficiency of plasma BCAA catabolism to delineate the effect of dietary protein intake from impaired metabolism |
| Microbiome | ? | Determine how protein source (that is, amino acid profile, food matrix) affects relative abundance of beneficial microbes |
| Muscle mass | ↑, = | Evaluate protein intake in the context of overall energy intake; relate changes to glucose disposal and insulin sensitivity |
| Frailty | ||
| Mobility and functionality assessments | ↑, = | Utilize longitudinal measures to relate changes over time to protein intake; preintervention supplementation trials (for example, cancer and surgery) to assess differences relative to current standard care |
| Muscle mass | ↑, = | Evaluate influence of protein intervention in isolation or when combined with physical activity; when available, use tools to differentiate skeletal muscle from lean mass (for example, CT, MRI and D3-creatine) |
| Bone | ||
| Bone mineral content | ↑ | Use of HR-pQCT to assess incremental changes and differences in trabecular compared with cortical bone; DXA suitable for larger and longer assessments |
| IGF-1, osteokines | ↑ | Continued exploration of protein’s impact on muscle–bone crosstalk |
| Parathyroid hormone | ↓ | Confirm dietary protein’s role in suppressing increased bone turnover |
| Weight management | ||
| Appetite-regulating hormones (for example, GLP-1, PYY, CCK, and leptin) | ↑ | Continued assessment to differentiate effect of protein source and food matrix on satiety signals |
| Body mass and % body fat | ? | Reconciliation of short- compared with long-term study findings; control for dietary intervention compliance |
| Microbiome | ? | Determine potential influence of bacterial amino acid metabolism on satiety signals |
| Sleep | ↑ | Continued examination of the effect of dietary protein on quantity and quality of sleep, particularly the potential role for presleep protein ingestion |
Abbreviations: ↑, improved by dietary protein; ↓, worsened by dietary protein; =, no observed effect from dietary protein; ?, unknown effect of dietary protein; CCK, cholecystokinin; CT, computed tomography; DXA; GLP-1, glucagon-like peptide-1; HbA1c, hemoglobin A1c; HR-pQCT, high-resolution peripheral quantitative computed tomography; IGF-1, insulin-like growth factor 1; PYY, peptide YY; TC, total cholesterol.