がん患者の筋蛋白合成は高蛋白・高ロイシンで増加

東別府先生に教えていただいた論文を紹介します。がん患者での筋蛋白合成は特別食（高蛋白・高ロイシン）で増加するというRCTの論文です。

Deutz NE, Safar A, Schutzler S, Memelink R, Ferrando A, Spencer H, van Helvoort A, Wolfe RR.Muscle protein synthesis in cancer patients can be stimulated with a specially formulated medical food. Clin Nutr. 2011 Dec;30(6):759-68.

リサーチクエスチョンは以下の通りです。

P：がん患者25人に
E：640kcalで蛋白40g（カゼイン24g、ホエイ12g、ロイシン4g）の特別食を摂取すると
C：640kcalで蛋白24g（カゼイン24g）の食事摂取と比較して
O：筋蛋白合成が増加する

結果ですが、特別食（高蛋白・高ロイシン）摂取群のみ、筋蛋白合成が有意に増加しました。対象群では筋蛋白合成の増加を認めませんでした。がん患者ではアナボリックレジスタンス（同化抵抗性）を認めますが、高蛋白・高ロイシン食で改善できるという結論です。

実際に筋肉量が増えるかどうは今後の臨床研究を待たないといけませんが、がん悪液質患者には、高蛋白・高ロイシン食のほうが望ましい可能性があります。

Abstract
OBJECTIVE: Maintenance of muscle mass is crucial to improving outcome and quality of life in cancer patients. Stimulating muscle protein synthesis is the metabolic basis for maintaining muscle mass, but in cancer patients normal dietary intake has minimal effects on muscle protein synthesis. Adding leucine to high protein supplements stimulates muscle protein synthesis in healthy older subjects. The objective was to determine if a specially formulated medical food, high in leucine and protein, stimulates muscle protein synthesis acutely in individuals with cancer to a greater extent than a conventional medical food.

DESIGN: A randomized, controlled, double-blind, parallel-group design was used in 25 patients with radiographic evidence of cancer. Patients were studied before their cancer treatment was started or 4 weeks after their treatment was completed or halted. The fractional rate of muscle protein synthesis (FSR) was measured using the tracer incorporation technique with L-[ring-(13)C(6)]-phenylalanine. The experimental group (n = 13) received a medical food containing 40 g protein, based on casein and whey protein and enriched with 10% free leucine and other specific components, while the control group (n = 12) was given a conventionally used medical food based on casein protein alone (24 g). Blood and muscle samples were collected in the basal state and 5h hours after ingestion of the medical foods.

RESULTS: The cancer patients were in an inflammatory state, as reflected by high levels of C-reactive protein (CRP), IL-1 β and TNF-α, but were not insulin resistant (HOMA). After ingestion of the experimental medical food, plasma leucine increased to about 400 μM as compared to the peak value of 200 μM, after the control medical food (p < 0.001). Ingestion of the experimental medical food increased muscle protein FSR from 0.073 (SD: 0.023) to 0.097 (SD: 0.033) %/h (p = 0.0269). In contrast, ingestion of the control medical food did not increase muscle FSR; 0.073 (SD: 0.022) and 0.065 (SD: 0.028) %/h.

CONCLUSIONS: In cancer patients, conventional nutritional supplementation is ineffective in stimulating muscle protein synthesis. This anabolic resistance can be overcome with a specially formulated nutritional supplement.