■Low carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: prospective cohort study | BMJ

Objective To study the long term consequences of low carbohydrate diets, generally characterised by concomitant increases in protein intake, on cardiovascular health.

Design Prospective cohort study.

Setting Uppsala, Sweden.

Participants From a random population sample, 43 396 Swedish women, aged 30-49 years at baseline, completed an extensive dietary questionnaire and were followed-up for an average of 15.7 years.

Main outcome measures Association of incident cardiovascular diseases (ascertained by linkage with nationwide registries), overall and by diagnostic category, with decreasing carbohydrate intake (in tenths), increasing protein intake (in tenths), and an additive combination of these variables (low carbohydrate-high protein score, from 2 to 20), adjusted for intake of energy, intake of saturated and unsaturated fat, and several non-dietary variables.

Results A one tenth decrease in carbohydrate intake or increase in protein intake or a 2 unit increase in the low carbohydrate-high protein score were all statistically significantly associated with increasing incidence of cardiovascular disease overall (n=1270)―incidence rate ratio estimates 1.04 (95% confidence interval 1.00 to 1.08), 1.04 (1.02 to 1.06), and 1.05 (1.02 to 1.08). No heterogeneity existed in the association of any of these scores with the five studied cardiovascular outcomes: ischaemic heart disease (n=703), ischaemic stroke (n=294), haemorrhagic stroke (n=70), subarachnoid haemorrhage (n=121), and peripheral arterial disease (n=82).

Conclusions Low carbohydrate-high protein diets, used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins, are associated with increased risk of cardiovascular disease.

対象は30歳から49歳までのスウェーデン女性。アンケートで食事の内容を聞きとって平均15.7年フォローアップした前向きコホート研究。心血管系疾患の発生が主要なアウトカム。炭水化物の摂取量の10分の1の減少、蛋白質摂取の10分の1の増加、低炭水化物高蛋白食スコアにおける2単位の増加は、それぞれ心血管性疾患全体の増加と関連していた。発生率比(相対リスクのことだと思う)はそれぞれ、1.04 (95% C.I. 1.00〜1.08), 1.04 (1.02〜1.06), 1.05 (1.02〜1.08)。著者らは、低炭水化物高蛋白食は心血管系疾患のリスク増加と関連していると結論している。「関連」とあって「原因」だとは言っていないのはお約束。



「ただ相対リスク1.05なのでそうはリスクは大きくない」と当初は思ったけど、「炭水化物の摂取量の10分の1の減少」「蛋白質摂取の10分の1の増加」「低炭水化物高蛋白食スコアにおける2単位の増加」あたりのリスク増加だから、低炭水化物高蛋白食スコアが大きくなれば相対リスク1.05では済まないのか。Table 3によれば、総心血管疾患のIncidence rate(10000人年あたりの罹患率のようだ)は、Low carbohydrate-high protein scoreが6点以下の群で14.4が、16点以上で23.0に上昇する。相対リスクで約1.6。量-反応関係もしっかりあるように見える。