膳食纤维为 0：肉没有纤维。光吃肉的一餐对肠道菌群不友好，搭蔬菜、全谷、豆类补上维生素 C 几乎没有：这一点反而能利用——维 C 能促进植物里非血红素铁的吸收，配一盘彩椒、西兰花、番茄，同盘米饭、豆子、绿叶菜里的铁会吸收得更好（见 铁）碳水和钙也很低：牛肉不是碳水或钙的来源 最划算的吃法是牛肉加大量蔬菜：蔬菜补纤维和维 C，也稀释了这一餐的饱和脂肪和血红素铁密度。有烹饪实验报告，腌肉时加大蒜、迷迭香、柠檬能减少高温产生的杂环胺。
反过来，牛肉加精制碳水加高温油（汉堡套餐）是最不划算的组合。
机制 · 维 C 帮的是菜里的铁
配蔬菜能让整餐的铁吸收得更好这句话是对的，但它很容易被读成维 C 让牛肉的铁吸收更多。那是两件不同的事，分清楚才知道该怎么配。
维 C 干的正是这件事：递一个电子过去把铁还原，顺手再把它抓住，不让植酸和茶多酚把它抱走。所以维 C 的作用点在植物铁那扇门上。牛肉的铁走的是另一扇门，维 C 帮不上，也不需要帮。
于是这一餐该怎么摆就清楚了
配一盘彩椒、西兰花、番茄，提升的是同盘的米饭、豆子、深绿叶菜里那部分铁——而这些恰恰是平时最容易被浪费掉的铁茶和咖啡里的多酚是同一场争夺里的对手方，所以它们拖住的主要也是植物铁。想让一餐的铁总量最大，把茶和咖啡挪到饭后隔开一段时间反过来说：一顿全是肉的饭，加维 C 几乎没有增益；一顿全素的饭，加维 C 的增益最大 再说纤维那一条，它比听起来重要
先改做法：把高温直火从日常降成偶尔，收益最大，也最不需要意志力再改处理：不吃焦的部分、别用会滴油进火的架法、下锅前腌一下最后才轮到总量：每周约 500 g 那个量级是一个上限，不是一个目标 这个顺序本身就是这一页的结论——同样的力气花在前两条上，拿到的改变比反复纠结克数大得多。
参考文献 · 14
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National Institutes of Health, Office of Dietary Supplements. (2024). Vitamin B12 — Fact Sheet for Health Professionals. Fact sheet (updated July 2, 2025; Wayback snapshot 20 September 2026): multivitamin/mineral supplements typically contain 5 to 25 mcg B12, B-complex products 50 to 500 mcg, B12-only supplements typically 500 to 1,000 mcg; absorption is only about 2% at 500 mcg and 1.3% at 1,000 mcg; a 2018 Cochrane review of 3 RCTs (153 participants) compared very high oral doses (1,000-2,000 mcg) with intramuscular B12; high oral doses (e.g. 1,000 mcg/day) might be equally effective in Crohn's disease and appear as effective as hydroxocobalamin injections after Roux-en-Y bypass. These are product contents and trial doses; the sheet gives no recommended daily supplement range (fact sheet). ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional
National Institutes of Health, Office of Dietary Supplements. (2021). Selenium — Fact Sheet for Health Professionals. Table 2: Brazil nuts, 1 ounce (6-8 nuts), 544 mcg selenium (989% DV); the text says Brazil nuts contain 68-91 mcg per nut and could cause selenium toxicity if consumed regularly, and that values from other analyses vary widely. The version read carries 'Updated: April 15, 2024' (Wayback Machine snapshot of 31 December 2024), newer than the 2021 date above (fact sheet, read 2026-09-24). The September 4, 2025 update (Wayback snapshot 19 September 2026) adds: the body absorbs up to about 90% of selenium from selenomethionine, selenium-enriched yeast, selenite and selenate; selenium-only supplements typically contain 100 to 400 mcg; Keshan disease, an endemic cardiomyopathy first identified in 1935 in low-selenium parts of China, fell dramatically after selenium intervention trials in the 1970s-1990s; in 2017 the American Thyroid Association issued a weak recommendation against selenium supplements for TPOAb-positive pregnant women (fact sheet). ods.od.nih.gov/factsheets/Selenium-HealthProfessional
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