Butter coffee (aka “Bulletproof”) went viral circa 2015 with “effortless weight loss” hype. I dug through the claims, tried it, and kept the good parts. First lesson: use unsalted butter or it tastes weird.

Where it came from

シリコンバレー式 自分を変える最強の食事

ダイヤモンド社

The book pitches a “flawless” diet: coffee + grass-fed butter + MCT oil, plus “mold-free” beans. Glossary:

• Grass-fed butter: better fatty-acid profile, hard to find in normal supermarkets.
  グランフェルマージュ バイオ・グラスフェッドバター 無塩 250g

  ユーリアル
• MCT oil (medium-chain triglycerides): digests fast, touted as “less likely to stick as fat.”
  [トクホ] 日清オイリオ ヘルシーリセッタ 600g

  日清オイリオ
  
  日清 MCTオイル 450g

  日清オイリオグループ
• Mold-free beans: worry centers on ochratoxin A, a mycotoxin. Japanese tests show levels far below strict EU limits; domestic beans are effectively a non-issue. Imports could vary, but it’s not the doom it sounds like.

Ketosis, weight loss, and reality

The book leans on ketosis: low carbs → burn fat/ketones. Butter/MCT coffee can delay hunger (fat is filling), so you might snack less. But “just drop butter in coffee and you’ll melt fat” is fantasy. The author even says you must blend it to form micelles; a butter pat floating in coffee won’t do it. Full protocol = low carbs + specific ingredients + blender + two “perfect” weeks. Hard mode.

Side effect: the fat can speed digestion—some friends got loose stools. Taste-wise, when blended it’s mild and pleasant, like a super-rich latte.

Brain claims

MCTs are studied as an alternate fuel (ketones) for brains that can’t use glucose well, e.g., some Alzheimer’s cases. Research is ongoing; “prevents dementia” TV sound bites are premature. Moving your body still has the strongest evidence for brain health.

Ingredient hassle (butter, ghee, MCT)

Grass-fed butter/ghee and pure MCT cost more and aren’t at every store. You can sub cheaper oils (e.g., “Healthy Resetta” medium-chain blend) but purity differs. Buying the whole branded kit even comes with a California Prop 65 warning about possible carcinogens—ironic for a “perfect” diet.

My take, compressed

• Sourcing is pricey and fiddly; cleaning the blender daily is a drag.
• Appetite suppression is real; weight loss is only likely if you also rein in carbs.
• Evidence is thin; feels like “my cool self-optimized system” more than rigorous science.
• If you like the taste and routine, enjoy it—but don’t expect magic fat loss or brain unlocks.

I’d rather drink good coffee, walk or bike more, and manage calories the boring way. Butter coffee can be a tasty breakfast, not a miracle.