Rhonda Patrick is thirteen days into a ketogenic experiment, and she's not here to sell you a lifestyle. She's here to understand a mechanism. The claim is precise: ketosis — not just low-carb eating, but actual measurable ketosis — produces a state of mental clarity and cognitive endurance that fasting reliably delivers. The question she's asking is whether a sustained dietary protocol can replicate what intermittent fasting achieves naturally.
That's a meaningful distinction. Most keto conversations start with weight loss. This one starts with the brain.
The mechanisms here are well-established. When glycogen stores deplete — typically after 13 to 36 hours depending on activity and carbohydrate intake — the liver begins converting fatty acids into ketone bodies, primarily beta-hydroxybutyrate. That molecule does two things simultaneously: it fuels neurons directly, and it acts as a signaling molecule that activates BDNF, brain-derived neurotrophic factor. BDNF is the protein responsible for neuronal growth, learning consolidation, and memory formation.
This is why fasted cognitive performance feels different. You're not just running on a different fuel. You're running on a fuel that actively promotes the cellular machinery of thought.
The epilepsy literature established this decades ago. Ketogenic diets were used clinically for seizure management long before anyone was talking about biohacking. The neurological benefit is real, documented, and mechanistically understood. What's newer is the extension of this research into neurodegenerative disease — Alzheimer's, Parkinson's — where neurons that struggle to metabolize glucose may still be able to use ketones effectively.
The honest disagreement in this space is about sustainability and completeness. Rhonda herself admits the challenge: 90 to 98 percent of people who think they're in ketosis aren't. They're eating low-carb, which is not the same thing. Actual ketosis requires hitting 0.9 to 1.2 millimolar at minimum — a threshold most people never reach without deliberate tracking.
The exogenous ketone debate sits in the same territory. They work, in the narrow sense that they can spike blood ketones to 3.3 millimolar within an hour. But they wear off in two hours, and they don't replicate the full metabolic adaptation that comes from sustained dietary ketosis. They're a preview, not a protocol.
If you want to experience the cognitive benefits of ketosis, measure. Don't guess. A blood ketone meter removes all the ambiguity. Aim for 1.0 millimolar or above before drawing conclusions about whether the protocol is working. Most people who report "keto isn't for me" have never actually been in ketosis — they've just been eating fewer carbohydrates than usual.
The transition period is real and it's uncomfortable. Rhonda calls it "a huge challenge," and she's someone who understands the biochemistry intimately. Give it at least three weeks before evaluating, and focus on fat quality, not just fat quantity.
Here's what most keto discussions miss: cold exposure and ketosis share more than a Venn diagram overlap in the wellness community. They converge mechanistically. Cold immersion — even a brief plunge — activates norepinephrine, raises metabolic rate, and can transiently elevate ketone production as the body mobilizes fat for thermogenesis. Regular cold exposure also improves insulin sensitivity, which makes the metabolic switch into ketosis easier and faster.
Both protocols work through the same underlying principle: controlled metabolic stress that forces adaptation. Ketosis teaches the body to run on fat. Cold teaches the body to generate heat from fat. They're not competing interventions — they're complementary signals telling the same biological story. Stress the system intelligently. Adapt. Become more resilient.
If you're serious about exploring ketosis, your contrast therapy (Contrast Collective's contrast therapy overview) practice isn't working against you. It's priming you for it.