Ketogenic Diet

How Ketosis Actually Works

Normally your body runs mostly on glucose from dietary carbohydrate, with insulin shuttling that glucose out of the blood and into cells. Cut carbs low enough — typically under 20-50g a day — and liver glycogen empties within a day or two, insulin falls, and the body starts breaking down fat into fatty acids. The liver converts a share of those into ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone), which the brain and muscles can burn in glucose's place. That metabolic switch is what "being in ketosis" means — it usually takes 2-4 days to happen, and longer to feel fully adapted to, which is where the "keto flu" (fatigue, headaches, irritability during the switch) comes from.

Why Refined Carbs Spike Blood Sugar — And Crash Your Energy

This is the mechanism keto is largely designed to sidestep.

⚡ The spike

Refined carbs — white bread, sugary drinks, pastries, white rice — have little fibre, fat, or protein left to slow digestion. They break down into glucose fast, flooding the bloodstream in minutes rather than the slower, steadier rise a whole-food meal produces.

💉 The overcorrection

The pancreas responds to a big glucose spike with a big surge of insulin to clear it. That response frequently overshoots — especially if you're already somewhat insulin resistant — pulling blood sugar down below where it started, not just back to baseline.

📉 The crash

That rebound low — reactive hypoglycaemia — is the "sugar crash": fatigue, brain fog, shakiness, irritability, and renewed hunger, typically 1-2 hours after a high-refined-carb meal. It's your brain and body responding to genuinely low blood glucose, not just "a feeling."

🔁 The cycle

A crash makes another quick-carb hit feel like the fix, which spikes and crashes blood sugar again — a cycle of unstable energy and cravings across the day. Keto flattens this out by keeping carbohydrate low enough that blood glucose barely moves, running instead on a steady supply of fat and ketones.

Whole, unrefined carbs eaten alongside fibre, fat, or protein don't do this to the same degree — digestion slows, the glucose rise is smaller and more gradual, and the insulin response is proportionate rather than a big surge-and-overshoot. See the nutrition guide for which carb sources behave which way.

Keto vs Low-Carb vs Standard, Compared

None of these is universally "best" — the right one depends on your goals and the kind of training you do.

Ketogenic (<50g carbs/day)

★★★★☆

Strong blood-sugar stability and appetite control for many people once fat-adapted, but a real adjustment period and a genuine hit to performance in hard, glycolytic training (sprints, high-rep sets) for some.

Low-carb (not full keto)

★★★★★

Enough carb reduction to blunt spikes and crashes for most people, without dropping low enough to force ketosis — easier to sustain and to train hard on than strict keto for most.

Standard, refined-carb-heavy

★★☆☆☆

The pattern most prone to the spike-crash-craving cycle above — not inherently "unhealthy" if carbs are mostly whole-food, but refined-carb-heavy versions of this are the least stable for energy and appetite.

Doing Keto Well

Ranked by impact — start at the top.

Tier S — Non-negotiable

Actually track net carbs

✔

"Low carb" isn't ketosis — most people need to stay under roughly 20-50g net carbs a day to reliably stay in it, and that's easy to drift above without tracking.

Electrolytes during adaptation

✔

Lower insulin means the kidneys excrete more sodium — replacing sodium, potassium, and magnesium is what actually prevents "keto flu," not just waiting it out. See the hydration guide.

Adequate protein, not just fat

✔

Keto is a low-carb diet, not a low-protein one — muscle is still built and kept by protein and training, and under-eating it just to hit a fat target works against that.

Whole-food fat sources

✔

Olive oil, avocado, nuts, eggs, and fatty fish over processed "keto snack" products — the diet's benefits come from the metabolic shift, not from any specific packaged food.

Tier A — Strong case

Fibre, deliberately

✔

Cutting carbs cuts a lot of people's main fibre sources too — low-carb vegetables, seeds, and nuts need to fill that gap on purpose, or gut health and regularity suffer. See the gut health guide.

Patience through adaptation

✔

Energy and training performance commonly dip for 1-3 weeks while the body shifts toward using fat and ketones efficiently — judging keto during that window is premature.

Watch high-intensity performance honestly

✔

Glycogen is still the preferred fuel for sprints and heavy, high-rep training — if performance stays down well past adaptation, that's real signal, not just needing to "push through" it.

Tier B — Situational

Targeted or cyclical keto

~

Adding carbs around hard training sessions helps some people keep high-intensity performance while staying in ketosis the rest of the time — worth trying if strict keto is tanking your training, not necessary otherwise.

Exogenous ketones / MCT oil

~

Can nudge you toward ketosis or provide a quick fuel source, but they're a shortcut around the metabolic adaptation, not a substitute for it — not required to do keto well.

Tier C — Skip it

"Dirty keto"

✘

Hitting the macros with processed meats, cheese, and low-carb junk food technically keeps you in ketosis, but skips the fibre, micronutrients, and food quality that make the diet worth doing well.

Ignoring fibre

✘

The single most common reason people quit keto early — constipation and gut discomfort from a diet that accidentally strips out most fibre sources, not the fat or protein itself.

Doing it because it's trendy

✘

Keto is one legitimate tool among several — not a diet everyone needs, and not automatically the best option for someone whose training or lifestyle it fights against.

Myths, Debunked

Myth: "Ketosis and ketoacidosis are the same thing."

Reality: Nutritional ketosis is a normal, diet-induced metabolic state in someone with functioning insulin. Diabetic ketoacidosis is a dangerous, distinct condition caused by an actual insulin deficiency, mostly in type 1 diabetes — not something diet alone causes in a healthy person.

Myth: "Keto burns fat faster than any other diet."

Reality: Fat loss still comes down to a calorie deficit — see the fat loss guide. Keto's edge for some people is appetite suppression that makes the deficit easier to hold, not a metabolic shortcut around energy balance.

Myth: "You can't build muscle on keto."

Reality: Muscle growth is driven mainly by protein intake and training stimulus, both compatible with keto — the real friction is that hard, glycolytic training can suffer without carbs, not that muscle itself needs them.

Myth: "Everyone should be doing keto."

Reality: Individual response varies a lot — some people feel steadier and more in control of appetite, others see mood and high-intensity performance drop. It's a legitimate option, not a universal prescription.