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Keto Flu: The Science of Fat Adaptation

Why Keto Flu Happens

Although completely unrelated to the influenza virus, folks who've taken on keto flu attest to experiencing feelings like fatigue, brain fog, headaches, muscle stiffness and cravings in the first 2 – 7 days.

When we restrict carbohydrate intake to such a degree as the ketogenic diet demands, our blood sugar levels decline.

By lowering our blood-glucose dramatically we compel the body to find alternative sources of fuel.

The first available source of carbohydrates to metabolize is the stored glycogen in the liver and muscles, waiting to be metabolized.

Here’s where things get interesting.

Something important to note, before we look at the consequences of glycogen metabolism, is how carbohydrates affect stored water in the body.

Carbohydrates, as compounds, love to hold onto water.

They do this even as they sit and wait in your liver and muscles. Studies have shown that 1g of glycogen has the propensity to hold up to 3g of water.

Naturally, then, as we burn up our glycogen stores, we get rid of held water at the same time.

This flushing of water is amazing to reduce that bloated feeling and drop a quick few pounds, but there is also a down-side.

When we get rid of water, we also expel certain very important minerals our bodies need to function.

Minerals like potassium, magnesium, and sodium are considered electrolytes and are exceptionally important for regulating the flow of nutrients into, and waste products out of, our cells.

Unfortunately, as we lose water, our electrolyte balance is disrupted and we begin to feel sluggish and run-down.

Adapting to Fat for Fuel

When we first change to a ketogenic eating plan, our system is suddenly deprived of its usual, stable stream of readily-available glucose.

While our bodies learn to acclimatize to the new energy source, fat, people sometimes note feeling fatigued, lethargy, nausea, headaches, and constipation in the first week.

Because the body hasn’t yet had the chance to become fat-adapted, it might not be producing ketones efficiently enough for the first 3 – 5 days.

With no glucose to use for energy and an unreliable stream of ketones fueling the cells, we simply aren’t running on optimal energy levels in this period.

The way to get adapted to fat is just to stick to your ketogenic lifestyle, and let biology do the rest!

Eat enough good, healthy fats loaded with omega 3s (wild-caught salmon, macadamia nuts, avocados) to give your liver everything it needs for ketogenesis.

Also, beware of overloading on “secret starches” (keto-friendly veggies like squash and zucchini) in the first few weeks, as you are aiming for at least 70% of your total daily intake to be from fats.

Helping the Body Fight Keto Flu

Boost Your Ketone Levels

If you can’t imagine getting enough fats into your diet to meet this initial quota, consider adding an exogenous ketone supplement with goBHB (Beta-Hydroxybutyrate) to your routine to induce hyperketonemia.

Your cells will have more bioavailable ketones to utilize for energy as the mitochondria within cells adapt.

Just be sure to get an exogenous ketone supplement that contains goBHB!

Some supplements advertise themselves to be pro-keto, but are not actually ketone salts at all, just a blend of minerals and oils.

Products like Keto BHBoost tell you in their name that what you’re taking has goBHB it, so looking for very specific product names is always safest to avoid missing out.

Beta-Hydroxybutyrate (BHB) is an exogenous ketone completely bio-identical to the ones our bodies make, and is chemically fused to a substrate to create a "ketone salt".

Ketone salts are useful because they have energizing BHB, but also because the compounds used in higher quality exogenous ketones like Keto BHBoost are sodium and magnesium, both essential electrolytes.

The endogenous ketones our bodies make naturally can either come from adipose tissue (fat stores) being broken down for energy, or from metabolizing the fat you eat.

Even if you are not on the ketogenic diet, taking exogenous ketones as a supplement will still encourage performance-enhancing effects.

Replace Lost Electrolytes

Stay hydrated with filtered, mineral-enriched water.

The same principle applies as when athletes chug sports drink after a heated performance.

Try dissolving some pink Himalayan salt or sea salt (refined table salt not recommended) into your water to replenish your sodium levels.

If drinking salty water sounds kind of gross, and you’re not alone here, perhaps you should consider adding an electrolyte-replenishing supplement to your plan.

Just make sure the capsules are sugar-free and contain Calcium Beta-Hydroxybutyrate, Sodium Beta-Hydroxybutyrate, and Magnesium Beta-Hydroxybutyrate.

Also, why not try adding these mineral-rich, keto-friendly foods to your diet: spinach, almonds, avocado, cocoa, swiss chard, Bulgarian/Greek yogurt, salmon and coconut water.


What's great about the keto-flu is that we know it's a sign that we are sticking properly to the ketogenic diet.

No keto-flu means our liver is not engaging in ketogenesis, and that would be a lot more of a let-down than a few days of brain-fog.

The ultimate lesson here is that, together, if we use the power of patience, electrolytes, exogenous ketones, and clever food choices, we might just cure keto-flu, once and for all.


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