The human body can efficiently burn BHB for energy because…

We’ve been doing it for hundreds of thousands of years. It’s how our ancestors survived.

Let’s back up a bit:

Humans in the hunter-gatherer era survived thanks to metabolic flexibility — the body’s ability to use different fuels for energy depending on the nutrients available. This adaptation was vital during a time when the source, quantity, and frequency of food was uncertain. Most of the time, people were fasting, so their bodies ran on ketones, not glucose.

Nowadays,Sadly, our food environment pushes us to ditch ketones and rely on glucose when we grow up. Unless you’re a baby, a regular keto-er, a carnivore, diabetic, or a caveman, your body runs on glucose.

The good news is, it’s easy to start using ketones for fuel again.

Your body is always making BHB and AcAc, but on a regular carb-based diet, the levels remain below 0.5 mmol/L (micromolar per liter), which isn’t enough to fuel your cells.

Only certain conditions can boost BHB levels high enough to make the fuel switch:

Following a ketogenic diet. On low carb, high fat ketogenic diet, your body will produce consistent ketone levels above 2 mmol/L.

Fasting. BHB levels rise above 0.6 mmol/L after 12–16 hours of fasting and reach 1–2 mmol/L after 2 days of fasting.

Doing Intense Exercise. Doing intense exercise for 90 minutes can boost BHB to 1–2 mmol/L.

In these three circumstances, your body doesn’t have access to enough carbs (glucose) or stored glucose (glycogen), so it turns to stored fat for energy. The fatty acids are metabolized by your liver into ketones (mostly BHB), which can be used by your cells as an efficient fuel source.

When your ketone levels are consistently between 0.6 and <3 mmol/L, you’re in nutritional ketosis, which has many advantages, including:

Increased cognitive function (clearer thinking, higher focus)

Stable blood sugar

More energy

Healthy weight loss

Accelerated fat loss

Better workout performance

During therapeutic treatments under the supervision of a physician, your blood BHB may rise up to 10 mmol/L.

There are other circumstances that push your body to make more ketones, but these are detrimental to your health and should not be attempted:

Not monitoring insulin levels as a diabetic. If insulin levels are not controlled in diabetic patients, they can drop dramatically and make your body overproduce ketone bodies above 3 mmol/L. This may provoke ketoacidosis, which can be lethal (more on that later).

Entering starvation mode after extended fasts. Prolonged starvation will increase ketones to 6–8 mmol/L, but it’s not the healthiest approach. What’s the point of making lots of efficient BHB if you’re going to starve yourself and miss out on important nutrients? Remember, being in ketosis doesn’t mean you’re healthy.

The best way to reap all the health benefits of BHB is to keep it in the range of nutritional ketosis.

The three types of cells that consume the most BHB are:

Cardiomyocytes (cardiac muscle cells). The heart is the highest ketone body consumer per unit mass.

Skeletal myocytes (skeletal muscle cells).

Neurons.

Normally, your brain and muscles rely heavily on glucose, while your heart burns long-chain fatty acids, but switching to BHB can enhance their function and provide extra protection against disease.