β-Hydroxybutyrate (BHB)

β-Hydroxybutyrate (BHB) is the most important ketone body and indicates the degree of fat burning/ketosis. BHB is not only a fuel but also a signalling molecule: in cell and animal studies, BHB inhibited the NLRP3 inflammasome, a trigger of inflammatory reactions, and certain histone deacetylases, which control the reading of genes. Measurable in the organic acids. Raised with fasting, a ketogenic diet, diabetes (ketoacidosis) and mitochondrial stress.

What BHB does in the body

Chemically, BHB is not a ketone but a hydroxy acid: the liver makes it from the actual ketone body acetoacetate by transferring NADH to it. How much BHB is formed relative to acetoacetate therefore depends on the NADH/NAD⁺ ratio in the liver mitochondria. In the blood, BHB is the more stable transport form, because unlike acetoacetate it does not partly break down into acetone, which is given off via the breath. In the target cells – above all the heart, skeletal muscles, kidneys and brain – BHB is turned back via acetoacetate and the enzyme SCOT into acetyl-CoA, which flows into the citric acid cycle. BHB also acts as a messenger: via the receptor HCA2 on fat cells it slows further fat release, and it inhibits certain histone deacetylases, which control the reading of genes.

Low BHB – what does it mean?

When BHB is low, the cells obtain their energy mainly from glucose: insulin slows fat release, and the liver burns acetyl-CoA in the citric acid cycle or uses it to build fat instead of forming ketone bodies from it. This is to be expected with a regular, carbohydrate-containing diet. If the value stays very low even after a longer break from food, this can be linked to slowed fat utilisation – for example when little carnitine is available to transport the fatty acids or enzymes of beta-oxidation are not working sufficiently; muscles and brain then depend more on blood sugar during fasting phases.

High BHB – what happens in the body?

A high value shows that the liver is converting fatty acids into ketone bodies on a large scale and the tissues are using this fuel. A particularly high share of BHB relative to acetoacetate additionally shows that a lot of NADH is present in the liver mitochondria – pronounced during alcohol breakdown and with a lack of oxygen. Ketone bodies are acids: as long as insulin limits their formation, the body compensates for them via breathing and the kidneys; if they are formed unchecked with marked insulin deficiency, the pH of the blood falls. Raised values occur with fasting, a ketogenic diet, long endurance exercise, diabetes, alcohol consumption with little food and with SGLT2 inhibitors. BHB passes into urine when the kidneys filter more ketone bodies than they recover.

The interpretation is given in your report.