Ketones Explained: BHB, Acetoacetate and Acetone
The ketogenic diet shifts your metabolism to burn fat rather than glucose. When carbohydrate intake drops below about 50g per day, your liver begins converting fatty acids into three ketone bodies: beta-hydroxybutyrate (BHB), acetoacetate, and acetone. These molecules serve as alternative energy sources when glucose is scarce.
The Three Ketone Bodies
Ketone production occurs primarily in liver mitochondria through a process called ketogenesis. The three ketones differ in their structure and how your body uses them:
1. Beta-hydroxybutyrate (BHB): The most abundant ketone in blood during ketosis, making up about 70% of circulating ketones. Unlike the others, BHB isn’t technically a ketone chemically – it’s a hydroxyl acid. But functionally, it acts like one. Cells prefer BHB as it’s more stable and energy-rich than acetoacetate.
2. Acetoacetate: The first ketone produced during ketogenesis. Some converts to BHB, while the rest circulates for use by tissues like the brain. Acetoacetate levels typically peak during early ketosis before stabilising.
3. Acetone: A volatile byproduct of acetoacetate breakdown. Unlike BHB and acetoacetate, acetone can’t be used for energy. Most gets exhaled through breath (causing “keto breath”) or excreted in urine.
Research suggests BHB may have signalling effects beyond just fuel. A 2018 study in Diabetes Therapy found BHB appears to influence gene expression related to inflammation and oxidative stress (Hallberg SJ et al., 2018).
How Ketones Fuel Your Body
During prolonged carbohydrate restriction, ketones become the brain’s primary fuel source. The brain can derive up to 70% of its energy from ketones during sustained ketosis. This metabolic shift explains why many report improved mental clarity on a ketogenic diet.
Muscle tissue also uses ketones efficiently. Athletes in ketosis show similar endurance capacity to those using carbohydrates, according to a 2017 review in Nutrients (Kosinski C et al., 2017). The heart preferentially burns ketones over glucose.
the keto adaptation timeline varies between individuals, but most people reach stable ketone production within 2-4 weeks of strict carbohydrate restriction.
What This Means in Practice
Monitoring ketones helps assess nutritional ketosis. Blood meters measuring BHB provide the most accurate reading, with optimal ketosis ranging 0.5-3.0 mmol/L. Urine strips detect acetoacetate but become less reliable over time as your body conserves ketones better. Breath analysers measure acetone.
At Tesco, you’ll find keto-friendly foods to support ketone production – £1.80 for 200g of Tesco Finest Mature Cheddar provides both fat and protein without carbs. Seasonal berries like blackberries (currently £2.50 for 150g at Sainsbury’s) offer fibre with minimal net carbs.
common keto electrolyte mistakes often accompany the initial ketone surge. Increased water loss can deplete sodium, potassium and magnesium unless you consciously replace them.
Frequently Asked Questions
How long does it take to start producing ketones?
Most people begin producing detectable ketones within 24-48 hours of restricting carbohydrates to under 50g daily. Full adaptation where your body efficiently uses ketones takes 2-4 weeks.
Why does my breath smell fruity on keto?
The acetone byproduct of ketosis gets excreted through breath, creating a distinctive smell often described as fruity or nail polish-like. It typically diminishes after full adaptation.
Are ketones dangerous for people with diabetes?
Nutritional ketosis differs from diabetic ketoacidosis (DKA). In DKA, ketones exceed 10 mmol/L alongside high blood glucose. Those with type 1 diabetes should monitor closely under medical supervision.
The Bottom Line
Ketones – primarily BHB, with smaller amounts of acetoacetate and acetone – serve as alternative energy molecules during carbohydrate restriction. They allow your brain and muscles to function efficiently when glucose is scarce. While the biochemistry seems complex, the practical effects include sustained energy and mental clarity for many following a ketogenic diet. If you’d rather not do the macro maths yourself, the Keto Dieting app does it for you on Google Play and the App Store.
References
- Hallberg SJ, McKenzie AL, Williams PT, et al. (2018). Effectiveness and Safety of a Novel Care Model for the Management of Type 2 Diabetes at 1 Year: An Open-Label, Non-Randomized, Controlled Study. Diabetes Therapy. https://doi.org/10.1007/s13300-018-0373-9
- Kosinski C, Jornayvaz FR (2017). Effects of Ketogenic Diets on Cardiovascular Risk Factors: Evidence from Animal and Human Studies. Nutrients. https://doi.org/10.3390/nu9050517
