Ketones - the lesser-known energy source

Written by: Holly Rothschild


Healf Journal

We all know that we need to eat to fuel our bodies. The major macronutrients that we need to do this are carbohydrates, fats and protein. These are broken down via digestion to their simplest forms: glucose, fatty acids and amino acids respectively and the body will favour their use for energy production in the same order.

However, there is a less well-known but important energy source that the body uses, one that it cleverly synthesises in the liver from fatty acids. This energy source is provided in the form of ketone bodies.

Written by  Holly Rothschild - Registered Nutritional Therapist at Integral Wellness , specialising in cardiometabolic health and with a special interest in menopause.

So what are Ketones and why do we need them?

Ketone bodies are fat-derived compounds that the liver makes when it metabolises fatty acids for energy during a period of fasting or when carbohydrate intake is low and glucose availability is limited. Ketones can also be synthesised from ketogenic amino acids (protein).

Our bodies are constantly producing ketone bodies at a maintenance level, but this process will increase with the body’s needs, for instance, there may be less glucose available overnight or during periods of exercise and fasting.

Although most tissues in the body can use fatty acids for energy when glucose is in short supply, the brain can’t. The brain has a protective barrier, called the blood-brain barrier, it’s there to stop harmful substances from reaching the brain. While glucose can find its way across, fatty acids are stuck outside.

Ketone synthesis is therefore an essential survival mechanism because in the absence of glucose, the brain needs an energy source and this is where those clever ketones come in as they can get across and the brain happily uses them as fuel.

As well as being beneficial for blood sugars, ketones also have anti-inflammatory and antioxidant properties, protecting our cells against oxidative stress. 

What is Ketosis?

With low glucose supply and increased fatty acids, the body increases ketone production. When the body is in this metabolic state it is said to be in ketosis.

It takes roughly 12-14 hours of fasting for mild ketosis to develop, so if you finish dinner at 7pm and don’t have breakfast until 9am, chances are you will be in ketosis and burning fat. This is why intermittent fasting can be an effective and healthy way to achieve gradual weight loss - if done properly and with consideration for any medical condition.

The metabolic shift from burning carbs to fats for fuel can be challenging for some and requires a degree of metabolic flexibility. Metabolic flexibility allows your body to effortlessly switch between fuel sources depending on availability. Chances are if you have been eating a low-fat, higher-carb diet you will find that switch more challenging. Certain life stages such as menopause can also make this switch more challenging.

It can take 3-4 days for the body to adapt to being in ketosis and during this time there can be some side effects, often referred to as keto flu. As the body adapts to flicking its energy switch to work off fats instead of glucose you may experience diarrhoea, constipation and vomiting as well as reduced energy levels, muscle aches, brain fog and increased hunger.

Keto vs low-carb

You may have heard of the “Keto” or “Ketogenic” diet which is essentially a high-fat, low-carb diet that is reported to promote weight loss amongst various other health benefits. Eating in this way initiates ketosis and the body therefore burns dietary and stored fat for energy.

A keto diet restricts daily carbohydrate intake to under 50g, though some versions reduce this to 20g! Whilst weight loss can occur on a keto diet for many it can be incredibly challenging to adhere to, which can lead to weight regain when it is stopped. Yo-yoing weight can play havoc with your metabolism, which is why diets of restriction are not the right approach for most.

Whilst the keto diet can benefit certain populations, such as people needing to control their blood sugar levels or those with epilepsy, it also restricts key nutrients in the diet such as fibre. Fibre is found in plant foods and these are all sources of carbohydrates be that a bean, barley or a banana! Fruits, vegetables, beans, legumes and whole grains are also important sources of vitamins, minerals and other healthful polyphenols.

If you are considering going keto it is worth doing so alongside a professional who can ensure you are obtaining all of your daily nutrient needs.

However, you don’t need to do a strict keto diet to be in ketosis, a low-carb approach that focuses on obtaining carbs from non-starchy vegetables, prioritises lean proteins and focuses on healthy fats will also get you there and may be far easier to follow as it is less restrictive.

You may also be surprised to learn that you can supplement ketones too. They are particularly useful at providing energy without the jitters, cravings and crashes that often come hand-in-hand with caffeine and sugar. This is because they don’t increase blood sugar or insulin levels in the body. The benefits of ketone supplementation alongside appropriate dietary adjustments can also support weight loss, brain health, and athletic performance. However, they are contraindicated in some medical conditions so they may not be for everyone.

Whilst studies have shown ketosis to be beneficial for lowering blood sugar and insulin levels as well as reducing blood glucose variability, if you do have a health condition or are on medication it is recommended that you speak with a qualified health practitioner or nutritional therapist to ensure that any dietary changes and/or supplementation are done so safely. It is also recommended to monitor your ketone levels using a urine strip to ensure your ketone bodies don’t get too high.

Is there such thing as too much of a good thing?

Ketone bodies are acidic so if their levels rise too high it can alter the pH of the blood, increasing the acidity. This can be dangerous and results in ketoacidosis - which essentially means there is too much acid in the body’s fluids.

Ketoacidosis can occur due to starvation and alcohol abuse. There is the potential for a very low-carb/ketogenic diet to result in ketoacidosis too.

Most commonly, ketoacidosis occurs in type 1 diabetes when insulin levels are too low and blood sugar levels too high. It can also happen in advanced type 2 diabetes when insulin production is compromised. Without insulin, the body can’t get glucose into the cells and the body therefore up-regulates ketone production, but in diabetic ketoacidosis, ketone production can overwhelm the body. This is a medical emergency and immediate medical attention should be sought.

The takeaway

Ketosis has numerous health benefits and ketones are a clean fuel source that supports our bodies' energy needs without the ups and downs that so often accompany the caffeine and sugar fixes. Supporting the body's ability to flip to burning fat for fuel increases metabolic flexibility and optimises metabolic health outcomes.

There is now a significant bank of evidence that supports the high-fat, low-carb approach and it is time that we flip the historical low-fat, high-carb narrative that has exacerbated the increase in metabolic disease globally. If you are curious about whether this is the right approach for you, work with a Nutritional Therapist to get personalised support that encompasses a holistic approach to your health needs and goals.


This article is for informational purposes only, even if and regardless of whether it features the advice of physicians and medical practitioners. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. The views expressed in this article are the views of the expert and do not necessarily represent the views of Healf