Note: I am not a doctor and don’t play one on the Internet. This article is about my own experience and what I’ve learned and doesn’t constitute medical advice.
For most of my life I’ve experienced a background level of tiredness, struggle to focus and ‘brain fog’. I used to hate waking up in the mornings and some days I would struggle to think so much I felt like I had lost 50 IQ points. It was a frustrating experience: I knew I had more mental capacity available, but it was just switched off a lot of the time.
My life has been an experiment in tinkering with ways to feel good, or as I grandly call it, ‘to improve the quality of my subjective experience’. Life is too short to live as if through a veil.
I have implemented various habits around exercise, consistent sleep patterns, quitting caffeine, reducing alcohol and meditating daily. They’re all useful, but what has worked the best for me is the very low-carbohydrate ketogenic (“keto”) diet.
I’ve been on keto for about a year with some short breaks. I tend to go a few months and then come off for the occasional weekend, either when I travel or for a particularly special, non-keto, meal that I don’t want to miss. It doesn’t take long before I start to feel uncomfortable again, so I get back on keto pretty quickly.
I’ve seen a lot of benefits since settling into it. My mood, energy and quality of attention are better and more stable. I feel smarter. I don’t feel hungry as much and it’s no problem to miss meals. I can do three day water-only fasts without much difficulty.
I’ve seen a real improvement in symptoms of anxiety and depression, which have been lifelong companions, fortunately mild compared to many. I handle stress better. I sleep better, need less of it and wake up easily with less grogginess. My performance in the gym has improved.
I’ve also found it to be an extremely satisfying and sustainable way of eating. I get to eat lots of green vegetables, high quality fats and I can eat cheese, meat and fish.
If you research keto online you’ll find mainly dramatic weight loss stories. That’s great for people who want it, but as a 186 cm (6’ 1”) and 72 kg (159 lbs) guy trying to gain weight, that's not what I want. I'm in it for the cognitive benefits.
Keto is a very low carbohydrate, moderate protein, high fat diet. The most important factor to control is carbohydrate intake, which should be below about 20 g per day – not much – though that limit will vary by person.
Do this for a couple of days and interesting things start to happen. Your body uses up the glucose in your blood before moving on to a stored version of glucose, called glycogen, in your muscles and liver.
If you have eaten a traditional diet that includes carbohydrates all your life, and you have never done extended fasting, then this might be the first time this has happened to you since you were a newborn baby. There has always been plenty of glucose available, so your body has always used it for energy.
But when there’s no glucose around, your body switches to a secondary energy source: ketones. These are molecules created when your body breaks down fat and are where the term ketogenic comes from (‘ketone creating’).
People who follow the keto diet, or who do extended fasts, enter a metabolic state called nutritional ketosis, where ketone levels in the blood increase while blood glucose and insulin remain low. Some cells can only run on glucose, so your body creates all the glucose it needs from protein through a process called gluconeogenesis (‘new glucose creation’). This keeps your blood sugar at a stable, low level and shows that there is no metabolic need to consume glucose, since your body can make what it needs for itself.
Low insulin is why fat loss stories are so common with keto. Insulin is a storage hormone: its job is to move glucose into your cells for energy or to store it as glycogen or body fat. When insulin is elevated, and unless you’re exercising to burn off the glucose straight away, your body is creating more fat for long term storage. It’s only when insulin is low that the stored energy can flow out of fat cells. For the first time in their lives, people switching to keto for weight loss are creating the biochemical environment that’s actually required for fat loss, because their bodies start using the stored fat as their primary fuel.
This explains why it’s possible to carry a lot of body fat and still feel ravenously hungry every few hours. If your body is conditioned to run on glucose, then it isn’t adapted to creating and using ketones produced from body fat. As blood glucose and insulin drop, the body runs out of the glucose it uses for fuel, has nothing else to lean on, and signals that you’re hungry. You eat, elevate your blood glucose again, and never give your body the opportunity to adapt to accessing your own fat stores.
The first few days or weeks of keto can often suck, partly because your body needs to grow and modify mitochondria, the parts of cells that convert molecules like glucose and ketones into usable energy for your cells. This is known as ‘keto adaptation’ and until that happens you may have the ketones you need, but you don't yet know how to use them.
Studies suggest that this can take about 12 weeks , but once it’s done your body will be set up to run happily on dietary or body fat. Given that one kilogram of fat contains 9000 kcals (three to four days’ worth of energy), you can go a long time just on your own fat reserves, even if you don’t have that much body fat.
And because you’re adapted to using fat your cravings for carbohydrates will go away as well, so you won’t even want that slice of cake. I don’t really see starchy or sugary products as food anymore; they just don't trigger any interest, aside from any lingering emotionally-based craving from time to time (feel sad; want sugar).
Looking at energy levels first, using ketones from fat for fuel means that there is a steady supply of energy, so you don't experience huge swings in blood sugar before and after eating meals high in carbohydrates. That means no post lunch slump and no desire to eat every couple of hours.
The story of where the ketogenic diet came from is interesting to illustrate benefits for brain health. It was originally developed as a successful treatment for drug-resistant epilepsy in children, which shows that there is a link between keto and brain function . And in terms of general mental health – for example anxiety, depression, quality of attention – there are a few mechanisms for how this could happen.
One is the difference between how glucose and ketones are metabolised in the brain, which constitutes about 20% of the body’s energy needs. The way the body generates useable energy is via a molecule called Adenosine Triphosphate (ATP). Both glucose and ketones can be used to generate ATP, but it turns out that ketones produce ATP more efficiently than glucose . This means that, once adapted to using ketones for fuel, the brain gets more energy from ketones than from glucose, which is great for such an energy-hungry organ.
The effect of this can be seen clearly in Alzheimer's disease. One of the effects of the disease is to disrupt glucose metabolism in the brain, which reduces brain function as the brain is starved of energy. Supplementation of ketones and the use of the ketogenic diet has been shown to improve brain function in Alzheimer’s patients .
Another potential route to improved brain health is through reduction of inflammation, an immune response designed to protect the body from disease and injury, but which is damaging when chronic. Inflammation in the brain has been linked to anxiety, depression and Alzheimer’s disease  . The ketogenic diet has been shown to reduce inflammation, which suggests it has therapeutic value for these and perhaps more mental illnesses.
Perhaps the most interesting way the ketogenic diet could improve cognition is through the role of two important neurotransmitters: glutamate and GABA. Neurotransmitters are the messenger chemicals that allow neurons in the brain to communicate with each other and influence how sensitive they are in responding to stimuli.
Glutamate and GABA are essentially opposites, which are maintained in a balance within the brain. Glutamate is excitatory, which means it makes neurons more likely to fire in response to a stimulus. Higher levels of glutamate are associated with a range of mental illnesses, including anxiety , depression , obsessive compulsive disorder  and potentially even personality disorders like Borderline Personality Disorder (BPD) . As someone who has experienced anxiety, depression, and traits of BPD, it’s this mechanism that fascinates me the most. I know that when I go off keto, symptoms of all of these worsen and improve when I return to keto.
On the other hand, GABA is inhibitory, which reduces the sensitivity of neurones. Alcohol and benzodiazepines like Valium work by mimicking GABA, while nootropics like l-theanine (an amino acid) work by increasing GABA. All of these produce anxiety-reducing effects.
The ketogenic diet has been shown to change the balance between glutamate and GABA in the brain . When in ketosis, glutamate is reduced through more efficient clearing of it from synapses (the space between neurons where neurotransmitters operate) and the synthesis of GABA from its precursor, glutamine, increases.
Given all of these potential mechanisms, I’m confident that the benefits I see in my cognitive performance are linked to my use of the ketogenic diet. Not only am I giving my brain a steady supply of a more efficient fuel, I’m also reducing damaging inflammation and changing a chemical balance in my brain that positively affects symptoms of anxiety, depression, and Borderline Personality Disorder, all of which interfere with my ability to think clearly.
Having read that, you might be interested in how to experiment with a ketogenic diet yourself. There are plenty of resources out there you can refer to, which I’ll list below, but here are my quick start tips.
Eat fewer than 20 g of carbohydrates per day. This is on the extreme end of estimates out there, but will pretty much guarantee that you enter ketosis. This means you’ll be eating lots of green vegetables, healthy fats, fish, meat and some dairy. No starchy vegetables, fruit, grains, bread or anything sugary.
Weigh all of your food for a couple of weeks. You’ll be amazed how bad you are at assessing portion sizes and doing this will help recalibrate your intuition.
Use an app like Cronometer to track your food. Cronometer is great for keto because it includes calculation of ‘net carbs’, which is the number you want to track. This only applies to American users, where food labels mean you need to subtract fibre (which is undigested) from the total carbohydrate figure to get the number you want. In Europe you can just use the carbohydrate number on the label as fibre is already subtracted.
Avoid all processed foods. Anything that has a list of ingredients on it probably has added sugars. Best just to cook your own food for a while.
Supplement with electrolytes. It turns out that insulin causes your body to retain key electrolytes like sodium, magnesium and potassium. On keto, insulin stays low, so your body loses a lot of those electrolytes. That means you’ll lose a lot of water weight very quickly at first, as these electrolytes are bound with water, but you will need to supplement them.
Do it strictly for three months to let your body adapt. It takes time for your body to fully adapt to keto. If you really want to benefit, commit to doing it properly for about twelve weeks, which is how long evidence suggests it takes athletes who transition to keto to return to their previous performance .
I hope that was a useful primer into the cognitive benefits of the ketogenic diet. There’s a lot more you can dig into, so I’ve included a list of my favourite resources below.
The fat-fueled brain: unnatural or advantageous? This is a great article in Scientific American that introduces some of the same biochemistry that I’ve discussed here, with a focus on the effects of the ketogenic diet on brain health.
The Art and Science of Low Carbohydrate Living. This book by Jeff Volek and Stephen Phinney is a kind of keto bible. As two pioneers of keto research, Jeff and Stephen discuss everything you ever wanted to know about keto in this book. You can also follow Jeff and Stephen’s work via their company Virta Health, where they’re also exploring the use of the ketogenic diet to reverse type 2 diabetes.
Thomas Delauer. For those of you who prefer video, Thomas Delauer is the leading voice on YouTube for everything to do with keto and fasting. I have picked up a lot of my keto knowledge from Thomas.
Dietdoctor.com. If you’re looking for recipes or a more structured ‘plan’ approach to starting the ketogenic diet, then dietdoctor.com is a great place to start.
Dominic D’Agostino. Another world class researcher into the science of a ketogenic diet, Dominic is also particularly interested in the role of the ketogenic diet in treating and preventing cancer.
Mark’s Daily Apple. Mark Sisson is a veteran nutrition writer who has recently moved into the keto space. His book “The Keto Reset Diet” is a good introduction on how to transition from a conventional high carb diet to a ketogenic diet over a number of steps.