Low carb and ketogenic diets have many health benefits.
For example, it’s well known that they can lead to weight loss and help manage diabetes. However, they’re also beneficial for certain brain disorders.
This article explores how low carb and ketogenic diets affect the brain.
Although there’s a lot of overlap between low carb and ketogenic diets, there are also a few important differences.
Low carb diets:
- Carbs are typically restricted to about 50–130 grams per day (
- Protein is usually not restricted.
- Ketones may or may not rise to high levels in the blood. Ketones are molecules that can partly replace carbs as an energy source for the brain.
- Carb intake is limited to 20–50 grams per day.
- Protein is often restricted.
- A major goal is to increase ketone blood levels.
On a standard low carb diet, the brain will still largely depend on glucose, the sugar found in your blood, for fuel. However, the brain may burn more ketones than on a regular diet.
On a ketogenic diet, ketones are the primary fuel source for the brain. The liver produces ketones when carb intake is very low.
Low carb and ketogenic diets are similar in many ways. However, a ketogenic diet contains even fewer carbs and will lead to a significant rise in blood levels of ketones, which are important molecules.
You may have heard that your brain needs 130 grams of carbs per day to function properly. This is one of the most common myths about what constitutes a healthy carb intake.
In fact, a 2005 report by the National Academy of Medicine’s Food and Nutrition Board states:
“The lower limit of dietary carbohydrates compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed” (2).
Although a zero-carb diet isn’t recommended because it eliminates many healthy foods, you can definitely eat less than 130 grams per day and maintain good brain function.
It’s a common myth that you need to eat 130 grams of carbs per day to provide the brain with energy.
Low carb diets provide your brain with energy via processes called ketogenesis and gluconeogenesis.
Glucose is usually the brain’s main fuel. Your brain, unlike your muscles, can’t use fat as a fuel source.
However, the brain can use ketones. When glucose and insulin levels are low, your liver produces ketones from fatty acids.
Ketones are actually produced in small amounts whenever you go for many hours without eating, such as after a full night’s sleep.
However, the liver increases its production of ketones even more during fasting or when carb intake falls below 50 grams per day (
When carbs are eliminated or minimized, ketones can provide up to 75% of the brain’s energy needs (4).
Although most of the brain can use ketones, there are portions that require glucose to function. On a very low carb diet, some of this glucose can be supplied by the small amount of carbs consumed.
The rest comes from a process in your body called gluconeogenesis, which means “making new glucose.” In this process, the liver creates glucose for the brain to use. The liver makes the glucose using amino acids, the building blocks of protein (
The liver can also make glucose from glycerol. Glycerol is the backbone that links fatty acids together in triglycerides, the body’s storage form of fat.
Thanks to gluconeogenesis, the portions of the brain that need glucose get a steady supply, even when your carb intake is very low.
On a very low carb diet, ketones can fuel up to 75% of the brain. Glucose produced in the liver can fuel the rest.
Epilepsy is a disease characterized by seizures linked to periods of overexcitement in brain cells.
It can cause uncontrolled jerking movements and loss of consciousness.
Epilepsy can be very difficult to treat effectively. There are several types of seizures, and some people with the condition have multiple episodes every day.
Although there are many effective antiseizure medications, these drugs are unable to effectively manage seizures in about 30% of people. The type of epilepsy that’s unresponsive to medication is called refractory epilepsy (6).
Dr. Russell Wilder developed the ketogenic diet in the 1920s to treat drug-resistant epilepsy in children. His diet provides at least 90% of calories from fat and has been shown to mimic the beneficial effects of starvation on seizures (7).
The exact mechanisms behind the ketogenic diet’s antiseizure effects remain unknown (7).
Low carb and ketogenic diet options to treat epilepsy
There are four types of carb-restricted diets that can treat epilepsy. Here are their typical macronutrient breakdowns:
- Classic ketogenic diet (KD): 2–4% of calories from carbs, 6–8% from protein, and 85–90% from fat (
- Modified Atkins diet (MAD): 10% of calories from carbs with no restriction on protein in most cases. The diet starts by allowing 10 grams of carbs per day for children and 15 grams for adults, with potential slight increases if tolerated (
- Medium-chain triglyceride ketogenic diet (MCT diet): Initially 10% carbs, 20% protein, 60% medium-chain triglycerides, and 10% other fats (
- Low glycemic index treatment (LGIT): 10–20% of calories from carbs, around 20–30% from protein, and the rest from fat. Limits carb choices to those with a glycemic index (GI) under 50 (11).
The classic ketogenic diet in epilepsy
The classic ketogenic diet (KD) has been used in several epilepsy treatment centers. Many studies have found improvement in over half of study participants (
In a 2008 study, children treated with a ketogenic diet for 3 months had a 75% decrease in baseline seizures, on average (
According to a 2009 study, around one-third of children who respond to the diet have a 90% or greater decrease in seizures (
In a 2020 study on refractory epilepsy, children who adopted the classic ketogenic diet for 6 months saw their seizure frequency decrease by 66% (
Although the classic ketogenic diet can be very effective against seizures, it requires close supervision by a neurologist and dietitian.
Food choices are also quite limited. As such, the diet can be difficult to follow, particularly for older children and adults (18).
The modified Atkins diet in epilepsy
In many cases, the modified Atkins diet (MAD) has proven to be as effective or nearly as effective for managing childhood epilepsy as the classic ketogenic diet, with fewer side effects (19,
In a randomized study of 102 children, 30% of those who followed the modified Atkins diet experienced a 90% or greater reduction in seizures (
Although most studies have been done in children, some adults with epilepsy have also seen good results with this diet (
In an analysis of 10 studies comparing the classic ketogenic diet to the modified Atkins diet, people were much more likely to stick to the modified Atkins diet (26).
The medium-chain triglyceride ketogenic diet in epilepsy
The medium-chain triglyceride ketogenic diet (MCT diet) has been used since the 1970s. Medium-chain triglycerides (MCTs) are saturated fats found in coconut oil and palm oil.
Unlike long-chain triglyceride fats, MCTs can be used for quick energy or ketone production by the liver.
MCT oil’s ability to increase ketone levels with less restriction on carb intake has made the MCT diet a popular alternative to the other low carb diets (11,
One study in children found that the MCT diet was as effective as the classic ketogenic diet in managing seizures (
The low glycemic index treatment in epilepsy
The low glycemic index treatment (LGIT) is another dietary approach that can manage epilepsy despite its very modest effect on ketone levels. It was first introduced in 2002 (29).
In a 2020 study of children with refractory epilepsy, those who adopted the LGIT diet for 6 months had a reduction in seizures and also experienced significantly fewer side effects than those who adopted the classic ketogenic diet or modified Atkins diet (
Various types of low carb and ketogenic diets are effective at reducing seizures in children and adults with drug-resistant epilepsy.
Although few formal studies have been done, it appears that low carb and ketogenic diets may be beneficial for people with Alzheimer’s disease.
Alzheimer’s disease is the most common form of dementia. It’s a progressive disease where the brain develops plaques and tangles that cause memory loss.
Many researchers believe it should be considered “type 3” diabetes because the brain’s cells become insulin-resistant and are unable to use glucose properly, leading to inflammation (
In fact, metabolic syndrome, a precursor of type 2 diabetes, also increases the risk of developing Alzheimer’s disease (
Experts report that Alzheimer’s disease shares certain features with epilepsy, including brain excitability that leads to seizures (
In a 2009 study of 152 people with Alzheimer’s disease, those who received an MCT supplement for 90 days had much higher ketone levels and a significant improvement in brain function compared with a control group (
In a small 2018 study that lasted 1 month, people with Alzheimer’s disease who took 30 grams of MCT a day saw their brain ketone consumption increase significantly. Their brains used twice as many ketones than they did before the study (
Animal studies also suggest that a ketogenic diet may be an effective way to fuel a brain affected by Alzheimer’s (
As with epilepsy, researchers aren’t certain of the exact mechanism behind these potential benefits against Alzheimer’s disease.
One theory is that ketones protect brain cells by reducing reactive oxygen species. These are metabolism byproducts that can cause inflammation (
Another theory is that a diet high in fat, including saturated fat, can reduce the harmful proteins that accumulate in the brains of people with Alzheimer’s (
On the other hand, a recent review of studies concluded that a high intake of saturated fat was strongly associated with an increased risk of Alzheimer’s (
Research is still in its early stages, but ketogenic diets and MCT supplements may help improve memory and brain function in people with Alzheimer’s disease.
Although these haven’t been studied as much, low carb and ketogenic diets may have several other benefits for the brain:
- Memory. Older adults at risk for Alzheimer’s disease have shown improvement in memory after following a very low carb diet for 6–12 weeks. These studies were small, but the results are promising (
- Brain function. Feeding older and obese rats a ketogenic diet leads to improved brain function (45,
- Congenital hyperinsulinism. Congenital hyperinsulinism causes low blood sugar and can lead to brain damage. This condition has been successfully treated with a ketogenic diet (
- Migraine. Researchers report that low carb or ketogenic diets may provide relief to people with migraine (
- Parkinson’s disease. One small, randomized control trial compared the ketogenic diet with a low fat, high carb diet. People who adopted the ketogenic diet saw a much greater improvement in pain and other nonmotor symptoms of Parkinson’s disease (
Low carb and ketogenic diets have many other health benefits for the brain. They may help improve memory in older adults, relieve migraine symptoms, and reduce symptoms of Parkinson’s disease, to name a few.
There are certain conditions for which a low carb or ketogenic diet isn’t recommended. They include pancreatitis, liver failure, and some rare blood disorders (
If you have any sort of health condition, speak with your doctor before starting a ketogenic diet.
Side effects of low carb or ketogenic diets
People respond to low carb and ketogenic diets in many different ways. Here are a few potential adverse effects:
- Elevated cholesterol. Children may experience elevated cholesterol levels and elevated triglyceride levels. However, this may be temporary and doesn’t appear to affect heart health (
- Kidney stones. Kidney stones are uncommon but have occurred in some children undergoing ketogenic diet therapy for epilepsy. The kidney stones are usually managed with potassium citrate (
- Constipation. Constipation is very common with ketogenic diets. One treatment center reported that 65% of children developed constipation. It’s usually easy to treat with stool softeners or dietary changes (
Children with epilepsy eventually discontinue the ketogenic diet once seizures have resolved.
One study looked at children who spent a median duration of 1.4 years on the ketogenic diet. Most of them didn’t experience any negative long-term effects as a result (
A very low carb ketogenic diet is safe for most people, but not everyone. Some people may develop side effects, which are usually temporary.
When transitioning to a low carb or ketogenic diet, you may experience some adverse effects.
You may develop headaches or feel tired or lightheaded for a few days. This is known as the “keto flu” or “low carb flu.”
Here are some suggestions for getting through the adaptation period:
- Make sure to get enough fluid. Drink at least 68 ounces (2 liters) of water a day to replace the water loss that often occurs in the initial stages of ketosis.
- Eat more salt. Add 1–2 grams of salt each day to replace the amount lost in your urine when carbs are reduced. Drinking broth will help you meet your increased sodium and fluid needs.
- Supplement with potassium and magnesium. Eat foods high in potassium and magnesium to prevent muscle cramps. Avocado, Greek yogurt, tomatoes, and fish are good sources.
- Moderate your physical activity. Don’t exercise heavily for at least 1 week. It may take a few weeks to become fully keto-adapted. Don’t push yourself in your workouts until you feel ready.
Adapting to a very low carb or ketogenic diet takes some time, but there are a few ways to ease the transition.
According to the available evidence, ketogenic diets can have powerful benefits for the brain.
The strongest evidence has to do with treating drug-resistant epilepsy in children.
There’s also preliminary evidence that ketogenic diets may reduce symptoms of Alzheimer’s and Parkinson’s disease. Research is ongoing about its effects on people with these and other brain disorders.
These diets aren’t for everyone, and it can be beneficial to check in with your doctor before starting this diet.