Adriana Lima, Halle Berry, LeBron James, and The Kardashians swear by it. General practitioners are beginning to promote and prescribe it. Social media and marketing can't get away from it. The keto diet has achieved attention and applause for it's rapid fat-burning, weight loss effects. But is this another fitness and nutrition fad? Or will the keto diet prove to prevent chronic disease and boost brain health and cognitive function?   

What are low-carb and ketogenic diets? 

Low-carb high-fat diets vary depending on their macronutrient ratios (carb, fat, protein) but they all limit or eliminate carbohydrate type foods (sugar, fruit, grains, alcohol, starchy vegetables) from the diet. The concept around these diets is based on the fact that carbohydrate foods get broken down into sugar. If we have too much, the extra calories are more easily stored as body fat. When the body doesn’t get enough carbs, it may start to burn fat instead.


The Dietary Guidelines for Americans recommended that healthy adults get 50-65% of total daily calories from carbohydrate [2]. It was previously thought that the brain needs about 100-150 grams of carbs per day however, a report by the US Institute of Medicine’s Food and Nutrition Board states that although a zero carb diet isn’t recommended, you can eat less than that amount of carbs and still maintain good brain function [1]. 


A low-carb diet technically implies anything lower than 45-50% of daily carbohydrates. This varies tremendously on the type of low-carb diet. Most studies define "low-carb" as less than 30% of carbs per total calorie intake [3]. 


The ketogenic diet, otherwise known as “very-low-carbohydrate diet”, “very-low-carbohydrate ketogenic diet”, or “keto diet” is based off of the concept that drastically decreasing carbohydrates and increasing fat content, will trick your body into thinking it's fasting. 

In the standard keto diet, originally created for epileptic patients, the macronutrient ratios were: 75% of calories from fats, 20% from protein, and 5% from carbs. In order to see most associated benefits, it’s fine to aim for about 30-50 net grams of carbs to start. Once used to this level, cut down to about 20 grams of net carbs per day. It’s important to note that the main benefits of the ketogenic diet can happen only if you can get and keep your body in a state of ketosis.


The ketogenic diet was originally developed to mimic biochemical changes associated with starvation or limited food [4]. In normal metabolism, carbohydrates that we get from food are converted into glucose, which is the body’s preferred substance for energy production. 


Before reaching a state of ketosis, your body provides energy through a function called gluconeogenesis. Glucose is what keeps your body running (brain function, digestive system, cardiovascular function). When you restrict your carb intake, your body will first burn through glycogen. Glycogen is the storage form of glucose, that gets tucked away in your muscles and liver. 

This system is intended to prevent starvation. During times that you eat a little excess fuel, the glucose molecules link together to form glycogen. Once it’s depleted, such as after intense exercise or when you're fasting, your body starts breaking down muscle to convert it into glucose.

Once all the glycogen is depleted, you’ll feel tired, fatigued, and have decreased fitness performance (hitting a wall for you expert fanatics out there). The glycogen found in your muscles are for “locals only”, meaning mainly used by the muscle where it’s located.  


Glycogen depletion is the first step towards reaching ketosis. The time it takes varies on your body, what you eat, and the type of activity you're doing:

  • Standard daily activity (cleaning house, working, walking): 12-22 hours
  • Low to moderate intensity exercise (distance running, hiking, biking): 90-120 minutes
  • High-intensity exercise (HIIT training): 20 minutes [7].

It typically takes about 3-4 days for stored glucose to be fully depleted and for your body to switch to fat as the primary fuel source [6]. 


When there aren't enough carbohydrates nor stored glucose to meet your body’s metabolic needs, fatty acids are favored. Since fatty acids can’t cross the blood-brain barrier, ketone bodies are created in order to enter the brain and provide energy. Ketones can provide up to 70% of the brain’s energy needs [5]. When insulin levels drop as a result of decreased carbs, your liver converts fat you get from food and fat stored in your body into fatty acids and ketone bodies.

Ketone bodies include acetone, acetoacetate, and beta-hydroxybutyrate. They are toxic acidic chemicals but proponents of the keto diet claim that it's safe to have lower ketone levels in the body. They build up in the blood and then get excreted through the urine. The body can also rid itself of acetone through the lungs which gives the breath a fruity odor. This is why some people on the keto diet will have acetone or fruity like smelling breath.


The ketogenic diet has been credited for its drastic and quick weight loss results but some clinical trials have shown that it can help prevent some chronic diseases.


Weight loss seems to be the most marketable benefit of the keto diet. Initially, there’s a drastic water weight loss, then the body burns more fat. The keto diet promotes rapid and radical weight loss, especially for those who are starting it when overweight or obese. According to one study, published in the British Journal of Nutrition, more people lose weight when following a keto diet when compared to a low-fat diet. This was both in the short and long-term [8]. 

When done right, the keto diet can decrease food cravings and regulate hunger levels. This is because dietary fat tends to be satisfying effect. It also can decrease appetite-related hormones such as insulin and ghrelin.


When you eat carbohydrates, your body releases insulin. Having too much insulin over time, may play a role in diabetes. Insulin is known as a “storage hormone” that signals to your cells to take in the glucose. It also is associated with weight gain, especially in your belly.

Eating too many processed carbohydrates, like sugar or white bread, can cause blood sugar and insulin to have extreme peaks and valleys. This may result in blood sugar imbalances and insulin resistance. Basically your cells get flooded with insulin and end up not being able to accept it any longer. Insulin resistance is an underlying problem contributing to diabetes.  


Studies on the keto diet have shown a reduction of the risk of heart disease. The keto diet may help decrease cholesterol levels and triglyceride levels. In one study, obese patients who followed the ketogenic diet for 24 weeks, had decreased triglycerides, LDL cholesterol, and blood glucose [9]. 


The exact mechanism for how the ketogenic diet offers neuroprotection and improvement in mental health is still poorly understood. It's thought that in the short-term, ketosis may improve mitochondrial function. Regardless of the "how", studies have shown promising results. 

The keto diet originated as a means to help improve symptoms of epileptic patients. The keto diet has also offered neuroprotective benefits in animal studies including several central nervous system disorders such as Alzheimer’s disease, schizophrenia, and traumatic brain injury [4]. 


The low-carb diet plan was originally designed for patients with epilepsy. Back in the 1920s, researchers working at the John Hopkins Medical Center found that fasting helped reduce the amount of seizures that patients were having [10]. Since patients obviously couldn’t starve, the keto diet was developed to mimic the same physiological effects. The classic ketogenic diet has shown improvement in about half of patients in epilepsy treatment centers, with about 90% of those having decreases in seizures [5]. 


A study conducted on mice following a keto diet, showed improved blood flow to the brain and better beneficial bacteria in the gut. The keto diet also appeared to increase the clearance of beta-amyloid protein in the brain. These components are related to Alzheimer’s disease [11]. 

In a study on Alzheimer’s patients who were fed a ketogenic diet, there was improvement of mitochondrial function [12]. Some researchers consider Alzheimer’s to be considered type 3 diabetes because the brain’s cells become resistant to glucose. So if conditions like metabolic syndrome and type 2 diabetes can be decreased, Alzheimer’s may also be improved [13]. 


Researchers have made some discoveries linking the keto diet with schizophrenia. A possible reason is because the ketogenic diet changes the ratio of GABA to glutamate in the brain, in favor of GABA. This could possibly compensate for unbalanced levels of GABA in schizophrenic brains [14]. In addition, some correlations have been observed between schizophrenia and celiac disease [15]. The keto diet is similar to gluten-free since grains are removed. 


Brain function and memory improvements have been seen in both human and animal studies. In one study, feeding obese mice a ketogenic diet lead to improvement in brain function [16]. The ketogenic diet also proved to help with traumatic brain injury. The healthy fat intake is protective for the brain while less sugar can help decrease inflammation [17].  


Following a very high-fat low-carb diet can be challenging to maintain. It takes a lot of preparation and lifestyle change. When starting the keto diet, you'll most likely experience symptoms and side effect such as hunger, fatigue, poor mood, constipation, headaches, brain fog, and irritability. 

In the long-term, some negative side effects of the keto diet include increased risk of kidney stones and osteoporosis, increased blood levels of uric acid (related to gout), and possible nutrient deficiencies [18]. Long-term studies on the ketogenic diet are limited. 

Take note that the keto diet may not be right for everyone. If you have a medical condition, disease, are pregnant, or are taking medication make sure to consult your physician to see if the keto diet is safe. If you're an athlete, the keto diet may not be the best option. Multiple studies show that when athletes are put on a low-carb diet, they experience fatigue, decreased performance, and symptoms related to overtraining [19].


When you first start the keto diet, you may experience headaches, fatigue, stomach upset, and lightheadedness for a few days. This is known as the “keto flu”. To help decrease symptoms of the keto flu and stay healthy on the keto diet:

  • Drink lots of water: Since glycogen is responsible for water retention, when you restrict carbs, you're at risk of dehydration. Drink at least 2 liters (about 68 ounces) of water per day [20]
  • Supplement with magnesium, potassium, and sodium: Along with the water, some minerals are lost when carbs are reduced. In order to prevent muscle cramps and keep your heart functioning well, aim to have more sodium foods (broth, table salt, olives) and foods high in magnesium and potassium (avocado, yogurt, fish, nuts) or consider a supplement
  • Decrease intense physical activity: For the first few weeks of transition, don’t push yourself with exercise. After you've adjusted, see how you feel when you exercise. The best thing to do is listen to your body. 


When it comes to eating keto, it’s important to focus on good quality fats, with low to moderate amounts of protein, and low to no carbohydrate type foods. 

  • Protein (20%)
    • Eggs
    • Beef
    • Fish
    • Poultry
    • Plain Greek yogurt
    • Cottage cheese
  • Some carbs (5%)
    • Broccoli
    • Tomato
    • Onion
    • Berries
    • Leafy greens
  • Fats (75%)
    • Butter
    • Ghee (fortified butter)
    • Avocado
    • Plant-based oils like coconut or olive oil
    • Medium-chain triglycerides 

Medium-chain triglycerides (MCT) are particularly helpful for promoting ketosis. These fats contain medium-length chains of triglycerides. The shorter length makes it so they're easily digested and absorbed by your cells and act as a quick energy source. They also pass the blood-brain barrier, making them a convenient source of energy for brain cells. Medium-chain triglycerides are most commonly extracted from coconut oil but are also found in palm oil and some dairy products. 

More on how to follow a ketogenic diet:


The type of foods you eat, whether on a keto diet or not, will impact the health of your brain. Aim to include a variety of vitamins, minerals, and nutrients through different whole foods. Try to keep inflammation to a minimum by avoiding processed foods and limiting sugar. Focus on a mix of fresh fruits and vegetables, whole grains (if not keto), nuts, seeds, and healthy fats (avocado, fish, oil) and add some extra support from supplements when needed. 

  • Antioxidants: Protect brain cells and fight free radicals that come from stress, poor nutrition, and pollution.
    • Berries, leafy greens, nuts and seeds
  • Essential Fatty Acids: Support communication between nerve cells and improve concentration and memory. 
    • Fish, walnuts, chia seeds, flaxseed oil
  • Vitamins and minerals: Such as B vitamins, vitamin C, folate, vitamin K and magnesium. These boost memory, improve brain function, create enzymes and help prevent stress and anxiety.
    • Meat, poultry, eggs, leafy green vegetables, berries 

More on the best brain foods:


Research on the keto diet is limited with most studies only lasting 12 weeks or less, without control groups. In the short term, a keto diet can be helpful for weight loss, decreased cholesterol, blood sugar, and blood pressure as well as preventing chronic disease and cognitive disorders. 

If you do choose to try a keto diet, you may want to consider doing it for intermittent periods rather than long-term. Keto is complicated -- reach out to nutrition experts for some extra guidance and support. 

Always listen to your body and consult with your health care practitioner before making any changes to your diet or activity. 


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