Even in endurance sports that don’t require sprinting, ketogenic-style diets are disadvantageous according to a ketogenic diet and exercise article published in Sports Medicine[5]: “a high-fat, low-carbohydrate ketogenic diet may impair exercise performance via reducing the capacity to utilize carbohydrates, which forms a key fuel source for skeletal muscle during intense endurance-type exercise.” The article concluded, “At present there are no data available to suggest that ingestion of ketone bodies during exercise improves athletes’ performance under conditions where evidence-based nutritional strategies are applied appropriately.”
Of the 1,580 survey participants, more than half reported staying on a low-carb diet for at least one year, and 34% reported more than two years. Further, those on the diet for two years or more said that they had largely maintained their weight loss. This is a self-selected sample, with an obvious bias for people who are experiencing success (dieters are less inclined to report on their failures). However, this data does show that long-term adherence is possible.
Even hibernating bears do not go into ketosis[2]. And predatory animals who undergo extended periods of food deprivation, such as elephant seals[3], are metabolically resistant to ketosis; instead, they have upregulated gluconeogenesis pathways through which they can steadily produce glucose. This makes perfect sense, since predators’ survival depends on their ability to catch their prey, which usually requires intense bursts of activity. And sprinting capacity is dependent on glucose, as humans who adopt a ketogenic diet quickly discover.
The ketogenic diet is indicated as an adjunctive (additional) treatment in children and young people with drug-resistant epilepsy.[26][27] It is approved by national clinical guidelines in Scotland,[27] England, and Wales[26] and reimbursed by nearly all US insurance companies.[28] Children with a focal lesion (a single point of brain abnormality causing the epilepsy) who would make suitable candidates for surgery are more likely to become seizure-free with surgery than with the ketogenic diet.[9][29] About a third of epilepsy centres that offer the ketogenic diet also offer a dietary therapy to adults. Some clinicians consider the two less restrictive dietary variants—the low glycaemic index treatment and the modified Atkins diet—to be more appropriate for adolescents and adults.[9] A liquid form of the ketogenic diet is particularly easy to prepare for, and well tolerated by, infants on formula and children who are tube-fed.[5][30]

We realize that the ketogenic diet can be very demanding of children and families, so we make sure that we stay with families throughout the entire treatment. Our multidisciplinary team includes a social worker that can help your child and their siblings cope with the stresses that come with the diet. Your child will also have regular, relationship-building contact with the same team of nurses. Additionally, we have an education specialist on staff who specializes in meeting with teachers and administrators to help prepare schools for children with epilepsy.
A Cochrane systematic review in 2018 found and analysed eleven randomized controlled trials of ketogenic diet in people with epilepsy for whom drugs failed to control their seizures.[2] Six of the trials compared a group assigned to a ketogenic diet with a group not assigned to one. The other trials compared types of diets or ways of introducing them to make them more tolerable.[2] In the largest trial of the ketogenic diet with a non-diet control[16], nearly 38% of the children and young people had half or fewer seizures with the diet compared 6% with the group not assigned to the diet. Two large trials of the Modified Atkins Diet compared to a non-diet control had similar results, with over 50% of children having half or fewer seizures with the diet compared to around 10% in the control group.[2]
When in the hospital, glucose levels are checked several times daily and the patient is monitored for signs of symptomatic ketosis (which can be treated with a small quantity of orange juice). Lack of energy and lethargy are common, but disappear within two weeks.[17] The parents attend classes over the first three full days, which cover nutrition, managing the diet, preparing meals, avoiding sugar, and handling illness.[19] The level of parental education and commitment required is higher than with medication.[44]
The popular low-carb diets (such as Atkins or Paleo) modify a true keto diet. But they come with the same risks if you overdo it on fats and proteins and lay off the carbs. So why do people follow the diets? "They're everywhere, and people hear anecdotally that they work," McManus says. Theories about short-term low-carb diet success include lower appetite because fat burns slower than carbs. "But again, we don't know about the long term," she says. "And eating a restrictive diet, no matter what the plan, is difficult to sustain. Once you resume a normal diet, the weight will likely return."

Because people with type 2 diabetes are at an increased risk for cardiovascular disease, there’s a specific concern that the saturated fat in the diet may drive up LDL, or “bad,” cholesterol levels, and further increase the odds of heart problems. If you have type 2 diabetes, talk to your doctor before attempting a ketogenic diet. They may recommend a different weight-loss diet for you, like a reduced-calorie diet, to manage diabetes. Those with epilepsy should also consult their doctor before using this as part of their treatment plan.
Missing Nutrients. One of the biggest concerns for dietitians is the keto diet’s lack of key foods. Many question the eating plan’s impact on the development of certain chronic diseases. Without milk, for example, getting enough calcium and vitamin D for sturdy bones becomes a challenge. Take away whole grains, fruit, beans, and potatoes, and it’s nearly impossible to consume enough potassium for healthy blood pressure or enough fiber to stay regular. And unless you’re eating lots of low-carb, leafy green vegetables, you miss out on vitamins A, C, K, and folate, too. 
Epilepsy is one of the most common neurological disorders after stroke,[7] and affects around 50 million people worldwide.[8] It is diagnosed in a person having recurrent, unprovoked seizures. These occur when cortical neurons fire excessively, hypersynchronously, or both, leading to temporary disruption of normal brain function. This might affect, for example, the muscles, the senses, consciousness, or a combination. A seizure can be focal (confined to one part of the brain) or generalised (spread widely throughout the brain and leading to a loss of consciousness). Epilepsy can occur for a variety of reasons; some forms have been classified into epileptic syndromes, most of which begin in childhood. Epilepsy is considered refractory (not yielding to treatment) when two or three anticonvulsant drugs have failed to control it. About 60% of patients achieve control of their epilepsy with the first drug they use, whereas around 30% do not achieve control with drugs. When drugs fail, other options include epilepsy surgery, vagus nerve stimulation, and the ketogenic diet.[7]
I was a Corpsman (not a corpse-man as some recent somewhat fanatical president would say), and I can tell you many stories of Marines and Sailors who maintained restrictive diets (aka picky eaters). Most obvious was lack of sustaining energy (hypoglycemia) at mile 15 (with 80lbs of gear including a 6.5lb rifle and 200 rnds of ammo, etc.) and depletion of essential vitamins, electrolyte imbalance. They were always the first to collapse and have to hear me scold “see I told you so.” An IV of D5W usually does the trick (D is for dextrose, OMG!)

Even hibernating bears do not go into ketosis[2]. And predatory animals who undergo extended periods of food deprivation, such as elephant seals[3], are metabolically resistant to ketosis; instead, they have upregulated gluconeogenesis pathways through which they can steadily produce glucose. This makes perfect sense, since predators’ survival depends on their ability to catch their prey, which usually requires intense bursts of activity. And sprinting capacity is dependent on glucose, as humans who adopt a ketogenic diet quickly discover.
Advocates for the diet recommend that it be seriously considered after two medications have failed, as the chance of other drugs succeeding is only 10%.[9][31][32] The diet can be considered earlier for some epilepsy and genetic syndromes where it has shown particular usefulness. These include Dravet syndrome, infantile spasms, myoclonic-astatic epilepsy, and tuberous sclerosis complex.[9][33]
Con: Results can vary depending on how much fluid you drink. By drinking more water, you dilute the concentration of ketones in the urine and thus a lower level of ketones will be detected on the strips. The strips don’t show a precise ketone level. Finally, and most importantly, as you become increasingly keto-adapted and your body reabsorbs ketones from the urine, urine strips may become unreliable, even if you’re in ketosis.
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