The Ketogenic Diet: A Breakdown of this Popular Eating Plan

A platter with an avocado, cheese and eggs.

Commonly called “keto,” the ketogenic diet refers to any diet therapy that creates the metabolic state of ketosis. It is defined as:

  • High in fat: typically 80 percent or more of total calories
  • Moderate in protein: 1 gram per kilogram of body weight
  • Low in carbohydrates: 40 to 60 grams per day from foods with a glycemic index under 50.

Compare these values to the acceptable macronutrient distribution range, or AMDR, of 45 to 65 percent of calories from carbs; 10 to 35 percent from protein; and 20 to 35 percent from fat — while limiting dietary saturated and trans fats. In normal metabolism of a carbohydrate-rich diet, carbohydrates are broken down into glucose and absorbed through the small intestine, where they travel to the liver and are stored as glycogen for the body to use for fuel as needed.

In ketosis, because carbohydrates are so limited, the body is forced to break down fat rather than use glucose for fuel. When glucose is depleted, ketone bodies (the compounds acetoacetate, beta-hydroxybutyric acid and acetone) are created and can cross the bloodbrain barrier as energy for the brain and central nervous system. This process
mimics a fasting state in the body but provides enough calories to support energy needs. Ketosis is achieved when blood ketone levels are greater than 0.5 mmol/L.

Potential drawbacks of this complicated diet include kidney damage, constipation, micronutrient deficiencies and social isolation. A strict keto diet requires close management by a health professional.

History of the ketogenic diet
Eating styles that today would be called the ketogenic diet were used to treat epilepsy in ancient times; there are references to it in the New Testament. A very low-carb diet became popular in the early twentieth century to treat epilepsy in children and adults, and has been used since the 1970s to treat obesity. Very low-carb ketogenic diets surged in popularity in the 1990s and now are more popular than ever. Several celebrities attribute their weight loss and physique to the ketogenic diet, and the hashtag #keto yields more than 8 million results on Instagram.

Types of ketogenic dietary patterns
There isn’t one specific keto diet, and people can enter ketosis with varying levels of dietary carbohydrates (usually fewer than 50 grams per day) and at varying amounts of time on the diet (generally 33 to 58 hours). The most restrictive types are the classic ketogenic and medium chain triglyceride, or MCT, diets, both of which prescribe four parts calories from fat to one part calories from protein and carbohydrates. Foods and beverages must be closely monitored, calculated, measured and weighed.

While these more restrictive diets can generate a higher ketogenic potential, they also can produce unpleasant gastrointestinal side effects, especially with a high concentration of MCT oil.

The Modified Atkins Diet, or MAD, and the Low Glycemic Index Treatment, or LGIT, do not require as strict a routine and rely on standard household measurements. On a MAD, net carbohydrates are limited to 10 to 20 grams per day for adults; as for LGIT, carbohydrates are restricted, but the diet is not designed specifically to promote a constant state of ketosis.

Because fasting can put a person in ketosis, intermittent fasting can be considered a type of ketogenic diet. Vegetarians can adapt a ketogenic diet with minimal alterations by consuming dairy or eggs, plus plant-based fats, nuts and seeds. Because of legumes’ carbohydrate content, vegan keto followers may need a modified version of the diet to ensure their micronutrient and protein needs are met.

Some athletes practice keto cycling, which involves going in and out of ketosis based on physical training cycles. Non-athletes also can follow this version of keto to better tolerate the restrictive nature of the diet, support high levels of physical activity and avoid skeletal muscle breakdown during training.

Efficacy and considerations
The ketogenic diet has proven to be effective in treating adults and children who have epilepsy that does not respond well to medication — although the reason why this works is not completely understood. One theory is that ketones may reduce seizures or inhibit neurotransmitter production, release and uptake. Children and adolescents on a ketogenic diet generally experience a reduction of 50 percent or more in seizure frequency. In more limited research, success rates are similar for adults. Improvements in cardiovascular risk factors and Type 2 diabetes management are commonly observed in adults on a ketogenic diet. Lipid profiles may fluctuate initially but often improve through increased HDL and
reduced triglycerides. LDL changes include a potential increase in particle number, size or both. When comparing a ketogenic diet to a calorie-restricted diet following the AMDR, greater improvements were seen in weight loss, waist circumference and HbA1c in the ketogenic group.

Labs should be evaluated at pre-diet baseline and after initiation at intervals determined by a health care team and may include a complete metabolic panel and fasting lipid panel, complete blood count with platelets, liver profile, ionized calcium, magnesium, phosphate, selenium, zinc, vitamins A, E, B12 and D, copper, ferritin, folate, free and total carnitine, pre-albumin, β-hydroxybutyrate, urinalysis and urine organic acids.

Research also continues to support the use of ketogenic diets for malignant brain tumors; neurological disorders such as autism, Parkinson’s disease, Alzheimer’s disease and traumatic brain injuries; acne; and metabolic disorders including PCOS.

Studies on weight change of participants on a low-fat diet (30 percent or fewer calories from fat) compared to a diet with 35 to 65 percent of calories from carbohydrate foods continue to find no significant long-term differences. However, there is strong evidence that ketogenic diets better support weight loss.

There are a number of possible reasons why keto diets work for weight loss, including reduced appetite due to satiety from dietary protein; changes in appetite control hormones including modifications in ghrelin and leptin; possible appetite-suppressing action from ketone bodies; increased body fat used for fuel paired with reduced body fat storage; and an increased metabolic rate due to gluconeogenesis — the creation of glucose in the body from non-carbohydrate sources.

A 2014 meta-analysis of 12 studies found participants on a ketogenic diet experienced less hunger and a reduced desire to eat, even as they lost weight, which ordinarily causes an increase in appetite. Another meta-analysis of 13 studies published in 2013 found decreased body weight, triglycerides and diastolic blood pressure at 12-month follow-up, with increased HDL and LDL cholesterol.

Potential side effects
Upon starting a ketogenic diet, people can expect four to 10 days of the “keto flu” — symptoms that occur due to electrolyte shifts that include increased urinary sodium, potassium and fluid loss causing dehydration, and dips in energy supply to the brain as the body’s metabolic processes adapt. Lethargy and depressed mood or irritability, constipation or diarrhea, headache and muscle cramps are hallmarks of this initial phase, after which many people report an improved mood and increased energy.

Because they’re eating fewer grains, legumes, fruit and vegetables, people on the ketogenic diet are at risk for nutrient deficits of calcium, vitamin D, selenium, magnesium, phosphorus, iron, essential fatty acids and prebiotics. Supplements may be necessary for the majority of people on a keto diet. Food restrictions also may decrease total phytonutrient and dietary fiber consumption, leading to constipation and deleterious effects on the gut microbiome.

Higher levels of nitrogen excretion during protein metabolism on a ketogenic diet could cause kidney damage, especially among people with renal conditions or those who have had a kidney transplant.

Keto diets require extensive meal preparation and planning, a support system and a well-equipped cooking environment. Because of the diet’s restrictive nature, people may have a hard time dining out with others, which could lead to social isolation.

Role of the RDN
Registered dietitian nutritionists play a crucial role for virtually anyone who embarks on a keto diet. RDNs working with patients on ketogenic diets to reduce epileptic seizures need highly specialized training and interdisciplinary team collaboration to ensure appropriate implementation and monitoring.

Patients or clients may inquire about a keto diet for weight loss, athletic training, cancer treatment or blood sugar management. Many people start a keto diet on their own and seek expert advice, support and guidance. RDNs should be educated on the basics of ketogenic diet therapy, including how to refer patients to experts when appropriate, such as for monitoring and evaluation of labs or when it is outside their scope of expertise. Educating patients and clients on potential side effects and contraindications is a critical part of the conversation: Help patients assess the sustainability of the keto diet on their lifestyle, including potentially restrictive behaviors or disordered eating.


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