High-fat, low-carb diets, also called low-carb, high-fat (LCHF) diets, are high in fat, low in carbohydrates, and moderate in protein. A typical LCHF diet ay be 80% fat, 15% protein, and 5% carbohydrate, though the ratios vary and can admit a higher percentage of carbohydrate. LCHF diet plans typically incorporate intermittent fasting as well.
These diets are based on the premise that high carbohydrate consumption increases levels of insulin in the blood while fat does not. Insulin is a hormone that helps the body convert food into energy in the form of glucose or sugar. High insulin levels have been linked to medical conditions such as type 2 diabetes, cardiovascular disease, and obesity. Foods low in carbs such as butter, eggs, avocado, and cheese do not raise insulin levels in the same way as carbohydrate-containing foods and lead to relatively small rises in blood sugar, which can help control appetite. Stretching out time between meals gives insulin levels time to drop and stay low for many hours, extending the time during which a person burns fat stores. LCHF diets have been used successfully to help people lose weight and reverse type 2 diabetes. Atkins, paleo, and ketogenic diets are all versions of low-carb, high-fat diets.
The earliest recognized publication of a high-fat, low-carb diet was William Banting's Letter on Corpulence, published in 1863, in which Banting reported weight loss and improved health by following a low-carbohydrate diet prescribed by his doctor, William Harvey. Banting suffered from obesity and hearing loss caused by fat compressing his inner ear. After following a low-carb diet, he lost weight and his hearing improved.
Diabetes was an extremely rare disease before sugar became widely available at the end of the nineteenth century. As sugar consumption increased, diabetes incidence began to increase as well. In the early twentieth century, Dr. Elliot Joslin in Boston used a low-carb diet to treat diabetics. Joslin believed that diabetes was a disease of carbohydrate intolerance, so the best treatment was to limit carbohydrates to a bare minimum. This method of treatment fell out of favor after insulin was discovered in 1922.
In the 1920s, the Epilepsy Center at Johns Hopkins Hospital began to use a high-fat/moderate-protein/low-carbohydrate diet called the ketogenic diet to treat children with intractable, or hard to control, seizures. The Johns Hopkins Epilepsy Center continues to use a modified version of this diet program.
Low-carb diets came in and out of fashion in the twentieth century, mainly because they had a high degree of success at producing weight loss. One of the most popular and well-known of high-fat, low-carb diets is the Atkins diet, first published in book form in 1972 by cardiologist Robert Atkins.
In the twenty-first century, people began to take a renewed interest in LCHF diets for several reasons. For one thing, obesity and diabetes rates had climbed steadily since the USDA's recommendation of low-fat diets in the late 1970s, causing many to suggest that low-fat high-carbohydrate diets were not the best way to maintain or lose weight. In addition, several books published in the 2010s called into question the basis of the recommendation that people should reduce fat in their diets. For example, Nina Teicholz, in her 2014 book The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy Diet, suggested that the low-fat recommendations of nutritional guidelines were not based on sound science. Gary Taubes in The Case against Sugar (2016) also questioned the validity of low-fat guidelines, but more particularly explored the way sugar is metabolized by the human body. He concluded that increased consumption of carbohydrates over the late twentieth century was the direct cause of the obesity and diabetes epidemic. Some medical professionals and authors have questioned low-fat, high-carbohydrate dietary recommendations and reported numerous health benefits to a LCHF diet, including reversal of type 2 diabetes, rapid hunger-free weight loss, reduced inflammation, better athletic performance, and overall better health.
Most national nutritional guidelines still recommend a diet lower in fat than that in a LCHF diet, although it has recently been recognised that type of fat rather than total amount in the diet is probably more important in relation to disease risk. Diet experts and many medical groups maintain that a diet high in saturated fat is not healthy. Yet, many countries have acknowledged that low carbohydrate diets can also support weight loss. For example, in Sweden an expert government review has concluded that low-carb diets work as well as a treatment for obesity as low fat diets and that there is no proof that they are dangerous.
A person following a high-fat, low-carbohydrate diet avoids foods high in carbohydrates. These include bread, pasta, soda, juice, rice, candy, cookies, and even many fruits, which are high in sugars. Instead, the person eats natural fats such as butter and oil, cheese, fish and seafood, meat, eggs, and vegetables that grow above ground.
High-fat, low-carb diets vary in the number of grams of carbohydrates recommended for consumption each day. Most low-carb diet plans consider the optimal range of carbohydrates to be between 25 and 45 grams per day. This number may vary based on the diet plan and individual; some people on low-carb diets are able to eat up to 100 grams each day. Individual tolerance to carbohydrates varies widely. In people who are insulin resistant, even a small amount of dietary carbohydrate can lead to blood sugar spikes.
LCHF diets rely for fuel in part on ketones, which are the products of the incomplete breakdown of fat used for energy when carbohydrates are not available. Ketone metabolism is a very efficient form of energy production that does not involve the production of insulin. Proponents of LCHF claim that the combination of ketone metabolism (ketosis) and the more stable insulin levels created in the absence of carbohydrates lead to rapid weight loss. Many people eat ketogenic diets, which are very low in carbohydrates, and spend much of their time in ketosis. Tracking ketone levels with urine test strips or blood tests is popular among some very dedicated LCHF practitioners. For years, diet authorities claimed that ketosis was a dangerous state, and there is still some confusion about the safety of ketosis. Ketoacidosis is a dietary crisis that can afflict diabetics, but ketosis itself is healthy and safe.
There is some debate about the proper protein content of a low-carb diet. A low-carb, high-fat diet may take between 70% and 85% of its calories in the form of fats, with perhaps 15% from protein. Some proponents of the diet claim that too much protein is counterproductive to weight loss because the body turns excess protein into glucose. Conversely, others recommend a higher percentage of protein for its satiety effects.
Other diet plans do not add in carbohydrates, and simply consider the very low carb range the best way to eat. Many people eat a ketogenic diet on a daily basis. Because many people adopt LCHF diets in an effort to lose weight or reverse type 2 diabetes, they see no reason to return to consuming the simple carbohydrates that could lead to spikes in blood sugar and weight gain.
Carbohydrate counts are determined by counting the number of grams per serving for each meal, minus the food's “net carbs.” The net carbs are the total grams of carbohydrates found in the food minus the number of grams of fiber (per serving). While insoluble fiber is technically a form of carbohydrate, it is mostly not absorbed by the body, so it does not raise blood insulin levels and it is not included in the overall carbohydrate count. Soluble fiber does have a modest effect on insulin and blood sugar, but this is not included in the total count. Sugar alcohol is another substance that can be subtracted from the net carbs. It is a chemically altered carbohydrate that adds sweetness to foods but is metabolized more slowly than sugar and is not as readily absorbed.
Many people who follow LCHF diets combine them with intermittent fasting. Hunger tends to decrease on high-fat diets, making it easy to go long periods without eating. Fasts can be of varying lengths, from a 12-hour daily fast to fasts of several days for people suffering from obesity and its related problems. The rationale behind this is that insulin levels rise after eating and take several hours to drop to the level at which the body will burn fat for fuel. The longer the body stays at a fat-burning level of insulin, the more fat it will burn.
Many high-fat, low-carb diets recognize that not all carbohydrates cause spikes in blood sugar levels. Some carbohydrates digest more slowly than others, causing a gradual rise in blood sugar after eating. The glycemic index is a system used to rank carbohydrates and other foods according to the effect they have on blood sugar, based on a scale of 0–100. Foods with higher glycemic index ratings break down quickly and cause a sharp rise in blood sugar. When blood sugar rises quickly, the body produces a surge of insulin to lower the amount of glucose in the blood. Foods with lower glycemic index ratings break down more slowly. They cause a more gradual rise in blood sugar, which means that less insulin will be needed. Lower blood sugar and insulin levels have been shown to prevent or treat type 2 diabetes and heart disease. Lower glycemic foods are also thought to help with weight loss by promoting satiety, or a feeling of fullness.
Foods that have a high glycemic index rating include white bread, white rice, white potatoes, beer, corn products, and products containing refined sugars. Foods with moderate glycemic index ratings include whole grain breads and pastas, brown rice, sweet potatoes, green peas, many fruits (especially when eaten alone), and yogurt. Low glycemic index foods include rye grain; nuts; legumes, such as black beans and lentils; green vegetables; apricots; and cherries.
Foods that are high in fiber tend to have lower glycemic index numbers, because fiber takes longer to digest. Studies have shown that fats like olive oil and acidic products like vinegar can also slow digestion and keep blood sugar from rising too quickly. The glycemic index can be used along with a high-fat, low-carb diet to help choose which carbohydrates can be eaten with the least effect on blood sugar.
In the 2010s, LCHF diets proliferated as people embraced the easy weight loss and corresponding improvements in blood glucose and insulin levels. There are several versions of the LCHF diet, including:
Low-carbohydrate diets are based on the premise that weight gain and obesity are tied to inefficient or unhealthy insulin cycles created by eating carbohydrates. The carbohydrates a person eats are converted to glucose in the body. Glucose raises blood sugar levels and stimulates the body to produce the hormone insulin. Insulin is a hormone that helps the body transport glucose from the bloodstream to cells, where it is used for energy. Any excess glucose is stored in the form of glycogen in the muscles and liver. These glycogen stores are used as fuel by the body when glucose is not available. If the stores are not used, however, excess carbohydrates may be converted to fat.
High-fat, low-carb diets aim to avoid these spikes in blood sugar and reduce the amount of glycogen stored in the body. Experts such as Tim Noakes attribute the obesity and diabetes epidemic to prevalent hyperinsulimia, high insulin levels that are caused by insulin resistance, a state in which the body does not respond well to insulin, resulting in the pancreas producing ever-higher levels when carbohydrates enter the body.
People who follow an LCHF diet for a long period are thought to become adept at burning fat. They are said to be fat-adapted, or keto-adapted. Once a person becomes fat-adapted, he or she does not feel the need to eat as frequently as people do on high-carbohydrate diets. This makes for easier calorie control and weight loss.
Humans do not need to eat any carbohydrates at all to survive. It is true that the brain runs on glucose, but the body can produce glucose through a process called gluconeogenesis, furnishing the brain's needs. Carbohydrate-containing foods such as vegetables and whole grain foods do, however, contain fiber and many other nutrients that are beneficial to human health.
Consumers who adopt LCHF diets claim that they make it easy to lose weight, quickly and without hunger. Some advocates make larger claims. They suggest that low-fat diets, which are by necessity high-carbohydrate, are the cause of the obesity epidemic, that low-fat dietary recommendations are groundless, and that LCHF diets present an easy-to-follow nonmedicalized solution to obesity, diabetes, metabolic syndrome, and a host of other diseases.
A number of medical professionals have reported success at treating patients suffering from high insulin levels, high blood sugar, high blood pressure, obesity, diabetes, and related problems. Several studies published in 2016 and 2017 found that low-carbohydrate and ketogenic diets were effective at improving glycemic control and weight loss in people with type 2 diabetes. A 12-month randomized trial of moderate-carbohydrate versus very low carbohydrate diets in overweight patients with type 2 diabetes or prediabetes found that the low-carb group lost more weight, had greater reductions in HbA1c, and greater reductions in medication use than the moderate-carb group. A study published in Obesity Surgery in 2018 found that a four-week micronutrient-enhanced ketogenic program was effective at reducing body weight, left liver lobe volume, and micronutrient deficiencies in obese patients who were preparing for bariatric surgery.
The Virta clinic uses ketosis and low-carb diets to reverse type 2 diabetes. Virta is an online medical clinic; it treats patients with continuous remote monitoring and coaching in a ketogenic diet. Patients who follow a ketogenic diet can maintain blood glucose values below the range defined as diabetic. The clinic notes that dietary modifications only reverse type 2 diabetes, not cure it; if a person returns to a high-carb diet, his or her diabetes will return as well. In 2018, the Virta clinic published the results of a nonrandomized, controlled study of the use of carbohydrate restriction in type 2 diabetes patients. This study found that an LCHF diet improved patients' weight and blood sugar and allowed them to reduce their use of diabetes medications. Randomized controlled studies are needed to further explore this treatment option.
Endurance athletes find that LCHF diets can noticeably improve their athletic performance. Fat stores provide a steady supply of fuel that can last for hours or even days. A fat-adapted athlete can compete without eating anything at all, simply running on stored fuel and using the energy that would go toward digesting food for performance.
LCHF diets are still used to treat epilepsy, and they might be useful for other conditions such as schizophrenia. Some researchers speculate that LCHF diets could be useful for treating cancer, which some doctors consider a metabolic disease that can feed on carbohydrates. So far little research has explored this possibility in humans, though some studies have found that ketogenic diets improve survival in mice with tumors.
A person who is accustomed to eating a high-carbohydrate diet may not feel great for the first few days on a low-carb diet. A phenomenon known as induction flu is common at the very beginning; a person may experience two or three days of headache, fatigue, nausea, and irritability. This is likely due to the rapid loss of water that is known to occur in the first few days of adopting a low-carb diet. As the body's ability to burn fat increases, these symptoms disappear. Drinking fluids or broth can help alleviate symptoms. Other common initial side effects include leg cramps, constipation, and reduced physical performance; all of these effects disappear as well after a few days.
Patients taking medication for a chronic condition such as diabetes or hypertension may require a dosage reduction if they lose a significant amount of weight. A large change in dietary intake may also alter the availability of vitamins such as vitamin K; therefore, the monitoring of patients receiving anticoagulation therapy is important both before and during the dietary changes. No changes in medication levels should be made without the consent of the prescribing physician. Patients with diabetes should not make changes to their diet without first discussing them with a physician because an LCHF diet can result in significant changes in blood glucose levels and a corresponding need for adjustment of insulin and other medications.
Though there have been concerns about the effect of a high-protein diet on the kidneys, this appears not to be an issue for most people. A 2015 study concluded that a high-protein diet is not dangerous for most healthy people and does not produce the loss of bone mass or kidney damage that has often been posited. The worry that a high-protein diet can cause kidney damage seems to be a concern only for those with existing kidney disease. In healthy people, excess protein is broken down into amino acids and glucose. Very high protein intakes over a prolonged period may cause nausea and dehydration. Drinking more water can counter the dehydration problem. A bigger concern for people trying to eat low-carb is that excess protein can be converted into glucose, which eliminates the benefit of reducing dietary carbohydrates.
Though some doctors do not recommend this diet for women who are pregnant or nursing, medical professionals who use LCHF diets in their practices see no problem at all with limiting carbohydrates during pregnancy or breastfeeding.
Restricting carbohydrates might result in a decrease in fiber intake, though many LCHF diets contain large amounts of fiber from the vegetables that take the place of grains and starches. Insufficient fiber intake can cause constipation and may increase the risk of developing diverticulitis, hemorrhoids, and certain types of cancer. High fiber intake is also associated with a lower risk of cardiovascular disease and type 2 diabetes.
The human body does not actually need carbohydrates to survive, but it does need many vitamins and minerals that people might previously have obtained from carbohydrate-containing foods, such as fruits, vegetables, and whole grains. A person adopting an LCHF diet should take care to eat a range of natural foods, including vegetables. In practice nutritional deficiencies are not typically a problem for people on these diets, and research from 2018 found that an LCHF diet could supply all micronutrient needs.
Medical professionals have expressed concerns over the long-term adherence to diets high in saturated fat. The American Heart Association advises against following any diet plan that encourages increased fat consumption and a reduced consumption of a variety of fruits and vegetables, with the concern that these types of diets will lead to increased risk of coronary heart disease, stroke, and cancer. Recent research, however, has called this recommendation into question. There is increasing support for the opposite position, that consuming fat is healthy and that saturated fat does not increase risk of heart disease. The British Journal of Sports Medicine, for example, in 2017 published an article expressly contradicting the claim that saturated fat clogs arteries and causes heart disease, and calling for a shift in guidelines involving saturated fat consumption.
Some practitioners warn that ketosis is dangerous. Ketosis is a natural, healthy state. Ketoacidosis is a dangerous condition that occurs when a diabetic's blood sugar and blood ketones are both high, and it can be life threatening, but it does not normally occur in a health person eating an LCHF diet.
A person who successfully loses weight on an LCHF diet can gain that weight back if he or she goes back to former eating habits. LCHF advocates recognize this and suggest that low-carb eating should become a way of life, not a temporary fix for a weight problem. This is especially important for people who have insulin resistance, because they may never be able to successfully metabolize large amounts of sugar or carbohydrates.
After years of being labeled dangerous fad diets, low-carb diets are becoming increasingly accepted. In January 2018, the Journal of the American Medical Association (JAMA) published an article on interest in the use of ketogenic diets for weight loss and type 2 diabetes, evidence that LCHF diets are being taken seriously by medical professionals. This article reported that experts are investigating the hypothesis that ketogenic diets might work in cases that low-fat calorie-restricted diets do not, and that the reported appetite-satiating properties of high-fat diets should be studied, as should the reported hormonal differences of a high-fat diet that actually encourages the body to burn its own fat stores. Other research from 2018 found that a low-carb diet improved liver fat metabolism in nonalcoholic fatty liver disease patients.
A study published in BMJ Open in 2018 found that an LCHF diet could furnish adequate micronutrients. The authors wrote: “This is an important finding for health professionals, consumers, and critics of LCHF nutrition, as it dispels the myth that these diets are suboptimal in their micronutrient supply.”
Some endurance athletes have found that their performance improves dramatically on an LCHF diet. Experts formerly believed that athletes needed to consume carbohydrates to supply adequate glycogen to power muscles, but that requires constant refueling. An athlete who has adapted to burning fat for fuel does not need to eat constantly and can burn fat at a rate double that of an athlete powered by carbohydrates. It can take several weeks or months to become adapted to burning fat, but once the transition has occurred, athletes find the ketogenic diet optimum for high performance.
Recent research has begun refuting the connection between dietary consumption of fat and heart disease. For example, a 2016 Norwegian diet intervention study called FATFUNC found that a high intake of total and saturated fat did not increase the calculated risk of heart disease. In 2017, the European Society of Cardiology called for a reconsideration of dietary recommendations in light of research indicating that high-carbohydrate diets (especially diets high in refined carbohydrates and sugar) are linked with worse mortality and moderate to high fat intake is associated with lower risk of cardiovascular mortality.
See also Atkins diet ; Bernstein diet ; Carbohydrates ; ChangeOne diet ; Intermittent fasting ; Ketogenic diets ; Obesity ; Paleo diet ; Protein ; South Beach diet .
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Revised by Amy Hackney Blackwell, PhD