Weight loss is an eternal topic for human beings. Initially, people used drugs to lose weight. Later, they used fruit juice, vegetable juice, and the fast diet to lose weight. Recently, the method of "weight loss through Ketotonic Diet" has become popular. What is the mechanism behind weight loss through Ketotonic Diet? Is it scientific? Is it suitable for everyone? What is KD? Ketotonic Diet (KD) is a formula diet that is high in fat, low in carbohydrates, and appropriate in protein. In classic KD, fat is responsible for up to 70% to 80% of the energy supply, protein is about 10% to 20%, and carbohydrates are only responsible for 5% to 10% of the energy supply. Usually, in this diet, carbohydrate intake is less than 50g/d. The fat intake is four times the sum of protein and carbohydrate intakes. In other words, you should eat more oil and meat every day. Do not eat staple foods, such as steamed buns, rice, etc. In addition, some root vegetables and fruits contain a lot of carbohydrates should be ingested less as well. So how did KD develop? In fact, KD first served as a medical treatment. As early as the 1920s, a diet of the replacement of glucose with fat as an alternative source of energy to promote the prior decomposition of body fat to produce ketones was discovered, and it was effected to curing intractable epilepsy by simulating fasting to initiate changes. Since then, relevant researches have also found that KD has potential adjuvant therapeutic effects on a range of diseases, including autism spectrum disorders, Alzheimer's disease, Parkinson's disease and other neurodegenerative diseases. Recent studies have also shown that KD may improve the efficacy of certain cancer drugs. From the medical point of view, KD does have its application value. Can KD help lose weight? For most ordinary people, the reason of being a fan of the "KD" is largely because of its weight-losing benefits. Not long ago, the Journal of the American Medical Association published an article about a clinical trial which was aimed at obese elderly people aged 60 to 75-year-old for a period of 8 weeks. In the KD group, the average weight loss was 9.7%, while in the low-fat diet group, the average weight loss was only 2.1%. But later, the European Journal of Nutrition published a paper and said that the short-term weight loss effect of KD varies among different people. At the same time, there is no evidence to support the long-term effect, safety or other health benefits of weight loss through KD. So, the academic circle has different opinions about weight loss effect through KD. First, let's look at the metabolic mechanism of the KD in human body: the physiological activities and other activities of the human body need energy. However, the human body uses the nutrients it ingested in a sequential order. First is the function of carbohydrates, that is the use of glucose produced by starch hydrolysis. Next is the use of glycerol and fatty acids produced by fat splitting. The last function is amino acids produced by protein hydrolysis. If the body is fasted with carbohydrates, it loses the energy supply of glucose. Then the body will automatically consume liver glycogen and will temporarily break down muscles to supply energy. After about three or four days, the liver glycogen stored in the body will be used up. Because the brain only accepts energy from glucose and ketones (acetylacetic acid, β-hydroxybutyrate, and acetone), the liver begins to break down fatty acids into ketones, then supplies the brain with energy via blood circulation. To be frank, the principle of KD is to force your body to use a different kind of fuel. For example, the original fuel is gasoline. Now you are forced to switch to alcohol. KD forces the body to no longer rely on the energy of carbohydrates generated from the decomposed glucose. On the contrary, it relies on ketones—— a fuel produced by fat stored in the liver. In this regard, KD should be able to help lose weight. However, KD in the medical field also has strict regulations: for example,you must eat fat every day; and must eat less than 20g to 50g of carbohydrates per day (a banana contains about 27g of carbohydrates). For example, a person needs to ingest 2000 kcal of energy per day, which is equivalent to eating 165g fat, 40g carbohydrates and 75g protein per day. Moreover, if too much protein is ingested, it will also affect the diet. In other words, you must eat more food with rich oil, such as fat meat. But if you eat too much fat, more than the body needs, you will also fail to achieve the purpose of weight loss. And there is a risk of becoming fatter. Are you fit for KD? Energy supply through direct fat splitting may be an idle way to lose weight, but it also generates certain health risks. For example, an unbalanced diet that only eats meat without grains, fruits and vegetables for a long time would cause the lack of a variety of vitamins and minerals, including B vitamins, vitamin C, selenium, magnesium, phosphorus and so on. Because the liver must metabolize too much fat, its function may be impaired and non-alcoholic fatty liver disease may occur. KD with too much protein may overload the kidney and increase the probability of kidney stones. In addition, studies have indicated that the short-term KD can cause many adverse reactions, including abdominal pain, diarrhea, nausea, vomiting, constipation, hypertriglyceridemia, hyperuricemia, and hypercholesterolemia. Long-term KD may affect the body's bone metabolism and cause osteoporosis. Studies also have found that high-fat KD can stimulate bile acid secretion, causing excessive growth of harmful intestinal bacteria thus inducing inflammation. The nutritional obesity will be then changed into inflammatory obesity. For nutritional obesity, as long as you follow the advice of "eat less, do more sports", you can surely lose some excess fat. But for inflammatory obesity patients, the energy stored in adipose tissues can hardly be consumed. However, even KD in medical practice can have a variety of banned population: for example, patients with primary carnitine deficiency, carnitine palmitoyltransferase (CPT) I or II deficiency, carnitine translocase deficiency, β-oxidation deficiency, and other diseases. Besides, patients with impaired liver function, pancreatic function deficiency, gallbladder disease, kidney disease, abdominal tumor or impaired intestinal function, and patients with type 1 diabetes, or type 2 diabetes which needed insulin therapy, and patients ingesting hypotensor, pregnant and lactating women, patients with weak gastrointestinal motility or malnutrition, etc., should also be careful to adopt KD. It is best to consult a doctor before performing a KD. If you can't take the risk of KD, you may follow the old way of "eat less, do more sports". References: 1.Paoli A, Bianco A, Damiani E, et al. Ketogenic diet in neuromuscular and neurodegenerative diseases [J]. BioMed Research International, 2014, 2014:1-10. 2.Knut H L, Md M H, Christine E R, et al. A ketogenic diet accelerates neurodegeneration inmice with induced mitochondrial DNA toxicity in the forebrain [J]. Neurobiology of Aging, 2016,48: 34-47.