Ketosis does not mean that you are losing weight. It really just means that your liver is turning a lot of protein and other noncarbohydrates to sugar. Today, many people on the Internet are urging people to eat a ketogenic diet: a diet that is so high in fat and so low in carbohydrates that it causes people to go into a state of ketosis. Ketosis means that “ketone bodies,” which are the chemical byproducts of an alternative method of burning fat, build up in the bloodstream. Ketogenic diets are often described as “Paleo” because many laymen imagine that human beings must have eaten ketogenic diets during the Paleolithic era (early stone age). Yet there is no reason to believe that stone age people ate a ketogenic diet.
Most people in the stone age would have eaten the starchy plant material, especially roots and tubers, that they could safely and easily obtain from their environment. As a result, stone age people would have gotten more than enough carbohydrate to keep them from going into ketosis. In fact, when anthropologists look at the skeletal remains of stone age people, they find starch grains embedded in the tartar on their teeth. Even the Inuit’s (Eskimos’) traditional winter diet, which consisted entirely of fatty meats and fish, did not produce ketosis. Studies done in the early 20th century found that the Inuit did not get ketosis unless they were fasting. The Inuit were eating raw meat that was either freshly killed or frozen immediately after being killed. Unlike the meat you would buy at a supermarket, this fresh or rapidly frozen meat still contained a starch called glycogen. The Inuit also used a method of meat preservation that converted some protein to sugar. As a result, the Inuit’s traditional diet contained a surprisingly large amount of carbohydrate: enough to keep people out of ketosis.
It is good that the Inuit diet did not cause ketosis. The Inuit already had extremely high rates of osteoporosis, because of the metabolic acidosis caused by their high-protein diet. Adding even more acid, in the form of ketone bodies, would have made this problem even worse. Eating a lot of calcium, in the form of fish bones, did not solve this problem.
Some “Paleo” advocates claim that ketosis means that you are burning fat and are therefore losing weight. Some of them even claim that you cannot lose weight or burn fat unless you are in ketosis, which is total nonsense. The Krebs cycle, which is the body’s normal way of burning fat, does not produce ketone bodies. Having ketones in your urine does not even guarantee that you are losing weight. To lose weight, even on a ketogenic diet, you must burn up more calories than you take in. Even on a ketogenic diet, you can still gain weight. The burst of insulin that is released in response to eating foods that contain protein could drive the fat from the food into the fat cells.
The ketosis does not mean that you are losing weight. It is simply a sign that your liver is turning a lot of noncarbohydrate substances, including protein, into a sugar called glucose. Your liver is working so hard to make glucose, to compensate for your low carbohydrate intake, that it is even using up oxaloacetate, which is one of the chemicals involved in the Krebs cycle. As a result, some of the fat gets broken down through an abnormal pathway that produces ketone bodies.
During a fast, a little bit of ketosis is a good thing. Your brain can use a little bit of the ketone bodies as an alternative fuel source. In contrast, the severe ketosis that results from a severe shortage of insulin in people with untreated type 1 diabetes mellitus is life-threatening. Before the discovery of insulin, people with what is now called type 1 diabetes would always progress to ketoacidosis, coma, and death. Ketoacidosis means that the ketosis is so bad that it lowers the blood pH. Patients with diabetic ketoacidosis have four problems at once: high blood sugar, dehydration, low blood pH, and an electrolyte imbalance. These problems must be corrected carefully, in an intensive care unit.
In a healthy person, the total amount of ketone bodies in the blood is usually less than 1 mg/dL. The amount of ketone bodies in the urine is normally too low to be detected by routine urine tests. You can boost your production of ketone bodies by fasting or by eating a low-carbohydrate diet. You can get into a state of ketosis either way. However, the effects of a fast are far different from the effects of a low-carbohydrate diet. Scientists are only beginning to understand the potential benefits of periodic fasting. Besides being a sure-fire way to lose weight, fasting can help to suppress a runaway inflammatory response. A medically supervised water-only fast is also a useful first step in identifying which foods might be triggering a patient’s health problems. The Paleo advocates are hoping that eating bacon and eggs—but no toast—would produce the same effect as eating nothing at all. It is a foolish hope.
Many people swear by the Paleo diet. They have managed to survive on it for months or even years, and they claim that they have achieved other benefits, such as weight loss. Yet these testimonials should be viewed with great skepticism. No populations anywhere on earth have managed to achieve good health statistics or a long life span on a ketogenic diet. The populations who eat a diet that is most like the ketogenic diet may seem healthy while they are young, but they have long been known to suffer from rapid aging and a short life expectancy. In contrast, the populations with the longest, healthiest lives are the ones who are eating the opposite of a ketogenic diet: they eat a diet based on low-fat plant-based foods. One of the important findings of an enormous epidemiologic study called the China-Cornell Oxford Project was that the less animal-source food a population eats, the lower its average cholesterol level is and the lower its risk of death from chronic disease is. There did not seem to be any safe level of intake of animal-source foods.
A ketogenic diet may be a useful as a desperate attempt to suppress seizures in children with some severe forms of epilepsy. Yet in those children, the diet can have side effects. It can cause dehydration, constipation, vomiting, high cholesterol, and kidney stones. Some children have had severe side effects, such as heart rhythm problems, inflammation of the pancreas, and possibly loss of calcium from the bones. In short, a ketogenic diet may be useful as a way to treat some rare but serious diseases that respond poorly to any other available treatment. However, it is unlikely to improve health for the general public in the long run.