What Does Ketosis Mean?


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.

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