KBs can cross the BBB but not in a homogenous manner. For example, past experiments have demonstrated that BHB utilization is different in various brain areas (Hawkins and Biebuyck, 1979). Areas without BBB, hypothalamic regions and the lower cortical layers have a higher BHB metabolism compared to the lower one of the basal ganglia (Hawkins and Biebuyck, 1979). Also the metabolic meaning of the three KBs is different: while the main KB produced in the liver is AcAc, the primary circulating ketone is BHB. The third one, acetone, is produced by spontaneous decarboxylation of AcAc, and it is the cause of the classic “fruity breath.” Acetone does not have any metabolic functions, but it can be used as a clinical diagnostic marker. BHB acid is not, strictly speaking, a KB because the ketone moiety has been reduced to a hydroxyl group. Under normal conditions the production of free AcAc is negligible and this compound, transported via the blood stream, is easily metabolized by various tissues including skeletal muscles and the heart. In conditions of overproduction, AcAc accumulates above normal levels and a part is converted to the other two KBs. The presence of KBs in the blood and their elimination via urine causes ketonemia and ketonuria. Apart from being the fundamental energy supply for CNS, glucose is necessary for the replenishment of the quota of oxaloacetate, since this intermediate of the tricarboxylic acid cycle (TCA) is labile at body temperature and cannot be accumulated in the mitochondrial matrix. Hence it is necessary to refurnish the TCA with oxaloacetate via the anaplerotic cycle that derives it from glucose through ATP dependent carboxylation of pyruvic acid by pyruvate carboxylase (Jitrapakdee et al., 2006). This pathway is the only way to create oxaloacetate in mammals. Once produced by the liver, KBs are used by tissues as a source of energy (Fukao et al., 2004; Veech, 2004; McCue, 2010): initially BHB is converted back to AcAc that is subsequently transformed into Acetoacetyl-CoA that undergoes a reaction producing two molecules of Acetyl-CoA to be used in the Krebs cycle (Figure ​(Figure22).

Nutritional ketosis is a natural metabolic state in which your body adapts to burning fat rather than carbohydrates as its primary fuel. It is clinically proven to directly reduce blood sugar (as measured by HbA1c), improve insulin sensitivity (as measured by HOMA-IR) and reduce inflammation (as measured by white blood cell count and CRP). Nutritional ketosis can be induced by following a ketogenic diet. Learn more in our FAQ below!
If you’re not sure after your initial test, explore other healthy diets such as clean eating and always have in mind that your number 1 goal should be to avoid overly processed foods (keeping this definition fairly broad of course, as we live in the 21st century and have to adapt to modern age as well, where hardly any of us have time to spend 12 hours a day evolving around food production, gathering and cooking).
If you’re following the keto diet, you will need protein, but you should limit your intake to about 20 percent of your total daily calories. (1) This is important because when you consume more protein than you need, your body converts the excess protein into carbs through a process called gluconeogenesis. This process pushes your body out of ketosis.
It is known that different dietary components exert some effects on gut microbiome composition, mainly in relation to obesity and inflammatory states. In general, a Mediterranean diet has a positive effect while a high-protein diet seems to have detrimental effects due to putrefaction phenomena (Lopez-Legarrea et al., 2014; Flint et al., 2015). Few data are available at this time about the effects of KD on gut microbiota. For example, a study by Crawford et al. (2009) investigated the regulation of myocardial ketone body metabolism by the gut microbiota and demonstrated that, during fasting, the presence of gut microbiota improved the supply of ketone bodies to the heart where KBs were oxidized. In the absence of a microbiota, low levels of KB was associated with a related increase in glucose utilization, but heart weight was still significantly reduced. The myocardial-mass reduction was completely reversed in germ-free mice feeded with a ketogenic diet. Regarding food control we can hypothesize that the particular metabolic state of ketosis could provide some benefit to weight and food control via synergic actions between butyrate production by gut bacteria and circulating high blood ketones (Sanz et al., 2015).
Because people with type 2 diabetes are at an increased risk for cardiovascular disease, there’s a specific concern that the saturated fat in the diet may drive up LDL, or “bad,” cholesterol levels, and further increase the odds of heart problems. If you have type 2 diabetes, talk to your doctor before attempting a ketogenic diet. They may recommend a different weight-loss diet for you, like a reduced-calorie diet. Those with epilepsy should also consult their doctor before using this as part of their treatment plan.
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