Ketosis: A Primer

We are interested in being healthy, lean, strong, energetic and athletic. To this end, we want a metabolic scenario in which we have access to the largest stores of energy in the body: triglycerides (stored form of fat). Many of us have more than we need. This has everything to do with hormone balance, which has everything to do with diet and exercise.

Let’s stick with diet for now. If you eat few enough carbohydrates, your body will not be getting enough sugar from your diet to keep blood glucose levels in the desired range. Lucky for us, the body has other mechanisms that can be called upon to maintain serum glucose levels. The backbone of stored fat molecules (triglycerides) can be converted to glucose in limited quantities, but the main source is a process called gluconeogenesis which takes place in the liver. This process involves the conversion of amino acids to glucose. In victims of starvation, these amino acids come from muscle tissue. In low-carbers, these amino acids come from the diet as long as there is adequate protein intake.

So, today I didn’t eat enough carbohydrates to maintain my blood sugar levels without other mechanisms kicking in. As a rule of thumb, this will be the case if you eat fewer than 120-130 carbs per day. Gluconeogenesis ramps up and converts amino acids into glucose in the liver. This process requires energy from fat. Gluconeogensis uses part of the fat, and the leftovers are converted into water-soluble fat molecules called ketone bodies. Ketone bodies act as an energy substitute for a chunk of our glucose needs (not all). So, now fat is being burned as part of the process that keeps our blood-sugar normalized.

Now, you’ll run into plenty of people who will tell you ketosis is dangerous. Usually this is because:

-Almost everyone in our culture eats a surplus of carbohydrates, meaning their bodies are exclusively metabolizing glucose for their main source of energy. Ketosis is seen as an abnormal state, often associated only with starvation.

-There is an adjustment period for the transition from glucose metabolism to ketone metabolism (note: you’re never completely off glucose metabolism; ketones act as a supplement). Short term studies tend to show a substantial decrease in performance in endurance tests. This effect disappears in longer term studies, as explained here.

-Diabetics can go into ketosis even when their blood sugar levels are high, which is not good. My understanding is that since they are insulin-resistant/deficient, the glucose in the blood stream is not being taken in by the cells for energy. A person with normal hormonal control should not experience this. Ketosis is not ketoacidosis. The body eliminates excess ketone bodies through the urine and breath to maintain blood pH levels. This is why you can test for ketosis with urine strips.

-I’ve heard the claim that ketosis causes bad breath. My experience with friends who test positive for ketosis contradicts this. I’ve never noticed bad breath on them, nor have I been told my breath is bad.

Dr. Eades explains these processes in a little more depth (and with a little more expertise) here and here.