If you eat Very Low Carb (15-30g/d) – not just low carb (50-100g/d) – you undoubtedly will know the term keto-adapted. There’s no formal definition of VLC because it varies according to your metabolism – the degree of your dysregulated glucose metabolism due to your degree of Insulin Resistance. However, VLC is generally meant to be a dietary intake of way less than 50 carb grams a day. It usually means 30 grams or less; for me it is just 15 grams a day.
When someone eats VLC, they generally eat less food because 1) dietary fat is filling, and fat, whether dietary or stored, does not induce the pancreas to secrete insulin, 2) protein digests slowly and make you feel full longer, and 3) carbs are digested quickly and they make your blood sugar rise and fall quickly and thus makes you “hungrier, quicker and oftener.” And finally, if you eat VLC, when your body has used up the energy from carbs you ate (and has stored in the liver as glycogen), the body can turn to fat for energy – the fat you ate and then fat that is stored on your body.
Protein isn’t used for energy directly. Its components, amino acids, have myriad other functions in the body; however, about half of the amino acids in protein can be used to make glucose in a pinch or, in Type 2 diabetics, even when not needed. That’s one of the reasons Type 2s take Metformin, to suppress this unwanted glucose production by the liver.
So then, generally, when a fat cell (a triglyceride) is catabolized (broken down) into its parts, it divides into 3 fatty acid molecules and a glycerol backbone molecule. A ketone body is a byproduct of this fat cell breakdown and oxidation. It’s a normal process. As such, being keto-adapted means that your body is making ketone bodies as part of this normal process where it is breaking down body fat molecules for energy.
When eating a VLC Ketogenic Diet (VLCKD), blood ketone concentrations are generally above the 0.5mmol/L level. When they are from 1.5mmol to 3.0mmmol/L, they are optimal. Eating in such a way as to achieve this level of ketone bodies in your blood is healthy. It is, in fact, the normal metabolic state when fasting…as when we eat just one meal a day or one meal every three or four days, the way our hunter/gatherer forebears did.
My recent personal experience with extended 2 and 3 consecutive day fasting supports this view. Many others report similar outcomes. My metabolism has not slowed down. I am fully energized. When I eat VLC on “feasting” days, I know that my body is fully fueled by stored fat while “fasting.” It can do this because, when consistently eating VLC, my body’s blood insulin levels drop, allowing access to my body fat (and ketones) for use as fuel.
The state of being in ketosis – this normal state – is not the same as having a condition called ketoacidosis. As the name implies, ketoacidosis is a diseased state, a serious form of acidosis. With ketoacidosis, the blood concentration of ketones is generally 20-30mmol/L, a full order of magnitude, i.e. 10x, higher. Ketoacidosis is a life-threatening condition and requires immediate treatment and hospitalization. I point this out because some current pharmaceutical advertising inexplicably uses the term “ketoacidosis” as though it were a condition that you could be walking around with. Acidosis is a serious, acute, unrelated medical condition and requires immediate hospitalization.
Ketosis, on the other hand, while a normal state, is NOT a necessary state to be in in order to be a fat-burner. I have in past somewhat carelessly used the term “keto-adapted.” I do not own nor have I ever used a meter to test ketone levels. I test my blood for glucose, not ketones. Neither have I ever used keto strips to test my urine.
I have just assumed that I was in ketosis when I ate as few as 15 or 20 or even 30 carbs grams a day, and certainly when I was full-day fasting (300kcal/day including only about 5 carb grams a day). If you are eating VLC (and fewer total calories), and your metabolism is operating at full energy, you are burning FAT for energy. You are FAT-adapted, whatever you level of blood ketones. And THAT IS YOUR OBJECT: When fasting – as when between widely separated meals – TO BURN BODY FAT WHILE YOU CONTINUE TO OPERATE AT FULL ENERGY LEVELS. Nature built us this way, to be in “nutritional ketosis.” Otherwise we, as a species, would have become extinct long ago.