The Nutrition Debate #58: What is Dietary Ketosis?

Fasting ketosis occurs “after a few days of fasting,” “when liver glycogen stores are depleted” and “the body shifts from a glucose-based metabolism to a fat-based one,” as Lucas Tafur explains at his Ketogenic Nutrition website. It is a physiologic state that Dr. Richard Veech, the “go-to” expert on ketone bodies at The National Institutes of Health, calls “the normal state of man.” But ketosis can “either be triggered by fasting or by diet,” Tafur says. Therein lies the key.

Dietary ketosis is the adaptive response, or “acquired evolutionary mechanism, [that] shifts [the body] from a glucose-based metabolism to a fat-based one,” Tafur explains. This shift occurs when the carbohydrates are unavailable for fuel. (Carbs were scarce in ice age winters.) The enzymes that break down fat for energy are controlled by insulin which is very responsive to the presence of carbohydrate. Dietary ketosis is achieved by the sustained and sharply curtailed intake of carbohydrates. How sharply? It varies. Your mileage may vary (YMMV), so I’ll give you my experience.

But first, a little more science and a little math. (Sorry, but I think some of my readers will find this both a useful proof and perhaps even a useful tool). A part of everything we eat becomes fuel, primarily glucose, or equivalent. That’s good because glucose quickly converts to energy, and the body (the brain, in particular) needs a little glucose – about 30-35 grams a day, either directly as glucose or as constituted in a form (e.g. ketone bodies) that substitutes for it perfectly.

Fat (either body or ingested) is a triglyceride and is made up of 3 fatty acid molecules and 1 glycerol molecule. Note the stem ‘gly.’ Each triglyceride molecule that is broken down to free fatty acids to enter the blood stream for energy leaves a glycerol molecule to join with another to make glucose. About 10% of ingested or stored (body) fat becomes glucose.

Protein is dismantled (digested) into its component amino acids which circulate to the muscles. What is left over goes to the liver and cannot circulate again in amino acid form. However, when the body needs glucose, the liver makes it from stored amino acids through a process called gluconeogenesis (“glucose-new-creation”). About 54% of the protein we eat is glucogenic, i.e. can become glucose, especially if we eat too much at any one meal. It is stored and then reconstituted and circulated as glucose!

Carbohydrates – almost all of them from the simple sugars to complex starches – digest to glucose. Some starches will be digested slowly, but simple sugars and highly processed carbs in products sold in boxes and bags will break down fast to the monosaccharides glucose fructose or galactose. In the case of fructose, they will stop at your liver which protects your body from them. Your liver will convert excess fructose into fat by lipolysis. The glucose circulates in your blood to be taken up by the cells as fuel. Circulating glucose raises insulin levels taking you out of ketosis.

The mechanism then to achieve dietary ketosis is this: eat a very low carbohydrate, moderate protein and high fat diet. Expressed as a formula (here’s the math part):

 K/G ratio = (0.9*FAT+0.46*PRO)/ (0.1*FAT+0.54*PRO+1*CHO.),

where K = ketogenic molecules and G = glucose molecules.

The fat, protein and carbohydrates (CHO) are all entered in grams (weight). The desired ratio of numerator to denominator is >1.5. That is considered a “ketogenic ratio.” Put another way, the ratio of ketogenic molecules to glucose molecules should be at least 1.5 to 1, stated >1.5:1, in each meal, every day.

Because this dietary regimen is very high in fat and very low in carbs, you will not be hungry between meals. Trust me. You will not. It’s 5PM as I write this and I haven’t eaten since breakfast. I forgot, honestly. My stomach did not remind me it was time to snack or to eat lunch. You will not crave snacks. You won’t want them. You will be satisfied (satiated) by the high fat and moderate protein in each meal…, so long as you don’t eat carbohydrates.

Once you are in dietary ketosis, fatty acids are used as the major source of fuel. But, the “balanced diet” folks say, this could cause a problem for the brain because fatty acids do not cross the blood-brain barrier. Fortunately, the liver uses the fatty acids from the breakdown of triglycerides (both body fat and ingested fat) to synthesize ketone bodies which enter the brain and substitute for glucose. This adaptive process in the brain’s energy metabolism increases its energy reserves. Ketone bodies are actually a more efficient fuel for the brain than glucose. The body’s fat stores are depended on, and depletion of the body’s protein store in muscle is avoided. In other words, your body uses fat for fuel. Your lose weight but not muscle.

 In the next column I will describe what I eat on a Very Low Carbohydrate Ketogenic Diet (VLCKD). Stay tuned.

© Dan Brown 7/8/12