Do you remember the first time when you read about low carb diet and its “metabolic advantage’? Wasn’t it exciting to discover limiting your carbohydrate intake would help you to burn down around 20% of your calorie intake “effortlesly”? Well I thought it would be amusing, and interesting, to know what the recent studies are saying about it.
What is astonishing to discover is it seems the question has not been addressed sufficiently with properly controlled trials and most of what can be said about it is still a sort of guess or, at least, an approximate deduction. Still, one thing that seems to be constant is someone needs to produce some ketones to get the effect. Because, as you know, many diets considered low carb are not restricting enough the said carb and these folk never gets in real ketosis. It seems now that to get this “metabolic advantage” is all about how deep you go into ketosis.
Talking about ketosis, it is interesting to note to differentiate “diabetic ketoacidosis (DKA)”, which requires levels of ketone over 3 mmol/l AND hyperglycemia over 300 mg/dl, we are now using the term “nutritional ketosis” for the healthy state in which your body produces ketones from fat to be burned as a fuel source.
So the highest quantity of ketones you will produce, the more this “metabolic advantage” will be high. The reason being there is an energy cost of making ketones from fat.
One study showed that if you get into significant ketosis on a LC diet your body will consume 139 cal extra per day, compare to burning only 86 calories extra a LC diet with no ketosis.
It seems that the effect of ketosis on increasing fuel expenditure is caused by an increase of liposis in adipose tissue and a subsequent intake of the released fatty acids by the liver having, as an effect, further increase of production of ketones.
The other question is how these produced ketones do increase your metabolism? Well it seems using ketones as a source of energy increase the your aerobic capacities, which means you ability of burning compounds using oxygen. One study showed when using ketones instead of glucose, the hearth increases its output. And associating this augmentation in aerobic capacities and cardiac output will have, as a final effect, an increase in performance especially an in muscle performance. So even it is said using ketones as a source of energy is not as efficient as glucose “calorie wise” still, the effect on the body performance capacities largely compensate for the loss of efficiency in production.
Maybe I already said it in other post, but I will repeat myself: glucose is only useful for immediate muscle contraction “without oxygen” and to red blood cells + a few cells in the eye and in the brain, cells that have a metabolism not compatible with the presence of oxygen. Not more.
All this being said, it comes out clear ketones offer an enormous thermodynamic advantage that may go up, according to one study, to 28%. Yes, 28 % of the fat you eat or burn from your reserves will be use extra to keep your body working!!!
Which explains nicely why many folks may eat extra calories on a VLCD in the form of fat, much higher then there body needs. Of course, this metabolic advantage comes only when the extra calories are NOT from protein, because the said protein would not lead to more ketone production, but will be transformed into glucose by neoglucogenesis.
The last question, which is not the least, and that do come up in many studies is if there would be an increase in “production performance” of ketones on a long term ketogenic diet, which would be translated on a lower caloric expenditure to produce the said ketones? If yes, could this explain why some folks do stop loosing weight after a long period on a seriously restricted carb diet even if they continue eating the same quantity of food? But I am not sure we are going to have an answer to this question in any soon future because nobody is interested to finance such as study as there is no money to make here…