My machine reads 2.7 to 3.5 depending on when I take a reading. I take this to mean I am making ‘a surplus’ of ketones if Attia is anything to go by.
If the body is making ore than it is actually using, other than the nutritional requirement, why do I need to eat until my body fat is used up?
Now I'm in ketosis
You can’t get unlimited energy from your bodyfat. If you have not much, you can’t even get your energy need from it so your capable body slows down your metabolism, there are the muscles to use up too…
Bikman points out that ‘wasting’ ketones via breath and excretion is actually losing fat mass. The ketones are synthesized from fatty acids, so if they end up in the atmosphere or toilet, it’s fat gone
As pointed out by @Shinita there’s a limit to how much fat you can use for energy per day. Here’s a calculator. If you run the calculator you will quickly determine that you can not consume enough of your own body fat to fuel your daily activities. If you try you will eventually end up lowering your BMR which will make it steadily more and more difficult to lose remaining weigth/fat. You have to provide additional fuel via eating to avoid that outcome. The calculator can determine how much.
Also, and counter-intuitively, eating fat and especially saturated fat increases your metabolism which in turn raises your energy requirement which in turn helps burn more fat. Increasing lean muscle mass also increases your metabolism since lean mass and muscle require more energy to maintain.
Taking this to its logical conclusion, does this mean there might be a benefit to eating keto, such that the amount of calories lost includes those lost through breath, respiration, and urine? Which are closed to those on a high carb diet?
In the link you provided, the ‘low carb’ diet was 100 grams of carbs, so not particularly relevant to keto. The study did, however, directly link increasing energy expenditure to reduction of carbs. So one might extrapolate that relationship down to the keto range of sub-20 grams net carbs. My guess is that at least part of that increase in energy expenditure in keto is due to ketone wasting. Overall I think we’re talking significant amounts of wasted energy simply because it’s a continuous process. For example, 5 kcal per hour doesn’t sound like much, but times 24/7… So I would agree that this is an additional benefit that non-keto eaters don’t share.
Around 22:00 Bikman starts talking specifically about energy wasting via ketones.
My guess is that at least part of that increase in energy expenditure in keto is due to ketone wasting.
In addition, better mitochondrial health also raises the consumption of fatty acids (although as muscles get more efficient, they consume less fat). Also, adipose tissue metabolism becomes “uncoupled” from need, raising the amount of fat that gets metabolised. Overall, there are a number of factors at play.
The short answer to the OP’s question is that the hormonal and metabolic pathways involved are complex, because they evolved to handle a multitude of possible situations. We can’t just yank a lever and force our bodies to perform as desired.
Another point is that ketone bodies are valuable for their epigenetic effects on our health, not just as fuel.
For those of you who just want to skip to the conclusion: Concluding Remarks and Future Perspectives Ketone bodies are emerging as crucial regulators of metabolic health. More than just a metabolite, the ketone body βOHB can regulate cellular processes directly via HDAC inhibition and binding to cell surface receptors, and indirectly by altering the levels of other regulatory metabolites including acetyl-CoA, succinyl-CoA, and NAD+. The ability of βOHB to regulate HDAC activity and thereby ep…