OAA is oxaloacetate. It is made from carbohydrates (glucose/fructose/galactose)-because these 3 entities are broken down to pyruvate and pyruvate is directly converted to OAA (and FYI, pyruvate also produces acetyl CoA). The reaction is like this: pyruvate + CO2+biotin+pyruvate carboxylase + ATP (meaning this reaction costs you energy) yields OAA.
The Krebs cycle runs to produce energy for survival-However, for this cycle to run, it must have both acetyl CoA and OAA combining together.
OAA can also be made from other sources because like the author said-glucose can be made from other sources. For instance, amino acids can produce OAA. Like wise, acetyl CoA can be formed from fatty acids, glucose metabolism (from pyruvate) and from certain amino acids.
The fatty acid unit from fat oxidation is processed further to yield acetyl CoA-this acetyl CoA, as the writer said, under normal carb consumption (v.s restricted low carb or no carb diet), enter the Krebs cycle to produce ATP to supple the body energy to live on. However, the Krebs cycle runs with the requirement of 4-carbon-units and one of those kinds is OAA from carbohydrate directly or indirect sources of carbohydrates. Because there is not enough OAA for acetyl CoA to work with in the Krebs cycle, the Krebs cycle cannot kick in and run at normal rate. Thus, the enormous amount of acetyl CoA supply from fat oxidation will not enter/be used in the Krebs cycle. But the liver comes to the rescue (to clear up the gigantic pool of acetyl CoA building up in the body.) The liver will take up 2 units of acetyl CoA and after a couple of reactions, we have acetoacetate-which can be broken down further to acetone and hydroxybutyrate. All 3 acetoacetate, hydroxybutyrate, and acetones are called ketone bodies-but mainly the acetoacetate and hydroxybutyrate play the game here. And both acetoacetate and hydroxybutyrate will be escorted by blood to tissues-here the hydroxybutyrate can be converted back to acetyl CoA and now, this acetyl CoA can enter (remember the huge pool of acetyl CoA a while ago has undergone this new pathway and taken care by the liver-and so we don’t have a bunch of acetyl CoA standing in front of the Krebs cycle yelling to get in-instead we have acceptable or workable amount of acetyl CoA at acceptable rate that the Krebs cycle with limited amount of OAA can handle and allow to enter and produce energy. Still, the rate of fat oxidation is too fast, and we have too much acetyl CoA. The liver can oxidize/metabolize acetyl CoA, but the products of this pathway by the liver produces ketone bodies-and the more acetyl CoA the liver works on, the more ketone bodies we have-and although the blood takes ketone bodies to tissues to use and convert those ketone bodies back to acetyl CoA, we simply have too much ketone bodies in the bloodstream-so while some will enter tissues and get converted to acetyl CoA to enter the Krebs cycle in “local” cells, tons of ketone bodies cannot be processed fast enough-and this condition, ketosis, is harmful defined by the human body, so the body will try to clear it up-and like other toxins, they will be eliminated via breath, sweat, feces, and urine. Yep, you bet you’ll feel and see them ketone bodies remnants in your breath and urine.

OAA is oxaloacetate. It is made from carbohydrates (glucose/fructose/galactose)-because these 3 entities are broken down to pyruvate and pyruvate is directly converted to OAA. There is no need for you to dig up research papers because this reaction is well accepted in biochemistry and nutrition metabolism as fact (like 1 plus 1 is 2). The reaction is like this: pyruvate + CO2+biotin+pyruvate carboxylase + ATP (meaning this reaction costs you energy) yields OAA.
OAA can also be made from other sources because like the author said-glucose can be made from other sources. In fact, amino acids can produce OAA, too.

A Mediterranean style of eating is best across the board. There is a mountain of epidemiological data showing it’s excellent for weight management and health and well-being. There is also good adherence data on it. If you can eat healthy and stick with it then you’ve found the safest path to health.

Hi Peter,
The fuel you burn during exercise is not a flip-the-switch sort of thing where one second you’re burning fat and the next second you’re burning glucose. The body tends to use both of them in varying degrees.

When it comes to losing stored body fat, everyone thinks you HAVE to be burning ONLY fat as a fuel source. In general, if you’re eating different foods of differing macronutrient contents, then yes, this will have an effect on which fuel source you’re using during exercise.

But for as confusing as all the “diet gurus” out there try to make it, it still matters that you create an energy deficit. I discuss this in a bit more detail in this article: https://drbillsukala.com/fat-burn-vs-cardio-button/

Cheers
Bill

In other words, if I go on a long run and I’ve already been fasting for 48 hrs, how does the consumption of a few packs of GU (or other energy gel) impact my ability to burn stored fat?

Obviously if I consume 100kcal of carbs, you could say that’s 100kcal less of energy I’d need from my body fat given a fixed effort, but if that 100kcal of carbs essentially helps leverage my ability to burn even more fat, and exercise harder and perform (say) 300kcal more of energy expenditure than I otherwise would have been able to do, then in the end the carbs actually helped me burn fat.

So, for fat loss during endurance exercise while fasting: consume a small amount of carbs, or just water? Same Q for when not fasting.

Thanks!

I agree. That’s why I put in a little disclaimer at the beginning of the article. Cheers

Hi, what is exactly OAA and how it is made from carbs or sugars? any research papers on this?