[Lotus]

I'm a huge fan of HMB! But, why use l-carnitine? As far as I know it helps with fat oxidation, right?

Hannah, I prepared this post sometime ago and never got around to posting it, again, apologies. 

Hannah, I'm glad you're picking up the science, and believe me lol...it's incredibly difficult breaking down the science aspect into relatable terms used for NBE. 

Funny, I can look at science abstracts and clearly see what parts are truisms for NBE...lol. Other parts I see non-related to NBE (are no less important though) come across as noise. 

Please let me answer your questions by explaining things this way:

HMB is an exogenous (produced outside the body)-ketones supplement.

Endogenous (produced inside the body) βHB (Beta-hydroxy-butyrate) are ketone bodies are produced mainly in the liver, and passed on into the brain and on to the pituitary, where that stimulates the boob growth pathway PKA/JSTAT5. 

βHB catalyzes Acetyl-CoA [acetyl coenzyme A] to produce ATP (the cellular currency....ENERGY) and increase ATP concentration, which triggers the release of aromatase via leptin inside cells. 

Production of endogenous KB (ketone bodies) can take several weeks for some via the keto diet or HIIT (high intensity interval training). 

We hypothesized that exogenous ketone supplements could produce sustained hyperketonemia (>0.5 mM) without dietary restriction and without negatively influencing metabolic biomarkers, such as blood glucose, total cholesterol, HDL, LDL, and triglycerides. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4743170/

(from the study):
hormone is amplified as the signaling pathway progresses. The binding of a hormone at a single receptor causes the activation of many G-proteins, which activates adenylyl cyclase. Each molecule of adenylyl cyclase then triggers the formation of many molecules of cAMP.

Sweetorange, my thought on using HMB with L-carnitine together is that they improve fat mobilization versus single use. But let's focus on Mitochondria Dysfunction for a minute shall we?. If I recall sweetorange you battle PCOS, which is basically mitochondria dysfunction. 

When you have mitochondrial dysfunction you lose (or lack) the essential parts from nutrients to produce energy (ATP to be exact), and it could be caused by quite a few things, e.g. reactive oxygen species (ROS) as by-products, microbiome, adrenal, thyroid and/or other issues. Or you're missing a part of a gene inside the mitochondria, but recent advances in gene therapy look real promising. But when you have dysfunction you lose protein synthesis and the Krebs Cycle no longer works during the Citric Acid Cycle, and that's not good, meaning the cells die. 

So, what does all this mean?, we need ATP (tons of it) for what's known as cellular respiration, and when there's dysfunction in the mitochondria, you'll get fatigued, develop diseases (like Parkinson's), and or brain fog, crappy food metabolism...you get the picture.
I can talk more about this topic later as it is related specifically to NBE.