#28. Effective Fat Loss Monday, August 23, 2021 Last week, we talked about fat. Its colors. Its functions. Healthy percentages. Survival insists that we store some fat. But hoarding it (especially in our Santa bellies) can result in some pretty severe cardiovascular and metabolic consequences (Powell-Wiley et al., 2021). So how do we prune our pudgier portions? How do we eliminate the adipose we've accumulated over the years? Two things must happen (physiologically). First: lipolysis (mobilization of fatty acids). Second: beta-oxidation ("burning" what we just mobilized). Triglycerides (or triacylglycerols) are the storage form of fat. A pillowy midriff is chock-a-block full of triglycerides, and each one is composed of a glycerol backbone (a three-carbon carrier compound) and three fatty acids (strings of carbons, which vary in length). Short-chain fatty acids have up to six carbons in a linear sequence, and medium-chain fatty acids have up to 12 (Schonfeld et al., 2016). Most of the fatty acids in your midriff and elsewhere are of the "long-chain" variety, typically containing either 16 or 18 carbons (Tan et al., 2015). When you puzzle all of these pieces together (three long-ish fatty acids and one stubby glycerol), you get a pretty substantial molecule. Your body isn't capable of "burning" a hunk of chemistry that cumbersome. Think of it like a fireplace: can you shove a whole tree in there? Or do you have to chop it up first? Triglycerides require similar chopping. That's what lipolysis is: the process of separating the fatty acids from the glycerol. Once split, they're ready for the fireplace (i.e., mitochondria). There's a little more to it. Fat metabolism is a systemic endeavor. During a bout of cardiovascular exercise, triglycerides from your upper body will supply much of the fuel for your scuttling legs. That's how treadmills trim our tummies. It's also the reason crunches don't do much tummy trimming. Instead, you take fat from your all-overs and deliver it to the metabolically active cells. Once inside of those cells, fatty acids are transported into the mitochondria. Only there, inside of a mitochondrion, can fat be oxidized: chopped into a bunch of two-carbon chunks. These chunks are the metabolic equivalent of kindling; they enter the Krebs cycle en route to the eventual generation of energy in the form of ATP (Houten et al., 2016). If you want to burn fat effectively, neither lipolysis nor oxidation can be impaired. And with that, we have plenty to tip about: Tip 1) Are you doing "metabo" with the goal of fat loss? Consider the intensity of your exercise. No matter how you go about it, the main energy substrates you'll be using are carbohydrate and fat. The percent contribution of fat is much higher in low to moderate exertion. More interestingly, the absolute amount of fat oxidation decreases when intensity gets too high (Purdom et al., 2018; Achten et al., 2004; Horowitz et al., 2000; Romijn et al., 1993). During low-intensity exercise, plasma lipids (coming from peripheral adipocytes) account for a great deal of the metabolic cost. As intensity creeps up, those adipocytes release fewer and fewer fatty acids. Local lipids (residing in the tissue) will contribute a bit more to the cost. But only to a point. If you increase the intensity further, even that contribution diminishes (Horowitz et al., 2000; Romijn et al., 1993). There are multiple reasons for this, beginning with impaired peripheral fatty acid release. Think of it like dropping kids off at school. At light to moderate speeds, you can offload them okay. "Just tuck and roll, Aubrey!" But on the interstate in top gear? Good luck getting Aubrey and her siblings out of the car. In addition, the fatty acids that are present in the active cells don't even get oxidized at the same rate. Because you'll be creating a large supply of acetyl-CoA molecules from carbohydrate. That's the two-carbon chunk of kindling we talked about earlier. You can make it from carbs or fat, and if you make a bunch from carbs, that inhibits the transport of fatty acids into the mitochondrial matrix... which prevents their oxidation (Jeppesen et al., 2012). That said, the rate of fat oxidation after the workout session (not during, but following) will be higher if your workout was more intense (Warren et al., 2009). In other words: if you're a maniac at the gym, you won't be punished for it; you can still get good fat oxidation with higher intensity training (Burgomaster et al., 2008). But if your schedule permits, long bouts of moderate-intensity exercise will likely serve you best. And it'll serve you even bester over time. Because the more trained you become, the better you get at fat oxidation (Horowitz et al., 2000), so don't give up if the results aren't yet blitzing in your direction. Tip 2) Lots of stuff can promote or inhibit lipolysis (Braun et al., 2018). A major inhibitor is insulin, which has both acute and chronic effects (Choi et al., 2010; Kershaw et al., 2006). It's not a simple calories-in, calories-out equation. Yesterday's pasta feed can affect tomorrow's lipolysis. Managing your carbohydrates (the primary promotor of insulin) is wise if you wish to become more lipolytic in your exercise. How do you do that? You could try eating a lower-carb diet; you will find yourself oxidizing fat at a faster rate compared to high-carb alternatives (Purdom et al., 2018; Zajac et al., 2014; Prins et al., 2019; Howard et al., 2020). And, if you want to exert control over the rest of your energy substrates while you're at it, exercising before breakfast, in an overnight fasted state, associates with higher fat oxidation rates as well (Hansen et al., 2017; Frawley et al., 2018; Vieira et al., 2016). Tip 3) Get sleep. Lots of it. We've talked about this topic before. And we'll talk about it again. It's too important not to. For today, let's consider the relationship between sleep, growth hormone (GH), and fat loss. The largest GH secretions occur during deep or slow wave sleep. Disruptions and persistent sleep deprivation can impair the release and signaling of GH (Smiley et al., 2019; Lyu et al., 2020; Chennaoui et al., 2020). Among the diverse roles of GH, it promotes lipolysis both directly and indirectly (Gibney et al., 2007; Braun et al., 2018). So, for many reasons, including this one, make sleep a priority.