Metabolism v. Fat Burning
I was reading Alcohol Revisited on Low Carb by Dana Carpender and something she said jumped out at me:
No doubt, however, that alcohol can be fattening, not only because of the calories it contains, but because it slows metabolism - to quote a medical journal article I read, "Alcohol profoundly inhibits lipolysis." In English this means that alcohol slows fat-burning to a crawl. Like carbs, your body burns alcohol preferentially. Don't expect to burn any fat until you've burned through all your alcohol calories.
First of all, Carpender makes the all-to-common mistake of equating lipolysis with actual fat-burning. As I summarized in Lip-ocabulary , lipolysis is the breaking apart of triglycerides to glycerol and free fatty acids. This occurs constantly in our bodies, inside the fat cells by hormone sensitive lipase (HSL) to release FFA's continually as part of the triglyceride/free fatty acid cycle, and in the capillary beds by lipoprotein lipase (LPL). To further complicate the matter, lipolysis is not stimulated systemically in the same manner. LPL can be activated in fat tissue so as to release FFA's temporarily so that they can be taken up into the adipose tissue, while it is reduced in muscles that don't need the fuel at the moment. In any case, we continually recycle up to 60% of FFA back into triglycerides (storage form) both in fat cells and peripheral tissues. Bottom line, lipolysis rates are not necessarily predictive of ß-oxidation - e.g. "fat burning".
That said, alcohol does inhibit fatty acid oxidation as summarized in Nutrient Fates after Absorption. This should not be surprising to any of us. The human "engine" works on a mixture of fuels at all times, and there is a heirarchy for usage based on storage capacity. At times of high availability of fuels where storage capacity is limited, we use less of the fuel that is easily stored: fats. So since we have no metabolic pathway to convert alcohol to a storable form, we will have to burn it off as it is ingested. So yes, Carpender is correct to state that on the whole, we'll be using those alcohol calories first before we use any net fatty acids (dietary or otherwise). But we never stop burning fats completely, we "burn fat" all the time. There is nothing ultimately preferable for fat loss about burning more fatty acids vs. carbs (or alcohol) for energy if we're not in a caloric deficit. Otherwise whatever fat burning we're doing, we're just filling the tank back up with each meal and fat mass will stay constant.
OK, so perhaps Carpender did mean ß-oxidation after all instead of lipolysis. She still made another error here equating the rate of fat burning with metabolism. Metabolism refers to our total energy usage, or total daily energy expenditure (TDEE). Since alcohol has a surprising (to me) 20% thermogenic effect (almost rivaling protein, and certainly exceeding the avg. 7.5% for carbs and 2.5% for fats), if anything, it would increase metabolism barring compensatory adaptations (e.g. I suspect that since alcohol is also a CNS depressant, NEAT would probably decline). If there's anything to TEF-metabolic advantage stuff, we should consider replacing fats with alcohol! However I also suspect that alcohol can be a significant appetite suppressant and isn't inherently "fattening". Most alcoholics I know tend to be thin and have little interest in food. Beer drinkers and to some extent wine drinkers are the exceptions, get to them in a minute.
OK, I'm not encouraging alcoholism here. But I have found that alcohol does not impact my weight loss drinking low carb. This has nothing to do with the carbs, it's all the calories! Vodka with sf soda is my choice. Every now and again I like a frozen daquiri or margarita. ONE of those packs like 500 cals. Is it any wonder why folks drinking such concoctions with meals or every weekend don't lose and/or gain weight?? Regular beer is fairly low in alcohol. May not have as many calories as a mixed drink, but most beer drinkers drink more to get their "fix" = weight gain. Same for wine where the calories do add up. I'm one who finds that wine will impact my weight more than vodka.
Bottom line, if someone substitutes ethanol calories for fat or carb calories, if they are in energy deficit, they'll still be burning fat. And if TEF is not compensated for, perhaps a bit more in the end. If you're supplementing with ethanol, you'll gain. If the effects of ethanol are such that impaired judgment leads to making poor food choices or overindulging, then it will lead to weight gain. But that is independent of any effect that ethanol may have on "fat burning" or metabolism.