August 26, 2002
From the desk of Jane Galt:Well, everyone was yelling at
Well, everyone was yelling at me and saying I didn't understand fatty acid metabolism, which was true, but also true of my interlocutors, so I don't feel too bad. I've had a poke around at some data, and here's what I've gleaned so far:
1) Fat can indeed be turned into glucose, and is on a regular basis, by your liver. Whereupon it enters your bloodstream as sugar. Protein can also be turned into sugar with little effort by your body.
2) Your body likes your blood sugar steady. If you stop eating carbohydrates, your body will turn protein and fat into glucose. There is, at least as far as I can tell, no magic about getting your blood sugar from sugar vs. fat or protein, except the blood sugar spikes caused by ingesting large amounts of refined carbohydrates that I discussed below. You do not lower your blood sugar by cutting carbohydrates out of your diet; you just make it steadier.
The pancreas is the primary organ that figures out how much energy you have and how much you need, by monitoring glucose concentrations in the blood. Low blood glucose stimulates the secretion of glucagon (it's like the opposite of insulin: where insulin sweeps extra sugar out of your blood and stores it as fat, glucogen puts extra sugar into your blood from carbohydrate, protein, and fat stores); high blood sugar stimulates the production of insulin. If you eat fewer carbohydrates, the preferred source of blood sugar is protein, either from your diet or your muscles, because it's easier to break down. Your body turns to fat only as a last resort. That's why the protein content of Atkins et al. has to be so high; otherwise your body would start cannibalizing your muscles.
3) Fat does indeed turn into fat quicker than sugar or protein. Why? Because the liver is responsible for turning all your extra food into storable form. Since the fat is, well, already fatty, it's easier for your liver to pass it through to your adipose tissue than to initiate the transformation of carbohydrate or protein into fat for storage. Also, because the fatty acids require less synthesis, turning fat into fat is much more efficient than turning carbohydrate or protein into fat. This isn't based on some sort of sympathetic magic "fat makes you fat" study as some have argued; it's based on what we know about cellular metabolic mechanisms. From what I can see, arguing against this would require overturning current medical understanding of the entire fat metabolism process. Anyone who says they're consuming 4,000 calories a day on Atkins and losing weight either has a hell of a metabolism, a hell of a metabolic disease, or a tapeworm. Your body doesn't just excrete the extra fat you consume; it stores it. The same way it stores extra protein, or extra carbohydrate: as adipose tissue. AKA body fat. Arguing otherwise requires arguing that your body simply excretes the extra fat -- how? There's no organ responsible for excreting it, it doesn't appear in your urine, and it sure doesn't get reabsorbed into your intestines to be eliminated in your feces. Where's all the extra fat going?
4) Your body gets its quick energy from glucose; most of your working muscles use glucose unless you engage in sustained (+10 minutes) activity with one muscle group. Your brain and many cells in muscle tissue can only use sugar. That's why your body keeps your blood sugar steady. Other muscles that are used all the time, like your heart and lungs, prefer ketones or fatty acids, which deliver a longer, steadier kick. But they can get the ketones they need from sugar as well as fat; the only difference is where the ketone bodies are produced; in a high carbohydrate environment, they're synthesized in the cell, while in a low carbohydrate diet, they're synthesized from fat in the liver.
5) The average American gets 40% of their diet from fat. Guess what's way under the FDA recommendations? I'll give you a hint -- it isn't protein. In other words, we haven't been following the dietary recommendations that Taubes says are making us fat.
6) Calorie counts are roughly accurate, and are based on how much weight people gain over the long term from eating given substances. Saying "A fat calorie is different from a carbohydrate calorie" is true but not useful; the calculations are not based on some theoretical idea about how much energy they should provide, but how much energy they in fact do. In other words, a gram of butter causes an average observable weight gain of more than twice that of a gram of sugar. Now, they may have different, significant effects on appetite and satiety (they also may not).
7) Unless you are severely dehydrated, your kidneys don't care how much water you drink. As long as there's enough water in your system to allow you to pee, the stuff from your kidneys passes out of your system just fine. It's overwork that can damage your kidneys, not concentration of metabolites.
8) Eating too much sugar probably makes susceptible people diabetic by causing insulin spikes. But sugar isn't the only culprit. If diabetics go on a high-calorie, low-sugar diet, they don't have as much success as if they go on a low-calorie diet. Because insulin is involved in the fat metabolism process, total body weight also matters. Interestingly, sugar isn't the only thing that triggers insulin production; so does high levels of amino acids, which is the symptom of consuming more protein than you need for cellular repair and muscle-building.
9) The Atkins diet cuts out more fat than people think. While it's true that there's more fat from animal soures, there's less fat from french fries, Cinnabons, and the like. And it's easier to consume an entire bag of potato chips than a 20-oz steak.
10) You need fewer calories than you think. I'm a very tall woman, and my basal metabolism rate (the number of calories you'd consume if you were lying flat on your back all day, and doesn't that sound nice?) is 1500. If you're shorter than me (and a female with an office job), yours is less than that. Most people only need 1,500 to 1,800 calories a day, not the 2,000 the FDA recommends.
Other resources on digestion and fat metabolism can be found here, here, here, and here.
Posted by Jane Galt at August 26, 2002 3:39 PM | TrackBack | Technorati inbound links