Resistant Starch & Butyrate: Eades' Shmashthematics
While finally finishing off my last post on short chain "fatty" acids, I was reminded of a whopper of a post on Dr. Eades' blog that I came across a long ago on resistant starch and butyrate. This post, too, has been in my Drafts for a very long time waiting for some finishing touches.
I came across this whilst I was looking into soluble fiber, low carbing and stalling and discovered that for all intent and purposes, SCFA's are carbohydrates metabolically, not fats at all. On LC forums I was repeatedly told or reading that soluble fiber is not really a carb because it is converted to a fat therefore doesn't stimulate insulin (I've got a fair amount of info on this to summarize in a future post). So this was one of the first things I began inquiring after.
I had read several highly informative pieces by Eades through links in discussions, etc. But when I found and read this one, it perked my "fact check" bunny ears right on up. He seemed to get so caught up in his smug condescension of the RD in the video (unfortunately no longer available) that he was discussing, that he put out quite a bit of erroneous information of his own. Don't get me wrong, the misinformation she was putting out deserved criticism and correction. But Eades only compounded things with his analysis.
So Eades quotes a list of foods that are suggested to be high in resistant starch content and the RD's contention that you need only about a half cup of these a day to get all the benefits she attributed to the resistant starch. Then he writes this:
One half cup of any of these foods – so she says – contains all the resistant starch one needs to provide all the above benefits. Let’s take a look.
According to the USDA database if we consume a half cup of cooked potato we’ll end up with 12.9 grams of carbohydrate (almost three teaspoons), of which 10.5 grams are starch. If we go by our RD’s estimate that 5 percent of the total starch is resistant starch, we calculate that our half cup of potato contains about half a gram of resistant starch (0.5265 g to be exact). If we then convert this starch to butyrate we find that we have about 2.3 grams of butyrate (assuming 100 percent conversion to butyrate, which isn’t the case because some is converted to other short chain fatty acids).
Ummmmmmm ... we can convert about 0.5g of anything into 2.3g of something else?? Nope. If we have 100% conversion of r.s. to butyrate, 0.5g r.s. will yield 0.5g butyrate AT MOST.**
Edited In 2/27/11: Starch is a polymer of glucose so for any given amount of starch you get however many of the glucose monomers. The number of molecules is the same, the mass upon cleavage negligible difference. The fermentation process basically boils down to:
glucose (C6H12O6) → butyric acid (C4H8O2) + 2H2 + 2CO2
FWIW, the bacteria gets 3ATP from this for its energy needs. The gases, well ... give us gas! If we have one mole (a chemistry unit for the number of molecules, 6.02 x 1023 to be more exact) of glucose, it weighs approximately 180 g. From each mole of glucose, we produce one mole (or the same number of molecules) of butyric acid. One mole of butyric acid weighs approximately 88 g, or roughly half the mass of the glucose. So, mass-wise, 0.5g starch will yield at most 0.275† g butyrate assuming 100% conversion. /Edit
... even if butyrate really does all it is cracked up to do, we wouldn’t really need the potato with all its accessory easily absorbed carb because we can get the equivalent amount of butyrate from a single pat of butter. (Or almost the same – a pat of butter contains 1.45 g butyrate. Two pats of butter contain 3 g or about 1.5 times the amount generated by the resistant starch component of the potato.)
Nutrition data for butter indicates that of 100g butter, contains just ~1.8g butyrate, but one oz (weight) with 15.4g total fat contains ~0.5g butyrate. The latter reporting seems erroneous (1 oz by weight butter would be 2T), but for the sake of argument let's use approximately 3% butyrate for butter. A "pat" of butter is approximately 1 teaspoon and contains approximately 4g fat. So, a pat of butter contains a little more than a tenth of a gram of butyrate. I'll generously allot 0.15g butyrate/pat butter. Seems we have an order of magnitude error here. To get the half gram of butyrate from a half cup of potatoes one would need to - and this is a low ball - eat almost 1.2 tablespoons of butter!
If the benefits of the resistant starch come from its conversion to butyrate as our RD avers, and if it requires the amount per day found in only one half cup of potato (or of the other foods she lists) as she also avers, then why not provide ourselves with one and a half times as much by eating a couple of pats of butter per day, which come without the extra three teaspoons of sugar? We get the butyrate without having to convert and we don’t get the extra carbs. Makes perfect sense to me.
I think comparing these two sources of butyrate also deserves some scrutiny. Butyrate is a small water soluble compound. Delivered orally in butter, one wonders how much actually reaches the colon (large intestine) vs. the butyrate generated by bacterial fermentation of fibers "on location". Think what you will of the pharmaceutical industry, you can learn a lot from delivery methods employed. Indeed sodium butyrate is used in the treatment of Crohn's disease, and supplements are coated to ensure release in the ileo-caecal region and colon. This would lead me to believe that the majority of butyrate in butter is absorbed well before it gets to the end of the small intestine and large intestine in the fully developed digestive system. May well be why it's found only in the infant food of mammals that have yet to establish bacterial populations in their guts. It seems to me that soluble fibers are a much better source of butyrate than butter. We get more from high fiber sources, delivered directly at the point of use/need with fewer calories and a larger bulk of food. I would suggest inulin is a better source of butyrate than resistant starch simply because foods high in inulin tend to not be overly high in digestible starch.
Eades made one last error:
While I’m at it, I have to mention one other little porky she tells during the interview. Says she…and because resistant starch doesn’t get digested or absorbed it fills you up but you don’t get any calories from it.
Okay. Let me get this straight. First, she tells us that it converts to butyrate, a fat, which is absorbed and works miracles once it is absorbed. Second, she tells us that we don’t get any calories from it. Have I got that right?
She is correct in saying that resistant starch (as well as any other type of fiber) gets converted to short-chain fatty acids. And she is correct in saying that the short-chain fatty acids get absorbed. But when they do get absorbed, they contain 9 kcal per gram, just the same as any other fat. So they are not free of calories. That’s why fiber is counted in the total calorie count on nutritional labels. Fiber does make it’s way through the upper digestive tract without being absorbed, but it does get converted to fat and absorbed in the lower GI tract, i.e., the colon. So, I guess we could say she’s a fibber when it comes to fiber. At least in terms of its calorie content.
Ummm... MCT's contain fewer calories per gram than LCT's. SCFA's will contain even less. By Eades' math, about 0.5g carb = 2 calories is magically converted to 2.3g fat = 20.7 calories. Bacteria can magically increase nutritional content of something 10-fold, all the while using some of the original energy content to sustain their own lives? (And we're to take seriously anything he says on the topic of thermodynamics with this type of sloppy analysis?) I don't know that one would call this a porkie from Eades, but it's utterly abominable!
Butyrate likely contains <4 cal/gram as it only contains 4 carbon atoms as compared to 6 for glucose. I can't find the chemical reactions of butyrate for energy and I keep finding lots of uncertainty in the literature discussions on this metabolic pathway. But I'll go out on a limb here and say that no way it's 9 cal/g!!
According to Wikipedia: "Regardless of the type of fiber, the body absorbs fewer than 4 Calories (16.7 kilojoules) per gram of fiber, which can create inconsistencies for actual product nutrition labels. In some countries, fiber is not listed on nutrition labels, and is considered 0 Calories/gram when the food's total Calories are computed. In other countries all fiber must be listed, and is considered 4 Calories/gram when the food's total Calories are computed (because chemically fiber is a type of carbohydrate and other carbohydrates contribute 4 Calories per gram). In the US, soluble fiber must be counted as 4 Calories per gram, but insoluble fiber may be (and usually is) treated as 0 Calories per gram and not mentioned on the label."
If it is the case that fiber calories are counted 4 cal/g, then you can legitimately subtract 2 cal/g from the calorie count of the food.
** An exception to this would be a chemical reaction A + B → C or C + D. If we're just looking at the masses of A and C, then if all or part of the B molecule is tacked onto A, then yes, the mass of product C will be greater than that of reactant A. However, the mass of A+B must equal the mass of C or C+D. This isn't the case here anyway so this is a moot point.
† Adjusted for ~10 % mass increase adding water to hydrolyze the starch polymer to glucose