Saturated Fat Kills Gut Bacteria & Modifies Genes in the Distal Small Intestine - Another Reason Why We Get Fat? Plus: Bacteria, Fiber, SCFA, GLP-1 & PYY Revisited

Image 1: Bacteria, there are >100 trillion of them right inside of your digestive track, you can hardly know them all and scientists do neither - the only thing we are beginning to understand, though, is that it may be a good idea to get them to know at least somewhat better ;-)
I guess some of you have already noticed that I was (and probably am now, again) somewhat behind, as far as answering your questions, comments an wise remarks are concerned. Actually it is still more of a coincidence that today's SuppVersity news, which, as you see is not an Adelfo Cerame post (don't forget to keep the fingers crossed for him! This is his weekend!), could actually be interpreted as my somewhat lengthy response to a comment from Vincente on the effects of GLP-1 on chocolate preference in rats and an interesting hypothesis of his, on how this could all relate to my previous post on the fat burning effects of GLP-1 ("Eat More, Burn More and Lose Fat Like on Crack with GLP-1!?"). What, that was Vincente's reasoning, what, if those obese individuals had just messed up their gut bacteria an would lack those beneficial bacteria, which convert the fiber and resistant starch that makes it through your small intestine, right down into your long one to short chain fatty acids?

Does obesity come from within?

I guess by now some of you may already be asking themselves, where all that relates to GLP-1 and eating more, burning more and losing fat like on crack. Well, the missing link if you will is actually not a link, but rather a receptor - the free fatty acid receptor, FFR, which "sniffs" the presence of the short chain fatty acids and triggers the release of GLP-1 and PYY. Those two incretin hormones, of which researchers have found within the past 10 years or so that they are way more than mere "satiety signals. Several research studies in rodents have shown that the anti-obesogenic effects of GLP-1 and PYY are if at all, only partly mediated by reductions in food intake, yet mostly via complex downstream effects on total energy expenditure, glucose and fatty acid oxidation.

Contrary to exogenously administered GLP-1, which is actually being used in the treatment of diabetes an the metabolic syndrome, the in-vivo data from rodent studies, which suggests that high fiber diets protects those little critters from diet induced obesity (Aziz. 2008; Shen. 2008; Zhou. 2008) have, as Robertson et al. pointed out only recently, not yet been confirmed in humans trials (Robertson. 2012). Moreover, the latest results from the Merck Reserach Lab show, contrary to previous evidence from the Cambridge Institute for Medical Research (Tolhorst. 2012), that even our current assumption with respect to the underlying mechanism, could at least be incomplete (Lin. 2012). This does not mean that the short chain fatty acids would not produce the desired increase in GLP-1 nad PYY, but rather that their effects are not solely mediated by  the aforementioned free fatty acid receptor in the gut.

Let's make things even more complicated and bring some long chain fatty acids to the table!

What is yet self-evident though is that the way GLP-1 and PYY modulate energy utilization punches yet another huge hole in the prostrated "calories in vs. calories out hypothesis", one that has little to nothing to o with insulin and one that acquires yet another shade of gray, when we look at the long-chain counterpart of the "bacterial excrements" the dreaded or beloved (depending on the standpoint of the individual) saturated fatty acids (SFA) and a recently published study by scientists from the Wageningen University in the Netherlands (De Wit. 2012), who investigated the long-term effects (8 week, study conducted on mice) of high fat diets with fats from different fat sources
  • palm oil - representing the saturated fatty acids,
  • olive oil - representing the mono-unsaturated fatty acids, and
  • safflower oil - representing the polyunsaturated fatty acids
on body weight gain, liver triglycerides and the whole other standard parameters and their relation changes in the gut microbiome and the amount of fat that "left" the animals undigested.
Figure 1: Fecal fat and energy loss, total energy intake and relative (to control on normal chow) liver triglycerides, oral glucose tolerance and weight gain over the 8 week study period (de Wit. 2012)
A casual look at the data in figure 1 should suffice to see that there is a profound mismatch between almost all classic features of the metabolic syndrome of which we would usually expect that they would be closely associated:
  • the rodents in the palm oil group ate the least amount of energy, excreted the greatest amount of fat and total energy in their feces and still gained the greatest amount of body weight and had the highest amount of liver triglycerides (beginning non-alcoholic fatty liver disease)
  • the rodents in the olive oil group did not consume significantly more amount of energy or excrete significantly more amount of fat / energy in their feces and still gained ~40% less body weight and did not exhibit similarly high triglyceride storage in the liver as the rodents on the saturate fat (palm oil)
  • the rodents in the safflower oil group were comparably ravenous (+20% energy intake), but although they did not excrete more energy and fat than their peers, their bosy weight gain was profoundly reduced and their liver triglycerides were better than in the "non high fat control group" and yet their glucose tolerance was not the best, but the worst of all the three groups
All that does only make sense, when a second parameter, or I should say another 100 trillion bacterial parameters come into play and the SFA induced reduction in microbial diversity and
composition (increased the firmicutes/bacteroidetes ratio) are accounted for, as well. those, this is at least what de Wit et al. believe are namely responsible for the complex changes in genes that regulate the fatty acid metabolism and expression of inflammatory markers, the scientists observed

Chicken or egg, cause of correlation? Or just gut optimization?

Even tde Wit et al. do yet point out that their observations do not provide significant evidence to establish a causal relationship between the bacterial changes, which are a direct result of an overflow of (selectively) antimicrobial saturated fats into the distal part of the intestine, the subsequent disturbances in the bacterial balance and (human!) gene expression in the gut and the  particularly pronounced obesogenic effects of saturated fatty acids.

You could, at least in my humble opinion, even argue that these are simply adaptive effects that ensure that the "host", in this case the rodents, "gets the most" out of his diet - after all, this is exactly what we are seeing here: A modulation of genes related to the conservation and storage of energy, such as the downregulation of the Bcmo 1 gene that predisposes to the development of obesity and non-alcoholic fatty liver disease (Hessel. 2008),  which allows for maximal energy efficiency despite greater fecal energy loss.

Conclusion? Drink safflower oil?

That these results should not be taken as an incentive to guzzle safflower oil (or drop your coconut oil for the latter) should be obvious. Just as obvious, by the way, as the realization that despite all the hoopla and my own excitement about the newly discovered importance of the gut microbiome as one of the possible contributers to the global obesity epidemic. We are understanding way too little about its interactions with its host, i.e. us, to exclude that we are not - yet again - confusing cause and effect, causation and correlation and take our gut microbiome, which is eventually nothing else than a mirror of our healthy or unhealthy lifestyle for the real deal, and try to modulate and fix the mirror image with anti-, pro- or prebiotics without working on what stands right before the mirror: The sedentary, convenience food consumer, who works to jobs and rather watches TV till late at night instead of getting his 7-8h of sleep....

References:
  1. Aziz AA, Kenney LS, Goulet B, Abdel-Aal el-S. Dietary starch type affects body weight and glycemic control in freely fed but not energy-restricted obese rats. J Nutr. 2009 Oct;139(10):1881-9. Epub 2009 Aug 19. 
  2. Hessel S, Eichinger A, Isken A, Amengual J, Hunzelmann S, Hoeller U, Elste V,  Hunziker W, Goralczyk R, Oberhauser V, von Lintig J, Wyss A. CMO1 deficiency abolishes vitamin A production from beta-carotene and alters lipid metabolism in mice. J Biol Chem. 2007 Nov 16;282(46):33553-61.
  3. Lin HV, Frassetto A, Kowalik EJ Jr, Nawrocki AR, Lu MM, Kosinski JR, Hubert JA, Szeto D, Yao X, Forrest G, Marsh DJ. Butyrate and propionate protect against  diet-induced obesity and regulate gut hormones via free fatty acid receptor 3-independent mechanisms. PLoS One. 2012;7(4):e35240.
  4. Robertson MD. Dietary-resistant starch and glucose metabolism. Curr Opin Clin Nutr Metab Care. 2012 Jul;15(4):362-7. 
  5. Shen L, Keenan MJ, Martin RJ, Tulley RT, Raggio AM, McCutcheon KL, Zhou J. Dietary resistant starch increases hypothalamic POMC expression in rats. Obesity  (Silver Spring). 2009 Jan;17(1):40-5. Epub 2008 Oct 23.
  6. Tolhurst G, Heffron H, Lam YS, Parker HE, Habib AM, Diakogiannaki E, Cameron J, Grosse J, Reimann F, Gribble FM. Short-chain fatty acids stimulate glucagon-like peptide-1 secretion via the G-protein-coupled receptor FFAR2. Diabetes. 2012 Feb;61(2):364-71.
  7. Zhou J, Martin RJ, Tulley RT, Raggio AM, McCutcheon KL, Shen L, Danna SC, Tripathy S, Hegsted M, Keenan MJ. Dietary resistant starch upregulates total GLP-1 and PYY in a sustained day-long manner through fermentation in rodents. Am J Physiol Endocrinol Metab. 2008 Nov;295(5):E1160-6.
  8. de Wit NJ, Derrien M, Bosch-Vermeulen H, Oosterink E, Keshtkar S, Duval C, de Vogel-van den Bosch J, Kleerebezem M, Müller M, van der Meer R. Saturated fat stimulates obesity and hepatic steatosis and affects gut microbiota composition by an enhanced overflow of dietary fat to the distal intestine. Am J Physiol Gastrointest Liver Physiol. 2012 Jun 14.
  9. Zhou J, Martin RJ, Tulley RT, Raggio AM, McCutcheon KL, Shen L, Danna SC, Tripathy S, Hegsted M, Keenan MJ. Dietary resistant starch upregulates total GLP-1 and PYY in a sustained day-long manner through fermentation in rodents. Am J Physiol Endocrinol Metab. 2008 Nov;295(5):E1160-6.