High-Fat Diets: Exploring the Nuances of Animal Studies and their Translation to Human Outcomes

Transcription

1 High-Fat Diets: Exploring the Nuances of Animal Studies and their Translation to Human Outcomes Craig H Warden, PhD Professor UC Davis chwarden@ucdavis.edu Office phone Recent news media titles based on high fat diet studies in mice (1) Blocking Single Gene Prevents Obesity in Fat-Fed Mice Daily update May 4, 2018 Genetic Engineering & Biotechnology News European Scientist May 5, (2) How obesity makes it harder to taste Daily update March 21, 2018 Science News NPR March 20, NY Post March 20 (3) Dietary fat, changes in fat metabolism may promote prostate cancer metastasis Daily update January 15, 2018 Medical Xpress Prostate Cancer News Today JANUARY 22, 2018 New York Times Jan 16, 2018 Link to article: The problem how do we know if these results apply to humans? 1

2 Methods for diet studies in mice Ideal: Compare two diets with identical ingredients that differ in relative amounts for instance varying amounts of fat and carbohydrate. A small minority do this. However, typical methods are: compare a complex grain based chow diet to a purified ingredient high-fat high-sucrose diet. These have no ingredients in common, but authors and press releases always blame fat for any bad outcomes. Even worse methods are common: Many papers provide no information at all on the ingredients used for a diet study. Grain based diets GB diets, which are often and unfortunately referred to vaguely as normal chow, normal diet or standard diet in most publications, are made with grain and cereal ingredients and animal by-products. These unrefined ingredients include ground corn, ground wheat, ground oats, fish meal, alfalfa meal, brewers dried yeast and animal fat preserved with BHA. These ingredients contain multiple nutrients and nonnutrients, and their inclusion level in GB diets (i.e. the formula) is not only closed (kept secret from the research community) as it is considered proprietary, but the formula itself may vary over time depending on changes in nutrient levels in key ingredients. 2

3 Purified diets The typical mouse purified diet contains protein from casein, carbohydrate from sucrose and maltose (no corn starch), and fats from lard, soy or corn oil (no fish oil). Cellulose is usually the only fiber. Typical sources of nutrients and non-nutrients in rodent purified ingredient diets and grain-based diets Table 1 Typical sources of nutrients and non-nutrients in rodent purified ingredient diets and grain-based diets Nutrients or Non-nutrients Purified Ingredient Diet Typical Sources Grain-Based Diet Typical Sources Protein Casein Dehulled soybean meal, ground corn and wheat, whey, alfalfa Fat Soybean oil, corn oil Porcine animal fat, fish meal, meat meal Carbohydrate Corn starch, maltodextrin, sucrose Dehulled soybean meal, ground corn, ground oats, wheat middlings Fiber Refined Cellulose (INSOLUBLE Fiber) Ground corn or wheat, dried beet pulp, ground oats, alfalfa, wheat middlings (SOLUBLE and INSOLUBLE Fibers including cellulose, hemicellulose, lignins and pectin) Micronutrients Vitamin and mineral premixes Most ingredients, extra micronutrients added Phytoestrogens None present in diet Mainly soybean meal, alfalfa meal Heavy Metals None present in diet Mainly from grains and meat meals Pellizzon MA, Ricci MR. Nutr Metab(Lond) Jan 15;15:3. doi: /s ecollection

4 Dietary Studies in Animal Models of High-Fat Feeding: Guidelines for Diet-Comparisons and for Reporting Results (2008) Warden CH, Fisler JS. Cell Metab Apr;7(4):277. doi: /j.cmet Pie chart showing the percentage of 35 original research papers evaluated that used appropriate diet comparisons (14%), that compared chow and defined high-fat diets (43%), or that presented insufficient information to evaluate diet comparisons (34%). Table 1 Journal Summary of diet comparisons in papers published in 2007 in five journals and identified by search terms mouse high fat in PubMed. Papers identified using search terms Insufficient information to determine diet Number Chow compared to defined diet Both chow and defined diets, but not compared Defined diet compared to defined diet Cell Metabolism Diabetes 11 (of 36)* Journal of Clinical Investigation Nature 2 2 Nature Medicine *Only the first 11 of 36 total papers in Diabetes identified using the search terms were used in the diet evaluation. Papers used in evaluation of diet comparison. From Cell Metabolism [1-7]; From Diabetes [8-18]; From Journal of Clinical Investigation [19-30]; From Nature [31, 32]; From Nature Medicine [33-35] Warden CH, Fisler JS. Cell Metab Apr;7(4):277. doi: /j.cmet

5 The common use of improper control diets in diet-induced metabolic disease research confounds data interpretation: the fiber factor Michael A. Pellizzon and Matthew R. Ricci Nutrition & Metabolism (2018) 15:3 Mouse diet studies 2018 Pellizzon MA, Ricci MR. Diet comparisons in recent research publications. Pie chart showing the percentages of 69 publications evaluated (using search terms mouse high fat ) that used appropriate diet comparisons (19%), that compared GB diets and purified high-fat diets (41%), and that presented insufficient information to evaluate the types of diets used (41%). NutrMetab(Lond) Jan15;15:3. doi: /s ecollection

6 Little to no change in quality of mouse diet studies 2008 to Warden CH, Fisler JS. Cell Metab Apr;7(4):277. doi: /j.cmet Cited90 timesas of June6, 2018 Pellizzon MA, Ricci MR. NutrMetab(Lond) Jan15;15:3. doi: /s ecollection 2018 (1) Blocking Single Gene Prevents Obesity in Fat-Fed Mice We gave the mice a diet that more or less corresponds to continuously eating burgers and pizza, comments Karen NørgaardNielsen, who is a Ph.D. student at the Novo Nordisk Foundation Center for Basic Metabolic Research, and first author on the team s published paper in Molecular Metabolism. Still, it was impossible for them to expand their fat tissue. Mice were genetically engineered to not make the protein nicotinamide adenine dinucleotide (NAD+) biosynthetic enzyme Nicotinamide phosphoribosyltransferase (NAMPT). NAMPT acts intracellularly to catalyze the rate-limiting step of the NADþ salvage pathway, the main source of adipose NAD+. NAMPT-mediated NAD+ biosynthesis is indispensable for adipose tissue plasticity and development of obesity. The source paper is: Nielsen KN, PeicsJ, Ma T, KaravaevaI, DallM, ChubanavaS, BasseAL, DmytriyevaO, Treebak JT, Gerhart-Hines Z. MolMetab May;11: doi: /j.molmet Epub2018 Mar 7 The quotes are from: Daily update May 4, 2018 Genetic Engineering & Biotechnology News 6

7 What was actually done The chow control diet was Altromindiet number 1310 which was compared to a purified diet from Research Diets. The 1310 formula is a grain-based (soy, wheat, corn) fixed formula which is free of alfalfa and fish/animal meal and deficient in nitrosamines. There is a variant of this diet deficient in phytoestrogens in other words phytoestrogens are in the regular diet! The D12492 purified diet used was from Research Diets. It contains casein, maltodextrose, sucrose, lard, fiber from cellulose and some soybean oil. So the high fat diet is could be described as a pork fat based ice cream diet, rather than the press release description of burgers and pizza. Alternate explanation The two diets used have no ingredients in common see Table 1. Therefor the only accurate conclusion is that diet did something. Although the chow diet contains Arsenic and other metals, the authors choose to describe it as the healthy low fat diet alternative. Likely relevance to choosing a healthy human diet? 7

8 (2) What the press release said about HFD and taste buds As mice plumped up on a high-fat diet, some of their taste buds vanished. This disappearing act could explain why some people with obesity seem to have a weakened sense of taste, which may compel them to eat more. Compared with siblings that were fed normal mouse chow, mice given high-fat meals lost about 25 percent of their taste buds over eight weeks. Buds went missing becausemature taste bud cells died off more quickly, and fewer new cells developed to take their place. Chronic, low-level inflammation associated with obesity appears to be behind the loss, researchers report March 20 inplos Biology. Concluding paragraph Along with learning more about how taste buds are damaged by inflammation, Dando is interested in working toward new treatments for obesity, perhaps by countering the dulled sense of taste. These mice lose taste buds, he says. Can we bring them back? This quote is from Science News Inflammation linked to the disease caused the loss of taste buds in mice BY AIMEE CUNNINGHAM 2:00PM, MARCH 20, 2018 SOURCE PAPER Citation: Kaufman A, Choo E, Koh A, Dando R (2018) Inflammation arising from obesity reduces taste bud abundance and inhibits renewal. PLoS Biol 16(3): e journal.pbio What Kaufman et al did We have analyzed the effects of obesity on taste buds and demonstrate that mice consuming a high-fat diet display a pronounced loss of taste buds when compared to littermates sustained on a healthy diet. When the inflammatory response is impeded via genetic manipulation, we observe that mice no longer suffer taste loss, suggesting that taste dysfunction in obesity is a result of systemic inflammation. 8

9 Diets for Kaufman et al Control diet was Harlan Teklad Ingredients (in descending order of inclusion)- Dehulled soybean meal, wheat middlings, flaked corn, ground corn, fish meal, cane molasses, ground wheat, dried whey, soybean oil, brewers dried yeast. Experimental diet was a purified diet Harlan Teklad TD Ingredients: Casein 230 g/kg, Lard 350g/kg, Sucrose 150g/kg Maltodextrin 191g/kg Vitamins minerals methionine. No mention of cellulose or any other fiber. Alternate explanation for Kaufman and taste buds The authors have compared a fiber rich Grain based chow to a purified defined high-fat high-sucrose diet. The two diets have no ingredients in common. Take your pick of causal ingredients. Finally, the authors assume that obesity causes a change of inflammation which causes a decrease of taste buds, but it is also possible that different ingredients of the two diets have direct influences on taste buds or inflammation. For example, lots of data says that fiber reduces inflammation! 9

10 (3) An aberrant lipogenic program promotes metastatic prostate cancer Chen et al What the authors said: Lipids, either endogenously synthesized or exogenous, have been linked to human cancer. A high-fat diet (HFD) induced lipid accumulation in prostate tumors and was sufficient to drive metastasis in a nonmetastaticmouse model of Prostate Cancer. Thus, our findings uncover a prometastatic lipogenic program and lend direct genetic and experimental support to the notion that a Western HFD can promote metastasis. Nature Genetics VOL 50 FEBRUARY What the New York Times said about the Mouse Prostate Cancer study Obesity is linked to prostate cancer, scientists know, but it s not clear why. On Monday, researchers reported a surprising connection. When prostate cancers lose a particular gene, they become tiny fat factories, a team at Beth Israel Deaconess Medical Center in Boston reported in a paper published in Nature Genetics. Then the cancers spread from the prostate, often with deadly effect. Prostate cancers that have not lost that gene also can spread, or metastasize in mice, at least but only if they have a ready source of fat from the diet. That finding suggests that dietary fat can substitute for the loss of the gene, fueling prostate cancer. Moreover, the investigators found, an obesity drug that blocks fat production can make metastatic prostate cancers regress in mice and prevent them from spreading...more They also wonder if low-fat diets might help these patients, and what kinds of dietary fat might fuel prostate cancers. 10

11 What they actually did They chose a lard-based HFD enriched in saturated and monounsaturated FAs and capable of inducing classic HFD effects in rodents (reference 61) Here is what reference 61 says Diets were prepared in pellet form by Altromin (Lage, Germany). Rats had free access to either a standard rodent chow (SC, fat content 11% of energy), or a high-fat diet (fat content 42% of energy), based on lard (HF- L). NO OTHER INFORMATION WAS PROVIDED. Alternate explanation Diet ingredients are not provided in the paper nor on the web site for the manufacturer. This is common practice for non-us producers. Although diet does something, no conclusions can be made about the role of any one ingredient. The only thing we know for sure is that the high fat diet contains lard, presumably from Germany. Lard fatty acid composition depends on the food sources for pigs. The HFD likely contains less fiber because of less carbohydrates. 11

12 Overall conclusions Mice are an excellent model of genetic human obesity. Most genes that cause obesity in humans cause obesity in mice and vice versa. Mice may be a good model of diet induced obesity, but most experiments are not designed to determine effects of one or two ingredients. Most mouse diet studies can only conclude: Diet does something to health. 12