An estimated 50,000 mice worldwide are charting new territories of chubbiness as they chow down on the infamous, lard-based, high-fat rodent diet, “D12492.” As I reported a few days ago over at The Daily Lipid, it turns out these mice are chowing down on twice the amount of polyunsaturated fatty acids (PUFAs) as Research Diets, the producer of D12492, has heretofore been reporting. In this post I’ll address a few questions that came up in the comments, like which fatty acids the PUFAs had displaced, and what we can expect from higher-quality, pastured lard.
Here’s a graph showing the difference between the new and old estimates (1):
The graph shows the difference between the actual fatty acid profile as determined by direct analysis of the lard and the previously reported fatty acid profile, which had been estimated using the USDA database. We can see that the actual fatty acid profile is much higher in PUFAs, at the expense of both saturated and monounsaturated fats. In fact, the company had originally estimated the diet to provide 17 percent of its fat as PUFA, but now estimates it to provide a whopping 32 percent!
The particular fatty acids that are decreased the most are palmitic, stearic, palmitoleic, and oleic acids. These are the primary fatty acids that pigs, humans, and other animals produce when we make fat from carbohydrate. This suggests that the pigs are consuming seed oils, which would increase their intake of PUFAs at the expense of the carbohydrates found in grains and legumes.
The ratio of omega-6 linoleic acid to omega-3 linolenic acid is almost double what had been estimated based on the USDA database, suggesting that the oils the pigs are consuming are particularly rich in omega-6 fatty acids.
Raising pigs on pasture isn’t in itself a very effective way to reduce the PUFA content of lard. In one study (2), lard from pigs fed pasture and acorns was 8.7 percent PUFA while lard from pigs fed barley, wheat bran, soy meal, lard, and nutritional supplements was 6.9 percent PUFA. Grass has many benefits, but including it doesn’t lower the PUFA content of lard beyond what could be accomplished simply by banishing vegetable oils from these poor piggies’ diets.
The most effective way to minimize the PUFA content of lard that I’m aware of is to feed the pigs a traditional Pacific Island diet rich in coconut. Here is the fatty acid profile of lard from the island of Tokelau (3):
The lard is only 3.1 percent PUFA — more than ten times lower in PUFA than that darned chubby-mouse diet — and the ratio of omega-6 linoleic acid to omega-3 linolenic acid is 3.3. At least this was the case when it was measured back in 1981. Even the chicken fat on this island was only 3.2 percent PUFA.
The islanders reserved meat for special feasts. Day by day they subsisted mostly on coconut, fish, and various starches. As a result, they obtained about half their calories from saturated fat, but only two percent of calories from PUFA, most of which came from fish.
In the grand scheme of things, then, we can say that the lard used in Research Diets D12492 is incredibly high in PUFA, and the diet itself, which also contains a small amount of soybean oil, is a very high-PUFA diet. We can probably expect at least one new high-profile study using this diet to hit the press every couple of months. Will they continue to blame the effects on “saturated” fat? Only time will tell.
Read more about the author, Chris Masterjohn, PhD, here.
1. Dr. Matthew Ricci, Vice-President and Science Director of Research Diets. Personal communication. November 18, 2011.
2. Timon ML, Martin L, Petron MJ, Jurado A Garcia C. Composition of subcutaneous fat from dry-cured Iberian hams as influenced by pig feeding. J Sci Food Agric. 2002;82(2):186-91.
3. Prior IA, Davidson F, Salmond CE, Czochanska Z. Cholesterol, coconuts, and diet on Polynesian atolls: a natural experiment: the Pukapuka and Tokelau island studies. Am J Clin Nutr. 1981;34(8):1552-61.