Ray Audette reported some time ago that fruit-living orangutans were found in a study (Knott, Cheryl D. "Changes in orangutan diet, caloric intake and ketones in response to fluctuating fruit availability," International Journal of Primatology (1998), 1061-79.) to spend about half of the year in ketosis when, according to Ray, "high carb fruits were not available" (
http://listserv.icors.org/SCRIPTS/WA-ICORS.EXE?A2=paleofood;8abf49f3.1002) and he guessed it was due to "low carb". I had also read claims that there are times of the year when little to no fruits are available in tropical Africa. Then I recently learned that wild figs, one of the favorite foods of wild chimps, are available year-round in tropical Africa. I remembered what Ray had written about orangutan ketosis and I wondered if there are fruits that provide ketones, such as figs, perhaps, and whether they might contribute to ketosis in primates. Sure enough, figs and other fruits provide ketones:
[Edit insertion:
http://www.academicjournals.org/ajb/pdf/pdf2012/10May/Darjazi%20and%20Larijani.pdfhttp://www.ncbi.nlm.nih.gov/pubmed/17929094http://onlinelibrary.wiley.com/doi/10.1002/ffj.2730100404/abstract/edit]
To many LCers on the Internet, fruits are "sugars" and therefore "toxic." Ketones from "sugars"? How ironic.
Then I found a free full-text version of the study that Ray cited (
http://tinyurl.com/7ro8ycz) and found that even in the "fruit-poor" ketogenic period, 21% of the orangutan diet was still fruit and 37% was bark (not animal fat), plus epiphytes, pithy plants, flowers, leaves, insects and seeds, with bark as the "primary dietary component". Bark is not low carb:
"There are considerable differences among species of trees, but all barks contain sugars, starch, cellulose, hemicellulose, and mineral elements.
http://www.extension.purdue.edu/extmedia/FNR/FNR_203.pdf"
Could bark contain ketones? Sure enough, it can:
http://www.ncbi.nlm.nih.gov/pubmed/15621606. The study didn't attribute the ketosis to LC, but to low calorie conditions resulting in the burning of body fat. In other words, starvation ketosis, not a LC ketogenic diet.
I also learned recently on this forum of an observation of orangutans intentionally fermenting durian fruit to the point where alcohol was produced [edit insertion:
http://www.finewinemag.com/docs/22%20WaltersAstonishment.pdf]. They then gorged on it and became quite drunk. Guess what else can apparently provide ketones? That's right, alcohol ("alcohol converts more easily to ketones than fatty acids" --Doreen, Ketosis & Ketone Test Strips,
http://www.lowcarb.ca/tips/tips011.html). What about durian fruit? Yup:
"A study conducted in 1995 found that esters, sulfur, and ketones - the compound responsible for "morning breath" - combine to produce the durian's powerful smell." (Gregory Rodgers, Durian Fruit: Interesting Facts About Southeast Asia's King of the Fruits,
http://goseasia.about.com/od/malaysianculturepeople/a/durian_fruit.htm)
So in the wild, orangutans can apparently achieve ketosis on a low-calorie, high-carb diet that includes foods that also provide some ketones, plus hindgut fermentation of fiber into fats. Of course, none of this means that you should necessarily emulate orangutans. What it does seem to suggest is that nature has proven once again to be far more complex than the Internet debates and dietary dogmas would lead one to believe.
What about foods rich in protein? Paul Jaminet investigated this and reported that even amino acids from muscle meat can be ketogenic:
From: Ketogenic Diets, I: Ways to Make a Diet Ketogenic
Posted by Paul Jaminet on February 24, 2011
http://perfecthealthdiet.com/2011/02/ketogenic-diets-i-ways-to-make-a-diet-ketogenic/
Leucine and lysine ... are purely ketogenic.
Isoleucine, tryptophan, phenylalanine, and tyrosine ... can be either ketogenic or glucogenic.
The other amino acids ... are purely glucogenic.
