The real chimpanzee diet – Fat, Glucose, Protein and a little Fructose

“Our lineage goes back directly to the Chimpanzee. There is no need to look for a common ancestor”. I heard that statement not long ago in a lecture given by a famous physical anthropologist that has discovered an Australopithecus or two during his long career.

If that’s the case (and even if it isn’t) the Chimpanzee’s diet may be a profitable line to follow for an aspiring evolution-nutrition researcher.

Conklin-Brittain NL, Wrangham R, and Smith CC (1) attempt to do just that in a paper published in 2002 . The name Wrangham should be familiar to students of evolutionary nutrition as the developer of the much publicized “Cooking Hypothesis” to which, in due course, I will devote a post.

The paper presents a hypothesis that the evolution of the hominin diet is characterized by a reduction in fiber content and therefore Underground Storage Organs (sweet potatoes and the like) was likely major component of the Australopithecines diet. Australopithecines stand between us and the chimps on the evolutionary timeline.

If there ever was an example of the importance of distinguishing between facts and interpretations in a scientific paper this is the one.

The Chimpanzee’s diet is a side issue here but the author take advantage of the opportunity to express their opinion about the current “Westernized humans'” diet. The authors, all of them primatologists I believe, provide a detailed analysis of the chimpanzee’s diet based on years of observations. We will come back to the actual numbers in a moment, but if you were not interested in the small details of the Australopithecus’ diet, you would end up with the following interpretations and recommendations regarding human nutrition as quoted below:

“Peak lipid [in primates’ diet] was only about 8.5% of dry matters and the average intake was only about 2.5%. As a point of reference, human fat intake probably does not need to be more than 5%…”

Also: “Modern, Westernized humans consume fat far in access of need or recommendations ….”

They end their human nutrition advice with the following statement: “This [the chimpanzee diet] coincides with what we believe to be the healthiest human diet, one that contains high amounts of complex carbohydrates and only small amounts of fat”

In other words if “Westernized humans” only reverted (6 million years) to the chimpanzees’ typical diet of plenty of fruits we would all be well and dandy.

Sadly, one flaw in the authors’ analysis turns their interpretations upside down.

They write: “…so we include soluble fibers in the category of carbohydrates digestible by chimpanzees”.

While calling fibers carbohydrates is correct from a chemical nomenclature point of view, it would be incorrect from a nutritional point of view because fibers are just not metabolized in the same manner as other carbohydrates such as starch and glucose. And why bother distinguishing between food nutrients at all if not for their different digestion and metabolism?

Animals are unable to obtain energy directly from fibers. Any student of nutrition knows that soluble fibers are fermented by bacteria in animals’ gut to produce short chain saturated fatty acids (SCFA’s). SCFA’s are absorbed by the intestine walls into the blood stream and henceforth are digested as any externally sourced SCFA’s, like SCFA’s in butter or coconut oil, would. Dr. Barry Grove wrote an excellent post about the importance of this energy extraction route for most non-meat eating mammals.

Here are the raw numbers for the chimpanzee’s diet from the paper; in weight percentage from dry matter:

The authors indicate that a typical chimpanzee diet is of 75% ripe fruit and 25% pith. For some reason nutrients percentage numbers by weight pervade the ancestral nutrition scientific literature but they really mean very little so, assuming 1.5 fat calories for each gram of fiber (2), 4 calories per gram of protein and sugars and 9 calories per gram of fat  we can calculate the typical diet in terms of caloric percentage as follows:

So the chimpanzees consume only 29% of their diet as “Carbohydrates”, as the term is normally used.

However in terms of load on the human metabolic system, insulin and all, the amount is even smaller. According to Milton (3) glucose composes 60-70% of the sugars in ripe wild fruits so the glucose caloric percentage of the chimpanzee’s diet is 19% (29% X 65%). The difference – 10% – is made up of fructose but in terms of metabolites we are not done. Fructose is almost exclusively metabolized in the liver to either glycogen (a source of glucose) or triglycerides (basically fat with little sugar). The ratio of fructose metabolism to either one will change, depending on the liver glycogen depletion status, so let’s assume a ratio of 50/50 for glycogen/triglyceride.

We finally end up with 24% of the metabolites of the chimpanzee’s diet of what most people call carbohydrates. In terms of a typical diet of 2200 calories per day we are talking about 530 calories or 130 grams.

While 530 calories may not be considered strictly “low carb” it is not so far from Atkins’ “Maintenance Level” for some people and not far from the Jaminets’ paleo based Perfect Health Diet ‘s recommendations.

There are two additional lessons we might learn from this analysis:

1. If we retained the fructose processing capacity of our chimp forefathers than, assuming a 2200 calories diet, we can safely consume a whapping 450 grams (1 lb) of apples, as each 100 grams  of apples contain 5.9 grams of fructose. That’s about 4 apples. I doubt that all of us did actually retain that capacity to the full extent however. Although Australopithecines retained their tree climbing capacity and probably did consume a fair amount of fruits, their high fiber content in nature would probably rule them out as common food for us with our quarter size colon compared to chimps. Additionally, fructose malabsorption and intolerance is presently quite prevalent  in some populations so it may be safer to use this number cautiously.
2. From an evolutionary point of view fats and particularly SCFA’s should be the preferred source of energy for hominins as they are for almost all mammalians. High consumption of healthy (non-omega 6) fats intermitted fasting with the resulting ketosis and some degree of coconut oil consumption seems to be ideal in the context of an evolutionary compliant chimp diet.

In summary, the chimp diet is 50-55% fats, 24-29% glucose and 21% protein  – not “one that contains high amounts of complex carbohydrates and only small amounts of fat” quite the opposite. Luckily for the chimps their diet has no resemblance whatsoever to the SAD diet and if analyzed properly may indeed show the way to “the healthiest human diet” – high in fats and moderate in protein, and carbs with some fruits included for old time’s sack.

1. Conklin-Brittain NL, Wrangham R, Smith CC (2002) A two-stage model of increased dietary quality in early hominid evolution: The role of fiber. In: Ungar PS, Teaford MF, editors. Human diet: Its origin and evolution: Greenwood Publishing Group. pp. 206.
2. Popovich DG, Jenkins DJ, Kendall CW, Dierenfeld ES, Carroll RW, et al. (1997), The western lowland gorilla diet has implications for the health of humans and other hominoids. The Journal of Nutrition 127(10): 2000–2005.
3. Milton K., (1999) Nutritional Characteristics of Wild Primate Foods: Do the Diets of Our Closest Living Relatives Have Lessons for Us?, Nutrition Vol. 15, No. 6

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