Surprisingly, most of the questions I get through emails about “skepticism” ask about the science or myths in popular diet fads. It’s clear that there are a lot of websites, pundits, and websites with pundits who think that changing your diet is the most important thing in the world. Eat this to make your immune system strong. Don’t eat that because it causes cancer. But do eat this because it reduces your risk of cancer. Eat this. Don’t eat that. Drink this. Eat more of that.
My thoughts have always been that the human physiology is amazingly resilient, and as long as you have no chronic diseases, there is nothing one can do that will make the situation much better or much worse. Yes, maintaining levels of certain nutrients, such as vitamins C and D, iron, and others, are critical, but in the modern world, it’s almost impossible to miss out on those micronutrients. Yes, we should limit fats and “sugars”. But the thing is human physiology is complex, so marathoners eat lots of carbohydrates, and they are mostly healthy. It all depends.
And as I’ve mentioned, you’re not going to prevent or cure cancer with supplements (or presumably foods that are rich with those nutrients). Antioxidants don’t really help prevent cancer. Soy won’t stop certain types of cancer. Nor will certain foods make you lose weight. Most of these beliefs about foods, health and weight loss are based on either a boatload of anecdotal evidence, or use very preliminary laboratory research, make a leap of faith, and assume that laboratory evidence is equivalent to clinical evidence. Then, when the gold standard of research, a randomized clinical trial is done, the results generally show nothing. And in some cases, the negative effect is with the supplement or food.
And if you’re looking to try the newest diet craze, be aware that most fad diets just have no long-term successes, and may actually do harm.
A lot has been written about the diets of our great ape or human ancestors; some of these beliefs about our ancestor’s diet are used to support whatever food craze is trending at the time. Some vegans will claim that humans evolved to be vegetarians, but according to modern scientific research,
…since the evolutionary split between hominins and pongids approximately 7 million years ago, the available evidence shows that all species of hominins ate an omnivorous diet composed of minimally processed, wild-plant, and animal foods.
Some vegans, to contradict the lack of evidence that ancient humans, or our ancestors, were 100% vegetarian, will then make a claim that humans “evolved” to be more vegetarian over the past few thousand years as we moved to an agrarian based culture, but that ignores the fact that evolution does not work that quickly on a species that has such a long lifespan and such a low population. There just is no scientific evidence that we evolved to be an exclusively vegetarian species.
On the other hand, there is a current fad for the paleolithic diet, which is based on the supposed ancient human diet of wild plants and animals that various hominid species habitually consumed during the Paleolithic era. It consists mainly of fish, grass-fed pasture raised meats, vegetables, fruit, fungi, roots, and nuts, and excludes grains, legumes, dairy products, salt, refined sugar, and processed oils. It really attempts to be scientific (much more so than vegans), but it seems to border on the edge of pseudoscience, and can be considered a vogue diet, without much science backing it. Maybe its a good diet for health (we have no real evidence supporting it), but is there any evidence that our paleolithic ancestor actually ate a paleolithic diet?
Clearly, real science can provide us with strong clues and evidence as to the sources and quality of foods eaten by ancient humans (and their relatives). It is fairly straightforward to determine what our ancestors might have consumed, just based on a quirk of plant photosynthesis. First, we need to provide a bit of a chemistry lesson. Carbon, the so called building block of life, has two stable isotopes: carbon-12 (12C) and carbon-13 (13C). Around 98.9% of naturally occurring carbon on Earth is 12C (which has six protons and six electrons). 13C, which comprises about 1.1% of the planet’s carbon, has six protons and seven neutrons. Both types of carbon exist in every biomolecule, and as far as we know, the human physiology is incapable of selecting one type of stable carbon over the other. (I don’t want to look, but I bet someone out there is pushing a carbon-13 diet, because it’s better.)
Stable isotope analysis can measure the 12C/13C ratio, which is useful because different organisms have different ratios depending on what organisms they ingest. Importantly, plants have different ratios based on the type of photosynthesis they use to fix CO2. Plants that use C3 photosynthesis (mostly trees, shrubs and herbs) don’t select for one type of stable carbon over the other, so the 12C/13C ratio in these plants is the same as the ratio of carbons in the natural environment. However, plants that rely on C4/CAM photosynthesis (including tropical grasses and sedges, such as corn and sorghum) are much more selective toward 13C. Since animals build molecules in their bodies from the foods they eat, analyzing the stable isotopes of fossilized remains can tell scientists a lot about an ancient organism’s diet. Furthermore, the 12C/13C ratio in fossilized remains represents the type of diet over a lifetime, rather than from one meal. Think of the ratio as a measurement of the “average” diet of the organism over its lifetime
An analysis of the 12C/13C ratio in Australopithecus afarensis, a hominin (apes that include humans and their immediate ancestors that split from chimpanzees, about 5.4 and 6.3 million years ago) from the middle Pliocene (3.0 to 3.7 million years ago) showed that it had already shifted to a C4-based diet, that is, it had already made the switch to grains. Another paper showed that hominins made the shift to the C4-based diet around 2.3-1.2 million years ago, which coincided with the retreat of heavily forested areas that were replaced by open savannah. A third study, which analyzed stable isotopes to investigate the diet of several species of Theropithecus, the ancestors of the modern gelada baboon (a grass-eating ape that lives in the highlands of Ethiopia). The results showed that Theropithecus species almost exclusively ate C4 plants, similar to the diets of the modern gelada baboons.
In a recently published review article, the authors hypothesized that large brains and upright walking are two of the main factors that distinguish humans from other primates. However, a third significant factor in distinguishing humans from other apes may be a shift in diet from leaves to grasses. As ancient hominims left the forests and ventured into new habitats such as grasslands, they had access to more diverse food sources than found in forests (where most primates have stayed). Researchers are just beginning to understand what ancient humans ate, and these recent studies show that grasses and grains have been part of the human diet for millions of years.
Coincidentally, in a recent article in Scientific American researchers described how chimpanzees eat in the wild. As a bit of background, chimps and bonobos (subtribe Panina), diverged from the line that lead to humans about 5-6 million years ago, and also shares about 97% of genetic material with humans. So they can be used as a proxy to human dietary preferences in the wild, though with a few million years of intervening evolution, including the move to the grasslands. But they can be a “crude measure” of our ancient diets, prior to the move to a C4-based diet.
A study by David Watts of the chimpanzee diet in the Kibale National Park in Uganda provided some detailed analysis of their diet in the wild:
- Diversity—The Kibale chimpanzees consumed around 102 species (and possibly many more) of plants either in the form of fruit or leaves. I don’t mean to be picky, but how many species of plants are in your local Whole Foods? And 20 different varieties of apples is still one species of apple. Human ancestors, in a planet with limited food resources, probably were just as fungible with their choices in plant foods as chimps. Modern humans just aren’t.
- Figs—Nearly half of all of the food consumed by chimps appears to be one or another kind of fig, fruit of the Ficus trees. Fig trees produce large amounts of fruit that are favored by a number of animals including most primates (including gorillas and many human cultures) and fruit bats. They are highly nutritious and contain a lot of energy, and have a wide number of ecological niches so that it would be distributed throughout the chimpanzee habitat. Early humans would have also found figs throughout their habitats in Africa, and figs were domesticated about 10,000 years ago, and have been a significant part of human agriculture in certain societies. It’s clear that along with increasing the number of plant varieties in our diet, we need to seriously increase the quantities of figs.
- Clumps—Chimps eat a wide variety of fruit throughout the year, but only eat one or two species of fruit at one time. So they might eat apples one day then oranges the next. So, they may eat what is “in season” or what is available. Many plants fruit seasonally, or even just for a few days, so the chimps eat what is available. There are a few continually fruiting plants, but they are rare, even in the tropics, so the chimps choose what is available.
- Meat–Although we focused on fruits and plant foods, chimps do eat meat, and are considered omnivores, just like their closely related cousins, humans. Chimps favor eating seven kinds of primates, including their favorite, red colobus monkeys along with three other mammal species. However, only 3% of the average chimp diet comes from meat. Given the availability of high energy plant foods, the energy expenditure required to acquire mammalian food probably is too high unless it’s easily obtained.
- Variety—One of the myths of our ancestral diets is that our ancestors ate some imagined ideal diet for their bodies. The observation of the chimp diet is that there isn’t an ideal diet, and they eat what they find. Even though figs are a significant portion of their diet, when they find no figs, they don’t eat figs, and change to something else. Some chimps eat more mammal meat than others, if that meat is available, not because of some evolutionary advantage to do so. The authors determined that although some species must eat a specific mix of foods to survive; chimps (and man) are not one of those species.
- Termites and ants (and their chitin)—Some chimps are good at eating termites, honey bees and driver ants. It’s unclear if chimps have any special ability to digest the chitin (exoskeleton of insects), but insects do have a lot of energy content. Again, chimps seem to have a broad choice in foods, and eat almost anything that is available.
- Other–Chimps at Kibale ate dirt. Gorillas eat wood and the occasional stone. What we might assume is not food seems to be food for the apes of the Kibale National Park. So, if you want to have an ancestral diet, apparently you have to open your mind to food sources that aren’t just plants and animals.
Before we head to the conclusions from this article, one thing is important-figs. Really, we almost have to wonder if primates would not have evolved without figs. That fruit is a critically important part of the chimpanzee diet, and, given the ubiquity of the plant, we must presume that it was also critical to early Hominims that evolved into modern humans. Figs were domesticated for agriculture fairly early in modern human history, so it must have some importance.
The article makes a cogent argument against making any conclusion about what the “ancestral diet” might have been:
…and that eating some ancestral diet on its own will not make us healthy. Our ancestors did not eat diets perfectly in tune with their body. Rather, they took the best advantage of the foods around them they could in light of their bodies which, like ours, were whittled by evolution out of more ancient forms and so flawed, complicated, and filled with tradeoffs.
The paleolithic diet itself probably has no more validity than any other diet (lots of anecdotal evidence of success, and no actual scientific clinical studies). The problem is that there is little evidence that ancient humans, hominins and other great apes ate a particular diet. Clearly, their diet probably was in response to a huge seasonal, annual and longer duration environmental variability in food sources. Keep in mind that we haven’t even considered the difference in food sources over the planet from Arctic tundra to deserts. But more than anything, is there any evidence that paleolithic humans lived longer or healthier than modern humans? Well, actually the Paleolithic lifespan was around 33 years, whereas modern man is around 67 years (varying from country to country). In other words, despite what many consider to be a terrible modern diet, we’re living longer (which is a result of a lot of things including hygiene, sanitation, medicines, vaccinations, and probably, better nutrition).
So while there remains little doubt that many modern humans eat too much sugar and processed foods, the studies presented in this article provide strong evidence that it’s impossible to define a “paleo diet”, that our ancestors shifted to grains (a no-no in the paleo diet faith) millions of years ago, and humans are intelligent, so obtained whatever food sources were handily available. Our bodies are what they are, thanks to millions of years of evolution. There is little you can do to your body with food (except for those figs, I suppose), so you take advantage of what food is available to you. You’re not going to live longer if you eat something or another. You’re not going to prevent or cure cancer. Don’t eat more than you burn is about the best advice you’re going to get.
Whether a “paleo diet” can cause you to lose weight or can provide better nutrition is another topic of discussion for another time. But if you think that a paleo diet represents some idealized diet of our evolutionary ancestors, it doesn’t. It’s an invented diet (again, irrespective of it’s actual clinical usefulness), and imparting some greater characteristic than that is not very scientific.
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