The video above is a presentation given by Dr. Miki Ben-Dor, MBA, Ph. D entitled "Man the Fat Hunter: Animal Fat Shortage as a Driver of Human Evolution and Prehistory" at the Ancestral Health Symposium in 2012. I found quite a few little nuggets in this video that I found interesting. Most countries ignore the importance of evolutionary biology in their Health/Nutrition paradigm which is a big mistake. Dr. Ben-Dor makes a pretty compelling case as to why what the past shows us is important. Dr. Ben-Dor's primary assertion is that we evolved to eat animal fat.
On the surface it seems as though it would be very difficult to prove such an assertion since it's not really a testable hypothesis given the technology we have today. It is true that, at this point, we could never prove this theory. However, you can't prove that carbohydrate is the preferred fuel source for humans either. We can make some guesses based on things we know, but at the end of the day we could never prove that. In fact, the notion that carbohydrate is our preferred fuel source is based on faulty logic discussed in the blog titled, "Myths, Metabolism, & Appetite". Yet somehow this myth continues to be repeated time and time again.
One thing that seems to run counter to Dr. Ben-Dor's hypothesis is that our closest genetic relatives, the Chimpanzee and other primates, live on a diet fairly high in carbohydrate and low in fat. However, while primates may eat a lot of vegetation high in carbohydrate, by the time it enters their bloodstream most of it is not glucose, it's fat. Dr. Ben-Dor goes on to explain that most of the energy from food on the planet is locked away in fiber we cannot digest. He explains that while we are unable to break most of this fiber down, our chimp brethren can. The gut of a primate is filled with bacteria that digest this fiber in to fatty acids such as butyric acid that gets absorbed in to circulation while our digestive systems lack this bacteria in significant amounts. In humans, some soluble fiber gets fermented in to butyric acid which is used to repair the gut lining, but other primates have a much higher capacity to do so. So while a chimpanzee's diet may not appear to provide a high amount of fat, by the time the substrate hits the bloodstream 50% is fat and only 30% is glucose/fructose. Why is this important?
Approximately 70% of the human brain is fat. We need fat to rebuild cell membranes, insulate nerve fibers, as well as a host of other processes in brain function and development. In fact, the greatest source of DHA, the most plentiful fatty acid in our brain, is human breast milk. If fat is so necessary for brain development, why would we lose some of our ability to ferment fiber in to fatty acids in our gut? Because we didn't have to.
The human genome, as well as the genome of every living thing on the planet, is constantly changing. Life forms tend to shed genes that no longer serve a purpose to them. Obviously a life form that is capable of providing a resource to itself is no longer in need of a gene that manufactures that resource. The bacteria in our gut actually serve as a secondary genome often referred to as the human microbiome. In fact, there are more genes in the bacteria in our gut than there is in the entire human genome. While the mechanism by which the human genome sheds genes is not known, understanding why we shed bacteria that make up our microbiome is as simple as understanding real estate and basic biology.
If you were to place a bowl of cat food outside of your house every night, you would eventually have some feline company. You provided a fuel source and the kitties started showing up. If you then removed the cat food and started placing a bowl of dog food on the porch, cats may show up for a couple of nights, but once the dogs start showing up there won't be a cat in sight. You would no longer be providing fuel for the cats and a competing animal would keep them away. In much the same way, a bacterial organism will make a significant presence in your gut when you provide food and an environment friendly to it's proliferation. In our gut that means real estate low in competition. When you don't provide food for that bacteria it eventually dies and gets replaced with bacteria that is being fed and, also, serving a purpose. This process, when reiterated over millions of years, will eventually remove bacteria that were once crucial for our survival. Is there any evidence that this is happening?
In a recently published study from the University of Oklahoma, scientists looked at the microbiome of ancient human fecal samples including Otzi, the well preserved remains of a man who lived 5500 years ago. The authors found that the microbiome of the remains from ancient humans more closely resembles those of non-human primates and modern hunter gatherers than those of westernized people1. They believe that our current diet as well as the widespread use of antiobitics and overuse of antiseptic practices is driving this change. Of course, now the question shifts to whether or not this change can fuel changes in health status. The authors of the study believe the change in the microbiome could be what is fueling the increase in autoimmune disease and other negative health states. It makes sense since one of the functions of the microbiome is to train the immune system, 70-80% of which is housed in your gut. Other studies looking at different health problems have found fairly good correlations between health status and changes in the microbiome.
There have been many studies showing the correlation between the gut microbiome and obesity. Specifically, in both mice and humans, changes in the amount of 2 bacterial species found in the gut, bacteroidetes and furmicutes, correlates very well with obesity. In mice, transplanting the microbiome from lean mice to obese mice results in the obese mice becoming lean. Implanting the microbiome of obese mice in to lean mice causes the lean mice to become obese2. One of the drivers of this phenomenon is that the microbiome of obese animals makes more energy available from the diet3. In humans, it is believed that this change can make 150 more calories available to the host per day. While this may seem like a small number of calories, over the course of a single year it would lead to the accumulation of 10-15lbs of weight.
The effects of the microbiome on human health don't stop there. In a study recently published in Nature Communications, researchers found that changes in the gut microbiome appear to play a role in stroke and atherosclerosis4. It has long been theorized that carotenoids play a major role in prevention of diseases of the cardiovascular system, which has lead to the use of supplements as a preventative measure with mixed results. The interesting finding of this study is that the microbiome of healthy subjects contained more bacteria that contain the genes to manufacture carotenoids than those who had suffered a stroke. This could potentially explain the mixed results seen in the use of carotenoids as a supplement for prevention of cardiovascular disease as not all carotenoids are created equal.
These are just a few of the examples where your gut microbiome affects your health. In my opinion, the future of health and medicine is in manipulating the microbiome to provide a truly symbiotic relationship between host and symbiont. In order to do this effectively, we need to look at not only evolution as it pertains to the human genome, but also the evolution of our partners in the gut. It seems, based on Dr. Ben-Dor's video and evidence from these studies, that the evolution that is occurring in our gut is happening at a much faster rate than the evolution happening to our bodies and the evolution of the bacteria in the gut is driving evolution of our bodies. This mismatch in evolutionary symbiosis may be one of the primary drivers of poor health seen today. This can be particularly problematic when bacteria that were once used to manufacture a resource that we need are selected away because we provide that resource directly through diet and then stop providing it as is the case in the modern era of fat phobia.
References
1Raul Y. Tito, Dan Knights, Jessica Metcalf, Alexandra J. Obregon-Tito, Lauren Cleeland, Fares Najar, Bruce Roe, Karl Reinhard, Kristin Sobolik, Samuel Belknap, Morris Foster, Paul Spicer, Rob Knight, Cecil M. Lewis. Insights from Characterizing Extinct Human Gut Microbiomes. PLoS ONE, 2012; 7 (12): e51146 DOI: 10.1371/journal.pone.0051146
2Vaibhav Upadhyay, Valeriy Poroyko, Tae-jin Kim, Suzanne Devkota, Sherry Fu, Donald Liu, Alexei V Tumanov, Ekaterina P Koroleva, Liufu Deng, Cathryn Nagler, Eugene B Chang, Hong Tang, Yang-Xin Fu. Lymphotoxin regulates commensal responses to enable diet-induced obesity. Nature Immunology, 2012; DOI: 10.1038/ni.2403
3Peter J. Turnbaugh, Ruth E. Ley, Michael A. Mahowald, Vincent Magrini, Elaine R. Mardis & Jeffrey I. Gordon. An obesity-associated gut microbiome with increased capacity for energy harvest. Nature, 2012. 444, 1027-1031.
