Clearly one of the most important features distinguishing humans from all other mammals is the size of our brain in comparison to the rest of our body. While it is certainly true that other mammals have larger brains, scientists recognize that larger animals must have larger brains simply to control their larger bodies. An elephant, for example, has a brain that weighs 7500 grams, far larger than our 1400 gram brain. So making comparisons about “brain power” or intelligence just based on brain size is obviously futile. Again, it’s the ratio of the brain size to total body size that attracts scientist’s interest when considering the brain’s functional capacity. An elephant’s brain represents 1/550 of its body weight, while the human brain weighs 1/40 of the total body weight. So our brain represents about 2.5 % of our total body weight as opposed to the large brained elephant whose brain is just 0.18% of its total body weight.
But even more important than the fact that we are blessed with a lot of brain matter is the intriguing fact that gram for gram, the human brain consumes a disproportionately huge amount of energy. While only representing 2.5% of our total body weight, the human brain consumes an incredible 22% of our body’s energy expenditure at rest. This represents about 350% more energy consumption in comparison to body weight compared to other anthropoids like gorillas, orangutans and chimpanzees.
So it takes a lot of dietary calories to keep the human brain functioning. Fortunately, the very fact that we’ve developed such a large and powerful brain has provided us the skills and intelligence to maintain adequate sustenance during times of scarcity and to make provisions for needed food supplies in the future. Indeed the ability to conceive of and plan for the future is highly dependant upon the evolution not only of brain size, but other unique aspects of the human brain.
It is a colorful image to conceptualize early Homo sapiens migrating across an arid plain amongst carrion of animals less able to survive as they lacked our advantageous clever brain. But our earliest ancestors had one other powerful advantage compared to even our most closely related primates. The human brain has developed a unique biochemical pathway that proves hugely advantageous during times of food scarcity. Unlike other mammals, our brain is able to utilize an alternative source of calories during times of starvation. Typically, we supply our brain with glucose provided by our daily food consumption. We continue to supply our brains with a steady stream of glucose (blood sugar) between meals by breaking down glycogen, a storage form of glucose primarily in the liver and muscles. But relying on glycogen stores provides only short term availability of glucose. As glycogen stores are depleted, our metabolism shifts and we are actually able to create new molecules of glucose, a process aptly termed gluconeogenesis. Gluconeogenesis involves the construction of new glucose molecules from amino acids harvested from the breakdown of protein primarily found in muscle. While this adds needed glucose to the system, it does so at the cost of muscle breakdown, something less than favorable for a starving hunter-gatherer.
But human physiology offers one more pathway to provide vital fuel to the demanding brain during times of scarcity. When food is no longer available, after about 3 days, the liver begins to use body fat to create chemicals called ketones. One ketone in particular, beta hydroxybutyrate (beta-HBA), actually serves as a highly efficient fuel source for the human brain, allowing humans to function cognitively for extended periods during food scarcity. Our unique ability to power our brains using this alternative fuel source helps reduce our dependence on gluconeogenesis and therefore spares amino acids, and the muscles from which they are derived. Reducing muscle breakdown provides obvious advantages for the hungry Homo sapien in search of food. It is this unique ability to utilize beta-HBA as a brain fuel that sets us apart from our nearest animal relatives and has allowed humans to remain cognitively engaged and therefore more likely to survive the famines ever present in our history.
This metabolic pathway, unique to Homo sapiens, may actually serve as an explanation for one of the most hotly debated questions in anthropology, the disappearance of our Neandertal relatives. Clearly, when it comes to brains, size does matter. Why then, with a brain some 20% larger than our own, did Neandertals suddenly disappear in just a few thousand years between 40,000 and 30,000 years ago? The party line among scientists remains fixated on the notion that the demise of Neandertals was a consequence of their hebetude. As William Calvin described Neandertals in his book,
A Brain for All Seasons, ” Their way of life subjected them to more bone fractures; they seldom survived until forty years of age; while making tools similar to overlapping species, there was little inventiveness that characterizes behaviorally-modern Homo sapiens (p306).
While it is convenient and almost dogmatic to accept that Neandertals were “wiped out” by clever Homo sapiens, many scientists now believe that food scarcity may have played a more prominent role in their disappearance. Perhaps the simple fact that Neandertals, lacking the biochemical pathway to utilize beta-HBA as a fuel source for brain metabolism, lacked the “mental endurance” to persevere. Relying on gluconeogenesis to power their brains would have led to more rapid breakdown of muscle tissue ultimately compromising their ability to stalk prey or migrate to areas where plant food sources were more readily available. Their extinction may not have played out in direct combat with homo sapiens but rather manifested as a consequence of a simple biochemical inadequacy.
Our ability to utilize beta-HBA as a brain fuel is far more important than simply a protective legacy of our hunter-gatherer heritage. As Harvard Medical School professor George F. Cahill stated, “Recent studies have shown that beta-hydroxybutyrate, the principal “ketone” is not just a fuel, but a “superfuel” more efficiently producing ATP energy than glucose… It has also protected neuronal cells in tissue culture against exposure to toxins associated with Alzheimer’s or Parkinson’s” (Trans Am Clin Climatol Assoc. 2003; 114:149-61; discussion 162-3. Ketoacids? Good medicine? Cahill GF Jr, Veech RL).
Indeed, well beyond serving as a brain “superfuel,” Dr. Cahill and other researchers have determined that beta-HBA has other profoundly positive effects on brain health and function. Essentially, beta-HBA is thought to mediate many of the positive effects of caloric restriction and fasting on the brain including improved antioxidant function, increase in mitochondrial energy production with increase in mitochondrial population, increased cellular survival, and increased levels of BDNF leading to enhanced growth of new brain cells (neurogenesis).
"I fast for greater physical and mental efficiency.” –Plato (428-348 B.C.)
Clearly, the idea of substantially reducing your daily calorie intake will not appeal to many people, despite the fact that it is a powerful approach not only to brain enhancement, but for overall health as well.
What seems to be more appealing to most people is the idea of intermittent fasting. That is, a complete restriction of food for a defined period of time at regular intervals. Research has clearly demonstrated that many of the same health providing and brain enhancing genetic pathways activated by caloric restriction are similarly engaged by fasting, even for relatively short periods of time.
Not only does fasting turn on the genetic machinery for the production of BDNF, but the Nrf2 pathway is also powered up, leading to enhanced detoxification, reduction of inflammation, and increased production of brain-protective antioxidants. Fasting causes the brain to shift away from using glucose as a fuel to a metabolism that consumes a special type of fat, manufactured in the liver called ketones. When the brain is metabolizing ketones as a fuel, even the process of cell suicide (apoptosis) is reduced, while mitochondrial genes are turned on leading to mitochondrial replication. Thus fasting shifts the brains basic metabolism and specifically targets the feminine DNA of mitochondria enhancing energy production and paving the way for not only better brain function and clarity, but also a deeper connection with the divine healing feminine energy.
As my colleague Gabriel Cousins explained,
"I often observe in fasting participants that concentration seems to improve, creative thinking expands, depression lifts, insomnia stops, anxieties fade, the mind becomes more tranquil, and a natural joy begins to appear. It is my hypothesis that when the physical toxins are cleared from the brain cells, mind-brain function automatically and significantly improves, and spiritual capacities expand." –Gabriel Cousens, M.D. (Founder, Tree Of Life Rejuvenation Center, Patagonia, AZ)
The expansion of spiritual capacities referred to by Dr. Cousens is a manifestation of the opening of the gates to the divine universal energy by the expansion of mitochondrial number and function brought about by the shift in brain metabolism that fasting imparts. It is through this functionally enhanced and increased population of mitochondria that the eternal energy is imbibed into our being. As Paramahansa Yogananda eloquently put it in his collection of essays entitled, Man’s Eternal Quest. "Through fasting, let your mind depend on its own power. When that power manifests, the life force in the body becomes increasingly reinforced with the eternal energy continually flowing into the brain and spine from the cosmic energy around the body…”
Indeed the utility of fasting in spiritual quests is an integral part of the human religious history. All major religions to this day retain fasting as far more than simply a traditional ceremonial act. It remains a fundamental part of the spiritual practice to gain enlightenment as in the Muslim fast of Ramadan and the Jewish fast of Yom Kippur. Yogis practice austerity with their diets and shamans fast during their vision quests.
Father Thomas Ryan, Director of the Catholic Paulist Society's North American Office for Ecumenical and Interfaith Relations summarized the gifts offered by fasting by stating, "Fasting as a religious act increases our sensitivity to that mystery always and everywhere present to us. It is an invitation to awareness, a call to compassion for the needy, a cry of distress, and a song of joy. It is a discipline of self-restraint, a ritual of purification, and a sanctuary for offerings of atonement. It is a wellspring for the spiritually dry, a compass for the spiritually lost, and inner nourishment for the spiritually hungry."
"Fasting is the master key to mental and spiritual unfoldment and evolution."–Dr. Arnold Ehret (1866-1922; German Father of Naturopathy, a.k.a. Naturopathic Medicine)
Image by moosold9, courtesy of Creative Commons license.