Our Paleolithic ancestors were remarkably well-adapted to their environment. As nomadic hunter-gatherers, hundreds of thousands of years of evolution perfected their metabolism to endure extended periods searching for food and ensuring survival. They were perfectly adapted to function at high levels, both physically and cognitively, despite being in a food-deprived state. Modern humans also benefit from this evolutionary adaptation. However, cultural and societal norms regularly prevent us from realizing it. The continuous consumption of carbohydrate-rich processed foods means we face a problem our bodies have not evolved to overcome. Caloric excess, obesity, and obesity-related health issues now prevail rather than scarcity of food and potential starvation. Recent studies regarding intermittent fasting show that physiological similarities between modern and Paleolithic humans may be the key to overcoming our current dietary consequences.
12,000 Years BC (Before Cheeseburgers)
The human body continually seeks a state of homeostasis, a balance when all systems perform most efficiently. To maintain homeostasis and survive extended periods without food, it evolved a sophisticated system that signals when to eat, when to stop eating, how to process and store energy from a variety of food sources, and when to enter a state of self-healing.
The slight discomfort and growling stomach we experience, called somatic hunger, signals when to eat. Ghrelin, a hormone produced in the stomach, and nerve signals provide the physical sensation of somatic hunger. It is similar to the reminder to pull your hand out of hot water before it burns. However, rather than debilitating pain, somatic hunger evolved to serve as a gentle reminder that allowed ancient hunters to focus on the hunt.
Your “sweet tooth,” called limbic hunger, is also triggered by ghrelin and is an ancestral carryover to encourage the consumption of specific foods like fruits and vegetables for vitamins and nutrients. Limbic hunger ensured primitive humans ate as much food as possible while it was available. Leptin, a hormone secreted by adipose (fat) tissue, signals the body to stop feeding when it is satiated.
After a meal, the digestive tract converts food into glucose, the raw material the human body uses most readily. The pancreas produces insulin which signals cells to absorb glucose and convert it to fuel for immediate use or to glycogen and fatty acids for storage. The amount of insulin produced depends on the meal’s composition, the number of carbohydrates consumed, and the body’s sensitivity to insulin (8).
Three to four hours after eating, the body enters a fasting state that lasts up to eighteen hours. During this state, the body depletes glycogen stores, insulin levels decline, and a process called lipolysis begins. During lipolysis, fat cells are broken down into smaller molecules to be used as an alternative fuel source (8).
After 18 hours, when all glycogen is depleted, a metabolic switch occurs where the body enters a state of ketosis and solely utilizes fat stores. The body also enters a state of self-healing called autophagy. Autophagy is a process of homeostasis when the body removes and recycles old or dysfunctional cells to make new cells. Limited research suggests that autophagy may play a key role in preventing or treating cancer since all cancers start from defective cells (7). This evolutionary trait would seem to suggest that the scarcity of food our Paleolithic ancestors endured was actually beneficial.
The domestication of livestock and agriculture that defines the Neolithic era meant humans no longer needed to expend so much energy sourcing their next meal. Farming eliminated food scarcity and created a surplus of foods higher in carbohydrates from wheat, corn, and potatoes. Unfortunately, the new diet, combined with the new-found sedentary, agrarian lifestyle, exacerbated new diseases and significantly shortened lifespans. While Paleolithic humans enjoyed an average of 35 years, subsequent generations only averaged 25–30 years or less. Humans wouldn’t enjoy longer lifespans again until the early 19th century.
Compared to our ancient ancestors, Americans enjoy a near-limitless food supply with minimal effort required to obtain it. Processed foods, intended initially to feed soldiers, gained incredible popularity in kitchens across the United States during the Great Depression. Convenient canned and pre-packaged foods augmented or replaced fresh-made meals despite being nutritionally inferior. The industrialization of food contributed to the concurrent meteoric rise in fast food popularity. Whole meals no longer needed to be diligently prepared; people could enjoy ready-made meals with the least amount of effort. However, the convenience and availability of processed foods comes with a steep price to our health today.
Besides being nutritionally inferior to their fresh-made counterparts, processed foods laden with sodium, sugar, and refined carbohydrates, create a double-jeopardy when consumed. Refined carbohydrates from processed and fast food cause insulin to rise and stay elevated. At the same time, the absence of nutrients ensures the body does not stay satiated for long. Research also suggests that some additives found in processed food, such as monosodium glutamate (MSG), cause the brain to ignore leptin signals, thereby urging consumption of yet more processed foods (6). The uninhibited presence of insulin leads to insulin resistance and keeps the body in a constant fat storage state. Insulin resistance means the body doesn’t react as efficiently to insulin, doesn’t convert glucose into ATP as effectively, and allows glucose in the bloodstream to rise unabated. This vicious cycle is known as type-2 diabetes.
Our stress response, which is also an evolutionary holdover, operates on a feedback loop. The extended presence of glucose in the bloodstream triggers elevated blood pressure, leading to metabolic syndrome. Metabolic syndrome is the combination of obesity, insulin resistance, and high blood pressure. It is a significant risk factor for heart disease, heart attack, and heart failure (12). Studies link obesity and metabolic syndrome with higher incidences of colon cancer, liver cancer, multiple myeloma, non-Hodgkin’s lymphoma, gallbladder cancer, pancreatic cancer, leukemia, ovarian cancer, breast cancer, and endometrial cancer.
Research suggests that intermittent fasting can potentially prevent or correct many diseases and abnormalities, including metabolic syndrome, because it utilizes the metabolic switch acquired through hundreds of thousands of years of evolution (4).
Intermittent fasting (IF), which is the periodic and voluntary abstinence from food, has gained attention in recent years due to the numerous potential health benefits it confers. Fasting gives the body a break from processing food to attain homeostasis and focus on its repair.
Numerous studies show that, by allowing the body to enter autophagy, IF can decrease insulin levels, increased insulin sensitivity, improved glucose metabolism, improved cardiovascular health, reduced cholesterol, decreased blood pressure, reduced inflammation, and body fat reduction (2). Additionally, promising preliminary research shows IF’s effect on lowering insulin and leptin has the potential benefit of decreasing the risk of obesity-related cancers (9), congestive heart failure (5), and potentially protecting the brain against degenerative disorders like Alzheimer’s disease, Parkinson’s disease, and stroke (2). Even abstaining from carbohydrate-rich food for as little as 12 hours per day can have a lasting positive effect on weight loss and insulin resistance.
The scarcity of food necessitated that primitive humans evolve to adapt to survive. Although our environment differs drastically and we enjoy a surplus of food, modern humans are nearly identical to primitive humans genetically. As such, we are perfectly adapted to manage the scarcity of food our ancestors faced and the associated benefits. But, western society is culturally attuned to eating regularly. Modern cultural norms ensure we continuously remain in the fed state. We do not allow our bodies to flip the evolutionary switch that enables repair at the cellular level. The slightest discomfort of being hungry causes mental anguish or is considered socially unacceptable. So we rarely voluntarily abstain from food and drink except for religious reasons.
Consequently, over 42% of the US population is obese. Abstaining from food for more extended periods could be the solution to obesity and many related health issues.
Author’s note: If you’re considering fasting, please consult with your doctor or healthcare provider, particularly if you are taking any medications, are pregnant, breastfeeding, or wish to become pregnant, or have a chronic condition such as heart disease or diabetes. Fasting with any of these conditions may be hazardous or detrimental to your health.
Citations
- Abu-Taweel, G. M. (2016). Effect of monosodium glutamate and aspartame on behavioral and biochemical parameters of male albino mice. African Journal of Biotechnology , 15(15), 601–612.
- Anton, S. D., Moehl, K., Donahoo, W. T., Marosi, K., Lee, S. A., Mainous, A. G., 3rd, Leeuwenburgh, C., & Mattson, M. P. (2018). Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring, Md.), 26(2), 254–268. https://doi.org/10.1002/oby.22065
- Antoni R, Johnston KL, Collins AL, Robertson MD. Effects of intermittent fasting on glucose and lipid metabolism. Proc Nutr Soc. 2017 Aug;76(3):361–368. doi: 10.1017/S0029665116002986. Epub 2017 Jan 16. PMID: 28091348.
- Azevedo, F. R., Ikeoka, D., & Caramelli, B. (2013). Effects of intermittent fasting on metabolism in men. Revista da Associacao Medica Brasileira (1992), 59(2), 167–173. https://doi.org/10.1016/j.ramb.2012.09.003
- Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019 Apr 18;11(4):873. doi:10.3390/nu11040873. PMID: 31003482; PMCID: PMC6521152.
- He, K., Du, S., Xun, P., Sharma, S., Wang, H., Zhai, F., Popkin, B., Consumption of monosodium glutamate in relation to incidence of overweight in Chinese adults: China Health and Nutrition Survey (CHNS), The American Journal of Clinical Nutrition, Volume 93, Issue 6, June 2011, Pages 1328–1336, https://doi.org/10.3945/ajcn.110.008870
- Lindberg, S. (2018, August 23). Autophagy: What You Need to Know. Retrieved February 24, 2021, from https://www.healthline.com/health/autophagy
- Link, R., MS, RD. (2021, January 19). What Are the Different Stages of Fasting? Retrieved February 24, 2021, from https://www.healthline.com/nutrition/stages-of-fasting
- Mattson, M. P., Longo, V. D., & Harvie, M. (2017). Impact of intermittent fasting on health and disease processes. Ageing research reviews, 39, 46–58. https://doi.org/10.1016/j.arr.2016.10.005
- Mattson, M. P., & Wan, R. (2005). Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems. Journal of Nutritional Biochemistry, 16(3), 129–137. https://doi.org/10.1016/j.jnutbio.2004.12.007
- Margetic, S., Gazzola, C., Pegg, G. G., & Hill, R. A. (2002). Leptin: a review of its peripheral actions and interactions. International journal of obesity and related metabolic disorders : journal of the International Association for the Study of Obesity, 26(11), 1407–1433. https://doi.org/10.1038/sj.ijo.0802142
- Pothiwala, P., Jain, S. K., & Yaturu, S. (2009). Metabolic syndrome and cancer. Metabolic syndrome and related disorders, 7(4), 279–288. https://doi.org/10.1089/met.2008.0065