Fasting: It’s Not What You Eat, It’s How Much You Eat
We used to hunt & gather -- now we just order from DoorDash!
Tough to miss a meal when it’s all so convenient!
That’s at least part of the reason why we’re seeing obesity skyrocketing the way that it is!
We’re eating all the time, yet we’re hardly ever active!
Humans aren’t a newly formed species – we’ve been around for over 300 thousand years! When we missed meals back then it was just another day in the life! When we miss meals now it’s called fasting!
As a species that’s survived both feast & famine; clearly, we can handle going without food for a little while! But it’s not unreasonable to wonder, to what extent?
What effect does going hours to days without food have on our bodies?
Regular fasting isn’t exactly standard practice, but it is fairly common these days!
Proponents of fasting point to benefits for health & wellness, weight loss, mental acuity, and even spiritual well-being! It’s amazing to think that simply not eating would have so many benefits, but does the literature support these grand claims?
Well, if we’re starting with the obvious, regular, prolonged fasting will definitely lead to weight loss! That should go without saying – you’re not eating! Caloric restriction is the essence of weight loss; fasting is caloric restriction to the extreme! The effects on body composition have been proven in every capacity.
“…It appears that intermittent fasting programs are able to reduce body weight and body fat. Alternate-day fasting has been shown to reduce body weight [3%–7%], body fat [3–5.5 kg], total cholesterol [10%–21%], and triglycerides [14%–42%] in normal-weight, overweight, and obese humans. Reductions in LDL and blood pressure and increases in LDL particle size have also been seen in some, but not all, alternate-day fasting studies. Whole-day fasting has also been shown to reduce body weight [3%–9%], body fat, total cholesterol [5%–20%], and triglycerides [17%–50%]”
In the absence of exogenous, or outside, energy sources, your body starts to pull from what it already has: fat, muscle, & glycogen (stored glucose)!
One of my earliest introductions to scientific literature was through the work of George Cahill – a human metabolism & diabetes expert, prominent in the mid to late 20th century. Cahill led a number of fasting experiments that were taken to a level that we’ll likely never see again! In a 1967 study completed with Dr. Oliver Owen, three obese subjects were taken through a fast of 38 to 41 days, ingesting only a Unicap multivitamin, 17 mEq of Sodium Chloride (salt), and 1500 ml of water each day!
41 days! And you can’t skip breakfast?!
In his later work, Cahill was able to outline 5 metabolic stages of a prolonged fast, detailing the amount of glucose used, where it comes from, & where in the body it’s utilized for every hour one goes without food! Glucose, of course, being our primary energy source!
The five metabolic stages between the postabsorptive state and the near-steady state of prolonged starvation (Cahill; 2006)
All that to say, we’ve found that our bodies are pretty good at making things work! We’re built to do a lot with a little but nobody eats a little anymore!
Our modern eating habits are even more unfortunate when we consider that most of the noted benefits of fasting really are borne out by the literature!
In their 2020 study looking at protein signaling & cell responses in subjects fasting for Ramadan, Mindikoglu et. al found that intermittent fasting for 30 days from dawn to sunset may be preventive against cancer, dementia, Alzheimer’s, and metabolic disease, as well as inflammatory & immune diseases!
A graphical abstract representing Mindikoglu et. al's Ramadan study published in 2021
The research is very much in agreement that due to its effects on cell metabolism, fasting can bring about some pretty impressive changes in your general health! Specifically, fasting leads to increased autophagy, or self-eating, a recycling process for cells that allows the replacement of old, worn out parts for healthy, new ones.
For the noted reasons, it’s hypothesized that fasting is able to improve cognition both transiently & in the long-term, slowing down age-related cognitive decline! It’s not quite proven yet in humans, but it has been shown in animal models!
“Fasting improves cognition and prevents cognitive decline in non-neurodegenerative animal models. Rodents on fasting regimens display enhanced cognitive performance compared to those fed ad libitum. TRF (Time-restricted feeding) stalls age-related declines in brain white matter integrity, energy production, and cognition observed in rodents fed ad libitum. Mice maintained on TRF also show increased hippocampal BDNF (brain-derived neurotrophic factor) levels, synaptic strength, and neurogenesis’...”
So, if you were looking for a sign to start fasting, here it is!
When done right, the occasional fast is a huge game changer! Coupled with adequate resistance training, you’ll see minimal loss of muscle mass as well (Keenan, Cooke, & Belski; 2020)! It’s a body composition cheat code that can extend your life & boost your cognitive function!
There’s a lot of good & very little bad; that being said, fasting isn’t for everyone. For those that are pregnant, very old, or very young, it’s probably best to continue the regularly scheduled meals! Definitely consult with your trusted healthcare providers to be safe, and you should always be safe!
It’s easy to forget what being hungry feels like these days; we’d all benefit from the occasional reminder!
Works Cited & Further Reading
Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition reviews, 73(10), 661–674. https://doi.org/10.1093/nutrit/nuv041
Owen, O. E., Morgan, A. P., Kemp, H. G., Sullivan, J. M., Herrera, M. G., & Cahill, G. F., Jr (1967). Brain metabolism during fasting. The Journal of clinical investigation, 46(10), 1589–1595. https://doi.org/10.1172/JCI105650
Cahill G. F., Jr (2006). Fuel metabolism in starvation. Annual review of nutrition, 26, 1–22. https://doi.org/10.1146/annurev.nutr.26.061505.111258
Mindikoglu, A. L., Abdulsada, M. M., Jain, A., Choi, J. M., Jalal, P. K., Devaraj, S., Mezzari, M. P., Petrosino, J. F., Opekun, A. R., & Jung, S. Y. (2020). Intermittent fasting from dawn to sunset for 30 consecutive days is associated with anticancer proteomic signature and upregulates key regulatory proteins of glucose and lipid metabolism, circadian clock, DNA repair, cytoskeleton remodeling, immune system and cognitive function in healthy subjects. Journal of proteomics, 217, 103645. https://doi.org/10.1016/j.jprot.2020.103645
Phillips M. C. L. (2019). Fasting as a Therapy in Neurological Disease. Nutrients, 11(10), 2501. https://doi.org/10.3390/nu11102501
Keenan, S., Cooke, M. B., & Belski, R. (2020). The Effects of Intermittent Fasting Combined with Resistance Training on Lean Body Mass: A Systematic Review of Human Studies. Nutrients, 12(8), 2349. https://doi.org/10.3390/nu12082349
Wilhelmi de Toledo, F., Grundler, F., Sirtori, C. R., & Ruscica, M. (2020). Unravelling the health effects of fasting: a long road from obesity treatment to healthy life span increase and improved cognition. Annals of medicine, 52(5), 147–161. https://doi.org/10.1080/07853890.2020.1770849
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
