The Intermittent Fasting Diet

By Jonathan Jones

Section 1: What is the Intermittent Fasting Diet?

Section 2: What Do the Studies Show?

Section 3: References

Section 1: What is the Intermittent Fasting Diet?

What if I told you that the secret to dieting is to eat essentially eat whatever you please, but only in a certain time window? That’s right. You have the freedom to eat all the foods that you love, but the catch is that you can only eat them inside a certain time interval. The process that I have just explained can be summed up into one simple term: intermittent fasting. Throughout the years, we as humans have developed many different types of intermittent fasting. A common intermittent fasting practice is time-restricted feeding, or also known as the the 16/8 intermittent fast, which is where you fast for 16 hours every day and only eat during an 8-hour time interval each day (Moodie 2019). Another common practice of intermittent fasting is alternate-day fasting. This is where you alternate between 24-hour intervals of feeding and fasting (Stiehl 2018).

It is universally understood that an unhealthy diet can increase your risk of obesity, heart disease, cancer, stroke, diabetes, and many other diseases. The understanding of this comes from the different physiological and metabolic effects that a diet can have on your body. You might see a lot of false presentations in the world regarding different diet plans and what you should do to improve your life through diet. However, many “cure-all” diet plans have been debunked after a little bit of research has been done about their true effects on our metabolism and other processes within the body. The goal of this blog is to provide you with some insight into what intermittent fasting is and some findings from previous research on its effects. For this blog, I focused on the effects of both alternate-day fasting and time-restricted feeding.

(Back to the Top)

Section 2: What Do the Studies Show?

Let’s start with the effects that intermittent fasting has on weight loss. Weight loss is likely the first thing that comes to someone’s mind when thinking about which diet plan to choose, and rightfully so. Luckily, numerous studies have shown that intermittent fasting has a positive effect on weight loss. A 10-week long study on alternate-day fasting in 16 obese participants had astounding results. The study consisted of three phases: a 2 week control phase, a 3 week alternate day fasting period with controlled food intake, and a 3 week alternate day fasting period without controlled food intake (eating whatever your heart desires). The average weight loss after this study was 5.8%, and the average pre- and post-study BMI calculations dropped from 33.7 kg/m2 to 29.9 kg/m2, respectively (Varady et al 2009). Another study that I found was a comparison between a normal calorie restriction diet (25% energy restriction daily) and an alternate-day fasting regimen. After a 3-month period, the average weight loss found between both diets was similar (Zubrzycki et al 2018). However, the intermittent fasting group had a higher fat mass reduction and lesser lean body mass reduction as compared to the normal calorie restriction group (Zubrzycki et al 2018). This might be seen as a healthier way to lose weight because you are conserving your lean body mass which is desirable! Furthermore, an 8-week intermittent energy restriction study consisting of 26 obese participants had an average weight loss of 9% (Antoni et al 2017).

I could continue providing you with data on how much weight loss has been observed with intermittent fasting studies, but I think you get the point. Even though weight loss is very important, it is not the only thing that needs to be brought up and researched in a diet plan. We need to consider other factors of the diet such as its impact on biomarkers. Some important biomarkers to consider with a diet plan is the diet’s effect on your cholesterol levels, hormone levels, blood glucose levels, and many others. With regards to cholesterol levels, there has been quite a bit of contradicting results from the research that I looked into, but at the same time some studies have shown significant improvements in cholesterol levels. An 8-week alternate-day fasting study consisting of 26 obese participants resulted in reductions in LDL cholesterol (Antoni et al 2017). However, another 8-week study on time-restricted feeding showed increases in LDL cholesterol (Antoni et al 2017). Given these polar opposite findings, I needed to find more research on intermittent fastings effect on cholesterol, specifically LDL. One analysis of a few intermittent fasting studies showed that a 22-day alternate-day fasting regimen resulted in an increase in HDL, LDL, and triglyceride levels, but an 8-week time-restricted feeding study showed improved HDL/LDL ratio (Patterson et al 2015). Again, very contradicting results, but the two different studies were significantly different in length and the amount of time spent fasting. Nonetheless, an analysis by the American Heart Association of 10 different short-term intermittent fasting studies showed a decrease in LDL levels ranging from 7% to 32% (Tinsley & Horne 2018). This is significant in my opinion. From these results discussed above, there are many things that need to be considered for explaining the mixed results. In my opinion, these differences likely came from the different baseline LDL levels and the different food groups the participants were eating. Remember, many of these intermittent fasting studies allowed the participants to eat as they pleased during feeding times, and the foods you decide to eat can have an impact on your LDL cholesterol. Therefore, though not completely necessary, you might want to still watch what you eat if you decide to proceed with intermittent fasting.

What about diabetes? It is well known medically that what you eat may put you at risk for developing diabetes, which is a condition where your blood glucose levels are elevated due to your body not being able to store blood glucose properly (Medline). It is also important to realize that your diet has a significant impact on the management of your diabetes (Medline). An important component to think about with treatment or management of diabetes is the level of resistance to insulin, or insulin sensitivity, in the body. When our insulin resistance is high, we have a low sensitivity to insulin and we are unable to store a significant amount of glucose from our blood because we are not responding to the insulin sufficiently and we therefore end up with elevated blood glucose levels (Medline). A 2-week study involving 10 healthy participants fasting for 20 hours every other day resulted in an increased insulin sensitivity (Halberg et al 2005). However, in an identical cross-over study with 8 participants four years later, no significant change in insulin sensitivity was observed (Soeters et al 2009). It is important to note that there were a low number of participants in these studies and they were also healthy at baseline, which likely contributed to the no change in insulin sensitivity seen in the cross-over study. Now let’s look at how intermittent fasting can impact blood glucose concentrations. One 8-week alternate-day fasting study showed improvements in blood glucose concentrations in individuals with diabetes, and no significant changes in blood glucose concentrations in individuals without diabetes (Antoni et al 2017). It is important to realize that these findings show that having baseline hyperglycemia can be reversed simply by intermittent fasting. This could potentially make for a strong dietary component for treatment of diabetes, and could lead to decreased medication dosages or even straying away from medications all together.

Surprisingly, what you eat can also have an impact on the amount of hormones circulating through your bloodstream. A specific hormone that I would like to discuss is a stress hormone called cortisol. Cortisol has many important functions in the body including raising blood glucose levels at certain times when needed, but persistent elevation of cortisol can be detrimental (Hormone Health Network). Prior research that I found on the association between cortisol and intermittent fasting involved measuring serum cortisol levels before and after a 5-day fast. Yes, 5 days without food. The results of the study showed that serum cortisol levels almost doubled after a 5-day fast (Vance and Thorner 1989). This finding is interesting, however, it is not exactly surprising given that going 5 days without food would likely cause a stress response in your body. I feel that the authors should have provided data regarding how serum cortisol levels were altered each day during the 5-day fast. By providing us with this data, it would help show at what point a time of fasting becomes too long and induces too much of a stress response. The finding that serum cortisol concentrations almost doubled after a 5-day fast demonstrates that prolonged periods of fasting can actually induce a stress response and alter your cortisol levels, which can be deleterious so be careful when fasting. Further research on how much of an increase in cortisol there is during a short period of time restricted feeding or alternate day fasting is necessary. All in all, I think that you would be safe from having too much of a harmful cortisol level when alternate day fasting or with time restricted feeding as you are not going five days without food!

There is a strong genetic component to cardiovascular disease (CVD), however, the risk or effects of CVD can be reduced or even prevented through diet. The American Heart Association decided to dive into the research behind intermittent fasting and its effects on the biomarkers associated with CVD. 10 different short-term alternate day fasting studies showed decreased total cholesterol levels (6-21%), decreased triglyceride levels (16-42%), decreased in LDL levels (7-32%), and decreased blood pressure (Tinsley & Horne 2018). These findings for the short-term study are stunning, as decreases in all of these biomarkers significantly reduces your risk for CVD. However, the American Heart Association went even further and looked at the effects of long-term alternate day fasting studies. A year-long alternate day fasting study tht they looked at showed no changes in HDL levels but also showed an increase in LDL levels at the end of the year (Tinsley & Horne 2018). The American Heart Association concluded that long-term alternate day fasting was not as beneficial as short-term alternate day fasting due to the differences in cholesterol levels seen between the two (Tinsley & Horne 2018). Based on the research by the American Heart Association, I also recommend proceeding with short-term intermittent fasting rather than long-term if your desire is to lower your risk for CVD.

A specific cardiac disease that has been studied with intermittent fasting is cardiomyopathy. Desmin-related cardiomyopathy is caused by a buildup of misfolded proteins in muscles of the heart (Mukai, Zablocki, Sadoshima 2019). Autophagy is a process in the human body that consists of destroying unwanted things such as tumor cells, misfolded proteins, other unwanted buildups, or even organelles that are not functioning properly (Mukai, Zablocki, Sadoshima 2019). Research has shown that intermittent fasting actually activates genes that code for the autophagy-lysosome system in the heart, which can counteract the effects of cardiomyopathy (Mukai, Zablocki, Sadoshima 2019). By increasing the amount of autophagy in the heart, the body is able to get rid of these misfolded protein aggregations which can lead to higher blood flow to the heart and a lower the risk for damage.

Another disease that intermittent fasting has had substantial effects on is cancer. Cancer, just like CVD, has a strong genetic component, but there are other factors that contribute to your risk of cancer, including your diet and other lifestyle habits. Previous research has shown that intermittent fasting likely has a beneficial impact on cancer. Activating these autophagy systems in the body that we previously discussed can be a useful way to treat cancer because this is another way to destroy tumor cells after they develop. It has been shown that periods of intermittent fasting can stimulate autophagy in the body and can also improve the response to chemotherapy when combined with this type of treatment (Antunes et al 2018). Furthermore and more interestingly, combining intermittent fasting with cytotoxic treatments can produce a differential stress response (Antunes et al 2018). Cytotoxic treatments essentially kill or destroy all cells in its path. However, producing a differential cell response causes healthy cells to inactivate their growth factors which helps them become less susceptible to cytotoxic treatments while cancerous cells remain vulnerable to this treatment (Antunes et al 2018).

So what have we learned from this informational blog? First, we learned that just like many other diet plans, intermittent fasting has its benefits but also has its limitations and weaknesses. The undesirable results of intermittent fasting included elevated cortisol levels and the rise in LDL levels seen with the long-term study. To try and avoid these effects, I recommend that you use intermittent fasting as a short term remedy, and also try to eat relatively healthy even though it might not be required or recommended by others. By consuming a healthy diet while intermittent fasting, you will likely avoid having this unwanted rise in LDL cholesterol levels. There are a wide variety of benefits seen with intermittent fasting. We saw that intermittent fasting is a more desirable diet plan to lose weight than the normal calorie restriction diets, because you conserve your lean body mass with fasting and lost relatively close to the same amount of weight. Additionally, intermittent fasting has the potential to significantly improve your lipid profile, blood glucose levels, and decreases risk for diseases such as CVD or cancer. Overall, intermittent fasting has its benefits, but if you do proceed with this diet regimen please keep in mind the possible unwanted effects that may arise.

(Back to the Top)

Section 3: References

Antoni, R., Johnston, K. L., Collins, A. L., & Robertson, M. D. (2017). Effects of intermittent fasting on glucose and lipid metabolism. Proceedings of the Nutrition Society,76(03), 361-368. doi:10.1017/s0029665116002986

Antunes, F., Erustes, A., Costa, A., Nascimento, A., Bincoletto, C., Ureshino, R., . . . Smaili, S. (2018). Autophagy and intermittent fasting: The connection for cancer therapy? Clinics,73(Suppl 1). doi:10.6061/clinics/2018/e814s

Diabetic Diet. (2019, February 07). Retrieved from https://medlineplus.gov/diabeticdiet.html

Diabetes: MedlinePlus Medical Encyclopedia. (n.d.). Retrieved from https://medlineplus.gov/ency/article/001214.htm

Halberg, N., Henriksen, M., Söderhamn, N., Stallknecht, B., Ploug, T., Schjerling, P., & Dela, F. (2005). Effect of intermittent fasting and refeeding on insulin action in healthy men. Journal of Applied Physiology,99(6), 2128-2136. doi:10.1152/japplphysiol.00683.2005

Cortisol | Hormone Health Network. (n.d.). Retrieved from https://www.hormone.org/hormones-and-health/hormones/cortisol

Moodie, A. (2019, February 06). The Guide to Intermittent Fasting for Beginners – A Complete Guide. Retrieved from https://blog.bulletproof.com/intermittent-fasting-guide/

Mukai, R., Zablocki, D., & Sadoshima, J. (2019). Intermittent Fasting Reverses an Advanced Form of Cardiomyopathy. Journal of the American Heart Association,8(4). doi:10.1161/jaha.118.011863

Patterson, R. E., Laughlin, G. A., Lacroix, A. Z., Hartman, S. J., Natarajan, L., Senger, C. M., . . . Gallo, L. C. (2015). Intermittent Fasting and Human Metabolic Health. Journal of the Academy of Nutrition and Dietetics,115(8), 1203-1212. doi:10.1016/j.jand.2015.02.018

Soeters, M. R., Lammers, N. M., Dubbelhuis, P. F., Ackermans, M., Jonkers-Schuitema, C. F., Fliers, E., . . . Serlie, M. J. (2009). Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism. The American Journal of Clinical Nutrition,90(5), 1244-1251. doi:10.3945/ajcn.2008.27327

Stiehl, C. (2018, September 13). Time Restricted Feeding vs. Intermittent Fasting: Which One Should You Do? Retrieved from https://www.msn.com/en-au/health/nutrition/time-restricted-eating-vs-intermittent-fasting-which-one-should-you-do/ar-BBNfBdH

Tinsley, G. M., & Horne, B. D. (2018). Intermittent fasting and cardiovascular disease: Current evidence and unresolved questions. Future Cardiology,14(1), 47-54. doi:10.2217/fca-2017-0038

Vance, M. L., & Thorner M. O., (1989). Fasting alters pulsatile and rhythmic cortisol release in normal man. Journal of clinical endocrinology and metabolism, 68(6), 1013-1018. doi: 10.1210/jcem-68-6-1013

Varady, K. A., Bhutani, S., Church, E. C., & Klempel, M. C. (2009). Short-term modified alternate-day fasting: A novel dietary strategy for weight loss and cardioprotection in obese adults. The American Journal of Clinical Nutrition,90(5), 1138-1143. doi:10.3945/ajcn.2009.28380

Zubrzycki, A., Cierpka-Kmiec, K., Kmiec, Z., Wronska, A. (2018). The role of low-calorie diets and intermittent fasting in the treatment of obesity and type-2 diabetes. Journal of Physiology and Pharmacology, 69(5), 663-683. doi: 10.26402/jpp.2018.5.02

(Back to the Top)