Fasting, or intermittent fasting, is a dietary approach in which one refrains from consuming any calorie-containing foods and beverages for a certain period of time.
The most well known form Intermittent fasting is known as the “16/8”, in which one eats during a chosen 8 hour window, and fasts for the remaining 16 hours of the day. The popularity of the 16/8 diet is likely owed to claims that it’s easy to follow, convenient, and a generally effective way to lose weight while improving overall health.
While there is a large body of knowledge on calorie restriction, scientists and fitness enthusiasts have much to learn about how the 16/8 diet can help improve human health. However, there are a few legitimate reasons that may explain how a 16/8 dietary pattern can be beneficial.
The first reason is the circadian rhythm. Many, if not most, of our body’s organs and bodily processes follow an approximate 24-hour circadian rhythm based on the cycle of the sun. This is basically a fancy way of saying that your bodily functions change as the day goes on and then starts over the next day.
We evolved to have changes in bodily processes to conserve energy during certain times of the day to maximize our chances of survival. For example, during the daytime (when we eat), certain pathways related to digestion increase whereas at night (when we should be sleeping) those pathways decrease(1,2,3). Think of it like this - when you are sleeping, so are the processes related to digestion.
Many studies have shown that disruptions to our circadian rhythm can increase one’s risk for insulin resistance, hypertriglyceridemia, high blood pressure, increased weight gain, among others(4,5,6).
One of the ways to disrupt the circadian rhythm is by constantly eating throughout the day(6,7). For example, have you ever eaten food very late at night and woken up with a “food coma” where you feel especially tired, unmotivated, and maybe a little sick? This is likely because you ate food after your digestive processes “went to sleep.” Or have you ever been on a long flight and gotten jet-lag? This is because you disrupted your circadian rhythm. You don’t like your sleep pattern being disrupted and neither does your body!
Another potential reason the 16/8 diet can be beneficial is because it increases one special compound called AMP-activated protein kinase (AMPK). AMPK is thought to be able to detect when we are low on the body’s stored sugar supply. When this happens, AMPK will change different bodily functions in a way that is thought to be beneficial for one’s health(8,9).
Most scientists who study AMPK agree that bouts of elevated levels of AMPK can help lead to decreased body fat mass, decreased blood pressure, decreased blood triglycerides, decreased total cholesterol, decreased LDL-cholesterol, decreased blood sugar levels, among others(10–17). Don’t think this means you should fast for days and days to increase your AMPK levels! The key is to increase it temporarily and to do this daily.
Another way the 16/8 diet can improve overall health is by “teaching” the body to use more stored body fat and less stored glucose for metabolic processes even during the fed state. Increasing the use of stored fat for fuel means your body is literally breaking down and using your stored fat more than it was before. This directly translates to decreased body fat and a decrease in risk of different diseases associated with excessive body fat (18).
There may be other ways the 16/8 diet can help improve overall health, but these seem to be some of the most understood methods as of right now.
Other than the metabolic benefits we discussed earlier, there are some other benefits to adhering to the 16/8 intermittent fasting diet.
For starters, it is easy to adhere to and therefore, can be more sustainable long-term.
The 16/8 diet also doesn’t require you to count your calories. Counting calories is exhausting and it can contribute to an unhealthy approach to eating food by causing stress…eating should be fun and an enjoyable experience!
Like all diets, the 16/8 diet does have some drawbacks.
For example, if you are someone who typically eats in a 14-hour or more timeframe, cutting this down to 8 hours may be difficult at first. You might feel hungry, irritated, and fatigued during the first 1-2 weeks. This might make adhering to this diet difficult.
Because calorie counting isn’t required for this diet, some people may see that as an excuse to eat very high-calorie meals during their eating window. This may cause the opposite effect that they would like.
As we’ve mentioned, the 16/8 diet means that you only eat for 8 hours of the day while fasting for the remaining 16 hours. This basically means that you need to extend the overnight fast into the morning or starting the fast early in the evening.
To get started, pick an 8-hour window where you will be eating. Be realistic with yourself and pick a window that will be the easiest for you to adhere to. Many people find that an 11am-7pm or a 12pm-8pm window is the easiest but if you are someone who can’t live without eating an early breakfast, a 7am-3pm window might be best for you.
Check out this other article to help you pick the best fasting schedule using the 16/8 method.
Your work schedule might also play a major role into how you should pick this. Whatever time you pick, what’s most important is to be consistent; don’t do a 7am-3pm window one day and a 1pm-9pm window the next.
Now let’s talk about calories. Some people choose to be in a calorie deficit while also doing the 16/8 intermittent fasting diet. This may help them lose extra weight quicker in the beginning, but this may not be the best plan for everyone. Let’s talk about why.
Long-term calorie deficient diets can also decrease the amount of muscle you have. This means that if you step on a scale and see that you lost weight, some of that weight loss is because you have lost some muscle.
The problem with losing muscle is that your muscles burn a lot of calories whether you’re moving around or watching TV. This means that you will burn less calories everyday no matter what you’re doing. The loss of muscle mass is a big reason why people tend to plateau in their weight loss goals when they restrict calories(19,20).
Restricting your calories also causes your body to enter what is commonly referred to as a “starvation mode.” This is where your body will make adjustments to different bodily functions to try to save energy and stored fat, making it very hard to lose body fat(19).
Because of this, you may have some trouble achieving all of the benefits associated with the 16/8 diet. However, there are no long-term studies that looked at the effects of following a restrictive calorie diet while following the 16/8 so we don’t know for certain if your body will enter a starvation mode, but this is definitely something worth considering.
But there are studies showing that maintaining your calories while following intermittent fasting dietary patterns does not affect the amount of calories you burn daily while also not affecting muscle mass(18,21). These same studies also show that you can still lose body fat and get all of the health benefits of intermittent fasting. What this means is that you can fuel your body by giving it all the calories it needs and still better your overall health!
A good strategy might be to try to determine how many calories you need based on your age, height, weight, sex, and activity level and aim for that. You might have to count calories for a few days to get an idea of how many calories are in your food, but you won’t have to do that for a long time. There are many resources online to help you determine this and will only take a few minutes. Your body needs food and energy and you want to make sure you are giving it what it needs!
Aim for about 30 minutes of exercise daily. The exercise doesn’t have to be intense-30 minutes of yoga, light stretching, or a walk is great! Exercise is great for your mental health and will help you burn some additional calories.
Lastly, making sure you are eating nutritious foods will help maximize the benefits of this diet. Aim to incorporate a variety of whole foods like fruits, vegetables, whole grains, healthy fats, and lean proteins all while minimizing sugar intake. But give yourself some leniency-if you’re celebrating something or are craving cake, let yourself have some! Restricting yourself of any of your favorite foods is no way to live!
The 16/8 intermittent fasting diet involves eating during an 8-hour window while fasting for the remaining 16 hours.
Adhering to this diet may help improve one’s overall health.
If you have any underlying health conditions or if you have any questions, it’s always best to talk to your doctor before starting this dietary pattern.
There are lots of other intermittent fasting schedules, you may want to check it out before jumping in.
1. Longo VD, Panda S. Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan. Cell Metabolism. Cell Press; 2016. p. 1048–59.
2. Khan S, Nabi G, Yao L, Siddique R, Sajjad W, Kumar S, Duan P, Hou H. Health risks associated with genetic alterations in internal clock system by external factors. International Journal of Biological Sciences. Ivyspring International Publisher; 2018. p. 791–8.
3. Kyriacou CP, Hastings MH. Circadian clocks: genes, sleep, and cognition. Trends in Cognitive Sciences. 2010. p. 259–67.
4. Jehan S, Zizi F, Pandi-Perumal SR, Myers AK, Auguste E, Jean-Louis G, Mcfarlane SI. Shift Work and Sleep: Medical Implications and Management.
5. Belle MDC. Circadian Tick-Talking Across the Neuroendocrine System and Suprachiasmatic Nuclei Circuits: The Enigmatic Communication Between the Molecular and Electrical Membrane Clocks. J Neuroendocrinol. Blackwell Publishing Ltd; 2015;27:567–76.
6. Bass J, Takahashi JS. Circadian integration of metabolism and energetics. Science. Science; 2010. p. 1349–54.
7. Paoli A, Tinsley G, Bianco A, Moro T. The influence of meal frequency and timing on health in humans: The role of fasting. Nutrients. MDPI AG; 2019.
8. Hardie DG, Carling D. The AMP-activated protein kinase. Fuel gauge of the mammalian cell? European Journal of Biochemistry. Blackwell Publishing Ltd; 1997. p. 259–73.
9. Hardie DG. AMP-activated protein kinase: A cellular energy sensor with a key role in metabolic disorders and in cancer. Biochemical Society Transactions. 2011. p. 1–13.
10. Wakil SJ, Abu-Elheiga LA. Fatty acid metabolism: Target for metabolic syndrome. Journal of Lipid Research. American Society for Biochemistry and Molecular Biology; 2009. p. S138.
11. Ruderman N, Prentki M. AMP kinase and malonyl-CoA: Targets for therapy of the metabolic syndrome. Nature Reviews Drug Discovery. Nature Publishing Group; 2004. p. 340–51.
12. Wu L, Zhang L, Li B, Jiang H, Duan Y, Xie Z, Shuai L, Li J, Li J. AMP-Activated Protein Kinase (AMPK) regulates energy metabolism through modulating thermogenesis in adipose tissue. Front Physiol. Frontiers Media S.A.; 2018;9.
13. Liu J, Li X, Lu Q, Ren D, Sun X, Rousselle T, Li J, Leng J. AMPK: A balancer of the renin–angiotensin system. Bioscience Reports. Portland Press Ltd; 2019.
14. Ma A, Wang J, Yang L, An Y, Zhu H. AMPK activation enhances the anti-atherogenic effects of high density lipoproteins in apoE-/- mice. J Lipid Res. American Society for Biochemistry and Molecular Biology Inc.; 2017;58:1536–47.
15. Kurth-Kraczek EJ, Hirshman MF, Goodyear LJ, Winder WW. 5’ AMP-activated protein kinase activation causes GLUT4 translocation in skeletal muscle. Diabetes. Diabetes; 1999;48:1667–71.
16. Wong AKF, Howie J, Petrie JR, Lang CC. AMP-activated protein kinase pathway: A potential therapeutic target in cardiometabolic disease. Clinical Science. Portland Press Ltd; 2009. p. 607–20.
17. Wu N, Zheng B, Shaywitz A, Dagon Y, Tower C, Bellinger G, Shen CH, Wen J, Asara J, McGraw TE, et al. AMPK-Dependent Degradation of TXNIP upon Energy Stress Leads to Enhanced Glucose Uptake via GLUT1. Mol Cell. Mol Cell; 2013;49:1167–75.
18. Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG, Leeuwenburgh C, Mattson MP. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity. Blackwell Publishing Inc.; 2018. p. 254–68.
19. Benton D, Young HA. Reducing Calorie Intake May Not Help You Lose Body Weight. Perspect Psychol Sci [Internet]. SAGE Publications Inc.; 2017 [cited 2020 Jun 28];12:703–14. Available from: /pmc/articles/PMC5639963/?report=abstract
20. Hall KD, Heymsfield SB, Kemnitz JW, Klein S, Schoeller DA, Speakman JR. Energy balance and its components: Implications for body weight regulation. American Journal of Clinical Nutrition. American Society for Nutrition; 2012. p. 989–94.
21. Hatori M, Vollmers C, Zarrinpar A, DiTacchio L, Bushong EA, Gill S, Leblanc M, Chaix A, Joens M, Fitzpatrick JAJ, et al. Time-Restricted Feeding without Reducing Caloric Intake Prevents Metabolic Diseases in Mice Fed a High-Fat Diet. Cell Metab [Internet]. Cell Press; 2012 [cited 2018 Mar 6];15:848–60. Available from: https://www.sciencedirect.com/science/article/pii/S1550413112001891?via%3Dihub
