Intermittent Fasting 18:6

July 21, 2020
Updated: March 8, 2022
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Intermittent fasting is a health and fitness technique that involves fasting periodically for short periods of time. 18:6 is one of the many fasting option windows that includes a 16 hours of fasting while eating within a 6 hour time frame. When done correctly, it can help you lose weight and provide you with other health benefits.


”Restriction of the daily food intake results in weight loss, which is also associated with better health outcomes including triglycerides, total cholesterol, low-density lipoprotein cholesterol, blood pressure, glucose, insulin, and C-reactive protein” (


How does 18:6 Intermittent Fasting Work?

Like the name implies, intermittent fasting involves fasting for short periods of time, with periods of non-fasting in between. “Intermittent fasting” is actually an umbrella term which incorporates a variety of related diet and fasting regimes. Examples include:

  • 18:6 diet:Food is eaten in a 6 hour window. This usually includes 2 meals and snacks. 18 hours of fasting is required on this diet. Some choose to skip breakfast. 
  • 5:2 diet: People eat normally for five days of the week, then restrict caloric intake the other two days (500 calories for women, 600 calories for men).1
  • 16:8 method (also called time-restricted feeding):Food is only eaten during an 8-hour window every day. (This is less intense than the 18:6 diet.)2
  • Religious fasting:Many religions observe periods of fasting or food restrictions on certain days of the year or week. These can come with the same health benefits as other forms of intermittent fasting.

All of the ways that intermittent fasting affects your health are not fully understood yet. However, if done correctly, intermittent fasting can provide several health benefits, including 3

  • Lower energy intake
  • Higher energy expenditure
  • Better sleep
  • Lower blood glucose
  • Healthier gut microbiome

Intermittent Fasting Helps with Weight Loss

Even when you eat normally the rest of the time, following an intermittent fasting diet plan can help you lose weight. If you keep healthy otherwise and make sure you are following the diet correctly, you can lose weight at a healthy rate. Several health effects of intermittent fasting promote weight loss:

  • Caloric restriction:People following a 5:2 diet consume about a quarter fewer calories every week than they otherwise would.2 Not only does this promote weight loss, but the caloric restriction is a way to reduce inflammation in your body and extend your life expectancy.4
  • Lower risk of type II diabetes: Consuming fewer calories, especially when avoiding eating late in the evening or during the night, results in lower blood sugar and lower insulin production.2 This helps keep your body from developing insulin resistance, which is associated with obesity and other health detriments.  
  • Temporary ketosis: Your body can enter a state of ketosis in as quick as 12-14 hours of avoiding carbohydrates.5 Even if only temporary, ketosis causes your body to burn stored fat faster.6

Women Benefit from Weight Loss and Reduced Menstrual Symptoms

There has been some debate as to whether women benefit from intermittent fasting as much as men do. Some studies have shown that women do respond to fasting somewhat differently than men. For example, men’s bodies process blood glucose faster than women do while fasting.7 However, clinical research has found that women still can lose weight at similar rates to men on this kind of diet.8

In fact, women may also benefit from intermittent fasting in other ways. One clinical trial found that women who fasted intermittently during the follicular and luteal phases of their menstrual cycles (before and after ovulation) had lower cortisol levels during these phases. High cortisol is associated with stress, and lower cortisol may help alleviate some of the symptoms women experience during the menstrual cycle.9        ;   


Long-Term Effects of Intermittent Fasting on Reproductive Health

Some doctors have warned against the potential effects of intermittent fasting on reproductive health. These concerns have come from research on rodents. The studies on rats that found impaired fertility used much harsher fasting regimens than what humans would normally use, such as no food at all every other day.10 The actual effects of intermittent fasting on the reproductive health of women are not well known yet.


[2] MP Mattson, VD Longo, and M Harvie. 2017. "Impact of intermittent fasting on health and disease processes." Ageing research reviews. 3946-58. 

[3] RE Patterson and DD Sears. 2017. "Metabolic Effects of Intermittent Fasting." Annu Rev Nutr. 37371-393. 

[4] P Balasubramanian, PR Howell, and RM Anderson. 2017. "Aging and Caloric Restriction Research: A Biological Perspective With Translational Potential." EBioMedicine. 2137-44.

[5] GF Cahill, Jr., TT Aoki, and NB Ruderman. 1973. "Ketosis." Trans Am Clin Climatol Assoc. 84184-202.

[6] LB Gano, M Patel, and JM Rho. 2014. "Ketogenic diets, mitochondria, and neurological diseases." J Lipid Res. 55(11):2211-28.

[7] G Keramida and AM Peters. 2017. "Fasting hepatic glucose uptake is higher in men than women." Physiological reports. 5(11):e13174.

[8] L Zuo, F He, GM Tinsley, BK Pannell, E Ward, and PJ Arciero. 2016. "Comparison of High-Protein, Intermittent Fasting Low-Calorie Diet and Heart Healthy Diet for Vascular Health of the Obese." Frontiers in physiology. 7350-350.

[9] K Ohara, Y Okita, K Kouda, T Mase, C Miyawaki, and H Nakamura. 2015. "Cardiovascular response to short-term fasting in menstrual phases in young women: an observational study." BMC women's health. 1567-67.

[10] S Kumar and G Kaur. 2013. "Intermittent fasting dietary restriction regimen negatively influences reproduction in young rats: a study of hypothalamo-hypophysial-gonadal axis." PloS one. 8(1):e52416-e52416.

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