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Intermittent Fasting Explained

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Intermittent fasting continues to be a popular trend in wellness. Intermittent fasting claims to aid in weight loss, reduce chronic disease risk, improve brain function and increase life span. Intermittent fasting first gained popularity with The Fast Diet, which originated in the United Kingdom in 2014. On The Fast Diet plan, fasting is recommended for two non-consecutive days per week and normal eating on the other days. On fasting days, women are recommended to eat 500 calories and men 600 calories. The premise behind intermittent fasting is to achieve a calorie deficit over time, which can result in weight loss.

Multiple variations of intermittent fasting now exist and can be categorized into three main types

  • Alternate-day fasting (ADF)
  • Modified intermittent fasting (IF)
  • Time-restricted eating (TRE)

Alternate-day fasting
Alternate-day fasting (ADF) alternates between fasting days and normal eating days. Many versions of ADF exist with fasting days consisting of 500-600 calorie consumption, only consuming non-caloric beverages, or variations of both of these options. Versions of ADF vary from eating 0-25% of total daily calorie needs depending on which ADF protocol is used.

Modified intermittent fasting
Modified intermittent fasting includes more non-fasting days in between fasting days, which can be complete fasts or partial fasts. The 5:2 modified intermittent fasting is one of the most popular methods, which involves fasting for two consecutive days consuming anywhere from 0-25% of daily calorie needs and eating normally for the following five consecutive days.

Time-restricted Eating
Time restricted eating (TRE) allows for normal eating during a specified time period each day. The most popular TRE pattern is the 16:8, which allows normal eating for an eight-hour window and fasting for 16 hours. A good portion of the 16-hour fast typically occurs during sleep. People like this approach because they do not need to count calories and can skip either breakfast or dinner based on their TRE protocol. Some people choose a specific calorie intake to follow during their eight hours of eating to further their weight loss efforts. However, there is some concern that participants are unable to consistently meet their nutritional needs with the TRE approach due to the short window of time allotted for eating.

Intermittent fasting for weight loss
Most of the body of research on intermittent fasting comes from animal studies, however, more research on humans has surfaced in the last several years showing some benefit to weight loss success and weight loss program adherence.

Two studies found intermittent fasting proved to have the same results as daily caloric restriction for weight loss. However, people might find intermittent fasting more sustainable than daily caloric restriction. Another study comparing ADF, TRE and daily caloric restriction found while they all had similar weight loss outcomes, ADF had the lowest adherence and highest drop-out rate of all three methods. The same study showed ADF participants experienced both weight and fat loss, however, participants complained of excessive hunger on fasting days along with increased lightheadedness and irritability. Yet another study showed participants found TRE more realistic due to the eating plan being similar to participants’ normal eating patterns.

Research points to intermittent fasting possibly influencing hormones that control hunger and satiety. Several studies have demonstrated both ADF and TRE resulted in a decrease in the hormone leptin that drives hunger. One study on TRE in conjunction with the natural circadian rhythms, or sleep-wake cycles of the body, found eating that aligned with the natural sleep-wake cycle boosted metabolism earlier in the day─which could mean eating earlier in the day is beneficial for weight loss. This study also showed that eating from 8 a.m. to 2 p.m. limited daytime hunger and increased nighttime fat burn. Increasing fasting time during the night could be more realistic and beneficial as it aligns with existing sleep patterns. Another benefit of daytime TRE was that nighttime eating from 5 p.m. to midnight was reduced─which is linked to over-consumption of calories, weight gain and increased inflammation. However, many people find the noon to 8 p.m. TRE pattern more conveniently aligned with their lifestyle.

Choosing the right eating plan for you
All three categories of intermittent fasting—alternate-day fasting, modified intermittent fasting and time-restricted eating—may be tools for weight loss and weight management. If you choose to try intermittent fasting, choose the method that best matches your lifestyle that will be realistic to adhere to. Although research shows weight loss levels of intermittent fasting are comparable to daily calorie restriction, one might find it easier to restrict calories a couple of days a week or for a specific number of hours during the day. It is important to note practicing a TRE pattern eating earlier in the day may help boost metabolism and curb nighttime eating, which are barriers to weight loss for many people.

Whichever approach you choose, make sure it aligns with your personal health and wellness goals and lifestyle. A Cooper Clinic Registered Dietitian Nutritionist can help form an individualized approach and eating pattern that works best for you and provide guidance to ensure that you are meeting all of your nutritional needs.

For more information or to schedule a nutrition consultation, visit or call 972.560.2655

​Article provided by Cooper Clinic Nutrition.