With countless FAD Diets out there we are totally confused in what we really should be doing when it comes to weight loss. We have all heard: low carb, no-fat, high fat, veggie-soups, juicing, small-frequent-meals, raw foods with no dressing, baby foods, gluten- free and the list continues. This supposedly helps you shed a few kilo’s in no time. Over the years people have been trying to lose weight in different ways, so instead of dieting they skip meals every now and then – this is known as fasting. Let’s take a closer look at what this entails.


Fasting is defined as the willing reduction or abstinence from all or some food or drink, or both food and drinks for a certain period1. Individuals fast for different reasons. These could include religion, weight-loss, health benefits or a spiritual cleanse – let’s take a closer look at the various types of fasting diets out there.


1. Intermittent Fasting

Intermittent fasting (IF) is an eating pattern where individuals cycle between periods of eating and fasting. This type of fasting does not take into consideration which food types you eat but instead places focus on when you should be eating. The different IF methods are explained below2,3:

  • Alternate day fasting (ADF): is the most extensively studied IF method. Individuals will typically fast for 24-hours and then alternate this with a feeding period of 24 hours. Weight loss and a decrease in fat mass has been observed when following this method as individuals do not completely compensate their intake on the feeding day for what they haven’t eaten on the fasting day2.
  • Whole day fasting (WDF): this fasting method involves one to two 24-hour fasting periods in the week, to achieve an energy deficient and thereby help people to lose weight. Many studies on WDF have shown effective weight loss results – it is however important to note that many of these studies conducted did not involve a zero-calorie intake on the fasting days and in most of the studies individuals struggled to fast for the entire 24 hours which makes interpreting results a challenge. One study conducted by Harvie et al. saw no difference in body weight and body fat reduction between a group that was doing a WDF and the control group that had a weekly energy deficit over a 6-month period2,4.
  • Time-restricted feeding (TRF): this method typically involves a fasting period of 16-20 hours and then a feeding period of 4-8 hours daily. The most extensively studied form of TRF is Ramadan, which runs for approximately 1 month, where individuals fast both food and drinks from sunrise to sunset as part of religious practices2. Unsurprisingly they do have significant weight loss, including a decrease in lean muscle mass and fat mass. Aside from Ramadan fasting studies, TRF studies have been limited until recently, Tinsley et al. conducted an 8-week trial that examined the effect of a 20-hour fast with a 4-hour feeding period done for 4 days a week on recreationally active but untrained individuals. Individuals had no limitations on the amounts and types of foods they could eat in the 4-hour eating time frame and were placed on a standardised resistance training program for 3 days per week. The TRF group lost weight due to a lower energy intake during the day4.


  • Weight loss

    Intermittent fasting diets that last for at least a 6-month period have shown to assist individuals to lose weight. However, these diets have not proven to be more effective than other dietary approaches that restrict calorie intake. A study that ran over a 6-month period, where 100 individuals were randomised into 3 groups: alternate-day fasting, a continuous energy restriction diet, or to no intervention. After the study they were followed for an additional 6-month period the results showed no difference between the diet group after a year6. Another review that compared various behavioural interventions for weight management showed that individuals following a low energy diet achieved slightly better weight loss for up to 2 years7.

  • Health benefits

    Research on intermittent fasting has shown an array of health benefits. Improvements in blood pressure and cholesterol levels have been documented therefore having heart health benefits. IF has also shown to improve insulin sensitivity and decrease the risk of diabetes. Other studies have shown that IF helps “reboot” the immune system by helping it generate new, healthy cells which may protect against damaged cells caused by chemotherapy as well as aging3,8-10.


  • Unhealthy

    Fasting diets are based on when you eat and not what you eat. Individuals could therefore overindulge on any food types, including very unhealthy foods like junk food, desserts, chocolates and sweetened beverages. Not eating a balanced meal including carbohydrates, proteins, healthy fats and 5 fruits and vegetables per day may lead to micronutrient deficiencies and constipation. The risk of developing eating disorders such as binge eating is amplified.

  • Dehydration

    Fasting diets can often lead to dehydration as your body isn’t getting enough fluid from food. Individuals need to focus on staying hydrated10.

  • Stress

    If you are used to eating your small frequent meals including snacks, such a major change can be a huge challenge thereby increasing stress levels and disrupting sleeping patterns. Dehydration, hunger, fatigue and lack of sleep all lead to headaches9.

  • Weight gain

    Fasting diets are not a long-term solution for weight loss, often individuals lose weight quickly but once stopping the diet they regain the weight even faster. Weight loss may in fact be fluid loss.

  • Not suitable for everyone

    Individuals that are already underweight should stay away from fasting diets. People with major medical problems that have recently undergone surgery or those taking a range of medications including insulin, should not go on them unless under strict medical supervision9. These diets are not suitable for children, in pregnancy or whilst breastfeeding. People with eating disorders or mental problems should stay away from fasting diets as this may exacerbate their condition.


More long-term research needs to be done to determine the effects of fasting diets. If anyone does consider it then they should see a health professional first. If there was an easy quick fix we would all look and feel amazing. Remember that following a healthy, balanced diet and doing physical activity is recommended to achieve and maintain a healthy weight. Drastic measures are not recommended.

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