You will have most likely heard of the term intermittent fasting or have seen someone post about it on social media. It has been a topic of interest in the last couple of years, but what actually is it, and what does the evidence say?
Intermittent fasting usually refers to three main types of fasting1:
Whole day fasting: An example being the 5:2 diet, where 1-2 days a week are 400-500kcal, with no food restriction on the remaining days.
Alternate day fasting: This is when every other day is fasted. During the fasted days most people are recommended to have one meal (25% of needs). Some people also refer to the 5:2 diet as alternate day fasting.
Time restrictive feeding: this narrows the time you are eating, for example in the 16:8 diet you only eat for 8 hours of the day
Whilst the research surrounding the topic has some interesting findings, the overall picture is that this is most likely due to overall calorie reduction, rather than the results of the fasting diet itself.
In one study, significant weight loss was found in overweight and obese adults adopting an intermittent fasting diet. This was comparable to the weight loss results from individuals on a normal diet, suggesting that whilst intermittent fasting may contribute to weight loss for some, it is not superior to other diets that incorporate daily calorie restriction.2
A meta-analysis looks at multiple studies on the subject, and one that included studies over 6 months also noticed a weight loss association for intermittent fasting. However, the conclusions made from the study showed it was not significantly different to results from continuous calorie restriction.3 This is supported by other studies on the subject, claiming that intermittent fasting could be used as an equivalent to other weight loss diets.4,5
This suggests that whilst there are some interesting findings on studies surrounding intermittent fasting, it has not been proven to be superior to other weight loss diets. For this reason, more studies using long term trials are needed to prove that it is more effective. Overall, the research on intermittent fasting is fairly new, and it will be exciting to see what future research concludes!
Whilst some research has indicated that intermittent fasting can be effective for weight loss it has not suggested it is any more effective than normal diets. There are also some side effects that people may experience when adopting this diet:
Fasting can lead to irritability and low mood due to lack of food
Fasting can lead to a reduction in energy levels due to periods of little energy intake
Prolonged periods of fasting can lead to overeating as a consequence, which is why it may not work as a weight loss tool for all
It is not suitable for everyone e.g. pregnant women, or individuals with certain health conditions.
The most important message to take from this is that it's important to adopt principles that work for you and make you feel good. If you enjoy breakfast, then there is no need to fast until lunchtime because someone else lost weight from it. There is no ‘magic’ behind intermittent fasting, and it is not superior as a weight loss tool, but it is an interesting area of research that may well expand. Perhaps we should be focusing on the types of foods that we are eating, rather than the time of day we are eating, as it is down to individual choice. Sustained and healthy weight loss is multi-faceted and involves a balanced, varied and enjoyable diet, along with quality sleep, body movement and reduced stress. There is no need to adopt weight loss diets that may put your health at risk if they do not work for you, but likewise, if it does work for you then there is no need change either!
1) Tinsley, G. and La Bounty, P. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition Reviews, 73(10), pp.661-674.
2) Davis, C., Clarke, R., Coulter, S., Rounsefell, K., Walker, R., Rauch, C., Huggins, C. and Ryan, L. (2015). Intermittent energy restriction and weight loss: a systematic review. European Journal of Clinical Nutrition, 70(3), pp.292-299.
3) Headland, M., Clifton, P., Carter, S. and Keogh, J. (2016). Weight-Loss Outcomes: A Systematic Review and Meta-Analysis of Intermittent Energy Restriction Trials Lasting a Minimum of 6 Months. Nutrients, 8(6), p.354.
4) Trepanowski, J., Kroeger, C., Barnosky, A., Klempel, M., Bhutani, S., Hoddy, K., Gabel, K., Freels, S., Rigdon, J., Rood, J., Ravussin, E. and Varady, K. (2017). Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults. JAMA Internal Medicine, 177(7), p.930.
5) Harvie, M., Pegington, M., Mattson, M., Frystyk, J., Dillon, B., Evans, G., Cuzick, J., Jebb, S., Martin, B., Cutler, R., Son, T., Maudsley, S., Carlson, O., Egan, J., Flyvbjerg, A. and Howell, A. (2010). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International Journal of Obesity, 35(5), pp.714-727.
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