Intermittent fasting is a HUGE buzz word in the health and wellness industry right now. Celebrities are doing it, social media influencers are recommending it and many of our clients are enquiring about it – but what does the research say?

What is intermittent fasting?

Intermittent fasting (or IF) is a type of diet or eating pattern where the timeframe within which a person eats is restricted. This is sometimes (but not always) paired with a restricted calorie intake.

The different types of fasting

• The 5:2 Diet, where the person fasts for two days of the week (may or may not be consecutive days).
• Alternate-Day Fasting, where the person alternates daily between fasting and eating normally.
• Time-Restricted Feeding, where the person eats all of their meals within a small timeframe (often 4 to 8 hours) and fasts for the remaining 16 to 20 hours a day.

What does the evidence say?

Before we dive into the research, let’s talk a little bit about quality when it comes to evidence. This is important to consider because not all studies are created equal! When we refer to the ‘quality of evidence’, this includes things like the design of the study, the methods, the number of participants, the duration and whether the authors may have a conflict of interest. All of these things affect how reliable the results are.

Now that we’ve cleared that up: there are a tonne of arguments in support of IF but unfortunately, not a lot of good quality research to back it up. The evidence is also incredibly inconsistent.

For example:

• Some studies have promoted IF as an excellent method of losing weight and improving blood glucose control, while others have found it to be no more effective than eating frequently throughout the day.^1-7
• A study looking into the effects of IF found that metabolism increased, while a similar study found that it decreased.^3,8
• Some studies report that the hunger sensation disappears after a period of fasting, while others report that hunger remains elevated throughout.^{1, 9-11}

Some experts have proposed that IF can improve body composition in ‘overweight’ individuals however, the effects of this dietary pattern in humans is unclear. Many of the studies have been found within animal models which have thus kindled scientific interest in the benefits of short-term fasting approaches in humans.

Overall, the evidence is mostly low quality and inconsistent, and a LOT more research is required to form any strong conclusions about the potential health benefits of IF.

Is intermittent fasting safe?

Proponents of IF differentiate it from starvation by saying that the former is a voluntary restriction of food whilst the latter is involuntary. Whilst this may be true, many of the health risks are the same, including: ^1,12

• Refeeding syndrome
• Malnutrition
• Increased susceptibility to disease
• Organ damage

Additionally, the side effects of IF range from mild, such as constipation, sleep disturbances, muscle pain and headaches, to more serious, such as cardiac arrythmia, gout, and hypoglycemia.¹

At EHL, we are committed to providing safe and evidence-based dietary advice, and there is just not enough good quality research for us to recommend IF to most people. More research into the potential health benefits and (more importantly) safety of IF needs to be done first.

However, at the end of the day, you are in charge of your body! We encourage all of our clients to do what they believe is best for them, and we will support you regardless of your decision.

To chat with one of our expert dietitians more about how you can improve your health through nutrition, please get in touch via [email protected].

Karli Battaglia MDiet, APD

EHL Team x

References:

1. Wilhelmi de Toledo F, Grundler F, Bergouignan A, Drinda S, Michalsen A. Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects. PLOS ONE. 2019;14(1):e0209353.
2. Klempel M, Bhutani S, Fitzgibbon M, Freels S, Varady K. Dietary and physical activity adaptations to alternate day modified fasting: implications for optimal weight loss. Nutrition Journal. 2010;9(1).
3. Zauner C, Schneeweiss B, Kranz A, Madl C, Ratheiser K, Kramer L et al. Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. The American Journal of Clinical Nutrition. 2000;71(6):1511-1515.
4. Lowe D, Wu N, Rohdin-Bibby L, Moore A, Kelly N, Liu Y et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity. JAMA Internal Medicine. 2020;.
5. Rynders C, Thomas E, Zaman A, Pan Z, Catenacci V, Melanson E. Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients. 2019;11(10):2442.
6. Seimon R, Roekenes J, Zibellini J, Zhu B, Gibson A, Hills A et al. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and Cellular Endocrinology. 2015;418:153-172.
7. Vitale R, Kim Y. The Effects of Intermittent Fasting on Glycemic Control and Body Composition in Adults with Obesity and Type 2 Diabetes: A Systematic Review. Metabolic Syndrome and Related Disorders. 2020;.
8. Nair K, Woolf P, Welle S, Matthews D. Leucine, glucose, and energy metabolism after 3 days of fasting in healthy human subjects. The American Journal of Clinical Nutrition. 1987;46(4):557-562.
9. Sutton E, Beyl R, Early K, Cefalu W, Ravussin E, Peterson C. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism. 2018;27(6):1212-1221.e3.
10. Heilbronn L, Smith S, Martin C, Anton S, Ravussin E. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American Journal of Clinical Nutrition. 2005;81(1):69-73.
11. Nymo S, Coutinho S, Jørgensen J, Rehfeld J, Truby H, Kulseng B et al. Timeline of changes in appetite during weight loss with a ketogenic diet. International Journal of Obesity. 2017;41(8):1224-1231.
12. Crook M, Hally V, Panteli J. The importance of the refeeding syndrome. Nutrition. 2001;17(7-8):632-637.