Conflicting views on intermittent fasting mean you’re unsure which path to take? Let’s take a deep dive and learn how to do it the right way.

What is intermittent fasting?

Intermittent fasting (IF) means you restrict food intake for a set time, followed by a period of regular eating. Fans of IF claim it results in rapid weight loss, improved gut health, mental clarity, improved sleep, and increased energy. Sounds great, sign me up!

There are various approaches to fasting

• Alternate day fasting: Involves alternating fasting days (no food eaten, or one small meal) with normal eating days.
• Time-restricted feeding: Eat normally within specific time frames, followed by regular, extended fasting intervals.
  • 16:8 – fasting for 16 hours (e.g., between 4pm and 8am), then eating meals in the 8-hour window (8am – 4pm).   
  • 14:10 – fasting for 14 hours, with a 10-hour feeding window.
  • 20:4 – fasting for 20 hours, with a 4-hour feeding window.
• Modified fasting regimens: Reduce food intake to 20–25 percent of energy needs on scheduled fasting days (the basis for the popular 5:2 diet). This approach calls for significant energy restriction on 2 non-consecutive days per week and normal eating for the other 5 days.
• Religious fasting: Variety of fasting regimens undertaken for religious or spiritual purposes (e.g., Ramadan).

Does intermittent fasting work for weight loss?

Yes, you can certainly reach weight loss goals following an IF regime. However, no research to date indicates it is any better for weight loss outcomes for overweight and obese people than conventional calorie restricted diets in the short or long term (Liu, D. 2022, Harris, L. 2018, Seimon, R. 2015).

Early research does indicate that continuous calorie restriction (conventional diet) may preserve lean mass more than intermittent fasting (Roman et al. 2018). If you’re keen to keep that muscle mass, reducing daily energy intake across the day may be the best approach, rather than a strict IF regime. But everyone is different, so experiment and do what works for you.

What about other benefits?

For decades, we’ve known that restricting calories by 40 percent in animals results in slowing down the aging process and extending lifespan. But does IF have any additional advantages?

Animal studies are looking promising; alternate day fasting in rodent models of obesity has been shown to reduce total plasma cholesterol, triglycerides and inflammation and have beneficial effects on cancer risk factors, such as cell proliferation.

Further human studies are needed to make definitive links between intermittent fasting and other health factors such as mental clarity and energy, insulin resistance and diseases such as heart disease, diabetes and cancer.

There are however indications that IF may offer protection against developing neurological disorders and early research indicates that fasting interventions may have a positive effect on anxiety and depression (Bethelot et al).

However, it may that the weight loss alone induced by IF is the factor that leads to the other metabolic benefits and mental health outcomes. Watch this space!

Why is intermittent fasting so popular?

The intermittent fasting approach has soared in popularity over the last few years, following the release of The Fast Diet book which outlines the 5:2 diet and The Fast 800 by prominent British doctor and journalist, Michael Mosley.

On the popular 5:2 diet; for the 2 fasting days, calories are restricted to about a quarter of the average Australian adult energy recommendations (no more than 500 calories/day for women or 600 for men). Essentially, this is a very low energy diet for those 2 days.

The Fast 800 calls for a reduction in calories to 800 calories every day (less than half of what is normally required) for 2 weeks, then transition to the new 5:2 diet; 800 calories on the 2 fasting days and normal eating on the rest. All meals on all days are to be eaten with a 10-hour feeding window. Confused? Let’s look at a 5:2 fasting day here:

Example of a fast day on the 5:2 diet

Breakfast: Quick Oats sachet of porridge (40g) - 255 calories
Lunch: nothing
Dinner: Beetroot and feta salad - 125 calories

beetroot (50g) - 13 calories
feta (30g) - 83 calories
spinach (60g) - 29 calories
squeeze of lemon - 0 calories

Snack: Sliced apple with 1 tbsp of almond butter – 145 cal

Total calorie count: 525 calories

Compared to the Australian Dietary Guidelines

• Significant reduction in calories (less than half or a quarter) compared to recommendations
• Risk of nutrient deficiencies on fasting days (e.g., you could eat 500 calories on a fasting day by having a slice of chocolate cake and a glass of milk only)
• Involves counting calories which is not promoted within the guidelines.
• Some people find training performance suffers when fuel is insufficient

Are there any risks?

Evidence suggests that intermittent fasting regimens are not harmful physically or mentally in healthy, normal weight, overweight, or obese adults (Patterson & Sears 2017).

However, some side effects of fasting include – no surprises here – hunger, fatigue and headaches. But in good news, current evidence suggests that periods of fasting do not necessarily lead to overeating.

What about diabetes and intermittent fasting? Under the guidance of a health professional, IF is safe for people with diabetes. Although IF can improve insulin resistance, the combination of glucose reducing medications and fasting, can potentially cause fatal hypoglycemia.

Socially, intermittent fasting can be risky. It’s engrained from an early age to eat three meals a day + snacks, so changing up your regime might mean you’ll be skipping dinner while the rest of the family chows down.

And what about eating out? Adjusting your intermittent fasting regime so you have flexibility for pizza and beer nights is important. Why? Strict dieting is a risk factor for developing an eating disorder, so a flexible, not rigid approach will ensure you attain the best long-term outcomes.

How to do intermittent fasting the right way?

Should you skip breakfast or dinner? Do the 5:2 or time-restricted feeding? The evidence suggests it doesn’t matter which approach you take to reap the benefits of IF. So, it depends on your lifestyle.

For me personally, skipping breakfast is hard as I train first thing in the morning, so need to refuel straight after. Having no dinner or a lighter dinner a few nights a week works best for me.
Also, there is strong evidence to indicate those who eat breakfast have more balanced glucose levels into the afternoon and evening (meaning you won’t be reaching for those sugary snacks in the afternoon).

Try starting with just one day per week eating within a 10-hour window (e.g. from 8am – 6pm). Then add in another day later in the week and see how you feel. Make sure you drink lots of water, to avoid dehydration.

The verdict:

I tried the 16:8 intermittent fasting approach for a week (eating between 8am and 4pm only) and found it was good to go to bed on an empty stomach and my sleep improved. But, I did find it hard to really push my workouts to the same level each day. If I did it again, I’d eat more in the feeding period to ensure energy levels are maintained.

Skipping meals is okay and is a form of fasting. That’s what I do now. Skipping 1 or 2 meals when you don't feel hungry or don't have time to eat is going to give the digestive system a rest and can help with weight loss as your total calorie intake will likely be less.

References:

Berthelot E, Etchecopar-Etchart D, Thellier D, Lancon C, Boyer L, Fond G. (2021) Fasting Interventions for Stress, Anxiety and Depressive Symptoms: A Systematic Review and Meta-Analysis. Nutrients. Nov 5;13(11):3947. doi: 10.3390/nu13113947

Ciera L Bartholomew, Joseph B Muhlestein, Heidi T May, Viet T Le, Oxana Galenko, Kelly Davis Garrett, Cherie Brunker, Ramona O Hopkins, John F Carlquist, Kirk U Knowlton, Jeffrey L Anderson, Bruce W Bailey, Benjamin D Horne. Randomized controlled trial of once-per-week intermittent fasting for health improvement: the WONDERFUL trial, European Heart Journal Open, Volume 1, Issue 2, September 2021, oeab026, https://doi.org/10.1093/ehjopen/oeab026

European Society of Endocrinology. (2018). Could intermittent fasting diets increase diabetes risk?

Harris L, Hamilton S, Azevedo LB, Olajide J, De Brún C, Waller G, Whittaker V, Sharp T, Lean M, Hankey C, Ells L. (2018) Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database System Rev Implement Rep. Feb;16(2):507-547. https://doi.org/10.11124/JBISRIR-2016-003248

Liu, D et al. (2022) Calorie Restriction with or without Time-Restricted Eating in Weight Loss New England Journal of Medicine; 386:1495-1504 https://doi.org/10.1056/NEJMoa2114833

Patterson and Sears (2017) Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition Vol. 37:371-393 https://doi.org/10.1146/annurev-nutr-071816-064634

Radhika V. Seimon, Jessica A. Roekenes, Jessica Zibellini, Benjamin Zhu, Alice A. Gibson, Andrew P. Hills, Rachel E. Wood, Neil A. King, Nuala M. Byrne, Amanda Sainsbury (2015) Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials, Molecular and Cellular Endocrinology, Volume 418, Part 2, https://doi.org/10.1016/j.mce.2015.09.014.

Roman YM, Dominguez MC, Easow TM, Pasupuleti V, White CM, Hernandez AV (2018) Effects of intermittent versus continuous dieting on weight and body composition in obese and overweight people: a systematic review and meta-analysis of randomized controlled trials. International Journal of Obesity Oct;43(10):2017-2027. https://doi.org/10.1038/s41366-018-0204-0

Schübel, R. et al. (2018) Effects of intermittent and continuous calorie restriction on body weight and metabolism over 50 wk: a randomized controlled trial, The American Journal of Clinical Nutrition, Volume 108, Issue 5 https://doi.org/10.1093/ajcn/nqy196

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