What is Intermittent Fasting, and What Does it Do?

The benefits, pitfalls, and what the research says

Unlike nutrition or diet plans that focus on what you eat, intermittent fasting focuses on when you eat.

It’s an approach to eating where you alternate between periods of fasting (not eating) and eating at a specific time. We’ve been hearing more and more about it over the last few years, but does intermittent fasting actually improve your health and longevity?

Let’s start with the different approaches. There are many different intermittent fasting protocols, but the most common ones include:

Time-restricted feeding

This involves limiting the eating window to a certain number of hours per day, such as an 8-hour window (e.g., eating from 12 pm to 8 pm) and fasting for the remaining 16 hours. The 8:16 approach is sometimes called the “Lean-gains” method.¹

Alternate-day fasting

Alternating between a day of unrestricted eating and a day of either full or partial fasting (usually consuming around 25% of daily calorie needs). A common version of this plan involves modified fasting, where you restrict calorie intake to 500-600 calories on fasting days.

5:2 fasting

You eat normally for 5 days of the week and restrict calorie intake to around 500-600 calories for 2 non-consecutive days of the week.

Each of these approaches has its benefits and drawbacks. If you decide to try intermittent fasting, the right approach for you will depend on your goals, lifestyle, and overall health and relationship with food.

“What is clear from the research is that more long-term studies are needed to fully understand the effects of different intermittent fasting protocols on health and longevity.”

What are the benefits of intermittent fasting?

Intermittent fasting has gained popularity as a potential tactic to help you lose weight (as with any diet that reduces overall calorie intake).¹⁻³ However, research also suggests that intermittent fasting may have other health benefits even if you consume the same number of calories as you would when eating normally. ²⁻⁶

Evidence shows that practising intermittent fasting regularly may:

Reduce inflammation: One of the key potential benefits of IMF is its ability to promote autophagy. The process by which the body cleans up and recycles damaged cells. Autophagy has been shown to have anti-aging effects, as it helps to remove cellular debris that can lead to chronic inflammation and disease.

Intermittent fasting has also been shown to improve insulin sensitivity, which can help to reduce the risk of type 2 diabetes and metabolic syndrome (Jamshad et al., 2019 and Patterson and Sears, 2017).

Research also suggests that IMF can improve lipid biomarkers, but it lacks consensus on whether this is due to intermittent fasting or the reduction in calories that comes with most of the methods.⁴,⁵

What is clear from the research is that more long-term studies are needed to fully understand the effects of different intermittent fasting protocols on health and longevity.

Whatever approach you decide on, it’s important to make sure you are getting the right nutrition during eating periods. Restricted eating windows may make it more challenging to consume the nutrients your body needs. Making healthy choices is also essential to reap the benefits of intermittent fasting. Eating a variety of nutrient-dense foods (during eating periods) will ensure you are getting enough essential vitamins, minerals, and macronutrients.

This all sounds pretty good. What’s the downside?

Like any diet, intermittent fasting may have potential side effects, especially when not approached correctly.

As with many ‘diets’, if you are someone with a history of disordered eating or vulnerable to development of one, intermittent fasting is likely not the appropriate tool to use as it can lead to binge eating and a negative relationship with food.

If you’ve seen a Snickers commercial, you’ll know the saying, “You're Not You When You're Hungry.” Some people may experience hunger headaches, fatigue, irritability, and difficulty concentrating during the initial phases of intermittent fasting, as the body adjusts to a new eating pattern.¹⁻³ These symptoms may be temporary and usually improve after a few days.

Caloric restriction as a result of fasting could also impact women differently. According to the Cleveland Clinic, the theory is that fasting “could make your body behave as if food is scarce and that you’re at risk for starvation. Not the ideal conditions for a healthy pregnancy. So, your body keeps ovulation from happening to prevent pregnancy.” This impacts the levels of estrogen and progesterone in your body, which can cause a range of symptoms, including changes in your menstrual cycle, hot flashes, low sex drive, hair loss, acne, heart palpitations, trouble sleeping, and more.

Intermittent fasting may also increase the risk of dehydration, especially if you are not drinking enough water during the fasting periods. You may find it difficult to stick to your intermittent fasting plan in social situations or when eating with family and friends.

Intermittent fasting can also hinder your ability to build muscle and, when done incorrectly, can even result in muscle loss. This is because our rate of muscle protein synthesis, or muscle building, is influenced by the food we eat and the resulting insulin release.⁷,⁸

Insulin has an anti-catabolic effect on muscle, meaning that the natural breakdown we experience while fasting is stopped by the consumption of food.⁷ This alters the net difference we experience over the day and can have cascading effects if building strength and muscle is your goal. However, if maintenance or small strength gains are the goal, then intermittent fasting coupled with resistance training has been shown to utilize the amino acids from the breakdown of muscle to create new muscle.⁷,⁹

When consuming food normally, an amount of ~0.25g/kg of body mass of leucine rich protein (things like chicken, salmon, lentils, or chickpeas) stops the breakdown of muscle and will achieve maximal muscle building for about 1.5 to 3 hrs and then revert to the base rate for a total of 6 hours. However, when you engage in intermittent fasting, you need to consume more protein for the same effect (0.3-0.4g/kg of body weight).⁷

A final note. Intermittent fasting may not be suitable for people with medical conditions such as diabetes, eating disorders, or certain gastrointestinal disorders. Additionally, pregnant or breastfeeding women and individuals who are underweight or have a history of malnutrition should proceed carefully and in consultation with a healthcare professional.

Is intermittent fasting right for you?

The answer to this question will be different for each person. A good place to start is to define what you are hoping to achieve (and how long you are willing to try intermittent fasting). You might try fasting to lose weight, but if the plan isn’t sustainable for your lifestyle, you may regain what you lose. However, if you are prepared to eat recommended portions and choose balanced meals during your non-fasting times, it might be a good choice.

Think about your eating habits now and how and when you could fit fasting times and non-fasting times into your schedule. Your approach to eating should keep you healthy and make you feel good. If sticking to a strict timetable or following specific rules seems challenging or makes you anxious, it might not be the right approach for you.

If you’d like to learn more or chat about intermittent fasting approaches, our Naturopathic Physicians, Dietitian, and Health Coaches are a great resource. Give us a call!

Disclaimer:

If you are someone who has a history of eating disorders, disordered eating habits, a poor relationship with food, or considers themselves vulnerable to developing an eating disorder, intermittent fasting may not be a suitable intervention as it is a form of limitation on when you consume your meals. Intermittent fasting is one of many tools used for health benefits, metabolic health, and body composition and isn’t suitable for everyone.

If you are someone struggling with their relationship with food, we are eager to support you. Book with one of our mental health providers here.

References:

Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019 May 30;11(6):1234. doi: 10.3390/nu11061234. PMID: 31151228; PMCID: PMC6627766

Patterson RE, Sears DD. Metabolic Effects of Intermittent Fasting. Annu Rev Nutr. 2017 Aug 21;37:371-393. doi: 10.1146/annurev-nutr-071816-064634. Epub 2017 Jul 17. PMID: 28715993.

Tinsley GM, Forsse JS, Butler NK, et al. Time-restricted feeding in young men performing resistance training: A randomized controlled trial†. Eur J Sport Sci. 2017;17(2):200-207. doi:10.1080/17461391.2016.1223173

Tinsley GM, la Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015;73(10):661-674. doi:10.1093/nutrit/nuv041

de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine. 2019;381(26):2541-2551. doi:10.1056/nejmra1905136

Allaf M, Elghazaly H, Mohamed OG, et al. Intermittent fasting for the prevention of cardiovascular disease. Cochrane Database of Systematic Reviews. 2021;2021(1). doi:10.1002/14651858.CD013496.pub2

Bhutani S, Klempel MC, Kroeger CM, Trepanowski JF, Varady KA. Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans. Obesity. 2013;21(7):1370-1379. doi:10.1002/oby.20353

Harvie MN, Pegington M, Mattson MP, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: A randomized trial in young overweight women. Int J Obes. 2011;35(5):714-727. doi:10.1038/ijo.2010.171

Williamson E, Moore DR. A Muscle-Centric Perspective on Intermittent Fasting: A Suboptimal Dietary Strategy for Supporting Muscle Protein Remodeling and Muscle Mass? Front Nutr. 2021;8. doi:10.3389/fnut.2021.640621

Vasim I, Majeed CN, DeBoer MD. Intermittent Fasting and Metabolic Health. Nutrients. 2022;14(3). doi:10.3390/nu14030631

Templeman I, Smith HA, Chowdhury E, et al. A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults. Sci Transl Med. 2021;13(598):eabd8034. doi:10.1126/scitranslmed.abd8034

https://health.clevelandclinic.org/intermittent-fasting-for-women/#:~:text=Intermittent%20fasting%20can%20have%20a,female%20at%20birth%20(AFAB).

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