Four Rules for Successful Fasting

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There are many different dietary approaches promoted online for improving body composition and increasing health. But which one should you choose?

Previously, I discussed the pros and cons of a ketogenic dietary approach to healthy aging. My conclusion, based on the scientific literature and my own ketogenic experience, is that ketogenic diets are sub-optimal for healthy aging.

In this article, I examine another dietary approach that’s oh-so-hot-right-now: Intermittent Fasting (IF). Should you include intermittent fasting in your dietary repertoire?

What is intermittent fasting (IF)?

Despite it’s sudden upswing in popularity, humans have been fasting for a very long time. Besides the involuntary fasting experienced by our hunter-gather ancestors, ancient civilizations routinely used fasting in medicine and religion. For example, fasting was used for medical purposes in ancient China, Greece, and Rome (1). Further, Muslims, Mormons and other religions incorporate periodic fasting into their religious practice (1).

Because of it’s long history, intermittent fasting is well studied, and there are several safe approaches to fasting, as summarized below (1, 2).

Time-restricted feeding (TRF)    

TRF involves restricting your food intake to within specific time periods of the day. The most widely used version consists of you only eating between 12 pm and 8 pm daily. As a result, you fast for roughly 16 hours per day and feed during an eight hour window in the evening.

Alternate-day fasting (ADF)         

ADF involves you alternating between consuming no calories on fasting days, followed by unrestricted food intake on the subsequent ‘‘feast’’ day. Be warned, this is a very hardcore approach to fasting.

Alternate-day modified fasting (ADMF)

ADMF involves you consuming less than 25% of baseline energy needs on ‘‘fasting’’ days, alternated with a day of unrestricted food intake on the ‘‘feast’’ day. This is a slightly less hardcore approach, but it’s still tough going.

Periodic fasting (PF)

Periodic fasting means that you fast for 1-2 days per week, and you feed normally for the remaining days. The best-known version is the 5:2 protocol, which involves you fasting for two out of seven days per week.

What are the health benefits of intermittent fasting?

There are a host of positive health benefits associated with IF, as evidenced by the many human and animal studies (1, 2). Health benefits associated with IF include fat loss, lower blood pressure and reduced inflammation (1, 2). Moreover, IF is also known to increase your healthy gut flora and improve your metabolic health (1, 2).

The long-term health benefits of IF include a reduced risk of cancer and cardiovascular disease (2). Recent research suggests that IF may also reduce the risk of neurodegenerative disease and cognitive decline (2).

In a nutshell, IF increases your disease resistance and makes you more resilient. Not too shabby!

What are the risks of intermittent fasting?

IF has been tested in humans within many different contexts, and when performed correctly is an incredibly safe dietary approach (1, 2). However, one potential risk associated with IF is losing muscle. Because older adults lose muscle as they age, we argue that diets that exacerbate muscle loss should be avoided.

Extended IF switches the body into ‘starvation mode’ where muscle protein breakdown goes up, while muscle protein synthesis goes down (3). The net effect of increased protein breakdown and decreased protein production can reduce your muscle mass, which explains why IF often causes muscle loss (1).

What the Research Says

It’s well known that resistance training builds muscle. The million-dollar question is, can the combination of IF with resistance training preserve your muscle mass while you lose fat?

To answer this question, Keenan and Colleagues gathered eight clinical trials that tested IF in combination with resistance training (3). The overall conclusion from the analysis was that in five of the eight studies, IF plus resistance exercise maintained the lean body mass of study participants, while significantly reducing their fat levels (3). Hooray!

The four rules for successful fasting.

The studies performed so far support the hypothesis that IF combined with resistance training can help you lose fat and get healthy while maintaining your muscle mass and strength. This is great news!

Unfortunately, there are too few studies for us to draw firm conclusions regarding the optimal IF dietary regime. That said, three of the most recent studies analyzed by Keenan et al provide four important clues on how best to use IF to reduce fat while retaining muscle (4-6).

Rule 1: Include Resistance Training!

You must perform some kind of resistance training during any fat-loss diet! This certainly holds true for intermittent fasting. Resistance training provides an essential growth signal to your muscles that helps you maintain your muscle mass and strength during periods of weight loss.

Barbells, dumbbells, kettlebells, machines or bodyweight, it doesn’t matter! Just get it done, ideally three times a week (4-6).

Rule 2: Use a time restricted feeding (TRF) approach.

All three of the studies used TRF as their preferred fasting protocol. Food was consumed in an eight hour block between 12pm – 8 pm, giving a daily average of 16 hours of fasting and 8 hours of feeding  (4-6). In contrast, the resistance trained subjects who used alternate day fasting lost muscle mass (7).

Thus, a time restricted fasting protocol (consisting of something like 16 hours of fasting and 8 hours of feeding), is currently the recommended IF method for losing weight while preserving muscle. Fortunately, it’s also the easiest intermittent fasting protocol to maintain.

Rule 3: Resistance training should always be performed in a fed, not fasted, state.

All three studies had their subjects perform resistance training three days a week, on non-consecutive days (4-6). Importantly, participants performed their resistance training sessions during the middle of the eight-hour feeding window.

Therefore, you should always train in a fed, not fasted state. Importantly, you should also eat after you’ve trained. And remember to consume nutrient-dense foods, not junk.

Rule 4: Consume large amounts of high-quality protein.

Protein ingestion is an anabolic stimulus, and protein is an essential building block for muscle growth. This explains why participants who consumed large quantities of high-quality protein maintained their muscle and stayed strong (4-6).

In Moro et al, participants consumed 20 gm of whey protein after training (4). In Tinsley et al, participants consumed whey protein daily and ingested more than 1.4 gm/kg/day of protein (5). Finally, the participants of the study performed by Stratton had a protein intake of 1.8g/kg/day (6). Moreover, these participants were provided with 50 gm of whey supplement to consume each on training day (6)!

Thus, the consumption of large amounts of high-quality protein, in addition to resistance training, appears to be important for maintaining lean muscle mass during IF fat loss.

The Take Home Message

There is now good evidence that intermittent fasting combined with resistance training is an effective approach for losing fat while maintaining muscle. And let’s not forget the host of other health benefits that go along with IF, including a reduced risk of death by cancer and heart attack!

For the best chance for intermittent fasting success, current evidence suggests the following four rules. First, you should combine intermittent fasting with some form of resistance training. Second, you should use a time restricted fasting approach. Third, you should always train in a fed state and make sure that you eat after you’ve trained. Finally, you should consume large amounts of high-quality protein while fasting.

Please click on the link below for your free PDF.


Four Rules For Successful Fasting

References and Further Reading

1.            S. D. Anton et al., Flipping the metabolic switch: understanding and applying the health benefits of fasting. Obesity 26, 254-268 (2018).

2.            R. de Cabo, M. P. Mattson, Effects of Intermittent Fasting on Health, Aging, and Disease. The New England Journal of Medicine 381, 2541-2551 (2019).

3.            S. Keenan, M. B. Cooke, R. Belski, The Effects of Intermittent Fasting Combined with Resistance Training on Lean Body Mass: A Systematic Review of Human Studies. Nutrients 12, 2349 (2020).

4.            T. Moro et al., Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of Translational Medicine 14, 1-10 (2016).

5.            G. M. Tinsley et al., Time-restricted feeding plus resistance training in active females: a randomized trial. The American Journal of Clinical Nutrition 110, 628-640 (2019).

6.            M. T. Stratton et al., Four weeks of time-restricted feeding combined with resistance training does not differentially influence measures of body composition, muscle performance, resting energy expenditure, and blood biomarkers. Nutrients 12, 1126 (2020).

7.            M. Oh et al., Effects of alternate day calorie restriction and exercise on cardio-metabolic risk factors in overweight and obese adults: an exploratory randomized controlled study. BMC Public Health 18, 1-10 (2018).


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Old Guy Looking Into Mirror

Why am I getting old? Molecular Changes Driving Old Age

Aging mechanisms interact within a network of complex feedback loops, leading to increased damage and degeneration over time.

Resilient Happy Older Woman

What is Positive Aging?

By applying the principles of Positive Aging, you can avoid disease and disability and lead a long, healthy, and fulfilling life.

Powerful Older Man

An Antidote Against Frailty

Frailty is preventable, and often reversible, if you are willing to put in the work and follow the four golden rules of resistance training.