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Fasting Diets - Which One is Best for Weight Loss?

Fasting Diets for Fat Loss Summary

  • Fasting diets have become extremely popular as a way to lose fat and weight.
  • It involves the conscious restriction of food/drink intake for a specific period of time rather than focusing on daily calorie restriction.
  • Also commonly known as intermittent fasting, there exists a range of diets such as the 5:2 diet; Alternate Day Fasting (ADF), the Lean Gains Protocol and the Fasting Mimicking Diet (FMD).
  • Each diet has its own pros and cons and beneficial effects and there isn't one best diet
  • The best fasting diet is the one that meets your goals and that you can stick to, so try each out and see which one suits your lifestyle the best.

What is Fasting?

"Fasting – the act of wilfully abstaining or reducing food intake, drink intake or both for a period of time."

Having been used spiritually and as a political statement for many, many years, the concept of fasting for health has shot up in popularity in the last decade or so. Now, the practice of fasting isn’t new; in fact, before agriculture, it was more a way of life than a wilful practice. Sometimes people were simply forced to fast because of unsuccessful hunting and gathering.

These days though, fasting has been suggested as a way to increase longevity, boost the immune system, and reduce the incidence and development of chronic diseases. As with all types of dietary practices, there isn’t one single way to fast. So what are the different types of fasting practice available and what are the pros and cons of each?

Intermittent Fasting - The Umbrella Term

Intermittent fasting is probably the most well known umbrella term for most fasting practices, but many people still don’t really understand what it means. To put it simply, intermittent fasting is the conscious splitting of a time period (days, weeks, months) into periods where you are eating and periods where you are fasting. Most intermittent fasting protocols rely on fairly short eat/fast cycles; usually centred around 24 hours or at most a week. These days, the terms fasting and intermittent fasting are generally interchangeable. Let’s take a look at four of the most common intermittent fasting methods.

Lean Gains Protocol - The 16/8 Method

Often known as time-restricted feeding, this fasting protocol recommends:

  • Eating for 8 hours of a 24 hour period
  • Fasting for 16 hours of a 24 hour period

For most people, this will mean eating all your daily calories sometime within 12pm-8pm, or 1pm-9pm for example. This protocol has shown promise in supporting lean muscle mass, decreasing fat mass, and improving biomarkers of inflammation, blood lipids and insulin sensitivity1,2. It’s a popular method amongst trainers and has even been suggested as the key diet to Hugh Jackman’s physique as Wolverine. Time restricted feeding can easily be altered simply by increasing or decreasing the fasting and eating times. For example, some people prefer to eat over a 4 or 6 hour window, but all protocols generally revolve around a 24 hour period.  

  • Pros: You have a lot of free time to focus on other aspects of your life, without needing to worry so much about when to eat or how much to eat.
  • Cons: This program can be difficult to incorporate for those who have an active social life and can be erratic if you’re chopping and changing the hours of fasting. You can also run the risk of grazing, which can have negative effects on health.

The 5:2 Diet - The Fast Diet

Perhaps one of the most well known of all intermittent fasting diets; the 5:2 Diet rose to prominence after the release of the 2012 book “The Fast Diet” written by Michael Mosely and Mimi Spencer. The fasting protocol recommends:

  • Eating regularly and unmoderated on 5 days of the week
  • Eating a heavily reduced calorie diet (600 calories for men; 500 calories for women) on 2 non-consecutive days of the week

The 5:2 diet is based on the premise that it is easier to stick to a modified fasting diet such as this than a daily reduced caloric intake diet. Studies on the 5:2 diet have shown similar benefits to weight loss with reduced muscle mass loss, along with moderate beneficial effects on blood glucose, lipid and inflammatory markers1. The 5:2 diet is still incredibly popular and is one of the most common fasting protocols used by people wanting to boost fat loss.

  • Pros: Easy to plan and follow and doesn’t require restrictions based on time of day.
  • Cons: Having such heavily reduced calories on the 2 days can be quite difficult for most people.

Alternate Day Fasting (ADF) - The 4:3 Diet

Similar in approach to the 5:2 Diet; Alternate Day Fasting (ADF) protocols recommend:

  • Fasting every second day – eg: eat, fast, eat, fast, eat, fast, eat
  • Fasting can be in the form of a total fast to a reduced caloric intake of about 25% of your normal intake
  • Eating days are generally ad libitum/unregulated – eat till full

The ADF approach is also known as the 4:3 diet as essentially you’re eating regularly for 4 days of the week and fasting for 3. As per the other fasting practices; ADF has shown benefit to weight loss, reduction in the risk of chronic diseases such as diabetes and cardiovascular disease as well as increasing hormones associated with decreased hunger. Unlike a usual diet approach of reducing the amount of calories eaten every day, ADF often preserves your metabolic rate and is better at maintaining lean muscle mass tissue1,3.

  • Pros: The ADF method is all about weight and fat loss and generally results in a higher reduction in weekly caloric intake than most other intermittent fasting protocols.
  • Cons: This method isn’t easy and it can be hard to sustain over a longer periods of time. Changing your diet so frequently can also have potential negative impacts on sleep.

Fasting Mimicking Diet (FMD) - The Longo Diet

Often called the new 5:2 diet, the Fasting Mimicking Diet is a relatively new approach to intermittent fasting, but one that has gained popularity over the past 2 years. Also known as the Longo diet thanks to Professor Valter Longo; a key scientist behind the new protocol, this fasting approach recommends:

  • 5 full, consecutive days of fasting every 1-3 months
  • Fasting days are more like reduced calorie days where you would have up to 1090 calories on day 1, followed by a maximum of 725 calories on days 2-5
  • The other days of the month/s will involve normal, regular eating.

The real key to the above diet is the specific macronutrient composition of the fasting days which looks like:

  • Day 1 – 10% Protein, 56% Fat and 34% Carbohydrate
  • Day 2 – 9% Protein, 44% Fat and 47% Carbohydrate

The reason why the FMD protocol is touted as the new 5:2 and one of the best ways to fast is because it’s been specially designed to counteract certain issues with other fasts; namely:

  • The unique macro composition helps users avoid hunger pangs during the fasting period.
  • The lower protein intake during the fast was intentional to speed up the benefits of a fast.
  • Fasting for 5 consecutive days helps to avoid the confusion the body might experience from alternate day fasts.

The FMD approach has shown promise in supporting cognition and decreasing risk factors and biomarkers related to ageing, heart disease and even cancer1,4.

  • Pros: Minimal effort required and one can get most of the beneficial effects doing this 3-4 times per year.
  • Cons: While the FMD approach can still support reductions in body fat, the weight loss from this diet hasn’t been as significant.

The Best Fasting Diet

The practice of fasting for health has grown exponentially in popularity over the past few years and will no doubt continue to flourish thanks to new research continuously coming out. With science on fasting diets continuing to grow, it’s still unclear which fasting protocol offers the best effects. Perhaps though, like other regional based diets, there isn’t one that is considered the absolute best. The FMD protocol is currently the new kid on the block and certainly has some excellent evidence supporting its effectiveness, but there have been plenty of research conducted on the other styles of fasting as well. At the end of the day though, the best fasting diet is the one you can stick to; so give each one a try, see which one you like and make a decision from there. 

1. Patterson RE, Laughlin GA, LaCroix AZ, Hartman SJ, Natarajan L, Senger CM, Martínez ME, Villaseñor A, Sears DD, Marinac CR, Gallo LC. 'Intermittent Fasting and Human Metabolic Health.' J Acad Nutr Diet. 2015 Aug;115(8):1203-12.
2. Moro T, Tinsley G, Bianco A, Marcolin G, Pacelli QF, Battaglia G, Palma A, Gentil P, Neri M, Paoli A.‘Effects of eight weeks of timerestricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males.’ J Transl Med. 2016 Oct 13;14(1):290.
3. Catenacci VA, Pan Z, Ostendorf D, Brannon S, Gozansky WS, Mattson MP, Martin B, MacLean PS, Melanson EL, Troy Donahoo W. 'A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity.' Obesity (Silver Spring). 2016 Sep;24(9):1874-83.
4. Brandhorst S et al. ‘A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced CognitivePerformance, and Healthspan.’ Cell Metab. 2015 Jul 7;22(1):86-99.

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