PSA: Intermittent Fasting Is Not a Miracle Weight Loss Tool

PSA: Intermittent Fasting Is Not a Miracle Weight Loss Tool

With the close of the year rounding the corner, talk of weight-loss tactics will likely follow. This is the time where many folks seek to set their new fitness and health goals, and unfortunately, dangerous habits can sometimes find themselves picking up traction.

First of all, let us be clear that you don’t need to bring a “new you” into a new year. You’re fine the way you are. But if you’d like to adopt healthier habits and improve your fitness, be sure you’re seeking the advice of health professionals first.

Fasting, in particular, has been enjoying a surge in popularity over recent years, thanks to proponents who claim it activates weight loss. Everyone these days, it seems, is skipping their breakfasts or drinking only water every third day. But is fasting actually good for you? And (more importantly to some) will it make you lose weight?

We do some digging.

The short answer is yes, not eating will make you “lose weight” for a while. Intermittent fasting involves severely restricting food intake for periods of time, which does cause weight loss. Until relatively recently, it was largely a behaviour associated with religious ceremonies or other spiritual works. Now it’s become a mainstream fitness craze.

Writer Julia Belluz did an explainer on how it works for Vox, breaking down the basic types of fasting routines that practitioners adhere to:

Intermittent fasts involve eating no food or massively cutting back on calorie intake (e.g., 500 calories per day) only intermittently (like the very popular 5:2 diet).

Time-restricted feeding involves consuming calories only for a four- to six-hour window each day (for instance, skipping breakfast and only eating lunch and an early supper).

Periodic fasts, the most extreme, typically last several days or longer. These diets involve drinking only calorie-free fluids or very few calories for long stretches to get the body into full fasting mode (instead of switching back and forth between fasts and feeding).

Fasting-mimicking diet, a plant-based diet that involves eating very few calories “through light foods like soups, energy bars, and energy drinks” for several days each month.

There is no denying that eating less functions for weight loss for some, but before you decide fasting is the best way for you to eat less, here are some basic misunderstandings about the “diet”.

There’s not much research on weight loss and fasting

There is actually not much science on fasting as a weight-loss tool. As Belluz explains, most research is focused on the potential health and longevity benefits of eating less. Proponents of fasting say that eating three square meals a day is a relatively new thing for humanity since we lived without agriculture for quite some time.

The scientists who research fasting are mostly focusing on whether it improves the outcomes for health markers for diabetes, cancer, and cardiovascular disease. And it does, according to Valter Longo, director of the Longevity Institute at the University of Southern California:

“A lot of organs start shrinking [during a periodic fast],” Longo explained.

“A lot of cells start dying and we have evidence a lot of the cells killed by this process are the bad cells. Then the stem cells get turned on, and we see the body starts regenerating itself.”

But this research only covers a few months of study a fairly brief period in a person’s lifespan. Other studies regarding the benefits of fasting for long-term health have been inconclusive.

It’s hard to do

The best diets aren’t diets at all; they’re changes to your lifestyle that are manageable and maintainable. It’s hard to describe a more difficult diet to maintain than “don’t eat”. Many people dropped out of Longo’s study because they were unable to stick with the fasting demand, even for science.

You can lose weight, but whether or not it’s a sustainable behaviour for you is important. Belluz shared this observation from a fasting researcher who conducted another study from 2018:

“Dropout rates have been as high as 40 per cent. Thus, despite the statistical significance of weight loss results, the clinical significance and practicality of sustaining an [intermittent fasting] regimen are questionable.”

If you can’t fast, you won’t lose weight and you will probably feel pretty lousy the whole time, too.

It can be unhealthy

The research on fasting hasn’t extended to every group. They don’t know what kind of negative impact it can have on the elderly, children, or people who are underweight. It can also be dangerous for people with a history of disordered eating, according to psychologist Debra Safer:

“The research evidence generally shows that patients with eating disorders do best when they eat regular meals and snacks,” Safer said.

“Intermittent restriction of intake is often one of the behaviours that people with eating disorders engage in as part of their eating disorder ” and it often sets them up to binge and/or purge.”

So in people with eating disorders, fasting is “potentially risky in that it disrupts attempts to build and maintain hard-won normalized eating patterns.”

Longo also added that fasting can increase the risk of gallstones when done incorrectly, and should not be attempted by people who are “diabetic and taking insulin or any other drugs, or if you have metabolic disorders.”

Other forms of calorie restriction are more effective

If you’re determined to cut calories from your diet, fasting is still not the most effective way to do so. Instead, try regular ol’ everyday restriction.

The researchers looked at randomised controlled trials of intermittent fasting and found that the people who fasted lost about 4 to 8 per cent of their original bodyweight, on average. So fasting worked, but, interestingly, it didn’t outperform regular, continuous calorie restriction (“eat less every day” dieting), and it didn’t lead to dramatic weight loss.

There are people (those who don’t fall into any of the groups who could potentially suffer dangerous health consequences) who find fasting beneficial. They prefer to just restrict the time in which they eat rather than count calories or worry about what they consume. Fair enough. Just understand the costs and benefits of not eating regularly, because there may not be too many of the latter.

Fasting diets are going mainstream ” ahead of the science. Here’s why. | Vox

This article has been updated since its original publication.


  • Having lost 40kg after gastric surgery, I plateaued. Increasing physical activity yielded results for awhile but ultimately I had to change the fuel intake to fuel spent ratio. I went 5:2 – but not religiously, fuck counting calories in the neck. On my 2 days breakfast & lunch are VLCD shakes, dinner is protein, dairy & roughage. I allow myself a 600ml Feel Good Iced Coffee as well. Have consistently lost 1kg/week on average for the duration. I do not think it’s the fasting alone doing it though.

    Yes, I lose the most weight over those two days (I weigh at beginning and end of fast) however I noticed the strategies developed to cope with hunger while fasting crept into my non-fast days. I drank more water, more no sugar soft drink and fewer snacks. Result? Overall calorie intake is way down.

    Christmas and being on leave has buggered the average a bit…

  • I’m trying it out now but also of concern is the extra cortizol created when in a fasting state, curious if this leads to premature aging. Haven’t been able to find any longterm data on it yet.

    • All the information I’ve read and watched indicates that it promotes longevity. Although most of the proponents I’ve seen look like Changi prisoners of war.

  • I’ve managed to lose (and keep off) almost 30 kilos since starting on the 5:2. I don’t bother counting calories, just stick with a selection of food I know is low calorie and good for me on my fasting days.
    I would recommend also trying to eat less/better on the other 5 days for best results. Once it became a habit I found I simply couldn’t eat as much as I used to anyways!

  • I think the point is not to expect intermittent fasting to be a miracle worker. It forms part of a healthier diet. Fasting is not bad in itself.

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