The Latest Fasting Study: Does 5:2 Fasting Yield Greater Weight Loss?

The Latest Fasting Study: Does 5:2 Fasting Yield Greater Weight Loss?

intermittent fasting weight loss

Some things in life are predictable: the way the media reacts to new diet research is unfortunately two of them.

We can predict, say, that every few months or so, there will be some crazy media headlines making some new nutrition research seem like it’s the greatest, most groundbreaking thing on earth.

Just as predictable is that when we take a look at that research, it ends up being completely unremarkable.

Sometimes, I’m wrong about this, but not often. Case in point: in the past two months, there have been two studies on intermittent fasting published.  

In October 2021, there was an intermittent fasting study was advertised by the headline, ‘Research review shows intermittent fasting works for weight loss, health changes.’

The first line of the article was this: ‘Intermittent fasting can produce clinically significant weight loss as well as improve metabolic health in individuals with obesity, according to a new study review led by University of Illinois Chicago researchers.’

Yes, thank you, this is nothing new. Fasting cuts calories. Cutting calories results in weight loss. 

The second line of the article was a quote from the study lead:

“We noted that intermittent fasting is not better than regular dieting; both produce the same amount of weight loss and similar changes in blood pressure, cholesterol and inflammation,” said Krista Varady, professor of nutrition at the UIC College of Applied Health Sciences and author of “Cardiometabolic Benefits of Intermittent Fasting.” 

Do you see what just happened?

Headline and first line, very fantastical.

Real story, not so much.

Fast forward a month, and I’m scrolling through the news today when I hit this headline:

‘Fasting 2 Days a Week Can Help Obese People Keep Off The Weight With Modest Result, Study Finds!’


I figured you all might see these headlines, and since I get asked a lot about intermittent fasting, I wanted to see what the fuss was about.

Turns out, there’s a new randomized controlled study on the 5:2 configuration of intermittent fasting that was just released in PLOS One, and predictably, the media has glommed onto it like it’s some sort of weight-loss miracle.

Let’s start from the beginning.

What is 5:2 fasting?

5:2 simply means that on two days a week, you eat between 500-600 calories. For the remaining five days, you eat ‘normally’ aka try not to binge out of hunger. 

People talk all about intermittent fasting benefitsaround fasting range from weight loss, to prolonging life and curbing aging, renewing cells faster, burning fat, reducing blood pressure, preventing all sorts of chronic disease…you name it, there’s someone out there claiming that fasting will cure it.

The internet is full of graphics like the one below:

intermittent fasting weight loss

Of course, we don’t have human research to prove that fasting will keep us from getting older or that increased cell turnover has any effect in the real world; these studies have mostly been done on animals, and like with a lot of diets, the claims are way ahead of the science. You can’t conclusively claim that fasting ‘delays the onset of neurodegenerative diseases.’ There’s just no good evidence to back that up.

As far as the ‘fat burning’ claim, if you’re in ketosis – which you probably won’t be in if you’re fasting for one day at a time – you’ll use fat for energy. But just fasting isn’t going to automatically burn fat. You might think that’s what’s happening, since fasting can be effective for weight loss.

But what’s actually occurring, is that you’re eating less. And eating less, means losing weight. At least, in most cases.

The other claims about fasting improving heart health and lowering blood pressure are again, not conclusive. If someone has resolution of symptoms or a lower risk for disease after fasting, this may very well be a product of weight loss itself, not the fasting.

How was this intermittent fasting study conducted?

The 12-month study looked at 300 subjects, mostly white, mostly female, with a BMI over 30. Each was randomized into one of three arms:

A Self-Help 5:2 arm: these individuals at 500 (female) or 600 (male) calories a day twice a week on non-consecutive days. They also received a single 20 minute consultation about how to cut calories on fasting days.

A Group-Support 5:2 arm: these individuals did the same 5:2 diet as the group above, but also received one-hour group counselling sessions once a week for 6 weeks. 

A Standard Brief Advice arm: this arm got basic NHS and British Heart Foundation literature about eating healthy, being active, portion size, etc. The single advice session lasted 20 minutes.

What did the study find?

Here’s the thing: all the groups lost weight.

The important this is that the difference between the fasting groups and the ‘standard’ arm was razor-thin. 

The 5:2 arm that had group support lost more weight at the 6 week mark, but after a year, the effect had ‘diminished,’ meaning that all groups were more or less equal in weight lost.

You don’t say.

Once again, and I’ll say it loud for the people in the back, intermittent fasting is NOT superior than conventional caloric restriction for weight loss. Studies consistently show this (here and here, for example)

Even though the 5:2 dieters rated their eating pattern more positively at the end of the study than the dieters in the Standard arm did, that didn’t stop them from quitting.

In fact, at the year mark, the percent retention (what percentage of the 100 participants in each group was still following the diet and providing data to the researchers) for all three arms was similar: Standard was 48%, Self-Help was 56%, and Group was 45%. 

Looks like diets are tough to maintain, but we already knew that. And as far as the original headline that dieters ‘kept the weight off,’ that was total malarkey. They kept it off WHILE they were dieting. We don’t have the numbers for the large number of people who dropped out. Did they keep the weight off, too? 

Here’s the study results for weight. As you can see, nothing significant between the three arms.

Intermittent fasting research

The study cited that the most common reason for attrition in fasting research is the ‘degree of hunger and discomfort’ from the fasting diet. In other words, it’s just too hard to maintain. The 8:16 configuration may be easier to do for the longer-term, but that’s not what the study looked at.

Still, fasting – whichever configuration you choose – is just another way to cut calories. For some people it works. For some, it doesn’t. 

All three arms were left to do their own thing for an entire year. Probably because they were counselled for just 20 minutes at the beginning of the research and then just left to their own devices, subjects in the Standard arm engaged in all sorts of diets through the duration of the study: Slimming World (a toxic, horrible diet from the UK), Weight Watchers, intermittent fasting (FOMO?), meal replacements, and even medication.

I’m not sure what the researchers expected here. Put 300 people on diets, don’t give them any support or even adequate information, then follow up a year later and see where they’re at. The group counselling did well in terms of weight loss, until the counselling ran out. 

There was no psychological intervention beyond that for anyone, which, let’s face it – if there had been, it may have increased retention for all groups. You’d think that if the study wanted to do something new and ‘radical,’…they’d look at the effect that consistent, intensive psychological intervention would have on any of these arms. Oh, and not starving people. That too.

But no, here we have the same old sh*t sandwich served up in a dirty ashtray. 

And, I’m sorry to say, there’s more.

As a dietitian, I’ve always had a beef with doctors who give flippant, unhelpful nutrition advice like ‘eat less, move more!’ and/or tell their patients to go onto restrictive diets *ahem* keto *ahem* without considering anything about the person’s life or situation. 

This happens all the time, so I was upset to read this gem of a paragraph in the study, meant for doctors:

‘In terms of intervention reach, the ease of delivery of the 5:2 instructions means that the intervention can be provided in a few minutes or via a brief leaflet. Interventions that can be delivered quickly and easily during clinical consultations and disseminated economically on a large scale are potentially particularly important.’

“In summary, a simple explanation of the 5:2 diet generated similar modest long-term outcomes as the traditional more complex advice and written instructions concerning diet and exercise.”

Apparently taking the time to speak to someone about nutrition, or GOD FORBID referring them to someone who actually knows what they’re talking about, like an RD, is just NOT ECONOMICAL.

Even more concerning is the researchers’ recommendations for doctors to suggest the 5:2 diet to patients, and to counsel them that the hunger they feel while fasting will go away if they ‘persevere.’

Oh, great! Just tell someone to starve themselves twice a week, throw them a leaflet, and send them on their way. And when the person complains that they’re starving, just tell them to continue doing it, because WEIGHT LOSS IS MORE IMPORTANT THAN YOUR HUNGER.

Nutrition advice doesn’t have to be ‘complex,’ and if it is, the remedy to that is not to put someone on a diet that’s simple but is ultimately going to be too hard to maintain.

We need doctors who see nutrition as more than just a soft science that can be summed up in a three-minute talk with a pamphlet. 

Who see people, not just numbers and weight loss. 

Who don’t use BMI as the sole indicator of health, and just prescribe a restrictive diet to anyone who they consider to be ‘obese.’ 

Who see the harm in starvation and who don’t ignore or patronize people who complain that they’re hungry when they’re dieting. 


When you’re making changes to your diet and lifestyle, all that matters is what works for YOU. 

At the end of the day, diets rarely work, especially without continued psychological support to figure out the ‘why’ of your eating habits and your relationship with food. In fact, getting counselling for that should be your first stop before you even touch your diet. 

And back to my original reason for writing this post, a reminder: it’s important not to jump on a diet bandwagon when you see it featured in media headlines. Read the study, ask someone who knows about it, and take a breath. If it’s important, you’ll know you’ll see something about it here.