Alternate Day Fasting: Should You Be Eating Every Other Day?

I was actually in the middle of another blog post when I got a message from a journalist wanting to interview me about a study that just came out on Alternate Day Fasting. I didn’t even know what that was, but suddenly it’s all over the place. I’m even having a Twitter spat about it (natch). 

I figured I should decode this latest research on ADF because I’m sure you’ve seen stuff about it too. 

What is Alternate Day Fasting?

Alternate Day Fasting, or ADF, is another method of intermittent fasting that entails eating every other day. I know, I know. One day on, one day off. Repeat. A recently published study  suggests that this way of eating improves health markers and causes weight loss. So of course, the media is all over it.

The Today Show headline touted the ‘benefits’ of ADF. Other headlines crowed, ‘Lose weight fast with alternate day fasting!’ and ‘Alternate day fasting is a safe alternative to caloric restriction!’

There’s also a book saying that you can ‘turn on your skinny gene’ by eating every other day. Dimwitted.

Leave it to the media to turn a study into completely idiotic clickbait headlines.

But what did the study really show, and is ADF a good idea? 

Should we eat every other day for health and weight loss?

Let’s find out.

The Research Behind Alternate Day Fasting

It’s important to note that this study wasn’t supposed to be about weight loss at all; the researchers were looking to see if ADF improves the risk of dying from a cardiovascular event, therefore prolonging life. Period. 

So it wasn’t about how much weight someone can lose by starving themselves 4 times a week, but the media is picking it up as that, because of course they are.

I’m willing to bet that some of the people who wrote those headlines haven’t even read the study at all. 

The study examined 60 healthy, non-obese people between 35 and 65 years old who were instructed to fast for 36 hours and then have a ‘feast day’ that was 12 hours in duration, for four weeks.

There was also a control group that ate their normal diet, and another group that had already been doing ADF for over 6 months. There was no baseline data for the over 6 month ADF group, meaning we don’t have any information about their health before they started on this diet. They were merely there to assess the ‘safety’ of this sort of eating pattern and as a comparison to the other groups. 

Here’s the thing about these sorts of studies: Researchers don’t go out onto a street corner and gather a bunch of random people for the study. They have all sorts of inclusion and exclusion criteria, which is a good thing. For example, you don’t want an elderly person on a trial like this. Or, a person with an eating disorder. 

But the bad side of this situation is that in many cases (including this one), it makes the translation of the study results into the general population a lot less applicable. 

The study authors admitted as much, saying that there may have been a selection bias toward participants who were already knowledgeable and/or interested in ADF. In other words, maybe a bit more motivated than the average person. 

The Findings of Alternate Day Fasting Study

The outcomes of the study weren’t surprising in the least.

The 4-week ADF group had an average of 37% reduction in caloric intake, which is huge, but if you’re not eating anything for 3-4 days, or even eating 500 calories or less on the fast days (as in some other studies), of course you’re going to eat less overall and lose a shit-ton of weight.

The actual weight loss of the group overall was no different than with daily calorie restriction of around 15% (which looks like 375 calories on a 2500 calorie intake); the ADF group just lost the weight a lot faster. 

30% of people regained weight lost, same as in a normal, every-day calorie restricted population.

Their Framingham Risk Score – which predicts likelihood of cardiac events within 10 years – decreased, leading the investigators to predict that this way of eating may extend life by lowering risk of cardiac events. 

But can you extrapolate four weeks of results into a long-term prediction? That seems like a bit of an overreach to me. 

Blood pressure, heart rate, lipids, and certain metabolites that are linked with aging were lower in the over 6 month fasting group. 

Effects of this diet on metabolism and bone mineral density long-term aren’t known. You might say, ‘why didn’t they check the metabolic rates and bones of the over-6 months group?’ That’s because they had no baselines – so the investigators didn’t know the starting metabolic rates and bone mass of the people in that group. Hm. That’s not very helpful.

The study authors say this: “we show in a clinical trial that a related intervention, alternate day fasting (ADF), also leads to striking reduction in overall calorie intake over the course of the study but is more easily tolerated than continuous CR”

Really? After only four weeks in 60 cherrypicked people, you’re saying that eating every other day is ‘more easily tolerated’ than every day caloric reduction? I can do pretty much anything for four weeks, but what happens after that?

We don’t know, because there wasn’t any long-term follow up. See where I’m going with this?

Why would you tout the ‘benefits’ of a 4-week intervention if you don’t know what happens when someone goes on it long-term? And holy hell – what happens to their quality of life? 

Their social interactions? 

Their emotional health? 

What happens when the general population, including people with fucked up relationships with food, go on a diet like this?

The focus on this study was on cardiovascular health and longevity, but in my experience, the people doing this diet are probably going to be doing it for weight loss. 

Disaster! But unbelievably, some RDs on Twitter who have done similar research on ADF were arguing with me this morning:

“You could look at it as you telling (people) that they don’t have to worry about dieting at all for half of the week,” one said to me. 

Um. They don’t have to worry about dieting because they’re on a binge-starve cycle? 

“We’ve actually shown just the opposite – that (alternate day fasting) has been shown to result in benign or beneficial alterations to disordered eating symptoms.” 

We then had words about walking the line between ‘eating disorder’ and ‘disordered eating,’ and I’m sad that I’m never going to get those hours of my life back. 

Seriously, I wasted a huge chunk of my morning arguing about this shit.

So Does Alternate Day Fasting Work?

This study was done to assess ADF’s effects on cardiovascular risk, not weight loss. 

People lost weight because they ate a lot less. That’s what happens when you starve for 3-4 days a week. 

Weight lost was no more and no less than a low calorie diet, but it was a lot faster.

We have no idea how this diet works for most people after four weeks.

A selection bias may have been the reason why the participants were successful with this diet. If prescribed by an RD or MD in general practice, the dropout rate may be a lot higher. 

It’s a pretty huge leap to predict after four weeks that a diet can extend lifespan. Like, don’t even go there.

It’s all fine and nice that researchers in a lab found that 60 people lost lots of weight by ADF, but why aren’t we taking into account how this sort of eating pattern will affect every other facet of someone’s life? Is it only about living longer and being thinner? What happened to quality of life? 

And most importantly: These new more extreme fasting programs are giving us a message that  food is the enemy. That to be ‘healthy,’ eating is something we shouldn’t do more than a couple times a week. What the fuck? 

I’m sorry, there are other ways to be healthy. Physically, emotionally, and socially. Why are we so one-sided, with tunnel vision to the most punitive, restrictive ways of living?

And lastly, some researchers who don’t do normal nutrition counselling – on clients, not on research subjects cherrypicked for a study – don’t seem to understand how their research would (or wouldn’t) translate into the real world. 

It’s not all about data. It’s about peoples’ lives. 

I’d never recommend this diet to anyone, at any time. Nope.