Intermittent Fasting: What You Need to Know About the Latest Diet Fad

Intermittent fasting, or IF, is one of the hottest new trends in the fitness industry.

The basic premise is that short fasts can accelerate your fat loss potential, and make you healthier.

For many of us, though, the idea of ‘fasting’ sounds waaay too extreme!

The consumption of 3 meals per day is the most common pattern of eating in industrialized countries, but a scientific rationale for this meal frequency with respect to ‘optimal’ health is surprisingly lacking.

If you think about it, each of us already fast on a daily basis.

I would say most people have at least 9 hours overnight when they don’t eat. That’s a fast, albeit brought on by your need to sleep, but you survive it nonetheless.

Aside from that, fasting is nothing new, whether it was forced due to times of food scarcity, or for various religious reasons.

But, is this concept a cause for concern? Or, something worth trying out?

At face value, it would be very easy to simply dismiss the whole thing as the next big fad.

But, clinical research does show a number of benefits for intermittent fasting, making it worthy of discussion.

Variations of Intermittent Fasting

There are number of books and website dedicated to this method of eating.

To give you an overview of the variations in this approach, let me tell you about 6 of them…

1. Alternate-day fasting (ADF)

Defined by its name, you basically eat every other day within a 12 hour window, then fast overnight and all day the next, eating again the following day (36 hours after your last meal).

One study concluded;

Alternate-day fasting was feasible in nonobese subjects, and fat oxidation increased. However, hunger on fasting days did not decrease, perhaps indicating the unlikelihood of continuing this diet for extended periods of time. Adding one small meal on a fasting day may make this approach to dietary restriction more acceptable.

2. Leangains

Leangains author, Martin Berkhan, recommends an 8 hour feeding window, followed by a 16 hour fast.

From what I’ve seen, I’d say this diet is a little more complicated, because it includes cycling of carbohydrates, and eating the bulk of your calories following exercise, amongst other things.

3. Warrior Diet

This diet recommends fasting for the first 20 hours of each day, working out during this period, then eating the majority of your calories within a 4 hour over feeding window.

4. Eat Stop Eat

On this plan, you fast for 24 hours once or twice per week, then eat sensibly the rest of the week. It is flexible in that you choose when you will fast, i.e breakfast to breakfast or dinner to dinner.

5. The 5:2 Diet

Similar to the Eat Stop Eat diet, this diet first reached the mainstream media in the UK following a BBC Horizon documentary, called Eat, Fast and Live Longer.

Again, the premise is relatively straightforward, you eat normally five days a week, and fast on the other two days.

6. Skipping Meals

Intermittent fasting is pretty popular amongst Paleo circles, who recommend eating and exercising randomly, like our ancestors did.

The idea is to randomly cycle daily calorie intake and randomly skip breakfast or dinner once or twice a week.

This is a very flexible approach, with no set guidelines.

As you can see, how someone approaches intermittent fasting is pretty much open to interpretation.

Is Eating Regularly Essential?

I’ll be the first to admit, I’ve always encouraged eating regularly to maintain a healthy, lean body, and a happy metabolizm.

The thing is, when most of us miss a meal we start to feel extremely hungry, and it can quickly start to effect our mood (or, maybe that’s just me!! )

Here’s a thought, though, do we experience this extreme hunger because we absolutely must have food?

Or, is it because we’ve conditioned our body to expect food every couple of hours?

I suspect that later to be the case.

For some people, they are able to adapt to this new way of eating in a few short days by switching their meal timing. However for others, the hunger continues on fast days, making it difficult for them to maintain.

Intermittent Fasting vs Eating Regularly

As I’ve said, in the past I would certainly have told you we all need to eat regularly.

Nowadays though, I think a more individual approach is appropriate.

Overall, I’d say most people do better eating around 4 times each day.

But, for others because of work life, personal life, cravings, preference etc., they do better eating less frequently, even skipping meals from time to time.

Benefits of Intermittent Fasting

The main problem with this whole area of intermittent fasting, is that research in humans is severely lacking, and what I’ve found online is something I can only describe as ‘evangelism’ in support of this way of eating.

That’s not to say some of what is being said isn’t true, but much of it should be taken with a pinch of salt!

Anyhow, some of the research suggests intermittent fasting may lead to;

Improved HDL levels in women, and other improvements in blood lipids for both sexes.
Improved insulin sensitivity in men and women, but impaired glucose tolerance in women.
Weight loss (also here).
Blood pressure benefits.
Extended lifespan (in rats).
Improved cognitive function, and protection against conditions such as dementia and Alzheimer’s disease.
One review looking at humans in terms of ‘real-world’ health outcomes, noted that intermittent fasting may have a protective effect against heart disease, type 2 diabetes and cancer. However, it concluded “more research is required to establish definitively the consequences of ADF (alternative day fasting)”.

Many of these benefits are also commonly cited for calorie restriction and exercise, which seems a more natural way to achieve better health, without the downsides of periodic food deprivation (see here and here).

One group of researchers, however, were extremely enthusiastic about this whole idea of fasting, claiming;

Since May 2003 we have experimented with alternate day calorie restriction, one day consuming 20-50% of estimated daily caloric requirement and the next day ad lib eating, and have observed health benefits starting in as little as two weeks, in insulin resistance, asthma, seasonal allergies, infectious diseases of viral, bacterial and fungal origin (viral URI, recurrent bacterial tonsillitis, chronic sinusitis, periodontal disease), autoimmune disorder (rheumatoid arthritis), osteoarthritis, symptoms due to CNS inflammatory lesions (Tourette’s, Meniere’s) cardiac arrhythmias (PVCs, atrial fibrillation), menopause related hot flashes. We hypothesize that other many conditions would be delayed, prevented or improved, including Alzheimer’s, Parkinson’s, multiple sclerosis, brain injury due to thrombotic stroke atherosclerosis, NIDDM, congestive heart failure.

Intermittent Fasting and Weight Loss

There are a lot of ‘evangelicals’ promoting intermittent fasting as the ultimate way to lose weight and maintain lean muscle mass, but is that really the case?

Let’s see what the research says…

One study took non-obese men and women, and placed them on an alternate day fast for a total of 22 days.

They lost an average of 2.1kg, despite instructions to eat double their typical day’s intake every other day.

In another study of alternate day fasting, subjects lost an average of 2.5% of their initial body weight.

The benefits included a decrease in fasting insulin levels and respiratory quotient (indicating a fat oxidation increase of around 15g per day).

There was, however, an increase in hunger, which continued throughout the duration of the trial.

Another study compared the effects of eating all of the calories needed for weight maintenance in either 3 meals per day, or 1 meal per day.

This study showed very interesting results, some positives and some negatives;

Subjects who completed the study maintained their body weight within 2 kg of their initial weight throughout the 6-mo period. There were no significant effects of meal frequency on heart rate, body temperature, or most of the blood variables measured. However, when consuming 1 meal/d, subjects had a significant increase in hunger; a significant modification of body composition, including reductions in fat mass; significant increases in blood pressure and in total, LDL-, and HDL-cholesterol concentrations; and a significant decrease in concentrations of cortisol.

So, eating once per day led to weight loss, a lower body fat percentage, and a slight gain in lean muscle mass.

For me, there is one very strong drawback to be noted with this study.

The sample size was small to begin with, and only 15 subjects actually completed the trial, making the dropout rate 28%, which according to the researchers, was abnormally high.

This begs the question as to the ‘do-ability’ of this style of eating in the general population.

And, a small sample size is never a good thing, in terms of reliable evidence.

Religious Fasting

There’s quite a bit of research looking at the effect of the Ramadan fasting period on health, which serves as a good knowledge base for our topic.

For Muslims at the time of Ramadan, a complete food and fluid fast is undergone from sunrise to sunset (12-16 hours), which happens daily for one month.

Research shows that during this time, traffic accidents peak, as well as there being a significant reduction in working hours.

This is consistent with research showing a decrease in daytime alertness, mood, and wakefulness during the whole month of Ramadan (see here, here and here).

Physical performance and endurance also declined in professional soccer players observing Ramadan, with their performance remaining low for two weeks post-fasting.

These are interesting results, but it’s difficult to say if we can apply these cautions to people who fast sporadically, as opposed to extended periods each day.

Women and Intermittent Fasting

It seems highly likely there are important differences between the sexes that should not be overlooked.

It is well known that severe calorie restriction can have nasty effects on a women’s reproductive health.

And, there is some indication that fasting too often, and/or for too long, can lead to problems such as sleeplessness, anxiety, irregular periods, and other symptoms of hormone impairment in women.

For this reason, women of reproductive age in particular, ought to be very cautious about fasting.

As a result, I do not think women should risk going long periods without eating.

The literature is so sparse in this area, but when it comes to hormones and women, it is best to err on the side of caution with fasting.

Ladies, please do be very prudent.

Closing Thoughts on Intermittent Fasting

Ultimately, whether you choose to fast or not is entirely up to you, and your individual preferences.

As the research clearly indicates, intermittent fasting is not an easy road, there are definite pros and cons, which ought to be remembered the next time someone comes to you with persuasive anecdotes.

Personally, I have learned that skipping a few meals here and there isn’t such a big deal after all. But, I certainly won’t be making a habit of it.

My main worry is what the long-term health consequences of this way of eating will be.

At present, the literature is so sparse that we cannot make any clear statements about the effects of fasting, other than that we just don’t know for sure.

From what I’ve seen, many of the benefits of intermittent fasting, are also commonly cited benefits for calorie restriction and exercise, so it is really worth putting yourself through?

A very logical conclusion from all of this is that most of the population eat too much, and for too many hours out of each day.

Perhaps a vast improvement in health could be seen if our ‘feeding’ hours were simply shorter than our ‘fasting’ hours.

Achieving that could be as easy as stopping eating after 6pm each night until 8am the following morning.

What a shockingly simply concept!

What are your thoughts on intermittent fasting? Have you tried it? 

Intermittent Fasting: What You Need to Know About the Latest Diet Fad