Topic Review: Intermittent Fasting

45,000,000 Number of Americans that go on a diet annually

48% US adults who believe that obesity is caused by diet

5 Major religions who practice fasting (Islam, Christianity, Judaism, Buddhism and Hinduism)

7 Number of regimes so far for intermittent fasting

1946 Earliest reported scientific publication on ‘Intermittent Fasting’ researching lifespans in rats

2016 Yoshinori Ohsumi wins the 2016 Nobel Prize in Medicine for discoveries of the mechanisms for autophagy

234 Number of scientific peer-reviewed articles with ‘Intermittent Fasting’ in title

68,204 Number of scientific peer-reviewed articles with ‘Diet’ in title

19 Completed clinical trials on intermittent fasting

9 Number of intermittent fasting apps to track your fast on iTunes

$4,000,000 Funds raised for Zero, one Intermittent Fasting app

ORIGIN STORY

How the BBC started it all..

Intermittent fasting may have the appearance that it’s just another short-term diet fad like so many others that preceded it, but in fact, there is nothing new, novel or faddish about it at all. The first meal of every day, no matter what time it is eaten, is the ‘breaking of the fast’ so you’ve been doing it your entire life. Just to be clear though, fasting is not the same as starvation. Starvation is the involuntary absence of food such as what happens during food scarcity and famine. While fasting is the voluntary withholding of food for spiritual, health, or other reasons.

Tracing back thousands of years, we have the ancient tradition of religious fasting which is common across all the major world religions. The daily sunrise-to-sunset month of fasting of Ramadan is probably the most well-known example of this.

So now we have the new trend of intermittent fasting which is the practice of alternating periods of normal food intake with extended periods (usually 16 to 48 hours) of low to no food intake. What has caused this explosion of interest in intermittent fasting can be traced back to a few defining moments. The first was the airing of Dr Michael Mosley’s documentary on the BBC called Eat, Fast and Live Longer in August 2012. A peek at Google trends shows a clear spike of interest in searches for intermittent fasting at this time and the interest has only grown since then. Throw celebrity endorsements from Hollywood and Silicon Valley and we’re rapidly approaching peak fasting.

Another explanation for the interest in intermittent fasting is the simplicity of it. Fasting bypasses all the debate about what nutrients and foods that should and should not be eaten and instead purely focusses on the length of time between eating. Fasting proponents are mostly agnostic about what foods are eaten during the ‘feasting’ times. A book about fasting is a short read indeed. Then there is the myriad of ways it can be done: from 12-hour fasts and longer, alternate days of fasting and feasting, or days of very-low-calorie intake. Pick whatever works for you. Simple.

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BACKGROUND

How does intermittent fasting work?

We all need energy to survive and our daily energy comes from food. Every time we eat, the food gets broken down by our gut and enters our bloodstream (except for the indigestible fibrous foods). Carbohydrates (e.g. rice, pasta, bread) get broken down into sugars that our cells use for energy. The excess not immediately used by our cells is either stored as glycogen in the liver or muscles or stored as fat. But sugar can only enter our cells via insulin, a hormone produced in the pancreas. Insulin, therefore, controls sugar levels between our blood and fat cells. So what?

Without any new energy coming into your bloodstream from food during a ‘fast’ – insulin levels drop. Since cells need energy to survive, fat cells then release their stored sugar from glycogen for use as energy. This means fat will be the primary energy source after an extended period without food. So the basic premise when fasting is to ensure insulin levels drop for long enough that fat will be burnt off – not sugar.

Autophagy and Fasting

‘Autophagy’ is a process that proponents of intermittent fasting claim as one big health benefit. Autophagy means “self-eating” and is a process by which cells repair/recycle damaged cell components by literally eating them. In 2016 Japanese scientist Yoshinori Ohsumi won the Nobel Prize for his discoveries into the mechanisms of autophagy for Parkinson’s and dementia.

Fasting “induces autophagy, sending a message of famine or scarcity to your body, thereby forcing your cells to do some inner maintenance by catabolizing waste products and repair themselves.” writes Dr Brenda Burgess from the University of Buffalo. By inducing autophagy, many claim that intermittent fasting provides anti-aging benefits that extend life and prevent chronic disease.

Now we know the basics behind intermittent fasting, let’s dive deeper with the experts to fact-check the big questions you want to know.

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THE CONSENSUS

Is intermittent fasting more effective for weight-loss than other diets?

100% Negative from 5 independent experts

Read the full answers to this question here. With 39% of people classified as overweight or obese, anything that can reduce the personal and social cost of obesity would be of huge benefit. So the first question we asked our experts was whether intermittent fasting was better for weight-loss. “Current evidence demonstrates that intermittent fasting is as effective as dieting every day for short term weight loss.” writes Dr Leanne Harris an Obesity expert from University of Glasgow.

A recent study comparing how people regain weight after 12months of dieting found no difference between traditional daily calorie restrictive diet and an intermittent fasting regime. “Both groups had regained similar amount of weight” writes Dr Sharayah Carter, a nutritionist from the University of South Australia. It’s unanimous amongst the experts that intermittent fasting isn’t superior to other forms of dieting.

What about appetite itself, can intermittent fasting help lower appetite? “Fasting will increase appetite” writes Dr Peter Rogers an expert on the psychology of appetite from the University of Bristol. “With an empty stomach we are ready to eat and enjoy food again (we are ‘hungry’). However, people who fast intermittently can adapt to its effects. They learn to find distractions and other ways to manage their appetite and they become less preoccupied with thoughts about eating.”

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THE CONSENSUS

Is Intermittent Fasting difficult to maintain?

50% Uncertain via 4 experts

Read the full answers to this question here. Going anywhere between 16 to 48hrs without eating is strange given the 3-meal a day habit we’ve been accustomed to as humans. “Intermittent fasting is not for everyone,” writes fasting expert Dr Krista Varady from the University of Illinois in Chicago. “Some people find the diet really easy, while others find it really hard”.

Some people skip breakfast and avoiding late-night snacking, so by default they are already Intermittent Fasting. This ‘time-restricted feeding’ is “the easiest form of intermittent fasting” writes Dr Varady.

The other popular type of fasting is known as “Alternate day fasting”. “Alternate day fasting involves a 500 calorie “fast day” alternated with a “feast day” where you can eat whatever you want,” writes Dr Varady. “Alternate day fasting seems to produce greater weight loss than time-restricted feeding, but it’s harder to stick to” she says.

The science suggests Intermittent Fasting is difficult to maintain long-term, just like the traditional diet and “one size definitely doesn’t fit all” writes Dr Natalie Lister from the University of Sydney. The best approach for dieting is the one that a person can stick to as it works best for them.

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THE CONSENSUS

Does intermittent fasting have health benefits?

53% Uncertain via 17 experts

Read the full answers to this question here. The explosion in interest in intermittent fasting goes well beyond weight loss. Many claim benefits for diabetes, cardiovascular disease, cancer, and anti-aging. Our experts agree there are not enough long-term human studies. “The jury is still out,” writes Dr Richard Holt, professor of diabetes and endocrinology at the University of Southampton. “Whether we should recommend these [IF] approaches remains debatable because it is uncertain what the long term effects are”.

There have been some studies reporting benefits to brain health, longevity and cancer – but only in animals. “The most striking benefits to date have only been detected in animal models (specifically, mice and C. elegans).. In animals, researchers have seen a reduction in the progression of Alzheimer’s and Parkinson’s disease, an increase in lifespan, and shrinkage of tumor growth” writes Dr Brenda Burgess from the University of Buffalo. But for humans “it’s too soon to tell,” she writes.

The problem is that animal studies rarely translate into humans. “There is currently insufficient evidence to support the suggestions that intermittent fasting can delay or counteract development of diabetes, heart disease, neurological disorders (such as Parkinson’s disease) and cancer in humans” writes Dr Alice Owen an epidemiologist from Monash University.

Any improvements in general health may also be due to loss of excess weight rather than to the specific effects of IF per se writes Dr Ivor Ebenezer, neuropharmacologist from University of Portsmouth. Other experts are more skeptical of intermittent fasting health claims. “30 years ago, it was thought that eating on small plates or keeping a food diary were cures for obesity” writes Dr Paul Ernsberger, a nutritionist from Case Western Reserve University.

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Uncertain. “Intermittent fasting” is being promoted as a way to lose weight, to get metabolic improvements such as lower blood glucose and lower blood pressure and the prevent aging. The data relating the success is mixed.

There is not even consensus on what constitutes intermittent fasting. Some protocol restrict eating to 8 hours in a 24 hour day or 16 hours of fasting. Some suggest complete lack of caloric intake 2 days out of the week while others would limit calories to 500 Kcal per day on “fasting” days. Each suggests healthy food choices. It is not surprising that some devotees will lose weight and see other benefits if they are more careful what they put in their mouths and this may be more important that the timing.

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TAKEAWAYS

1. Intermittent fasting is not superior for weight-loss than other diets.
2. It may be easier for some to maintain – others not. There is no one-size-fits all weight loss approach.
3. Most studies have only been done on animals. No human evidence exists that fasting promotes autophagy and extends life.
4. The general hype doesn’t match the science – more human studies needed. So don’t believe the celebrities and wellness gurus just yet.
5. Don’t start if you’re pregnant or breastfeeding. Always speak to your healthcare professional when changing your diet.