The user's guide to intermittent fasting

Intermittent fasting is currently one of the world's most popular health trends. Characterised by alternating periods of food absence followed by periods of normal eating, promoters of intermittent fasting claim that it is the ‘metabolic key’ to unlocking weight loss, reducing inflammation, cutting the risk of diabetes and heart disease and maybe….even extending your life. This show covers what intermittent fasting is, how to do it, and what the evidence says about that long list of health claims.

Links referred to in the podcast 

• Intermittent fasting vs traditional dieting for weight loss https://www.mdpi.com/2072-6643/11/10/2442 
• Review of the effects of intermittent fasting on health, ageing and disease https://www.nejm.org/doi/full/10.1056/nejmra1905136 
• Fasting during cancer treatment https://www.medicalnewstoday.com/articles/324169.php 
• Children's food choices after watching a healthy cooking show https://www.jneb.org/article/S1499-4046(19)31055-3/fulltext

Episode transcript
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Transcript

Intermittent fasting is currently one of the world's most popular health trends. Characterised by alternating periods of food absence followed by periods of normal eating, promoters of IF claim that it is the ‘metabolic key’ to unlocking weight loss, reduce inflammation, cut the risk of diabetes and heart disease and maybe….even extend your life. If you want to learn just what IF is, how to do it, and importantly what the evidence says about that long list of claims, then you’ve come to right place.

Intermittent fasting may have the appearance that it’s just another short-term diet fad like so many others that gone before 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 eating 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. That soon a spurred a swathe of popular books such as The Fast Diet, and the 5:2 Diet.

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.

So how to you do a fasting diet? There are several different ways - all of which involve splitting the day or week into eating and fasting periods. IF focusses on the time when you don’t eat. Kinda like the saying that it is the silence between the notes that makes the music” – that’s very Zen.

Here are some of the most widely used fasting schedules:

•  The 16/8 plan involves eating only during an eight-hour period followed by a 16-hour fasting window. So, if you have your last meal at 8pm at night, you don’t eat again until midday the next day. Rinse and repeat. This method is technically called TRF, but falls under the IF umbrella.
• Then there is the elegantly simple Eat-Stop-Eat way of doing fasting. Simply fast for a full 24 hours straight one or two days per week
• Then we have the popular 5:2 diet. This involves choosing two days each week where you will eat only 500 to 600 calories per day but eat normally the other 5 days.

Which is best? Science is nowhere near answering that question. Many people find the 16/8 method to be the simplest and sustainable method to stick to. If you find it becomes easy to do, then it is possible to move to more advanced fasts like a 20:4 (fast for 20 hours, eat for 4 hours) or even join the ‘one meal per day club’ and do true 24 hour fasts.

But it doesn’t stop there, delve into the IF subculture on reddit and you’ll read of all manner of self-experimentation. Here, days of water only fasts are the norm. And then some go even more hardcore and do ‘dry fasting’ – no water and often no showers or brushing teeth to avoid any ‘water absorption’. The premise of doing this takes bro science to stratospheric levels.

Then there are the IF debates whether outside of water, non-caloric drinks such as tea and coffee (without sugar or water obvs) are okay to have when fasting. There seems little to say that a short-black will do any harm in losing the benefits of a fast so if it helps, then do it. On that note: spoiler alert for an upcoming episode where I’ll delve into coffee and its effects on health and where the news is good, surprisingly good indeed.

Weight loss

In looking at the evidence for benefits of IF, let’s start with the big one first: weight loss. Here’s the super short summary. Some people lose weight, others don’t, and it doesn’t seem to be any better or worse than any other diet.

Now for the science. The idea of fasting is that when we eat after an extended fast, we don’t fully compensate for the food we’ve gone without. That creates an energy deficit and…..weight loss! Proponents also say that IF is easier to maintain, so that will help with adherence.

There has been enough human weight trials comparing IF against tradition CR to see how they stack up. And that was the topic of review paper published in the journal Nutrients in October of 2019. I’ll link to the study in the show notes. https://www.mdpi.com/2072-6643/11/10/2442 

11 RCTs were looked at and they all ran for at least 8 weeks and involved adults who were overweight. IF was compared to CR head-to-head in each study. And what did they find? Nothing to get excited about. 9 out of 11 studies showed no differences between groups in weight or body fat loss.

So, if there is a benefit, it is pretty small and not of much clinical significance.  There wasn’t a strong case either for greater loss of body fat in IF vs CR even though the odd study finds this happens. 

And as for ?sustainability. Not enough evidence. All diets are poor.

So, in summary, if IF works for you and meets your goals and you feel better for it, knock yourself out with whatever fasting protocol works for you. But you won’t be seeing me anytime soon proclaiming it as some next-level diet hack that is going to have you shredded for summer.

All diets can work, but few stick to it. Hands up who is still doing Paleo to the original letter it was promoted as? I rest my case.

Other benefits

Fasting for weight loss is hardly a new idea. But what is novel about the explosion in interest in fasting is the clinical research behind it with claimed benefits for health and longevity. The body of evidence on intermittent fasting in humans is still relatively small, but several studies have reported improvements in various health markers. It is still an active area of debate if there are any unique metabolic benefits to intermittent fasting over traditional chronic caloric restriction.

And once you start talking about benefits outside of weight loss, you’ll soon come up against a term called 'autophagy'. “Auto” means self and “phagy” means eat, autophagy is the body's way of cleaning out damaged cells literally by ‘eating ‘itself’. This is done as way for the body regenerate newer, healthier cells. It’s going on inside you right now. But during fasting, cells activate pathways that increase defences against oxidative and metabolic stress and systems that remove or repair damaged molecules. Think of this like a switch that is activated in periods of food scarcity as the body looks for more fuel sources. Less junk, means a leaner cleaner and better functioning running body. At least that’s the theory. In our modern times of food abundance and ‘three meals per day with snacks in between’, it is rare for this metabolic switch to be flipped. But the benefits of the switch have favourable advantages in improving blood sugar regulation, increasing resistance to stress and decreasing inflammation.

So, is IF the key to reducing inflammation, cutting the risk of diabetes and heart disease, improving the brain and neural systems and maybe….even extend life? A lot of this is really conjecture or based on animal studies at this stage, but a paper published just the last month highly regarded The New England Journal of Medicine has put the health claims about intermittent fasting diets under the microscope. I’ll link to the paper in the show notes. https://www.nejm.org/doi/full/10.1056/nejmra1905136

Weight loss aside, there are some initial indications that intermittent fasting may have some additional metabolic advantages. With animal studies and some human research to inform it, there appears a benefit of fasting on supporting cellular health. Cellular health is a broad term and includes things like resistance of cells to metabolic and oxidative stress, increased DNA repair and activation of antioxidant defence systems.

Other benefits uncovered by the review included some evidence for intermittent fasting on decreasing blood pressure, blood lipid levels and even resting heart rates. Clinical trials show that even independent of weight loss, intermittent fasting has an additional advantage on insulin sensitivity and abdominal obesity compared to just a traditional calorie-reduced diet.

In animals and humans, physical function is improved with intermittent fasting. For example mice maintained on alternate-day fasting have better running endurance than mice that have unlimited access to food. Balance and coordination are also improved in animals on daily time-restricted feeding or alternate-day fasting regimens.

More speculative, but there appears some preliminary research to show that intermittent fasting could benefit brain health too. One study found that mice that were on a brief intermittent fasting diet had better learning and memory than mice with free access to food. Further research in animals suggests that intermittent fasting can suppress inflammation in the brain, which has links to neurological disease. Other animal studies have found that intermittent fasting can reduce the risk of neurological disorders including Alzheimer's disease, Parkinson's disease, and stroke. One study with 220 healthy adults who maintained a calorie-restricted diet for two years showed signs of improved memory. There is a lot more that needs to be done here.

As for longevity unless you’re a worm or maybe a lab rat, there isn’t much evidence to show that IF will help you live longer. But if it helps with weight loss and reduces the risk of some chronic disease like heart disease and T2DM, then that is where the benefit could lie. 

And finally for cancer, animal studies suggest that intermittent fasting may prevent cancer, but there is nothing yet to say it will help in humans, As a side journey, there is absolutely fascinating work being done looking at how fasting during chemotherapy could improve treatment by promoting cellular regeneration and reducing side effects like nausea and vomiting. Very early days for this, but is an area I’m watching with interest. If you want to learn more, I’ve linked to a commentary article on this in the show notes. https://www.medicalnewstoday.com/articles/324169.php 

Safety

And finally, it would be remiss of me not to make the big statement that intermittent fasting is not for everyone.

If you’re underweight or have a history of eating disorders, IF is likely not for you unless under the supervision of a HP. Intermittent fasting could certainly be a dangerous triggering factor for someone vulnerable to an ED.

For anyone taking medications to treat diabetes, then IF should not be done without talking to your doctor first. These medications are designed to remove glucose from the blood and without any food, they can do their job too well and put a person at risk of hypoglycaemia.

Hunger is the main side effect of intermittent fasting. You may also feel weak and your brain may not perform as well as you're used to. This may only be temporary, as it can take some time for your body to adapt.

And if you’re pregnant or breastfeeding, probably best to give IF a miss.

Summary

So that’s your user’s guide to IF. It is something I’m asked about a lot on for my thoughts. And my standard response now is that if it connects with you, you find it works and you can fit it into your daily life and helps to make life easier, rather than harder, then go for it. But there is a long way to go before there is enough evidence to move intermittent fasting into the mainstream as first-line approach to lose weight or viable way to treat many health conditions.

Research Wrap

All this talk about fasting is making me hungry. So for the last part of the show, I like to do a quick research wrap up about a study that has grabbed my attention recently. And the topic of the research is cooking shows!

Cooking shows are not just a source of entertainment with a new study finding kids who watched a healthy cooking show aimed at kids were almost 3-times more likely to make healthy food choices.

The backstory here is that our food choices and habits as adults are strongly influenced by our experiences of food during childhood. Poor dietary habits during childhood and adolescence have many negative effects on several health and wellness indicators, such as keeping a healthy weight, growth and development patterns and even dental health.

Prior research has shown that when kids and adolescents are involved in the preparation of healthy foods, such as vegetables and salads, they are more likely to consume nutrient-rich foods, have higher intakes of important nutrients, and lower intakes of sugary and fatty foods. But today, there has been marked fall in the number of meals eaten in the home. Combine that with a greater reliance on pre-prepared food and this means less exposure of kids to modelling of cooking skills by adults.

So, could cooking programs be a useful way to improve children’s food and food preparation knowledge which could translate into better eating habits? To test this novel idea, Dutch researchers recruited children 125 children aged between 10 to 12 years from 5 different schools. https://www.jneb.org/article/S1499-4046(19)31055-3/fulltext 

The children watched one of two different videos. One was of video clips of a cooking program aimed at children containing healthy foods. While the other video was a cooking program containing unhealthy foods. Another group of children served as the control group and they watched a short video from a children’s quiz show.

After the video viewing, the children were offered a snack as a reward for taking part in the study. The snack was a choice of apple or cucumber pieces as the healthy options or chips and salted pretzels as the less healthy options. 

And what did they find? Children who watched the cooking program with healthy foods were almost 3-times more likely to choose healthy food as their snack.

The children were also asked to rate how healthy the food was that they saw in the video clips. And they were switched on as could clearly distinguish the difference between healthy and less healthy foods.

I like this research as it helps to reinforce the benefit of getting kids involved in the kitchen. And my help parents in being selective in choosing some better targeted cooking programs aimed at kids that they can watch. Good cooking skills developed through childhood has the potential to carry over into adult life in the food health choices a person makes.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.