Intermitent fasting: get your science right

Nothing strikes my frustration more than seeing people following a trend ever so blindly and falling into the hype without understanding it thoroughly. This is currently the case for intermittent fasting. It has been around the fitness and health industry for few year now and has become very popular and hyped up, associating it with all kind of health and wellness benefits without actually putting things into sientifical context.

Ranting isn’t the best way to start a blogpost but I had to let it out.

Intermittent fasting (IF) is now associated with weight loss, preventing cancer, improving appetite and delaying the onset of age related deseases. While most of it is true, you need to be aware of the context of its validity and the research behind it.

Unlike what you probably think, we’re designed to fast …

The idea of using IF has sparked from our evolutionary nature, where food was not ubiquitous and a lot of species had to adapt to long periods of fasting. Your grand-grand-grand-grand parents spent days wandering around the woods picking up nuts and hunting animals to survive. The abundance of nutrients and our excessive eating patterns nowadays have led to a lot of metabolic disfunctioning and diseases. We’re at a point where we believe that eating every 2 hours is necessary to keep metabolism up and prevent our catabolic reactions of muscles from eating themselves. If not eating for a certain period was as problematic as we make it to be, we wouldn’t be here today. Researchers have then started to dig into how can caloric restriction and IF in particular extend healthspan and lifespan by promoting atophagy (cell cleaning itself) and cell regeneration.

But first let’s settle in on a common definition of IF

Intemitent fasting isn’t a commonly used word in the scientific litterature, you will find time restricted feeding (TRD) more prominent. As its name suggests, TRD is putting your body in a fasted state and deploying a restricted feeding window. There are different TRD protocols:

– The alternate day fasting: aka the on/day off fast where you basically fast for 24hours and eat in the following day.
– 5/2 fasting: where two days of the week are dedicated to fasting and the five remaining ones are your feeding window
– Prolonged fasting: where you go beyond 3 days fast to 5 days extended fast.
– The 16/8 fast: which is the most common approach used in the fitness industry with the so called “lean gains approach” where you eat for a window of 8h and fast for the remaining 16. 

The idea of IF sounds daunting at first but its benefits makes it worth a try. I’ve personally been on and off IF for two years now (I’ll talk about the cycling benefits in another post).

So let’s dig into the benefits.
If you are too lazy to read the scientific details (although that defies the whole purpose of me writing this), you can go down to the by and large section.

1-Weight loss: Is the wait worth the weight ?

I had to start with this one since that’s the number one reason why people get into the IF wagon. But let me put a big emphasis on this one first :

” The only factor that is directly correlated to weight loss/ weight gain is your caloric balance. If you’re in a caloric surplus you gain weight, if you are on a deficit you lose weight ” – (until proven otherwise)

IF is one of the useful strategies that can help you create that deficit. By restricting your feeding time, you’ll find yourself unconsciously consuming less food. However, beware of the caloric intake; you can take in a small quantity of food but high in calories and still not achieve the caloric deficit to lose weight.

Yet, I am still pondering on the idea of whether intermittent fasting itself can help you lose fat; meaning if you eat ad libidum (as free as you want) while still intermittent fasting, can you still lose weight ? This goes at first glance against the calorie balance principle but the reasearch is worth digging into. Dr. Satchin Panda, famous in the sientific community with his work on TRD, has made an interesting conclusion around tuning your food intake around your circadian clocks. Your circadian clock is basically the program that regulates your metabolism from the moment you wake up until the moment you go to bed. In the morning, when you’re exposed to sunlight, your clock starts on with the secretion of cortisol hormone making you more insulin sensitive which means that your body hormones are all ready to receive the food you eat and convert it into energy to support your diurnal activities. When the sun starts to set, your cortisol hormone drops inversely to your melatonin that starts to rise up making you more insulin resistant. At this state, your body is ready to wind down and start the process of rejuvinating that will get disrupted if you consume food around this time. Your cells need enough time to rest, clean themselves and rejenerate, a process called autophagy.

In Satchin’s first time restricted feeding mouse study, he took mice from the same mother, identical in age and gender, and fed 1 group an around the clock high fat/high sucrose diet, and the other group the same diet but with a limited 8 hour eating window. Both groups ate the same number of calories : 60% of their calories were from fat, 20% from sucrose, and the rest from protein.

After 18 weeks, it was found that the mice who followed the 8 hour eating window, weighed 28% less on average

Satchin repeated this experiment 3 times, with similar results each time. While the whole eating around your circadian rythm makes sence, we’re still waiting for more research to be made on human metabolism to prove these results. The legitimate scientific explanation would be the increase in other energy expenditure (BMR) while increasing the caloric intake in the fasted individuals (the calories equation is still of course valid).

2- Muscle gain / Muscle loss :

To the fit and bodybuilders out there, you’re probably worried about how fasting may effect your progress since you might be eating less. However, IF has proven to promote lean gains (IF with 16-8 is well known in the fitness community with the lean gains approach). This has been proven through so many studies including this 2016 study that has examined the effects of time-restricted feeding (16/8 for 8 weeks) on basal metabolism, maximal strength, body composition and other biomarkers in resistance-trained males.

The participants were mostly in their late 20s or early 30s, and they all had at least 5 years of training experience. Half of them ate all of their calories in an 8-hour window, with meals at 1 p.m., 4 p.m., and 8 p.m.  The other half ate at 8 a.m., 1 p.m., and 8 p.m. each day. The study concluded that the IF group lost about 1.6kg (about 3.5lbs) of fat versus a nonsignificant loss in the ND group while significantly maintaining their musclemass. It is to be noted that these individuals maintained a good level of protein intake

In the previously mentioned Satchin’s research in mice with a 12hours fasting protocol, there was a significant increase in their muscle mass

The reason behind fasting helping individuals maintain muscle is that enhances growth hormone secretion which activates protein synthesis and decreases the reverse catabolic reaction of dismantling proteins.

3- Overall health biomarkers:

I really wish more people were as interested in their health the way they care about aestethics. While most of you in their 20s think that caring about diabetes, cardiovascular health and cancer can be postponed later on in life, know that right now you are depleting your organ reserve and damaging your cells which may certainly lead to all these age related deseases sooner than you’ll expect.

Fasting is amazing for all of your health facettes and is the primary reason why you should probably try IF. Its effect on cardiovascular health, glucose regulation and cancer prevention waaaay outweigh the fast loss/lean muscle gain arguments I’ve mentioned above.

Bellow an intersting figure that shows the effect of IF on some of your organs.

Ageing Research Reviews
Fig. 3 Examples of effects of intermittent fasting on different organ systems.
Abbreviations: 30HB, 3-hydroxybutyrate; CRP, C-reactive protein; IGF-1, insulin-like growth factor 1; IL-6, interleukin 6; TNFα, tumor necrosis factor α

IF and Type 2 diabetes :

Type 2 diabetes (T2D) is characterised by an elevated insulin resistance in the body which makes it unable to utilize glucose for energy. Several studies have shown a significant increase in insulin regulation that is very important for preventing T2D.

Heilbronn et al study found that after 3 wk of ADF, insulin response to a test meal was reduced, which implied improved insulin sensitivity.
Anson et al. study showed that mice on alternate-day fasting regimen who consumed the same amount of food in a 48-hour period as mice fed ad libitum, decreased glucose and insulin concentrations. 

Here’s how your glucose/ketones* profile look during the day:
Ketones*: chemicals made in your liver that get produced when your glycogen stores are depleted. They become the new energy fuel instead of glucose.

Ageing Research Reviews
Fig. 1 :Examples of the influence of eating patterns on levels of glucose
at ketones in the blood.

IF , cancer prevention and longetivity:

There’s so much science behind TRD or IF and cancer prevention and longetivity that deserves a thorough ABC explanation in a seperate blogpost. But I’ll give you a brief explanation and conclusion anyways.
One of the causes of cell proliferation and cancer is elevated IGF1 (insulin life growth factor) hormone and inflamation levels. IF has shown in so many studies to reduce both IGF1 levels and inflamation biomarkers (IL-6 , C-reactive protein …)

On one hand, inflamation leads to the shortening of telomeres (the little ends in your DNAs) which is the main cause of aging and development of cancerous cells. On the other hand, cancerous cells are known to have 10x more glucose receptors than normal cells and rely mainly on it to survice unlike normal cells that can retreive energy from fats when glucose is unavailable. Fasting reduces blood glucose and shifts your metabolism into ketosis where your body burns its own fat for energy and uses it to survive. Cancer cells are then straved and weakened. Fasting is now being introduced as a treatment for cancer in combination with chemotherapy. Autophagy, a necessary process for longetivity, is also promoted during fasting.

By and large,

Fasting has been around in so many culture and is not a foreign protocol for our body. Its implementation in our daily lives is still challenging with social events our nature of work …. However, implementing it at even a small scale can be very beneficial to your overall health.

Fasting helps combat inflamation which is the evil of all morbidities: cancer, brain related deseases, diabetes …. Your body needs time to detoxify and heal itself and continuously choving food in it disrupts this process. The secret to long lasting health is giving your entire systems time to rejuvenate.
If you’re looking for a new way to losing fat, you may want to give IF a try. I’ve personally noticed a huge difference in my hunger cues ( they don’t appear as often) and a shriking in my appetite and all is due to the regulation of one of the hunger hormones leptin. I feel my energy levels are more consistent (no more post lunch coma) due to the blood glucose regulation in the body. When it comes to losing fat and building muscle, IF isn’t actually very superior to other methodologies but can be a helpful strategy if it fits your lifestyle.

An important note to keep in mind is although we’ve been using a commonized definition of IF of not eating for a certain period of time, the periodicity itself plays a huge role in achieving these benefits. The 16:8 is ideal for the lean gains approach a more extended fast can be to stressful on the body and trigger catabolic process . While for other health benefits, a 2/5 days fast and or a prolonged fast are necessary to see tangible results.

Research on all the facettes of IF is still ongoing. While many mice studies demonstrated all the benefits, I cannot wait to see what will human trials reveil.

Still got questions of IF ? Leave them in the comments bellow.



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