Recap of some points from the last post:
According to the headlines, intermittent fasting helps “burn” fat, improves blood pressure, and gut health, and increases longevity and even brain function. I’m signing up now!
The problem is that these are often preliminary results of specific studies. Nothing confirmed by science.
Who wants to wait years for confirmation of what is seen in animals and see what happens in humans?! Or read the studies and analyze limitations? That doesn’t sell.
So many “gurus” and mainstream media take these preliminary results to sell their book, or magic diet plan.
So let’s dive in the real and confirmed health benefits of Intermittent Fasting.
Benefits of Fasting
What do we know about the human health benefits of fasting, in all its forms? Well, as we discussed in the previous blog post, it can help with weight loss. Some people, after fasting, do not eat enough to make up for the fasting period. Even if they eat a bit more than normal. This means that they generate a caloric deficit and ideally lose body fat.
So, for people looking to lose fat, intermittent fasting may be a viable option.
Some people prefer the simplicity of the time window of intake rather than worrying about what they eat all day. But is intermittent fasting better than any other method of reducing calories consumed? In most studies, it is equally effective for weight loss and the usual benefits that come with it, such as improved blood glucose and lipid levels.
In this second part on the topic of intermittent fasting, we will see if there are other benefits beyond weight loss related to fasting.
Intermittent Fasting and Autophagy
If there is one thing that has brought intermittent fasting to fame, it is the promise of keeping you young by increasing “autophagy”.
Unfortunately, most of the evidence for intermittent fasting and its relationship to autophagy comes from animal studies. In these studies animals sometimes do not even fast but are subjected to continuous, “traditional” caloric restriction.
But before we dive in a bit more into Autophagy, let’s start with the basics
What is Autophagy?
Popularly, it’s known as “eating yourself.”
Autophagy is the process that aims to clean damaged cells to create new and healthy ones. In this way, the body prevents the accumulation of waste and components that no longer function well. To achieve this, small microscopic vesicles called autophagosomes are necessary.
Prof. Guillermo Mariño, a researcher in autophagy, metabolism and aging, explains, these autophagosomes act in a similar way to modern domestic vacuum cleaner robots. That is, they move around inside the cell and engulf small portions of the cell, converting everything they find into energy and essential molecules.
At times when energy is conspicuous by its absence, such as when we go through a time of fasting, cells are able to increase their autophagy to supply the demand for nutrients and essential elements. Incidentally, it accelerates the renewal of cellular structures, delaying aging.
Many proponents of fasting believe that it is a process that works like a switch, meaning it is either on or off. Either it is happening or it is completely slowed down.
However, interpreting autophagy (or any other process that happens in the body) in this way is a serious mistake.
In physiology, these processes happen all the time to different degrees and in different tissues.
If someone were to ingest the largest meal of their entire life, there would still be autophagy occurring in their cells, albeit at a low intensity.
As we said, autophagy (like most cellular processes), has a “normal” intensity. This intensity can speed up or slow down depending on the situation.
Autophagy is indeed an essential part of healthy cell function. But is fasting necessary to optimise this process?
Fasting can increase the rate of autophagy, but that is not always a good thing. Autophagy is elevated in some metastatic tumours and is one of the ways they create fuel (1).
The bottom line is that fasting is not necessary for our body to experience autophagy.
Human biology and physiology are much more complex and there is no magic solution, unfortunately.
Autophagy and weight loss
A small study (2) observed that fasting can elevate autophagy rate.
However, in research of better quality and methodology, these findings could not be replicated (3). And, most importantly…there was no improvement over other forms of caloric restriction.
We do not lose fat by autophagy. Cells behaving in this way are not a key factor in weight loss. Increasing cellular metabolism a little does not translate into weight loss.
On the other hand, if you want to build muscle, increasing the rate of autophagy means you are increasing the rate of protein degradation, which will affect muscle building. Knowing how important it is (and sometimes hard) to gain and maintain muscle mass, is it worth it to make it even harder juts to have an increased autophagy rate? My answers is No.
That is, even in the scenario where starvation or fasting activates the autophagy process, it will not provide the caloric deficit necessary to lose fat and will make it harder to increase muscle mass.
Is Autophagy only achieved through fasting?
The relative rate of autophagy will increase during fasting, but is this the only way? NO
Autophagy also increases with caloric deficit and physical exercise (4).
As you can see in the graphic, when exercise is performed the organs start to increase the rate of autophagy activity.
Does Fasting prolong life?
There is a lot of evidence in animals that show that caloric restriction prolongs life. But of course, we are not talking about lifelong caloric restriction!
When researchers study caloric restriction in animals, they restrict about twenty per cent of their intake ad libitum. As a result, those animals lose weight for a period of time and then maintain a new body weight. (lower than what they had at the beginning of the research).
What is actually happening is that they prevent these animals from becoming overweight. They keep them relatively lean and consequently live longer.
Why? The main hypothesis points to low levels of body fat. Excess of body fat is associated with higher mortality rates.
It is very likely that this also applies to humans because we know that excess adiposity increases the risk of mortality from all causes.
The point is that these animals do not fast their entire lives. They have an initial caloric deficit that allows them to lose some weight which they then maintain and live longer than animals that ate as much as they want.
Regardless of what you believe about fasting and the protocol used, sooner or later you are going to have to eat in order not to die.
What will happen to autophagy in that period? Of course, it will be inhibited, and that inhibition will be proportional to the calories consumed.
So it is always better to focus on having a good body composition and being physically active than thinking about not eating.
So, is Intermittent Fasting Magic?
Most studies around IF select overweight people with metabolic problems. That makes a lot of sense for a weight loss study, but it doesn’t tell us much about the benefits of fasting for a healthy person.
I don’t rule out additional benefits of fasting beyond the reduction in calories ingested and loss of body fat.
We see it in mouse studies and some isolated human trials that show interesting findings sporadically, but overall, the evidence shows similar benefits between different fasting protocols and more traditional calorie control.
So no, there is nothing magic about fasting per-se.
If it had some special effect, we would see it consistently on every person who does IF, but for the most, it doesn’t do have any extra benefits.
Timing of intake and circadian rhythm
There are fascinating studies on the timing of meal intake and eating more in the morning vs. eating more in the evening.
The time at which you eat has a particular effect that is not explained by Calories alone.
In a study (5), people eating the same amount of calories at different times of the day showed different results.
One group ate at what most of us would call normal times: breakfast in the morning, lunch in the middle of the day, and dinner in the evening. The other group ate exactly the same three meals, but all were concentrated early in the day.
Those eating most of their meals earlier had several metabolic benefits, such as lower insulin levels and blood pressure, and less oxidative stress.
This is a bit confusing. The benefits of fasting are due to caloric restriction, but in this study, there were benefits beyond weight loss.
How could that be possible? Well, fasting may not be the only answer.
Let’s see what another study revealed.
In this other research (6), both groups ate at “normal times,” breakfast in the morning, lunch in the early afternoon, and dinner in the evening. Both groups consumed the same total calories throughout the day, but one group consumed more calories at breakfast while the other consumed more at dinner.
People who ate a “big” breakfast had better glucose metabolism and felt more satiated than the group that ate a “big” dinner.
So, at the same amount of calories, consuming them earlier in the day seems beneficial, even without fasting.
The hypothesis behind this is that our circadian rhythm makes us better adapted to eating during the day and not late at night. This hypothesis is known as “early restricted eating”. It suggests that it is best to avoid eating too much too late at night.
I suspect that before long we will realize that this is not as simple as it seems. There are studies that do not conform to this simple, linear hypothesis.
For example, a study (7) analyzing this issue showed that this way of eating worsened some markers, such as cholesterol levels.
Yes, it’s confusing. This is because it is a very young field, many of these studies are from 2018-2019.
I think circadian rhythm probably plays a role, there are enough studies that show it’s a factor to consider, but I suspect there are other factors as well. For example, our genetics. Some of us are morning larks and some of us are night owls.
And it’s not just about habits. Our circadian rhythm is determined by our genes, as we have known since the 1970s.
If you got here, you may still have a lot of questions. This is because Nutrition is a relatively new science and it is so individual that we can’t just give general advice.
But this is what I want you to understand:
- From what we know about intermittent fasting and time-restricted eating, we can say that fasting can help lose weight if there is a caloric deficit, and this will result in metabolic benefits that come thanks to the loss of body fat.
- Intermittent fasting does not seem to have an impact on human longevity beyond the caloric deficit it can generate, and the loss of fat mass that results.
- Does it have additional benefits beyond caloric control and weight loss? It is not fasting per-se, but it seems that the time of day when we eat does have an impact.
- Consuming most of our food earlier in the day, eating dinner early or a light dinner seems to provide benefits beyond Calories and body weight, at least for some of us.
When it comes to food, the what and how much may be the key players, but the when is the supporting character.
1. The Roles of Autophagy in Cancer: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6274804/
2. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans: https://pubmed.ncbi.nlm.nih.gov/31151228/
3. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity The TREAT Randomized Clinical Trial: https://jamanetwork.com/journals/jamainternalmedicine/article-abstract/2771095
4. Autophagy and aging: Maintaining the proteome through exercise and caloric restriction: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6351830/
5. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes: https://www.sciencedirect.com/science/article/pii/S1550413118302535
6. High Caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women: https://onlinelibrary.wiley.com/doi/full/10.1002/oby.20460
7. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans: https://www.mdpi.com/2072-6643/11/6/1234