Will Fasting improve my health or body composition?

Fasting has gained popular traction in the past few years and has been touted to have many beneficial effects on body composition and cardiometabolic health. However, so far, the body of data doesn’t stack up to support this.

The research on prolonged fasting in humans is pretty sparse. It is largely derived from animal models at the moment and doesn’t really translate to humans’ health outcomes. Basically, there isn’t enough well controlled, long term human research to be able to support or deny these claims. It’s certainly an interesting area of research and some of the animal research would suggest you don’t even have to fast, but a calorie deficit of around 40% is enough to induce the same effects.

Autophagy is a bit of a buzzword around the fasting movement. The idea behind fasting is that while they aren’t receiving nourishment, cells apparently ramp up their autophagy process, which is when they eat and destroy components that aren’t necessary or that are potentially harmful (they get rid of damaged cells).

Autophagy also appears to renew healthy cells. We know that autophagy is a normal process, and it happens in all of us. But it is thought that fasting increases the rate at which it occurs. In lab animals, severe caloric restriction seems to increase lifespan. We don’t, however, know how this affects people, because it’s unethical to starve people and nobody willingly submits themselves to a starvation diet! Exercise actually activates autophagy as well and protein inhibits it.

Because autophagy is upregulated as soon as you get into the post absorptive state (when food has been digested, absorbed, and stored after eating), perhaps one issue is that much of the overeating we see in society means people rarely get into this state.

So doing any sort of calorie restriction either continuous or intermittent fasting type of regime (e.g., 16:8) would be making it occur. As well as overnight when you aren’t normally eating for 12 hours.

Is autophagy something we need to focus on? Probably not.

The concept of metabolic flexibility – how easily the body switches between using carbs or fat for fuel – is often talked about in fasting circles. We know that metabolic inflexibility is associated (not necessarily the cause of) with several diseases and conditions, such as diabetes, heart disease, and metabolic syndrome. We suspect that chronic inflammation can trigger metabolic inflexibility.

But the science behind metabolic flexibility in humans is scarce. A small 2020 study suggested that diet doesn’t impact metabolic flexibility at all. We know that some people are just genetically less flexible in this way.

You can’t reset or recharge your metabolism. It’s not an electronic device. And as that new study I posted about last week showed, your metabolism doesn’t change that much at all.

FASTING AND WEIGHT LOSS. Intermittent fasting (IF), like any diet, works because it cuts calories. It hasn’t been shown to be superior for weight loss than any regular lower-calorie diet. In other words, there is nothing magical about fasting in terms of weight loss; weight loss happens when you take in fewer calories. No matter which diet claims it ‘burns fat’ faster, they all operate the same way.

A 2017 human study looking at fasting and disease risk did find that participants who were in the fasting group lost weight and decreased their levels of IGF-1, which is implicated in the risk of diseases and in aging. They also had lowered levels of C-reactive protein, which is an indicator of inflammation. So those are all good things.

This study was only three months long though, and 25% of the fasting group dropped out before the end, versus 10% of the control group. IF is tough for a lot of people to maintain…even for three months. For weight control, IF works for some people, and not for others. It’s not a guaranteed method, it’s simply another method by which to cut calories.

How fasting MIGHT help you Fasting isn’t just associated with fat loss –it can teach you to control your impulses. Once you learn how to control your impulses, dieting becomes that much easier. If you look around you, we are living in an abundance of energy. There’s food everywhere, easy to access and consume, you’re bombarded by food ads daily but here’s the thing: Hunger isn’t always the problem, impulse is.

Hunger > easy access to food > eat (impulse) > Hunger > easy access to food > eat (impulse). And that’s where a real benefit of fasting lies: it acts as a reminder that it’s not real hunger, it’s just impulse. And that you won’t die if you don’t eat for a few hours, or, realise that you do actually have control. It’s less about the actual act of fasting than it is the realisation of this fact – something many people have lost. So, do you have to fast? Well, no. But you don’t have to constantly eat, either. For some people it works, others it not for them. You find what works for you.

If you want to try it, it doesn’t have to be anything crazy, start small. Maybe you skip breakfast and eat when you get hungry after your workout; maybe you fast until lunchtime. It’s your call. It won’t be easy at first, but that’s the point –you want to feel that impulse to eat; feel “hunger” (it’s not really hunger), and then sit with that feeling so you realise that you won’t die if you don’t eat for a few hours.

TAKE HOME; Fasting isn’t magic It’s supposed benefits lie in creating a calorie deficit- Fasting is simply a tool in the dieting toolbox that may work for certain individuals (not everyone). There is little evidence to support fasting-specific effects on metabolic and cardiovascular health outside of eating in a calorie deficit. Does fasting extend life and prevent disease? We don’t know, we don’t have any human studies that confirm this. All we have are animal studies, and those can’t be extrapolated to humans. Fasting can be helpful in controlling your impulses and helping you be in tune with your hunger cues and therefore enabling you to eat less. If you want to fast and feel the benefits of it and it helps you, then go for it. Finding something that suits you and your lifestyle is the key to lasting change and success.