It’s a reaaaal hot topic at the moment and one we often get asked about: is fasting good and will it help me lose weight?
The answer in a sentence: on paper fasting is good, in reality it’s probably not.
In this article we’ll be going through some of the latest research on fasting and whether this is something you should or shouldn’t be doing.
What is fasting?
You’d think this definition would be fairly obvious, but there are actually a heap of different types of fasting diets. Essentially, fasting is just going for extended periods of time without any food.
The most popular type of fasting diet is intermittent fasting (I’m sure we’re all familiar with the 5:2 diet), where you restrict to >60% of your energy intake on 2-3 days per week or alternating days.
Another form is also gaining more traction lately known as ‘time restricted feeding’. This involves eating in a restricted window like 6-8 hours a day every day of the week.
Other fasting diets involve completely restricting calorie intake on 1-2 days a week for a 24 hour period.
Why do peeps think fasting is good?
There are a couple of different reasons why advocates think fasting is good. The most obvious reason is that restricting our eating window basically means we eat less overall in the day. In this way, fasting is just another calorie restriction diet, but instead of focusing on food, it focuses on time.
However, when it comes to weight and fat loss, fasting is on par with normal calorie restricted diets. A recent research review found that based on the currently available evidence, fasting diets produced equivalent weight loss when compared to general calorie restriction diets. Both groups showed the same outcomes for weight and fat loss overall.
So, thinking you’re going to lose more weight by fasting than you would by decreasing your calorie intake overall ain’t right sister.
However, fasting may have benefits that extend beyond fat and weight loss. If you want to read about all the proposed benefits, check out this monster review paper here.
One thing to keep in mind with all this though, fasting is still an emerging area of research so all these findings are preliminary. You might notice that heaps and heaps of the papers cited in that review were done on rats, and just FYI, humans are not the same as rats.
Anyway, because we know most of you can’t be bothered to read the whole paper, here are the summary points below:
The main sources of fuel for the body are glucose, fat and protein. The body will always use glucose first as it’s way easier to turn this into energy. Once it runs out of glucose, it will use fat next. Finally, protein is only used as a last resort.
When we eat something, our body takes the glucose from that meal and uses it for energy straight away. Any fat from the meal or extra glucose that we don’t use for energy then gets stored. This stored fat is like a petrol pump for the body.
When we fast, our body runs out of glucose to use for energy, so it switches to using fat. In order to turn fat into a fuel that can be used by the body, the liver needs to convert the fatty acids into ketone bodies. It’s these ketone bodies that can then be used as energy.
Ketone bodies provide a major source of energy for a lot of our body’s cells when there isn’t any glucose available, particularly the brain. And the brain loves ‘em, with studies finding that ketone bodies stimulate the expression of genes that can benefit our brain health and prevent psychiatric and neuro-degenerative disorders like Parkinson’s disease and Alzheimer’s disease.
This is why a lot of ketards advocate for the keto diet to improve cognition and mental functioning. Early research also suggests the keto diet may help to prevent migraines which is interesting!
How long does it take for our body to switch to using fat as fuel? Ketone bodies start to rise in the body around 8-12 hours after eating a meal. Hence why a lot of fasting regimes suggest fasting periods of >12 hours.
So metabolic flexibility from fasting basically means the body gets better at making energy from fatty acids and ketone bodies.
There’s a strong argument for the fact that our body was made to fast. Our ancestors certainly went for long periods without food due to ‘hunter gatherer’ lifestyles. It was more ‘fast and feast’ rather than the ‘graze for days’ patterns we have today.
Research shows that the cells in our body respond really well to intermittent fasting by increasing antioxidant defenses, repairing DNA, and downregulating inflammation. All of these are positive outcomes for almost any disease.
Fasting has also been shown to improve metabolic profiles associated with chronic diseases like type 2 diabetes. Studies have found that intermittent fasting could reverse insulin resistance, which is the major precursor for type 2 diabetes. Fasting has also been shown to improve cardiovascular health by lowering markers of inflammation and oxidative stress, blood pressure, and triglycerides.
Is it a good idea?
Ok yes, it’s likely that fasting has benefits for our body. But here are a selection of our filtered opinions on why you should think twice before fasting:
Focusing on the micros, not the macros
Fasting is what we like to refer to as a form of ‘micro-optimisation’.
It’s so easy to jump on these popular diet trends and assume they’ll be the solution to all our problems and generally make us feel like better people. The reality is though, for most of us there are other areas of our lifestyle that we really should be fixing first and which will have a much bigger impact overall.
- Firstly, and most obviously, exercise. If you’re not exercising regularly and getting a variety of workouts in your routine including cardio and strength training, then you really should focus on this first. The benefits of this have actually been tested on humans and extend wayyyyy further than any benefits found on fasting.
- Secondly, alcohol, smoking and drugs. If you’re going to fast and still binge drink, smoke a pack of ciggies and pop a bunch of pills, then you’ll be like a hamster stuck in a wheel – you’re on a road leading nowhere. These behaviours are seriously bad for our brain, mental health and waistline. Having up to 14 units of alcohol each week (which is within recommended guidelines) adds almost 3000 additional calories a week, which is like a whole extra day of calorie intake. This means you’re eating for 8 days, but only living for 7.
If you wanted more bad news on alcohol, research shows we have a ‘tipping point’ with alcohol, and when we pass that, we go on to make realll bad choices when it comes to food and more alcohol. For women, this tipping point is only 3.1 large glasses of wine – feck. Once we pass this, it’s estimated the additional calorie intake is 4,305 extra calories in the same night – SHOCK (this explains all my 3am visits to Fulham Fried Chicken and subsequent Heathrow injection).
And while it’s not necessary to cut out alcohol all together (…how could one possibly survive without a weekly ‘wine and whine…’), perhaps consider tackling that pesky binge drinking problem
Thirdly, vegetables. Just eat more, please. It should be your daily mantra: ‘how can I add more vegetables to this’.
- Fourthly, mental health. 1 in 2 of us will suffer from a period of mental illness before we’re 40. Your health is NOT just about what you eat. To be happy and the best version of yourself, it’s so important to look after your mental wellbeing. There’s absolutely no point fixing your body if your mind remains unhappy. And no, fixing your body will not fix your mind. But yes, fixing your mind may make you realise your body doesn’t actually need fixing.
The problem with these areas above? They’re not shiny, new magic pills like fasting. And as humans, we love shiny new stuff. But there’s honestly no point looking to micro-optimise our health before we’ve macro-optimised it. It’s like choosing a mooncup before mastering the tampon, it just ends in one big, bloody mess.
It makes you feel bad
Fasting has no focus on the types of foods you’re eating, only time and numbers. It puts us into an ‘all or nothing’ mindset where we have depressing days of ‘nothing’ and feasting days of ‘all’.
On the ‘all’ days, we’re likely to go ham and eat whatever we want, without thinking about what nourishes our body and makes us feel good. You also generally feel really shit on fasting days, and life is too short to purposely put yourself through a shit day.
In order to calculate how much we’re allowed to eat on fasting days, we can also become obsessed with numbers and calorie tracking. This again negatively affects our mental health, body image and relationship with food.
In addition to this, research studies have shown that when we’re depriving our body of calories, we experience cognitive and attentional changes that mean we become obsessed with food. So just when we’re trying to eat less food, our brain is making us constantly think about food.
When calorie deprived, our sense of smell increases and the reward centres in our brain have a heightened response to the taste of food. This provides further reinforcement from the body to eat the food, because it tastes so damn good.
Overall, this means we’re likely to vacuum up whatever we can get our hands on once we break the fast.
Alongside this, when we’re hungry our willpower is totally shot. So you’ll have a monstrous mental battle to avoid hoeing into the buffet bar when breaking a fast.
Fasting is essentially another one of those diets that moves us away from connecting with our body and working out how much we actually need based on physical cues.
It will ruin your social life
Fasting isn’t exactly conducive to a good social life.
And before you fall into the trap of thinking time restricted feeding sounds ok (eating from 12pm – 8pm sounds manageable right?), this isn’t necessarily the case.
It might sound ok to skip breakfast and have your last meal at 8pm, but the research suggests otherwise.
Studies have found that our body is much better at processing the nutrients from our meals in the morning, and gradually gets less efficient at this as the day goes on. This is believed to be related to the levels of our sleep hormone ‘melatonin’ in the bloodstream. Melatonin is highest at night and makes us sleepy, then understandably lower in the morning when we wake up.
High levels of melatonin have been shown to impact on glucose regulation in our body by impairing the action of insulin. This means our body becomes much less efficient at removing the glucose from our blood after a meal to our cells to be used for energy.
So, higher levels of glucose hang around in the blood for much longer in the evening than they would if we ate the same meal in the morning. High blood glucose levels over a long period of time can lead to increased fat storage and complications like type 2 diabetes. It can also damage our blood vessels, nerves and organs.
So, for time restricted feeding to be most effective, you’d have to eat breakfast in the morning and your final meal at around 3pm. That legit means you eat nothing from 3pm until 7am the next day. Sound practical? Probably not. Also remember that wine can still break a fast, so lunchtime drinking would become your new norm.
Ok fine, you can do fasting if you want. But as with any strict diet, we’ll always question the reasons why you’re choosing to do it.
We’d only ever recommend choosing a pattern of eating that you can maintain in the long run. Otherwise, a heap of research consistently shows that you will gain all that weight back (and some) when you go back to eating normally.
So, if you think you can continue to eat 40% of your usual energy requirements on 2-3 days of the week for the rest of your life, then fantastic! Fast away and enjoy reaping the likely benefits that will prevail, such as improvements to your metabolic health and weight loss.
BUT, if you want a quick way to lose weight and don’t think you’ll fast for life, then we’d encourage you to reconsider your fasting decisions and whether you need to be so dramatic.
We get it. There’s a strong lure to jump on any ‘diet’ bandwagon that guarantees weight loss fast. But this won’t make you happy in the long run – and that’s what we really care about.
However – we do have some more practical and realistic ways you could incorporate some elements of fasting into your routines to bring about those positive shifts in your metabolic health without sacrificing the things you love:
- Avoid eating late at night and overnight. We know ketosis and the production of ketone bodies kicks in 8-12 hours after eating a meal, so you could try increasing the time of your overnight fast. This might mean eating your breakfast meal an hour later and dinner meal an hour earlier.
- Consider having a lower-carb meal in the evening. We learnt above that the body can be less efficient at processing glucose later in the evening. Carbohydrates are the main source of glucose for the body, so limiting the amount of carbs we’re having at dinner can reduce the amount of residual glucose that our body has to clear from the blood. This might mean switching from pasta to zucchini noodles, or substituting brown rice for cauli rice instead.
- Try to stick to 3 main meals a day to increase your fasting period between meals. But remember, if you’re going to try and avoid snacking, you need to have filling, decent sized, balanced main meals.
So there we have it, our not-so-subtle opinions on fasting diets! Your opinions and rebuttals welcome, we thoroughly enjoy a good argument.