Fasting during Lent used to be a common practice, linked more with spiritual discipline than physiological benefit. The recent focus on fasting for weight loss has brought it back into vogue. Not only weight loss, there’s evidence to link it to a range of other health benefits. Fasting is increasingly a feature of popular diets, including The Dissident Diet, which includes it as a way to boost insulin sensitivity. But, while some people find it easy to go without food, others find it impossible. This article, written especially for Lent (you can take the girl out of the convent…) looks at what a fast really is, what happens in your body when you fast, and suggests ways you can incorporate the benefits of fasting into your life.

First let’s be sure about what we’re talking about. Historically, we have thought of fasting as going without food completely for a period of time; it was a practice more associated with religion than nutrition. More recently it has been used to describe a period of calorie restriction. But, for me, the fundamental definition of fasting is not about how much you eat, or don’t eat – it’s about where your energy is coming from.

Way back in the early days of my nutrition training we looked at the complex system of energy metabolism in the human body. Most of the time when we talk about making energy we are referring to the Kreb’s cycle, a biochemical process that happens in the mitochondria of the cell to make ATP, our energy currency. This is a good time to clear up a common misconception: there’s no such thing as an ‘energy cell’ – all cells make their own energy. Brain cells, muscle cells, liver cells, blood cells: they all contain mitochondria to make energy, and some are fussier than others about what fuel they use. If you’ve read The Dissident Diet, or follow the blog closely, you already know that we can make energy from all three macronutrients; the body prioritises carbohydrates when available, but can also use fats and proteins to make ATP.

Our body needs a small but steady supply of energy to stay alive, minute by minute. Energy production continues whether you’re fasting or filling your face. But one of the miracles of life is that we don’t always need to get the raw materials from a recent meal. Your body can store energy for later use! Normally it stores enough to get us through a couple of weeks’ scarcity. In my case, it prefers to store enough for a couple of years, but I digress…

The metabolic pathways differ significantly if the mitochondrial fuel is coming from a meal we have just eaten, or from food we have stored for later use. During the ‘fed state’, when we have just eaten, macronutrients enter the blood stream from the gut. During the ‘fasting state’ they are released from tissue stores. Both pathways, fed and fasting, end up in the mitochondria.

Although we can function well in both fed and fasting states, most healthy eating advice concentrates on keeping us in the fed state. The injunction to eat three meals a day and supplement with regular healthy snacks ensures our blood stream is never without a handy supply of recently ingested carbs, fats and proteins. In theory this abundance is designed to keep our brain and body working optimally, but the evidence is stacking up to suggest that it’s not working as well as we hoped.

Living constantly in the ‘fed state’ is not what nature intended. During our evolution the idea of eating little and often would have been as unthinkable as an en suite bathroom. Back then we ate huge quantities when we found food, went into a semi-comatose stupor while we stored it, then woke up to get on with life until the next antelope came tiptoeing by, sometimes days later.

Most of us now don’t go more than a couple of hours without a little something: a milky coffee, a few nuts, a biscuit. Our ‘fed state’ metabolic pathways are so well worn that our ‘fasting state’ mechanisms don’t work any more. When we try to go without food we can feel light-headed, nauseous, irritable, confused, headachey, or just plain ill.

To understand why this happens we need to look at the two major hormones involved in the fed and fasting state.

During the fed state the production of energy controlled by insulin; its job is to reduce blood sugar levels. In times of plenty (after a ‘normal’ meal that contains carbs, proteins and fats) insulin directs carbs into the energy pathways, proteins into the muscles and fats into the adipose tissue. Storage is a priority – after all, you never know where the next meal is coming from.

During the fasting state glucagon is the most important hormone; its job is to raise blood sugar levels. It is released only when blood glucose falls below optimal levels and it stimulates the utilisation of stored carbs, fats and proteins. This phase is often referred to as ‘glucose sparing’. In the fasting state we use our stores very carefully to provide just enough energy for all the cells to function well. More than that, the slightly adverse environment acts as a mild stressor and improves the performance of most cells. It’s this feature of fasting that is thought to provide the health benefits.

We function at our best when we are in the fasting state.

Trouble is, this glorious fasting state can be elusive. Glucagon and insulin are antagonistic to each other – if insulin levels are high then glucagon can’t work its magic. When we make too much insulin, a common condition often referred to as insulin resistance, we can go straight from an abundance of food to an absence of food without awakening the fasting response. The presence of insulin stops glucagon from playing its role of releasing stored calories. The result is that we run out of energy with a bang which feels very uncomfortable. So we eat again.

If you haven’t exercised your fasting muscle for a few years then – despite what the popular diet books say – you need to start gently. The unwary faster with poor insulin/glucagon balance goes straight from fed state to starvation. And that’s potentially dangerous.

If you are chronically stressed, very overweight, diabetic (or pre-diabetic) getting into the fasting state will be more difficult. If you’ve had years of yoyo dieting or eating junk food your nutrient status is likely to be compromised too, which makes it more difficult to sustain a fasting state. 

So why bother? You might think it’s more trouble than it’s worth, but the evidence in favour of fasting suggests it can bring about:

  • weight loss
  • improved insulin sensitivity
  • reversal of diabetes
  • reduction in cancer cell growth
  • protection from Alzheimer’s disease
  • sharper and more focussed mental state
  • better mood and sense of wellbeing
  • improved immune response
  • increased hormonal balance
  • increased autolysis (breakdown of unwanted accumulated cells and material e.g atherosclerotic plaques)

Far from being some crazy new food fad, both the historical and modern evidence suggests that it’s a state in which our body thrives. Fasting has also been associated with improved fertility and there is a growing body of evidence linking fasting and calorie restriction with longevity. It’s difficult to escape the conclusion that fasting is a wholly desirable metabolic state, not to be confused with starvation. As soon as we enter a fasting state – taking the pressure off our digestive system – we seem to give the body to catch up on its housework. When you think about at the number one killers in our society you can see that a little bit of fasting now and then might be a good thing. And then, if you think about the way a pride of lions lounges around after a kill, you get an insight into why being in the fed state all the time might explain why we all feel so tired and apathetic, and reluctant to exercise.

No wonder fasting became a central feature of all the main religious cultures. It wasn’t just about subjugating the flesh, it led to a more alert and enlightened state of mind.

But what can you do if fasting doesn’t work for you? If instead of making you feel good it makes you feel bad?

If this has been your experience of going without food, then your fasting mechanism needs repair. You need to coax it back into action. Even small fasts, like making an effort to avoid snacking between meals and extending the gap between meals and/or occasionally skipping lunch seem to provide the potential for health improvement.

Before attempting a day-long fast, start gently by increasing your fasting window in a gradual way. Try the following measures in incremental steps on a couple of days a week:

  • week 1 – stop eating after dinner – no TV or bedtime snacks
  • week 2 – stop snacking between meals during the day
  • week 3 – eat just three times a day at clearly defined intervals, no milky drinks
  • week 4 – increase your overnight fast – eating dinner earlier and delay breakfast
  • week 5 – try skipping lunch and eating two meals a day

Approaching fasting in this gentler way is kinder to your body, easier on your family and fairer to your employer. You can’t suddenly start fasting and expect everything to work perfectly. Fasting changes your mental as well as your physical state and, although you may not be aware of it, you won’t necessarily perform in your usual way, which may affect the way you cope with stress, do your job or drive your car.

I was discussing this issue with friends over the weekend and there was a feeling that fasting can’t easily be integrated into the demands of modern life. I couldn’t agree more. But, for me, that’s not a reason to ignore the potential benefits of fasting, it’s a reason to sort your life out as well as your diet so that it’s supportive to great health and a long and happy life.

I’ve been polishing my fasting mechanism on The Dissident Diet for the last 18 months, and my glucagon levels are working fairly well. But I still have that stubborn half stone that won’t seem to shift. This year, for Lent, I’m going to attempt to fast completely for one day a week.

If you’d like to join me then be my guest. Drop me an email if you like and let me know where you’re starting from. I shall be fasting from 7pm every Sunday night to 7pm every Monday night. My intention right now is to eat nothing on those days but I may need to adjust my plans as I go along.

I’ll let you know how I get on.

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5 Comments on “The not-so-fast guide to fasting

  1. Hi Dawn. I have been intermittent fasting for over a year and a half, eating only 500 calories for two non-consecutive days a week. I started it before it was rebranded as ‘The Fasting Diet’ and I tend to keep it quiet, as some people get very cross when they hear about it and treat you like a lunatic! It works for me, though I know people who didn’t get on with it at all. It gets easier as time goes on, and it does fit in with modern life and the demands of work, family and my usual exercise habits. I admit it sometimes leads to tiredness in the afternoons, but overall I feel it makes me mentally sharper. The feeling of the mind and body running better is a surprise, but your post helps to explain it!

  2. Hi Dawn. Yup I’m with you on this one. Very new to it, although in my case my own body is now fine with just eating a light LCHF lunch between 12.30 and one, and then a evening meal around 7 and, maybe the desert – berries and cream, between 8 and 9, and then nothing till next lunchtime. I am feeling great. It’s taken a few weeks, and also some of those really stubborn pounds I talked to you about are beginning to budge!! Skipping breakfast seems to be less anti-social too. So rather than going without food for a day or two per week, I’m just going without for about 15-16 hours per day!!

  3. That’s interesting. At first it sounds so extreme but so many people think it seems to work. I think it only sounds extreme because we’ve had the ‘never skip breakfast’ dogma drummed into us. As ever, if it works then do it!

  4. Absolutely. I think the key is LCHF, because otherwise I’m sure my blood sugar would plummet by 10am and I’d get the shakes and feel awful. It’s really so easy, I could forget to eat, even by lunchtime. It’s time to break free from the effects of the one-size fits all diet dogma we’ve been given over the last 30-40 years!! PS My ketostix are very purple :) xx

  5. Thats such a great explanation I am going to share with some friends I’ve been fasting on and off for a while and do enjoy the feeling of being in a fasted state but understand some people just can’t get there this totally explains it. Thanks. I’m new to The Dissident diet but am totally taking on board everything it seems to be working really well for me.

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