My first 5-Day Fast

How do you think your energy levels would be after 5 days of only eating one salad per day? The answer might be surprising.

This is a follow up to yesterday’s post on fasting, so make sure you are up to speed on the background knowledge before you read on! Or just read on if you’re only here to see me suffer!

After pulling my feeding window in from 13 hours (7am to 8pm) to 7 hours (12pm to 7pm) gradually over the last 6 months and doing lots of fasted training, I felt ready to take on a longer fast. Doing 3 hour runs in a fasted state without running out of juice or losing concentration proved that I have some degree of metabolic flexibility. That is, I have some cellular machinery to work with fat and ketones as a fuel source and the ability to produce ketones from fat in reasonable quantities. While I’m certainly not in nutritional ketosis, I suspect the endurance training puts me into post-exercise ketosis a few times per week and the intermittent fasting puts me in a state of mild ketosis daily. I cannot confirm though, since I have not taken any real measurements.

If you miss one meal and feel exhausted then you are not metabolically flexible and your body is likely dependent on a stream of carbohydrates to keep you going. For you a 5-day fast will be very tough, but therein lies greater potential benefit for your metabolic health.

I chose to be a little cautious and follow Dr Valter Longo’s fast mimicking diet (FMD) as opposed to a water-only, or a zero-calorie approach. I’ll tackle the water only fast in 2 months. While the experts are in agreement that water-only fasting produces a stronger regenerative response, Dr Longo applies some pragmatism by considering how requiring absolutely no food in busy lives increases the chance of failure and increases some risks. His studies show that this very low calorie diet produces most of the benefits of a water-only fast but is much easier to pull off.

Here are my macronutrient intakes and test jog measurements for the 5 days. The only thing that really stands out is the perceived energy levels. Rewording the enquiry to emphasise how much faster I could have run if required would reveal the same pattern. This is a pattern I’ve seen numerous times before in others trialling this diet. It is also worth noting that the test jogs were done by feel and I wasn’t taking feedback from my watch to adjust my effort and, conveniently, conditions and time of day were similar on all days.

Day	Carbs (grams)	Fat (grams)	Protein (grams)	Total Energy (calories)	Test Jog Time (mm:ss)	Test Jog Heart Rate (bpm)	Perceived Energy Level	Mood	Weight in morning (kg)
1	61	50	16	710	N/A	N/A	N/A	Irritable	67
2	63	26	13	500	16:49	148	Low	Unconcentrated and fatigued	66
3	63	26	13	500	16:24	142	Low-Moderate	Happy and concentrated	65
4	20	21	8	300	16:13	144	Moderate	Happy and concentrated	64
5	10	<1	<1	41	16:33	144	Low-Moderate	Fatigued, but not unhappy.	63
6	N/A	N/A	N/A	2000+	N/A	N/A	High	Happy and concentrated	63

Day 1

From the end of day 1, metabolism and energy management will be stressed as cells have less glucose/glycogen to work with.

I started my fast from dinner the previous night and since I’m used to eating a late breakfast nothing interesting happened until late in the evening. By then I was notably twitchy and a little irritable, some call this hangry (hungry-angry). This is very noteworthy for me as I am almost never irritated. I gave a few uncharacteristic responses to people and almost slapped a kitten across the room for scratching me. I had a relaxed day in front of the standing desk and the only training I did was was 20 minutes of stretch exercises. My energy was fine, but it was just my mood that had changed. I also found I was day dreaming in the evening, as I savoured my green leafy salad with 20 cashews and half an avocado.

Day 2

From day 2, autophogy (cellular recycling) will increase and old or dysfunctional structures will be removed.

I slept fine and woke up at a normal time. I did 20 minutes of strength exercises again and also a short run. Strength was no problem, but I felt quite drained when running. I was just cruising, but my heart rate was elevated and I felt like I had only one gear, similar to hitting the wall in a long race. Throughout the day I was moderately active with tasks around the home and some reading. I was happy, but found myself day dreaming even more. Often I’d find myself staring out the window with little recollection of what I was previously doing or why I was in the kitchen, as that was off limits to avoid temptation!

The cravings were also worst here. I opened a cardboard box at one stage and noticed how delicious it smelt. I went to bed with salted corn chips spinning around in my head, which lasted for a solid hour before I finally nodded off.

Day 3

I woke up on the early side on this morning – 7am, an hour earlier than usual. But I felt good! My energy was up and I did tasks around the house with some fairly heavy lifting followed by 30 minutes of strength. My mood was really good too. I figured I must have entered a state of ketosis and all systems were back online. I was day dreaming less and focusing just as normal. My short test jog was good, just about normal pace and heart rate. I felt like I could have gone faster if I wanted to, unlike the previous day where jogging was pushing the upper limits of my capabilities.

There was also no sign of sleepiness despite the shorter than usual sleep. Interestingly I took even longer to get to sleep on the evening of day 3. I simply didn’t feel sleepy and so lay in bed for some 2 hours.

Another surprise that arose was that my inner ears blocked up. Breathing heavily would dislodge the mucus was a short time, but in the end I had to get used to not being able to hear normally.

Day 4

From day 4, stem cells will become more active.

After an even shorter sleep, waking up at 6am from 6 hours sleep, I had another good day. Energy and mood were stable and I did my strength and jog without a problem. I was getting optimistic here and I had the finish line in sight. I reduced the size of my salad to take in 300 calories instead of the recommended 500.

Lying in bed that night, I could feel my heart beating very strongly. My heart rate was not raised significantly, but it was either beating stronger or it was just easier to feel for some reason. I’m unsure what to make of this.

Day 5

I slept in to my normal time on this day and it seemed like my energy was on the way back down. I had to have a rest on the couch after my 20 minutes of strength and the running was less comfortable, although still a similar pace to the other days. My concentration was a little light too. I had a little snack after training but held on to the evening to break the fast with a moderate dinner. I was full pretty quickly and agree with the recommendations to ease yourself back into eating normally again.

About an hour after eating my legs were really warm, much like on the night after a long hilly run. I take it that my body was indeed interested in rebuilding, possibly more so since I kept some training stress on these muscles throughout the 5 days.

Day 6

When nutrition is reintroduced, stem cell-based rejuvenation will rebuild lost tissues with new, healthy cells. 

While out of the assigned fasting period I suspect I was still in ketosis after only a small dinner and long sleep. I did 40 minutes on the bike with no problems and then had a good breakfast at midday, once again feeling full for longer than usual after eating. I suspect I ate enough oats and fruit to to kick me out of ketosis and now look forward to the festive season to refuel my body’s rebuilding and rejuvenation. My body weight will also return to normal once I have increased gut volume and topped up glycogen stores.

The next step is obviously a 5-day water-only fast, which I’ll do when I next want a break from training.