Intermittent Fasting: Wow! The effect of Feasting on IGF-1 Levels

Alistair Hall

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If you're following our blog posts you will know that my brother Ceri and I are acting as Medi-guinea pigs and are testing intermittent fasting aka the 5:2 diet to see whether we can achieve the benefits to our health that apparently come with severely restricting our calorie intake on 2 days per week. We're supposed to be testing the benefits of fasting but Christmas got in the way so the first test we conducted was the effect of feasting instead. It is estimated that the average person puts on a whopping half a stone over Christmas purely through over-indulgence and failure to move off the sofa for 2 weeks - no wonder January sees so many new diets and gym memberships!

You might remember that I described Ceri and myself as diametrically opposed when it comes to our attitude to food - he eats to live whereas I live to eat. However, in the interests of science, Ceri was prepared to forgo his normally frugal lifestyle to have the Christmas of all Christmasses eating all manner of festive treats all day long!. You will not be surprised to learn therefore that Ceri managed to put on half a stone no problem and came into the New Year at his heaviest ever level of 12st 4lbs. I, on the other hand, am a veteran dieter and know that I can't go out for endless lunches and extend the Christmas feasting without paying for it later. So I ended up only 2 - 3 lbs heavier but even that impacted my IGF-1 level.

We first had our IGF-1 level tested at the end of November and our results were quite different. Ceri's was close to the bottom of the range for a man of his age with a level of 15.2 nmol/l (range 12.2 - 32.8 nmol/l) whereas mine was closer to the middle of the range for woman my age: 21.6 nmol/l (range 11.3 - 30.0). Neither of us started our intermittent fasting until the New Year (although I had had a few practice days to limber up!) and  neither of us fasted in any way over Christmas. We tested our IGF-1 level again on 4th January and the results came through today.

I opened mine with trepidation - I expected it to have gone up and was disappointed to see that it had indeed increased to 24.7 nmol/l - not a massive increase but definitely going in the wrong direction. I then rang Ceri to see if his results were in - and wow - what a change! Ceri's feasting (some would say gorging!) over Christmas had resulted in his IGF-1 level increasing from 15.2 nmol/l to 24.3 nmol/l in just over 1 month.

So given that we're both going in the wrong direction how do we feel about it? Well surprisingly confident. I am pleased that my result was fairly stable when compared with Ceri's which accords with our relative weight gain. He is pleased that the theory seems to work: if he had stuffed himself with all these extra calories and his IGF-1 level had remained the same then what scope had he to reduce it?

We are both now into our 3rd week of intermittent fasting and are going to have our IGF-1 levels tested again in a few weeks. What are we hoping/expecting to see? I am definitely hoping for a significant drop in my level towards the bottom end of the range. Ceri is expecting to see his return to its pre - Christmas level and is interested to see if it can go much lower  - his natural eating pattern often misses meals and is of fairly low calorific value anyway. Maybe he already follows his own natural intermittent fasting regime?

Whatever the result, we'll keep you posted on our progress - just check into our blog for updates.


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