Dietitian: Dr Jaci Barrett Diet: 5:2 / Intermittent fasting
It’s finally over….
So, after teasing my colleagues with the anticipated ease of the 5:2 diet, I now acknowledge that it
was not that easy after all… 6 fast days (<500cal per day) in 3 weeks were a real struggle. I coped
well throughout the day, but from 5pm I was struggling, and from 8pm, I was very tempted to throw
in the towel… But I didn’t. Where did I get my motivation from? Primarily from wanting to see if it
worked – Did I lose any weight? Did I see some improvement in biomarkers or microbiome? I knew if
I didn’t stick to <500cal/day I would always wonder if lack of improvements were due to lack of
But this motivation makes me think about our patients that try the 5:2 diet. You really need
motivation to get through those fast days, and sure with any diet we stick to them initially, but if
weight loss isn’t quick, then people lose faith… And weight loss wasn’t quick for me.
1. WEIGHT LOSS
Here is the outcome people:
I LOST NOTHING! That’s right, zero, zilch, nudda.
3 weeks of the 5:2 diet and no weight loss.
I did however, have a 1.5% reduction in body fat mass and a 1.1% increase in lean body mass
after the three week trial.
How is this possible? My thoughts on a personal level and as a dietitian:
Firstly, my calorie intake was not that different between baseline and when on 5:2. This was not
because I made up for the fasting days by eating more. What my food diary told me was that I
eat a bit like the 5:2 diet normally. I love a social lunch or dinner out, with a few glasses of wine,
but on days following these high calorie indulgences, I typically reduce my calorie intake
Overall, I reduced my calorie intake on the 5:2 diet by an average of 9%, that’s only 150 calories
less each day. It’s still less, and if I had stuck to the diet for a few months I probably would have
lost ~1kg per month.
Secondly, I don’t have a heap of weight to lose. I imagine if I had >10kg to lose, there may have
been more of a shift in my weight.
2. OTHER NUTRITIONAL FACTORS?
What changes occurred with other nutritional parameters? There were in fact little changes in
my average intake of protein, carbohydrate, fat and sugar. My protein intake did not change
mostly due to the fact that I opted for high protein foods on the 5:2 diet to increase satiety. My
fibre intake did reduce on the 5:2 diet. I had very little fibre on my fasting days, something I
would correct if I was to repeat the diet.
3. FATIGUE, VITALITY, HAPPINESS, SLEEP
My fatigue, sleep and happiness were unchanged by the 5:2 diet. My vitality score reduced by 2
points, which is unlikely to be clinically significant.
There was no clinically significant change in my cholesterol, fasting glucose and insulin, LFTs or
IGF-1. I was hoping for a reduction in cholesterol and IGF-1 as these are commonly improved by
a 5:2 diet, but perhaps 3 weeks was not long enough. My readings were not particularly high to
begin with either.
So, what do I make of the 5:2 diet now that I’ve lived it?
Despite a lack of weight loss and reductions in blood markers in my case, I am actually a great
believer in this diet. As an experienced dietitian, I understand dietary intake patterns, and I can
imagine that two fast days per week for many people, particularly those that have struggled with
their weight long term, would be a great exercise. I think it teaches you a lot about calorie intake,
what it feels like to be hungry and gives you the freedom of being on a diet, but only having to be
particularly hard on yourself 2 days of the week. This latter aspect will be a major factor at improving
long term compliance.
Will I stick to it?
I said from the beginning if I had improved health outcomes I would stick to it, but at this point I do
not. I shall await the microbiome outcomes though before I make my final decision. For now, I am
back to my normal diet.