Anyone try the 5:2 diet? Effect on basals?

I have been looking to lose a bit of weight (a chronic lung condition has been restricting my ability to exercise recently) and thought I would try the 5:2 diet.

I am really surprised by the effect it has had on my basals. I am a pumper and use a Dexcom, and my basals were set pretty accurately. By the evening of the first fast day, I was going hypo constantly and in the end had to set a temporary basal of minus 40% more or less all night. This seems to be the pattern - on fast days my overnight basals are way down. Even on the non-fast days I am having to reduce my basals by around 10-20%. I suppose it makes some sort of sense that a diet that is supposed to put you into fat-burning mode will reduce your reliance of glycogen release to keep the metabolic economy ticking over.

I am glad I have the Dexcom - there’s no way I could have done this without it. I have still had a lot of hypos (bad news - 2 corrections of 15g of carbs and you have eaten your way through a fifth of your fast-day calories).

Anyone else tried this??


In case anyone was wondering, the 5:2 diet is a form of intermittent fasting. Although I am a T2 on insulin I regularly fast. Not 5:2 but regularly. My experience is that in order to safely fast you need to have your basals set spot on. It is very easy to get in a pattern where you have your basal partly covering meals or your meal bolus partly providing daytime basal coverage. A good way of checking this is simply to use staggered 8 hour fasting periods and do basal testing.

My basals are as near spot-on as achievable. I have basal-tested assiduously and there’s little or no crossover between bolus and basal insulin. Normally, if I go to bed with no bolus insulin on-board I will wake up with a number that’s probably within 1.5 mmol/L (30mg/dl) of my bedtime reading and a more or less flat Dexcom trace. After a fast day it was dropping by up to 2 mmol/L PER HOUR (unless I temp-ed it down).

I don’t see any effect on my bolus I:C ratios so I am sure this is metabolic. I just wondered if any other T1’s had experienced similar. For T2’s with remaining beta cell function, you might expect a really beneficial effect (akin to a big increase in insulin sensitivity).


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Brian, do you have a link to more information about this? Thanks.

John Walsh (of Pumping Insulin fame) has a good summary sheet on how to do basal testing. Walsh discusses basal testing in his book as does Gary Scheiner in Think Like a Pancreas.

Thank you very much, Brian.

Walsh’s book is excellent!


I did the 5:2 diet for a whole year ending this past March. I was enthusiastic about the diet for about 7 months. Weight came off as promised and my blood pressure normalized. I had the best A1c I’ve had in over a decade.

BUT, and it was a huge “but”–over the second half of the year things got ugly. First I started gaining weight despite eating exactly what I had been eating while losing. Then I found myself ravenously hungry on my non-fast days. Crazy, eat everything you see hungry.

Now mind you, I have been watching my weight very closely since 1998 and I had maintained a 17% weight loss for a decade without getting crazy about food, so I am no stranger to dieting. But I had never had the kind of problem with hunger I developed in those latter months of 5:2 except for before my diagnosis when I was getting blood sugars going up to the mid 200s and then back to the 90s after every meal. But with 5:2 diet what was happening was I was getting normal blood sugars but still getting that kind of ravenous hunger, which told me I had done something to really mess up my metabolism.

Moreover, I was participating in a diet support forum and learned that I was far from being alone in having this reaction. There were several other people who had gone through the same thing after a year on the diet. Many had become more stringent in attempting to counteract it, only to find that their weight gain continued. Many had regained all they’d lost.

So I came to the conclusion that the long-term fasting diet had somehow flipped my body over into a state where it was convinced I was facing famine. I stopped dieting, stopped looking at the scale, accepted that I was going to have to regain some weight in order to get back to my usual state. It has been two months now and I am only gradually getting back to where my relationship with food is getting away from the fast/binge cycle that it had gotten into. I have packed on the tummy fat that I had completely gotten rid of on the diet and a bit more.

So what I would advise now is do the diet for a while, but as soon as the weight loss stops, stop fasting immediately and go back to eating a reasonable amount of calories that would be appropriate for your new weight. Do not keep fasting.

And if you are still losing but feel like you are losing control of your eating on non fast days that might also be a good sign it is time to get back to something more balanced.

Some people don’t experience this problem, and for them fasting can be a good long term way of eating. But if you see the signs of issues arising, do not keep pushing because that seems to make the metabolic imbalance much tougher. Our brains are very devoted to keeping us from starving and if they thing that is what is happening, they will make us eat as much as possible to suvive!


Thanks for your interesting post. I shall certainly bear in mind your experiences and use them as guidance. My plans are to try to lose a modest amount of weight (8-10 kg) rather than looking at 5:2 as a long-term stragegy. Until the lung condition (which they now think is autoimmune and may be related to my T1 - ) worsened and I had to curtail my exercise, I never had a weight issue.

I see from your profile your are an atypical T2 (??MODY). As a “classic” T1, I obviously have a completely different set of ,metabolic problems to deal with. For one thing I have absolute control over the amount of insulin in my system. This removes one variable that might have an effect on appetite.



I seem to have one of the insulin sensitive forms of MODY. My local endo would never order the tests(knew nothing about MODY and wasn’t motivated to spend the 10 minutes it would have taken to research it). My blood sugars were pre-diabetic much of my life until I was given prednisone in my late 40s, at which point I became fully diabetic and stayed that way for 12 years using fast-acting at meals for most of that time until suddenly reverting to pre-diabetic a few years ago, for reasons no one can begin to explain but which happened right after I started taking a low dose of CoQ10. (Very crazy, but hey, I’ll take it.)

As you say, it was a lot easier to control appetite when I was using 2 or 3 units of insulin to cover meals than it is now.

But the thing about the 5:2 diet and hunger is that the people reporting this are people without diabetes some of them eating very low carb diets for non-blood sugar related reasons (these diets seem to have only recently become popular in the UK where most 5:2 dieters live.) And they are having the same issues. Which is why I think this is a case of the “famine response.”

Interestingly, this effect kicked in for me when I hit my lowest weight of the last 25 years–which is the weight where I started regaining weight when I was eating a Bernstein-style very low carb diet back in 2004. I dropped back to that weight after I started insulin and that time it happened without my dieting (after being told by all my doctors that insulin would make me gain weight.) I lost a good 10 lbs eating whatever I wanted and covering it with insulin and ended up being sent for a ton of tests because my doctor was convinced that the melanoma I had had removed some years before must have come back. It hadn’t. But as soon as I got down to that weight (137 lbs) I started regaining, again without making any changes.

Whatever it is, my body seems to have decided that the point where all the unsightly tummy fat is gone is the point where I’m in serious danger of starving and Steps Must Be Taken.

The other interesting thing that happened both times–not an issue for you–is that my estrogen dropped dramatically leading to all kinds of unpleasant symptoms. Apparently tummy fat is where us old ladies store the stuff.

So perhaps when estrogen stores drop to a certain level the body starts fighting really hard for that fat.

Whatever it is, I had a couple of lovely months looking slim and foxy in my skinny jeans (or as foxy as an old lady like me can look ) Now back to the baggy shirts!