Why have I gained/maintained weight doing The Fast Diet/5:2 diet?

During the first month of 5:2 intermittent fasting your body will go through a period of adjustment. Water weight is lost in the early stages, followed by fat loss – but some water is also regained.

For this reason many new Fast Dieters find that their weight can yo-yo somewhat during the first month of this way of eating. They lose a lot of water weight, then find the scales stay the same for a week or two as fat is lost but water is regained. Sometimes they’ll find the scales go up a little before going back down. This is perfectly normal. Although most fasters find that they will have a significant loss in the first week, others who were not retaining so much water will find that the loss comes along in week 2-3, with no initial loss at all.

The key to it is perseverance and gaining a better understanding of how your body weight fluctuates naturally.

If you were to weigh yourself every day (even if it is at the same time of day) you would find that the numbers can vary by several lbs (or even more, depending on your size). This is for all sorts of reasons, including what you’ve had to eat recently (some foods cause increased water retention), whether there is still food in your gut, hormones at different times of the month and any number of other mysterious reasons.

Bearing this natural weight variation in mind then it is easy to see how one might be deceived by the scales as a weigh in might indicate no loss or even a small gain – but this could very well be down to your natural weight changes. It is often only over the longer term that we can see the bigger picture and really notice the downward trend of the numbers on the scales. The moral of the story? Don’t put all your trust in the scales – try a measuring tape too as this will tend to be more honest with you! At the end of the day, what’s really more important? The number on the scales or the shape and size of your body?

If you are quite active or are exercising in addition to fasting then you also need to remember that muscle weighs more than fat, so even though you’re losing fat if you are gaining muscle too then your weight may very well go up – but your body shape will be changing for the better!

Unfortunately the above is not the only explanation for weight gain or maintain on the 5:2 diet…

There is the possibility that you are overeating on your feed days and therefore negating the calorie deficit from your fasting days. Many users at the forum report having gone through a phase of overeating in the early stages of intermittent fasting, but happily find that within a couple of weeks the novelty of no foods being forbidden soon wears off and normal eating resumes. It may not even be something as obvious as overeating – beware the calories that sneak in through drinks such as fancy coffees, fruit juices and smoothies! A single piece of cake or muffin can contain as many as 600 calories, so choose sensibly or have it instead of your breakfast or lunch (obviously don’t do this every day, that wouldn’t be healthy – but surely better to eat the cake instead of lunch rather than in addition to it?) If you think you may be eating too much on your feed days please see the post about TDEE for more information. Something interesting I picked up from The Men Who Made Us Fat is that most people don’t try to balance their eating – so for example if they have eaten an entire ‘sharing bag’ of crisps to themselves one would expect them to cut back on the following meal as they have already had plenty of calories. This is sadly not the case and most people will eat extra without trying to balance it out over the course of the week. There is no harm in skipping or reducing the size of an occasional breakfast or lunch to balance out your intake. Indeed, there is some debate as to whether breakfast as important as it has been made out to be over the years. I for one do not feel hungry on waking up but for many years have eaten breakfast because it’s what we’re told to do. These days I try not to eat unless I’m hungry (or if I really, really, really want something – not just fancy it) as I’ve learned to listen to my body more. If I don’t wake up hungry I don’t eat until I feel hungry – often this is midmorning or nearer lunchtime, by which point I find I don’t need such a large lunch later on as I’m still full from breakfast.

But I digress!

Another possibility, believe it or not, is that your are under-eating on your feed days. It may seem contrary but in some cases if you are calorie restricting on your feed days as well as fasting it can be detrimental to your metabolism. Although there is debate as to whether ‘starvation mode’ really exists, it does seem that if you don’t eat enough your body will try its best not to lose weight. In all fairness under-eating is not often the cause and if you are in any doubt about your intake please do check your TDEE and consider keeping a food diary at least in the short term to assess your intake vs your body’s calorific needs.

The final possibility (well, there may be others but this is the final one I’m listing) is that you have an undiagnosed medical condition such as a problem with your thyroid, metabolism or diabetes. If you are concerned that you are not losing weight (please do give it at least a month of no loss first) with this method and are not under or overeating then do consult your doctor.

There’s a really informative topic over at the forum which you might find useful too:

Why do the scales show an increase when I’ve been so good?