Why is it that my BMI can go down one day and back up the next. I started on March 1st, with a BMI of 28.36; yesterday I was down to 27.99 but this morning I am back up to 28.20 . The lowest I reached since starting, was 27.67. In 19 days, I missed only 3 days of working out. I do about 1 hour to 1.5 hrs per day. I am careful with what I eat and I have even cut down on wine. I am finding it extremely discouraging. I lost maybe 1 or 2 pounds in almost 3 weeks. It doesn't make sense. I read that some people can lose 10 pounds in 2 weeks...I've been getting 7.5 to 8 hrs sleep, drink lots of water. I very rarely eat fast food. I don't eat fried food. This is ridiculous. I do not snack during the day and at night.

This is silly. I just did the body test again, and now I am at 28.07 .. ??

Hi Danielle,

I know how you feel, it can be very frustrating.

The reason is simply that the human body is rather complex.

The total "throughput" of the human body is about 13.5 pounds in weight (6.13kg). The diagram below is courtesy of NASA:



To quote from part of The Hacker's Diet:

Every day your body ingests plenty of water and disposes of even more. Most of the changes in weight you see from day to day on a scale reflect nothing more than how much water is in the rubber bag (your body) at the moment. Consider: if you pig out to the extent of three slices of pizza before bedtime every night for a whole month, you'll gain about four pounds as the lingering souvenir of your month of wild abandon. Yet even that extreme weight gain is less than half your daily intake and disposal of water.

Most of the changes in weight you see have nothing to do with how many calories you're eating or burning. Instead, all you're seeing is how many pounds of water happen to be inside the rubber bag at the moment. How many bleak mornings of dark despair endured by forlorn dieters who indulged in a bowl of salted popcorn at midnight then slaked their thirst with a large glass of water in the middle of the night, would have been taken in stride had only the implications of human being as water pump been fully comprehended?

This is why all good diet guides will recommend that you either weight yourself once a week, or try to ignore the day-to-day fluctuations. The important thing is the long term trend. By long term I mean months.

Some people do lose many pounds in a week, but generally this is only for a short period of time, and is a very unhealthy way to lose weight over the long term. Crash diets are very bad for the human body as your body fat stores toxins that are released into the blood as you lose weight. Lose too much in a short time and the body has problems coping. Most people see more weight loss at the beginning of a diet as they shed water, and then it slows down. This is entirely normal.

I would also pay more attention to your weight, and less to the BMI figure, which is very sensitive to small changes. Set yourself a long term target and aim for that. Don't worry so much about day to day fluctuations.

This is actually one of my issues with Wii Fit, it places too much importance on day to day changes, when long term trends are much more important.

I would also look more carefully at what you are eating. It might be worth keeping a food diary for a while, and seeing just how many calories you are consuming. I've been doing that for a while and I've been very surprised at which foods actually contain many more calories than you think they would.

I have built a website, Graphomatic.net which allows me to record what food I eat, my weight, when I sleep and exercise etc, and plot them all on graphs.

I'd also thoroughly recommend reading The Hacker's Diet. It is one of the most down-to-earth guides to losing weight I've ever read, by a guy who got to his ideal weight after years of being overweight. It's free, and you can read it online or download it to print.

Sorry this reply is so long, but it's a complex issue that a lot of people don't know about, and can be very off-putting when you are just starting out losing weight. It's a long slog, but we are all in it together.

My BMI has only gone down up to now, which I'm happy about ! but I can imagine it must be very disheartening to get big jumps in BMI. I know from experience my weight fluctuates a lot anyway.

Myabe an idea would be to record a weeks worth of BMI's and work out the average.

Women especially are prone to a lot of fluctuation due to water.
That's an interesting article Paul, thanks for that.

Yes, averaging your weight or BMI is a really good way to see the trend, rather than worrying about the exact day to day number.

I do that with my weight. The graph below show the rolling average as the red line, and you can see it is much smoother than the yellow which is my actual weight which is all over the place.

Graphomatic uses something called an Exponential Weighted Rolling Average, which is a bit more complex than a simple average, but normally gives a better result for something like this.

I almost avoided wth weight thing this morning as I was convinced I'd have gone up a little, I was wrong, down again.

"Exponential Weighted Rolling Average", sounds complicated !

AlexaStJohn wrote:I almost avoided wth weight thing this morning as I was convinced I'd have gone up a little, I was wrong, down again.

Same here. I went out to a gig last night, had a few beers and snacks, and fully expected to have put on a bit this morning, but no, I was at exactly the same as yesterday

"Exponential Weighted Rolling Average", sounds complicated !

It's not as bad as it sounds. Basically (famous last words), yesterday is worth half of today, and the day before is half of that, and so on going back as far as you like.

However, it's a bit complex to work out on a regular basis, which is why Graphomatic does it for you

I did my wii fit later than usual so my BMI went up, I was told I'd put on a pound. I really felt like I was being told off ! I wasn't worried as I know it's just because I was about 3 hours later than last weeks workouts. But, if I think I'd be quite demoralised if this happened regularly. I haven't used the Wii fit at all over the weekend but have been very active otherwise. I didn't take very kindly to being asked for an explanation !

I must take a look at Graphomatic, thanks for the link !

Personally I think that Wii Fit should be much more forgiving about small changes from day to day.

Like you say, being nagged about the small changes can be very annoying.

That is one advantage of Wii Fit Plus, it has the "Simple Test" mode, there is no nagging, no snide comments, and no questions, it just weighs you and does the basic balance test, and gives you the numbers.

I've started to do the simple test most of the time now ! I was really disappointed today though, my weight has gone up to the same place I started, back in November. Yet, I hadn't gone up over Christmas.

Hope it's just a fluctuation or glitch of some kind !

I made myself do a longer workout today and must get back into a habit. I felt quite tired after a short jog.