Why is My Weight Going Up and Down While Dieting

In my articles on how to set calorie intake and when to bulk vs cut, I presented the following sketches representing fat, muscle, and weight changes for cutting and recomp phases over several months:

But in reality, the body weight line will look more like this:

The short-term fluctuations rule out any possibility of gauging progress on a day-to-day basis, or even week to week. But attempting to do so is a mistake people often make.

Educating yourself on the reasons these fluctuations in weight happen will help you tease out real progress from noise.

The Reasons For Large Daily And Weekly Fluctuations In Weight

It is essential to understand that scale weight change captures more than just fat mass changes.

Weight is affected by hydration status, gut and bladder content, liver and muscle glycogen storage, and any muscle mass changes.

Fat mass changes are slow to happen; muscle mass changes happen even more slowly. So, any large weight fluctuations you experience in a short time frame (hours or days) will not be muscle or fat.

You’ll no doubt have noticed that your weight fluctuates during the day. This is because of some obvious reasons, like toilet visits, water, and food intake, but also some less obvious ones, like sweat, and water loss through respiration at night. (This is why you always weigh less in the morning and your pee is yellow for that first toilet visit — you’re dehydrated.)

Just as you know not to weigh yourself at different times of the day and conclude whether you gained or lost any fat, you shouldn’t try to gauge progress day-to-day either.

Even when calorie balance is unchanged:

• If you eat saltier foods you will retain more water for a few days.
• If you eat more carbs than normal, they will be stored with ~3 g of water as glycogen. (And if you eat fewer carbs than normal, then you’ll use this glycogen and retain less water than normal.)

If you take a couple of days off, unless you overeat by a lot, the majority of your weight gain will not be fat:

Additionally, water retention, though common when we’re stressed, can also happen seemingly at random and can mask fat loss also. These fluctuations all affect your weight and how you look.

What is important then is not the short-term fluctuations, but the long-term trend lines. This is why the way we track our progress can make or break a diet.

Thank you for reading. This was a sample chapter from my book, The Diet Adjustments Manual .

Questions are welcomed in the comments and I answer daily.