Weight Fluctuations: Why Do They Happen?

By Ali Luke

One of the most frustrating moments for many dieters is the weekly weigh-in.

Sometimes, the results on your scales seem to bear very little relation to the week you’ve just had.

Maybe you’ve been really good – but not lost anything. Or you’ve had a couple of meals out, and eaten more than a few candy bars – and yet you’ve dropped a pound.

What the heck’s going on?

If you weren’t dieting and weighed yourself every day, you’d still find that your weight wasn’t steady: it might fluctuate by as much as several pounds.

These fluctuations in body weight are commonly due to 3 factors:

  1. Water retention
  2. Glycogen stores
  3. The amount you’ve eaten

Water Retention

2918-water-weight.jpgWater retention is caused by drinking too little water, or eating too much salt.

If you don’t drink enough water, your body will cling onto its water supplies; make sure you’re drinking enough. And if you eat too much salt, your kidneys hold onto water instead of excreting it.

Women commonly retain water during the few days of the month just before their period. This “phantom” few pounds will drop off as quickly as it went on. Some medications can also cause water retention.

Glycogen Stores

Glycogen – sugar – is carbohydrate stored in the liver and muscles; usually more than a pound in total, along with three or four pounds of water. This is your body’s energy reserve, and gets used up during the day if you’re not taking in enough carbohydrates to supply your energy needs.

When you eat, your body replaces the glycogen store and the water that goes with it – leading to a weight gain on the scales, even if you’ve only eaten a moderately-sized meal. This is absolutely normal and should not put you off eating carbohydrates!

The Amount You’ve Eaten

1851-wendys-salad.jpgDon’t think about the meal you’ve just eaten in terms of calories – think in terms of weight.

You could stuff yourself with pounds of fruit or salad for under a few hundred calories – but these pounds will show up if you stand on the scales straight after a meal. (Just imagine weighing yourself with all that food in your hands.)

Once your body’s had a chance to digest it, that food will disappear. The same applies with water – which has 0 calories, but definitely weighs something!

How to Accurately Measure Weight Loss

So how can you figure out whether you’re losing weight or not, if your body’s so prone to fluctuations? Try:

  • Only weighing yourself once a week, not every day
  • Always weighing first thing in the morning, before eating/drinking and after using the bathroom
  • Looking at the pattern of weight loss over time, rather than worrying if you’ve stayed the same or gone up in one particular week
  • Judging your success by the fit of your clothes, your energy and the good habits you’re forming – not just by the number on the scales.
  • Measure inches and body fat percentage instead of just weight.

Do you find that your weight fluctuates? How do you deal with this in your weigh-ins?


  1. Reese

    Ok. I am on a weight loss program. I have lost weight and inches. However how can it be that I weigh myself first thing in morning I am 167. I drink a cup of coffee and I am now 168.

    • Ted

      Because water has weight. Just 15 floz of water is equal to one pound.

  2. Debby

    how come when I weigh myself first thing in the morning I weigh about 100 pounds and within 6 hours or so with just water in me my weight goes up to 108 pounds? I am 5 feet tall and typically extremely active but have been very sick for a few months so unable to exercise. I would love to get feedback! thank you in advance!!

  3. Ann

    Ok then answer me this then… I weighed myself this morning before eating drinking or anything and I was 191 then I weighed in at night and was at 211… how can you explain that then? Maybe because I drank a lot of water and ate?

    • Ted

      That sounds like a bad scale. Weight fluctuations are 1-3 pounds, not 20 pounds.

  4. Joanne Edmondson

    when I wake up I weigh myself at 118 pounds then when I eat my weight goes up two pounds. So what is my true weight?

    • Ted

      Your true weight is usually found by weighing yourself in the morning, prior to eating and after a bowel movement. This shows your body weight with as little food/waste material in your system.