Dear Dr. Mo: Why does weight fluctuate during the course of a day? Normally my weight is lower early in the morning than it is at night.
Dear reader: The most common reason for such daily weight fluctuations is so called “water weight”.
What does “water weight” mean?
You retain some water during the day and this is reflected in changes in your scaled weight within 24-hour periods. These changes are not drastic and are usually anywhere between a few hundred grams to about 2 kilograms (a few pounds).
Now to be clear, these gains are certainly not in fat – to gain so much fat in a day (say about 2 kilos) one would have to consume about 14 000 to 15 000 calories, which is borderline impossible and probably not even survivable.
So, why do we retain water?
The most common reason would be due to mild dehydration – that’s right, decreased water intake for whatever reason.
It is really very similar to decreased calorie intake; both situations trigger a body’s response to conserve what’s available. In case of calories, we conserve energy and paradoxically gain some fat over time while in case of water, we retain water and this water increases our weight at the end of the day.
So make sure you stay hydrated enough (especially if you work out) and these gains in water should be minimal.
Another reason could be muscle-building exercise – when you train your muscles micro tears happen in the muscles and this is how they are built over a period of time. In the first few days of this process, such ‘injured’ muscles will retain water.
Carbohydrates also affect your weight. Carbohydrates tend to hold water – they draw it away from your blood stream and into the cells – you then drink to replenish this ‘lost’ water and the net result is more total water in your body (and more weight). After carbohydrates are spent, this water is lost and your weight slightly drops.
This is the reason why low-carb diets tend to have dramatic results in the beginning – one loses stored carbohydrates and accompanied water (in addition to fat an muscle) which doubles the effect, but this is not a healthy or long-lasting way of weight loss and I would advise against it.
One more common reason for short-term “water weight” is salt; water follows salt so any increase in sodium intake (a salty meal the night before) would result in more water and more “water weight”.
Travelling can oscillate your weight as well due to dehydration and consequential fluid retention or slight edema (swelling) because prolonged sitting could affect your circulation.
Women have their monthly hormonal cycles and these also affect water balance so their daily weight can normally very due to this reason.
If you are on an exercise or a weight loss program, I would suggest measuring your weight periodically rather than daily because as you can see, these daily values will vary and could put you off course.
Watch your calories, make sure you have a balanced diet to match your daily needs and take your time.
Yours in health,