Why Does Weight Fluctuate? Factors like sodium and carbohydrate intake, exercise, food intake, bowel patterns, a person’s menstrual cycle, medications, and alcohol can all contribute to daily swings in the number on the scale.
Basically, hormone fluctuations throughout the month can lead to weight change, elaborates Shapiro. “Estrogen can cause water retention, and progesterone is a natural diuretic, so depending where you are in your cycle you may see this reflected in your weight status.” That’s why you may feel bloated a week before your period plus a couple of days after it starts. Things like constipation or diarrhea (which can often come with your period) can contribute to feeling puffy, too.
The balance between energy in (eating) and energy out (burning off those calories) is why your weight goes up and down. If you take in more than you burn, you gain weight — sometimes right away. Losing that weight can be hard, too. To lose 1 pound, experts say, your calorie balance (eating minus burning off) needs to be 500 fewer than normal each day for a week.
Morning is usually the best time to get your most accurate reading. You’ve had some sleep, and you probably haven’t had much to eat or drink yet. As the day goes on, though, you will. Expect your scale to top out after a big meal. If you brace yourself, it’s a little easier to take.
Some athletes can drop 6% to 10% of their body weight after a single workout (that’s mostly in sweat). Your change may not be as drastic. But dropping a pound or two after you hit the gym isn’t uncommon.
Illness and disease can bring unexpected weight change. Cancer, diabetes, heart failure, and even the common cold can have ripple effects. If you lose your appetite or retain water, that may tip the scale one way or the other. Talk with your doctor if you see changes that you didn’t expect.