If your weight fluctuates from day to day, sometimes dramatically so, you're perfectly normal. You might step on the scale and discover you're up 4 or 5 pounds from your weigh-in yesterday, and wonder what gives? Chances are, nothing. It's not uncommon for people to weigh 5 or more from weigh-in to weigh-in.
Weight gain doesn't necessarily mean you've gained body fat. When your weight climbs that much in a day, it's usually for other reasons, like eating too much salt or eating a hefty meal. Let's look at seven reasons your weight can jump up to 5 or 6 pounds in a day.
You Ate a Heavy Meal
The food you eat weighs something, and if you eat a substantial meal, it can weigh a lot. You might have eaten at a buffet and overdid it, and now it's showing up on a scale. It can take a few days to recover from a large food binge and for the extra food you ate to pass through you. You should see the scale drop slowly over a few days.
You Overdid the Sodium
Sodium causes fluid retention, especially if you're not consuming enough potassium. If you go out for a big restaurant meal, don't be surprised if you're up a few pounds the next day from fluid retention. Like a giant meal, it can take a few days to restore a healthy fluid balance and release the excess fluid.
You're Taking a New Medication
Certain medications cause weight gain, but some also cause your body to retain more fluid, and that can manifest as a few extra pounds of weight. For example, corticosteroids and non-steroidal anti-inflammatory medications (NSAID) used to reduce inflammation cause fluid retention.
Once you stop taking these medications, your weight will drop. Some medications also cause real weight gain. Examples include medications used to treat seizures, insulin, and some medications used for mental health disorders.
Hormonal Fluctuations
Women, before menopause, are susceptible to weight fluctuations related to hormonal changes. During certain parts of a woman's menstrual cycle, fluid retention increases as estrogen and progesterone levels change throughout the cycle. Some studies also show that certain oral contraceptives cause weight gain, but it depends on the type. Most weight gain from oral contraceptives is fluid retention.
Women with a common condition called polycystic ovarian syndrome (PCOS) also experience fluid retention and water weight gain. If you have polycystic ovarian syndrome, you might experience other symptoms like irregular periods, hair loss, infertility, acne, skin tags, and dark hair growing on places other than the scalp.
Changes in Hydration
If you weigh yourself one day in a dehydrated state and the next after drinking a big glass of fluid, you may find a significant difference in your weight from hydration alone. That's why it's best to weigh in the morning before drinking or eating to ensure that weight changes aren't due to changes in fluid status. Alcohol can also deplete your body of fluid and cause a falsely low weight that comes back up once you resume normal eating and drinking habits.
Stress
Stress doesn't usually cause substantial fluctuations in weight from day to day, but it can cause water weight gain and an actual gain in body fat. The water weight gain can cause your weight to increase quickly, while gains in body fat are slower.
How does stress cause weight gain? The water weight gain comes from an increase in the stress hormone cortisol. When your cortisol level rises, it causes you to retain fluid. You won't notice swelling in your legs until you've retained at least 8 pounds of body fluid. So, don't expect the couple of pounds of water you retain from stress to show up as fluid accumulation in your ankles or legs.
Health Conditions
Health conditions can also cause weight gain. Some of the most common include an underactive thyroid, but also any condition that causes your body to retain fluid. Cushing's syndrome is another condition that causes weight gain. The weight gain comes from the adrenal glands, located just above your kidneys, producing too much cortisol. Weight gain and fluid retention can be quite dramatic with this condition. If you have sudden, unexplained weight gain, consult your doctor.
The Bottom Line
Your weight can fluctuate by as much as 5 or 6 pounds from day to day, but these changes in weight are not due to a sudden gain in body weight, but fluid retention, hormones, or the effects of eating a big meal. So, don't get upset if your weight is up one morning, and try to weigh as soon as you wake up to eliminate the effects of hydration. Always urinate beforehand too. A full bladder or colon can raise your weight by several pounds.
References:
"What Prescription Drugs Make You Gain Weight?." .webmd.com/diet/obesity/features/medication-weight-gain.
ObesityAction.org. "Prescription Medications & Weight Gain"
White CP, Hitchcock CL, Vigna YM, Prior JC. Fluid retention over the menstrual cycle: 1-year data from the prospective ovulation cohort. Obstet Gynecol Int. 2011;2011:138451. doi:10.1155/2011/138451.
"Polycystic Ovary Syndrome (PCOS) | Johns Hopkins Medicine." .hopkinsmedicine.org/health/conditions-and-diseases/polycystic-ovary-syndrome-pcos.