Most weight gain can be traced to a simple cause: Too many calories, not enough exercise. But weight gain - especially if it's sudden or rapid - that cannot be explained away by big changes in your diet or your physical activity habits could signal an underlying issue or condition.

Maybe it's medication inflation. Speak to your physician, primary health care provider, or pharmacist to discuss whether a drug you're taking could be adding pounds to your weight. Among those medications associated with weight gain are corticosteroids, beta-blockers, some antidepressants, tranquilizers, and anti-psychotic medications. People who are undergoing chemotherapy or taking insulin may notice weight gain. And certain medications can make your body retain more fluid, which can show up as "water weight" that comes and goes.

Maybe it's temporary water weight or bloating. Water weight may be due to medication, and women may retain more fluid before their menstrual period. A bloated, swollen belly can also be blamed on other intolerances like lactose intolerance. Take note if your weight seems to balloon at certain times of the month or after eating certain foods. Work to recognize your patterns and to eliminate triggers. A bloated belly much less often, but occasionally, indicates heart failure or, among women, uterine fibroids, ovarian cysts, or ovarian cancer.

Maybe sleep lost equals pounds gained. When you lose out on sleep, hunger hormones can go haywire. In one study, a couple of short nights of sleep led to spiked levels of hunger-inducing hormones and a dip in the hormone that tells your brain when you're full. Sleep deprivation could also have you starving for glucose and seeking a quick hit of it from the simple carbs in sweets and junk food, instead of from the complex, more filling carbs found in healthier food options.

Maybe it's your mood that's heavy. Tension, anxiety, and depression can certainly affect your appetite, and some people turn to food for comfort. But stress stresses not just your mind: it stresses your body, too. When you feel anxious or worried, your body creates more of the hormone cortisol, which in turn seems to cause fat to accumulate around your midsection. Beyond the dangers of excess weight, belly fat puts your health in particular danger - increasing your risk of heart disease, stroke, high blood pressure, diabetes, and cancer.

Maybe quitting smoking stoked your appetite. The nicotine you left behind when you quit that nasty habit? It was an appetite suppressant. That cancer stick you held between your lips? It may have been distracting you from cravings. And that toxic soup you inhaled into your lungs? It may have dulled your senses of smell and taste. Thus, you may notice that your appetite and metabolism get a boost - and that the number on the scale gets a boost, too. So as not to replace one health risk for another, manage your weight by finding ways to curb cravings and increased appetite and to add more exercise to your daily routine.

Maybe menopause approaches. Menopausal hormone shifts may make the scales tilt. Couple that with the slowing metabolism that comes as we age, and it becomes more important than ever to fit in fitness and to eat healthfully before, during, and after menopause. Your breast cancer risk soars by 20% if you gain 20 post-menopause pounds.

Maybe it runs in your family. Your genes may predispose you to a certain body size, shape, or composition. If you seem to be gaining weight despite your best efforts not to, your genes may be the reason. But as with many human traits, your weight is influenced by a combination of genetics and lifestyle, of nature and of nurture.

Maybe your thyroid gland is sluggish. This butterfly-shaped gland in your neck regulates your metabolism, among other things. If the thyroid does not produce enough of the particular hormones that affect metabolism, you could gain weight. Other symptoms might include fatigue, dry skin, joint or muscle pain, and depression.

Maybe it's your metabolism - or maybe not. It's an often-cited excuse for weight gain: "I just have a slow metabolism." And while our metabolism is likely to slow as we get older, a "slow" metabolism is actually rare. To metabolize means to turn calories into energy and then to burn up that energy doing the basic "being alive" stuff - breathing, circulating blood, cell repair. Gaining muscle mass may help your body burn calories more quickly.

Other conditions may lead to weight gain, like Cushing syndrome and polycystic ovarian syndrome. Consult your health care provider if you notice sudden weight gain accompanied by any of the following:

  • constipation
  • hair loss
  • sensitivity to cold
  • swollen feet and shortness of breath
  • uncontrollable hunger with palpitations, tremor, and sweating
  • vision changes