Evidence Based Research To fulfill our commitment to bringing our audience accurate and insightful content, our expert writers and medical reviewers rely on carefully curated research.
Read Our Editorial Policy
In the vast majority of cases, rapid weight gain (or loss) isn’t healthy.
It’s not just the number on the scale that can affect heart disease and diabetes risk, longevity, and other indicators of overall health, but how you get there as well.
In most cases, rapid weight gain—or loss, for that matter—is not a health-affirming process, but that doesn’t mean it’s never helpful within reasonable parameters.
It’s all about the details:
- Where was your weight initially?
- How did you gain so much weight in such a short amount of time?
- What is the weight composed of (muscle vs fat)?
The Answer: A Big Fat “Depends”
Gaining or losing five or more pounds in a week is never healthy, no matter what’s going on—this is often an effect of heart disease, muscle wasting, dehydration, or severe metabolic issues.
Moreover, rapid weight gain itself can cause more health issues, as in this study from Johns Hopkins University that found rapid weight gain can increase the risk of developing skin cancer in mice.
Even less extreme cases of rapid weight gain (1-2 pounds a week) are often related to health problems.
However, in a narrower set of circumstances, gaining between 0.5-1 pounds a week can be healthy (or at least safe).
First, let’s cover the much more prevalent scenario in its many forms: unhealthy (rapid) weight gain.
The Wrong Way to Bulk Up
According to the United Kingdom’s National Health Service, several medical concerns can stimulate rapid weight gain.
Here are a few of the most common issues related to rapid weight gain:
When the thyroid gland cannot release a sufficient amount of hormones into your system, you can quickly gain several pounds as your metabolism downshifts several notches.
This is because thyroid hormones are essential for keeping nutrient metabolism running at an optimal level.
Other common symptoms of hypothyroidism include fatigue, muscle cramps, and depression.
Many, many bodily processes get downgraded with age.
Our tissues become less elastic and hydrated, healing time increases, various types of cells make errors more frequently when copying themselves, and much more.
Included in these “rites” is a steady loss of muscle (sarcopenia), which gives way to fat—especially for those who don’t fight it with exercise.
Granted, you won’t gain five pounds of fat in a week due to aging alone, but it can certainly contribute to rapid weight gain when there are other exacerbating factors in the mix.
Did we mention this problem gets far better with exercise?
Prednisone and other steroid-based medications used to treat inflammatory diseases (glucocorticoids) have been proven to promote weight gain, as in this study from Johns Hopkins University.
Researchers combed through data from another trial involving the treatment of an inflammatory disease with prednisone (Wegener’s Granulomatosis Etanercept Trial) to assess the effect of this steroid-based treatment on 157 patients as it regards weight.
Sure enough, this population gained an average of just under 9.2 lbs in the year following their baseline assessment, and 35 of the 157 gained more than 22 pounds.
Most sources agree that steroid-based medications promote weight gain indirectly by increasing appetite.
Both the disorder itself and some of the treatments used to address diabetes can contribute to weight gain.
When the body realizes that its tissues are no longer responding to insulin, it ramps up production of the hormone.
Insulin causes increased hunger and weight gain, whether it’s the body producing the insulin or injections.
Also, many diabetics overeat in hopes of staving off low blood sugar (hypoglycemia) caused by overdoing the insulin, which, of course, worsens this effect.
Congestive Heart Failure
Generally, by the time you get to congestive heart failure, you’ve probably put on a few pounds already.
That’s because congestive heart failure usually results from high blood pressure, coronary artery disease, valve defects, obesity, and other issues commonly associated with weight gain.
Still, when the pump that is your heart weakens to the point that fluid begins to back up in your lungs and around your heart, your weight can jump up quickly.
In addition, feeling fatigued and short of breath (especially when fluid reaches the lungs) doesn’t help the weight gain situation.
Similarly, other disorders that can suddenly increase fluid retention, like lymphedema, along with simply getting too much sodium in the diet, share this effect.
When Rapid Weight Gain *Might* Be Okay
If you’re genetically predisposed to be underweight (an ectomorph), recovering from a serious illness that caused rapid weight loss, and/or building muscle without using questionable supplements, you may be able to gain weight at a faster pace without serious ramifications.
The operative word is “may,” because even healthy gainers still have a chance of experiencing kidney problems, various infections, menstrual irregularities, and more if they pack on the pounds too quickly.
Here’s a closer look at the circumstances that can swing your rapid weight gain experience in a healthier (or less healthy) direction:
A pound a week or less: It’s very difficult to gain two or more pounds per week, especially for a period of months or more, without experiencing one or more of the above health issues.
No “dirty bulking”: Filling up on sugar and fat so you can puff up faster, even if you’re a bodybuilder planning to “cut down” after the fact, is not going to do your heart, arteries, and blood glucose levels any favors.
Prioritizing muscle: As long as you’re safely and medically able to do so, lift heavy weights with longer breaks between sets (two minutes versus 45 seconds). If you don’t lift weights yet continue to diet for bulk, well—you’ll just get fat.
Eating (healthy) on a schedule: The fact that you need to gain weight is proof that your body is sending the satiety signal to your brain too early into mealtime to allow for an energy surplus. By scheduling your meals and budgeting your calories, you’ll not only break through this barrier (with a little discomfort, mind you), but you’ll help to keep blood glucose levels under control by spreading out calories.
A Gradual Approach Is Best
Yes, there are some instances in which semi-rapid weight gain can be okay, but it’s a narrow target to aim for.
It’s better to play the long game, because you won’t have to resort to such drastic measures when it comes to shoveling in calories and overclocking your kidney, pancreas (insulin), and more.
There are very few secrets left in health and nutrition; eat clean and exercise, and you can massively reduce heart disease and diabetes risk while pursuing the body you want.