I received a message from a woman who had some concerns related to her navel piercing:
I got my belly done yesterday but it looks quite bloated? Is it supposed to be? And also is it possible to loose weight whilst wearing a belly bar?
There could be some localized swelling but it would not be normal for a navel piercing to result in generalized abdominal bloating. In fact, I can't think of a single medical reason that a piercing could cause that to happen. More likley you have eaten something that doesn't agree with you.
Also, the ability to lose (or gain) weight relates to the intake of calories and output of energy. There is no relation between your navel piercing and your body's ability to gain, lose, or maintain your weight.
That said, during initial healing you need to be conscious of not injuring the area or causing excessive trauma during physical activities.
Below are a few related sections from The Piercing Bible:
Physical Activity and Exercise
Generally, you can exercise during healing if you avoid extremes of motion and prevent impact to the pierced area. Still, your activities often need to be modified—at least for a while—if they cause problems with your piercing.
A direct blow can cause delayed healing, excessive scarring, or traumatic tearing. Especially in exposed areas like the ear and face, jewelry could be snagged or possibly torn out during rough play. Soiled, sweaty equipment such as helmets can expose piercings to bacteria, resulting in infection. Friction from body motion or protective equipment can cause irritation and migration. Before wear, thoroughly clean any sports gear that comes near your piercing. Regular workouts enhance your overall health, which has a positive effect on your healing process. Don’t stop all fitness endeavors; just discover what works for you and take extra care during healing.
Even piercings concealed beneath clothes can be at risk unless you take extra precautions. A hard plastic, vented eye patch secured over the area can shield a nipple or navel from impact. Hold it in place with snug, stretchy workout clothing, or by winding a length of Ace bandage around your torso. Add a sterile gauze square or two between your skin and the plastic guard for a comfortable layer of clean, absorbent padding. These supplies are readily available at any drug store or pharmacy. The patch can be used for a range of circumstances, from shielding a navel piercing against tight panty-hose to protecting a nipple piercing from a bulletproof vest.
Don’t expose your piercing to a hot tub, pool, lake, ocean, or any body of water, even if it seems clean. The chemicals in heavily chlorinated pools could be as damaging as the microorganisms and dirt in natural bodies of water. Protect your piercing with a Nexcare Waterproof Bandage, a Tegaderm Transparent Dressing, or similar covering. If you don’t use a sealant bandage, then you should avoid submerging (or even splashing) your healing piercing. This type of bandage can also be used to protect piercings from contact with bodily fluids during sexual activities.