In the book of 1 Corinthians, chapter 15, Paul talks about the resurrection and the resurrected body. In verses 35 and following, he states that our heavenly bodies will be different from our natural bodies, with some stark contrasts. Whereas our earthly bodies are characterized by mortality (being susceptible to death), our resurrected bodies will be characterized by immortality (not susceptible to death). Likewise, while our earthly bodies are susceptible to decay (corruption), they will become incorruptible (1 Corinthians 15:53). Also, where our natural bodies are prone to weakness (ask anyone who has reached 40 years of age or older), our resurrected bodies will be characterized by strength (verse 43).
Another comparison is that now we have a natural body, but then we will have a spiritual body. This probably doesn’t mean that we will be like ghosts possessing no body at all and floating around unable to interact with things around us. After all, 1 Corinthians 15:49 states that we will have a body like Jesus’ resurrected body (see also 1 John 3:2). And Jesus, after His resurrection, told them to touch Him and to watch Him eat, demonstrating that He was not merely a spirit (Luke 24:37-43). Rather, it’s more likely that just as a natural body is fitted for this present life in our physical universe, the spiritual body will be that which will best suit us for the eternal existence we are destined for in our eternal abode. Jesus’ resurrected body was capable of entering locked rooms at will (John 20:19). Our earthly body limits us in ways (and/or dimensions) that our spiritual body will not.
First Corinthians 15:43 also describes the transformation from “sown in dishonor” to “raised in glory.” Philippians 3:21 says that Jesus “will transform our lowly body that it may be conformed to His glorious body.” Our decaying bodies are described with the word dishonor because they bear the mark of the results of sin. Sometimes our bodies are marred due to our own, personal sin, such as a brain that is no longer able to form complete thoughts because of drug abuse. Other times our bodies are marked by the sins of others, such as scar from someone acting violently against us. But these are not the only physical markings of sin. In more general terms, the decaying physical body is the direct result of humanity’s fall into sin. Had there been no sin, there would be no decay and death (1 Corinthians 15:56). But God, through Christ’s transforming power, is able to raise up His children with new, glorious bodies, completely free from the ravages of sin and possessing the glory of Christ instead.
To summarize, we are not told exactly what we will look like in the next life, what age we will appear to be, or if we will look thin or fat. But, while many believe we will bear some resemblance to what we look like now, we do know that in whatever ways our appearance or health has been altered as a result of sin (whether because of overeating or not eating right, hereditary malformations, injuries, aging, etc.), these traits will not be carried over into our appearance in the next life. More importantly, the sin nature inherited from Adam (Romans 5:12) will no longer be with us, for we will be made after the holiness of Christ (1 John 3:2).