Amina Inloes is originally from the US and has a PhD in Islamic Studies from the University of Exeter on Shi'a hadith. She is the program leader for the MA Islamic Studies program at the Islamic College in London and also the Managing Editor of the Journal of Shi'a Islamic Studies.
Sayyed Mohammad Al-Musawi,
Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to religious questions. In the past, he has also spent significant time in India guiding the community.
Pious persons who are the practicing believers will be in Paradise as young and nice looking, ( You will recognize in their faces the brightness of delight) Sura 83,Verse 24 ( تعرف في وجوههم نضرة النعيم ).
But those who insisted on committing major sins and wrong faith and or wrong acts will be looking ugly, though they will be known by those who knew them in this life ( They recognize each other
( يتعارفون بينهم)Sura Younis, Verse 45.
Allah (SWT) says in Quran about The Day of Judgement ( On that day, those who disbelieved and disobeyed the Messenger will wish to be crushed with the earth, although, they will never be able to hide anything from Allah). (Sura 4, Verse 42) (يومئذ يودّ الذين كفروا وعصوا الرسول لو تسوى بهم الأرض ولا يكنمون الله حديثا
There is Supplication recommended when we perform Wudhu; O Allah, make face bright when faces ( of the disbelievers) turn ugly, and never turn my face ugly when the faces ( of the believer ) turn bright.
اللهم بيّض وحهي يوم تسودّ فيه الوجوه ولا تسوّد وجهي بؤس تبيضّ فيه الوجوه.
We will appear in the afterlife in a recognizable form such that those who knew us in this life will recognize us there.
However from narrations it can be deduced that those who go to heaven will be in a more idealized form (for instance, youthful or full of light) and those who commit severe sins may see those sins manifested in their physical form in their bodies.
(Perhaps this is similar to how when we see someone in real life whom we haven't seen for decades, we can sometimes still recognize them even though they look different; there is something about the essence of the person that we recognize rather than the purely physical appearance.)
Whether it is ideal or not to be fat is of course cultural since in some cultures it is/has been considered a mark of beauty/handsomeness and in other cultures it is not. But what can be said is that the way the people in Paradise will appear will come across as positive, regardless of the details of what the actual appearance is.