For reasons varying from being unhealthy to being haraam, it's good to eliminate bad habits, and also because they can sabotage us in the end. We pay a price in this life and in the Hereafter when we choose to engage in these unhealthy habits. It might be a financial cost (buying cigarettes, for instance, or related medical costs), it might be a social cost (gossip might make you popular at first but can quickly destroy friendships), or health costs (overeating and smoking can rob your body of health by increasing fat, decreasing energy, or damaging vital organs.)
I think it's interesting, then, to find this particular tip on a Self-Development site that is not at all related to Islam. It indicates that these bad habits are non-productive from even a non-religious point of view--and our religion tells us to avoid them, so we should be doubly aware!
Starting with overeating, we have the following hadith from the Prophet Muhammad (saws) to discourage us, and at the same time to give us a better habit regarding what we eat.
No human ever filled a vessel worse than the stomach. Sufficient for any son of Adam are some morsels to keep his back straight. But if it must be, then one third for his food, one third for his drink and one third for his breath. [Ahmad, At-Tirmidhi, An-Nasaa'I, Ibn Majah – Hadith sahih]To learn about the dangers of overeating and the Islamic perspective, check out Obesity and Eating in Islam. Clearly overeating is a bad habit from which Muslims should abstain.
Secondly, it is common now to see fatawa indicating that smoking is prohibited in Islam. (What does Islam say about Smoking?, Ruling on Smoking) Evidence to support that view includes that smoking is harmful to the smoker and everyone around him who might be forced to inhale the toxins associated with it. So for Islamic reasons smoking is another bad habit which Muslims should give up.
And lastly, gossip is something clearly despicable in Islam, condemned in the Qur'an. At the very least bordering on vain talk, gossip might also fall under the category of backbiting or slander, two behaviors which are condemned in the Qur'an (Surat al Humazah) and counted among major sins in Islam, those which will land a person in hellfire. (Five Misconceptions of Backbiting.)
The Prophet Muhammad (saws) gave us good advice on this account also, in a hadith collected among Imam an-Nawawi's 40 Hadith (#15):
Let whosoever believes in Allah and in the Last Day either speak good or be silent.So if we don't have something that is good and decent to say, then the solution is to keep quiet.
Ultimately, for our own good, and for the good of the Muslim ummah, we should try to overcome any bad habits we might have, especially those which have been prohibited by Islam. Remember that Allah prohibited what is bad for us, though we might not always be able to see the wisdom behind it.