Narrated by A’ishah (may Allah be pleased with her) said: “The first calamity for this nation after the Prophet’s death is fullness of their stomachs; when their stomachs became full, they became obese and their hearts weakened and their desires became wild.” (Saheeh al Bukhari)
Let's derive three points:
1. Obesity. Note: Not fat. I am fat. I am not obese. Chubbyness is okay. People are made in different shapes and sizes and with different metabolism. Being obese means you eat with extravagance and don't care about your body - and by body I mean health, not looks. Generally those who are obese are lazy, and lazy people don't do much for the ummah. I'm not saying don't eat. Heck, I LOVE food. I think about food 23 hours a day. But everything in moderation. Islam is the middle path.
2. Heart weakened - taking this in a literal sense we can say heart disease and high cholesterol leading to heart problems can stem from obesity. Taking it in a metaphorical sense, eating a lot sometimes makes us ungrateful. Like we don't realize that there are those who have absolutely nothing to eat. Ghandi used to fast so he could understand the poor better. When we fill up our bodies we sit back and think "Damn, I'm so full" not "Allah please help those who are starving".
3. Desires. Remember the hadith where the Prophet (saw) told the teenage boys that if they can't marry [to fullfill sexual desires] then they should fast? Well, same here, eating gives you more energy, and energy is good in certain ways but sometimes it gets out of hand. And if you're a guy - it's been 7 Days since Ramadan started, aside from the fact that Shaytaan is locked up as well, you definitely feel less urges cause you're fasting. I mean, who thinks of girls when they're so busy being hungry?
And why am I saying all of this during Ramadan?
Right, cause we fast yes - but man do we stuff ourselves during ifthaar. And then of course the whole night . . .