A big health problem today is not losing weight. Can we find a verse in the Torah or maybe a Rabbi in the Talmud talking about this problem?
They must have had weight problems back then.
The short answer is found in Kitzur Shulchan Aruch, 32:1, which is based on what we learn from Rambam in the Mishnah Torah, Hilchot De'ot, chapter 4, which states clearly that it is impossible to know G-d or to understand how to serve Him if one is not healthy. That said, what is 'healthy' is different from one human being to another. So there is room for variety. But the general idea is that part of our 'Avodah' is to be healthy, physically, mentally and spiritually in order to properly serve the Creator of us all.
וַאֲכִילָה גַּסָּה לְגוּף כָּל אָדָם כְּמוֹ סַם הַמָּוֶת. וְהוּא עִקָּר לְכָל הֶחֳלָאִים. וְרֹב הֶחֳלָאִים שֶׁבָּאִים עַל הָאָדָם אֵינָם אֶלָּא אוֹ מִפְּנֵי מַאֲכָלִים רָעִים. אוֹ מִפְּנֵי שֶׁהוּא מְמַלֵּא בִּטְנוֹ וְאוֹכֵל אֲכִילָה גַּסָּה אֲפִלּוּ מִמַּאֲכָלִים טוֹבִים. הוּא שֶׁשְּׁלֹמֹה אָמַר בְּחָכְמָתוֹ (משלי כא כג) "שֹׁמֵר פִּיו וּלְשׁוֹנוֹ שֹׁמֵר מִצָּרוֹת נַפְשׁוֹ". כְּלוֹמַר שׁוֹמֵר פִּיו מִלֶּאֱכל מַאֲכָל רַע אוֹ מִלִּשְׂבֹּעַ וּלְשׁוֹנוֹ מִלְּדַבֵּר אֶלָּא בִּצְרָכָיו:
And gluttonous eating is like a deadly poison for every person and it is the essence of all the sicknesses. And most sicknesses that come to a person are only because of bad foods or because he fills his stomach and engages in gluttonous eating, even if it is of good foods. And this is what Shlomo stated (Proverbs 21:23), "He who guards his mouth and tongue, guards his soul from troubles" - which is to say, he guards his mouth from eating a bad food or from satiation, and his tongue from speaking anything except for his needs.
Other passages in this chapter that are relevant to overeating:
וְאֵלּוּ הֵן: לְעוֹלָם לֹא יֹאכַל אָדָם אֶלָּא כְּשֶׁהוּא רָעֵב. וְלֹא יִשְׁתֶּה אֶלָּא כְּשֶׁהוּא צָמֵא.
A person should always only eat when he is hungry, and drink when he is thirsty.
לֹא יֹאכַל אָדָם עַד שֶׁתִּתְמַלֵּא כְּרֵסוֹ אֶלָּא יִפְחֹת כְּמוֹ רְבִיעַ מִשָּׂבְעָתוֹ. וְלֹא יִשְׁתֶּה מַיִם בְּתוֹךְ הַמָּזוֹן אֶלָּא מְעַט וּמָזוּג בְּיַיִן. וּכְשֶׁיַּתְחִיל הַמָּזוֹן לְהִתְעַכֵּל בְּמֵעָיו שׁוֹתֶה מַה שֶּׁהוּא צָרִיךְ לִשְׁתּוֹת. וְלֹא יַרְבֶּה לִשְׁתּוֹת מַיִם וַאֲפִלּוּ כְּשֶׁיִּתְעַכֵּל הַמָּזוֹן.
A person should not eat until his belly is full, but rather he should reduce [his consumption from that by] about a quarter of his satiation. And he should only drink a little water during his meal and [it should be] mixed with wine. And when the food begins to be digested in his intestines, he should drink what he needs to drink.
According to the Gemara Shabbos 140b:
ואמר רב חסדא האי מאן דאפשר ליה למיכל נהמא דשערי ואכל דחיטי קעבר משום בל תשחית ואמר רב פפא האי מאן דאפשר למישתי שיכרא ושתי חמרא עובר משום בל תשחית ולאו מילתא היא בל תשחית דגופא עדיף
And Rav Ḥisda also said: One who is able to eat barley bread and nevertheless eats wheat bread violates the prohibition against wanton destruction. One who wastes resources is comparable to one who destroys items of value. And Rav Pappa said: One who is able to drink beer and nevertheless drinks wine violates the prohibition against wanton destruction. The Gemara comments: And this is not a correct matter, as the prohibition against destruction of one’s body takes precedence. It is preferable for one to care for his body by eating higher quality food than to conserve his money.
See also the other answers to this question.